CA2331203C

CA2331203C - Communication system

Info

Publication number: CA2331203C
Application number: CA 2331203
Authority: CA
Inventors: Mitsuaki Oshima
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1992-03-26
Filing date: 1993-03-25
Publication date: 2004-12-07
Anticipated expiration: 2013-03-25
Also published as: US20080069259A1; US20040086056A1; US7496146B2; JP2000299677A; PT1330089E; KR960002468B1; EP1049284A3; US7362813B2; EP1039673B1; ES2178995T3; JP3154707B2; PT1039677E; EP1039676A3; EP1039682A2; EP1049283B1; PT1039674E; EP1045541A2; ES2258181T3; EP1154608A3; DE69334312D1

Abstract

At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal apace diagram. The input signal is divided into, two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between first and second data streams is developed by shifting the signal points to other positions in the space diagram. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV
broadcast service, a TV signal is divided by a transmitter into, low and high, frequency band components which are designated as a first and a second data stream respectively.
Upon receiving the TV signal, a receiver can reproduce only the low frequency band component or both the low and high frequency band components, depending on its capability.

Description

r ~PECIFiCATION
TITLE OF THE INVENTION
Communication System BACKGROQND OF THE INVENTIQN
1. Field of the Invention:
The present invention relates to a communication system for transmission/reception of a digital signal through modulation of its carrier wave and demodulation of the modulated signal.
1~ 2. Description of the Prior Art:
Digital communication systems have been used in various fields. Particularly, digital video signal transmission techniques have been improved remarkably.
Among them is a digital TV signal transmission method.
So far, such digital TV signal transmission system are in particular use for e.g. transmission between TV stations.
They will soon be utilized for terrestrial and/or satellite broadcast service in every country of the world.
The TV broadcast systems including HDTV. PCM music, FAx, and other info~mation service are now demanded to increase desired data in quantity and quality for satisfying millions of sophisticated viewers. Fn particular, the data has to be increased in a given bandwidth of frequency allocated for TV
broadcast service. The data to be Transmitted is always abundant and provided as much as handled with up-to-date techniques of the time. It is ideal to modify or change the existing signal transmission system corresponding to an increase in the data amount with time.
However, the TV broadcast service is a public business and cannot go further without considering the interests and benefits of viewers. It is essential to have any new service 5 appreciable with existing TV receivers and displays. More particularl;, the compatibility of a system is much desired for providing both old and now services simultaneously or one new service which can be interceyied by either of the existing and advanced receivers.
10 It is understood that any new digital Tv broadcast system to be introduced has to be arranged for data extension in order to respond to future demands and tech~iological advantages and also, for compatible action to allow the existing receivers to receive transmissions.
15 The expansion capability and compatible performance of prior art digital TV system will be explained.
A digital satellite TV system is known in which NTSC TV
signals compressed to an about 6 Mbps are multiplexed by time division modulation of 4 PSK and transmitted on 4 to 20 20 channels while HDTV signals are carried on a single channel.
:~.nother digital HDTV system is provided in which HDTV video data compressed to as small as 15 Mbps are transmitted on a 16 or 32 GIA.'H signal through ground stations.
Such a brown satellite system permits ITV signals to be 25 carried on one channel by a conventional manner, thus occupying a band of frequencies equivalent to same channels of NTSC signals. This causes the corresponding NTSC channels to be unavailable during transmission of the HDTV signal.
also, the compatibility between NTSC and HDTV receivers or displays is hardly concerned and data expansion capability needed for matching a future advanced mode is utterly disregarded.
Such a common terrestrial HDTV system offers an HDTV
service on conventional 16 or 32 QAM signals without any modification. In any analogue TV broadcast service, there are developed a lat of signal attenuating or shadow regions 10 within its service area due to structural obstacles, geagraphical inconveniences, or signal interference from a neighbor station. When the TV signal is an analogue form, it can be intercepted more or less at such signal attenuating regions although its reproduced picture is low in quality-. if 15 TV signal is a digital form, it can rarely be reproduced at an acceptable level within the regions. This disadvantage is critically hostile to the development of any digital TV
system.
This problem is caused due to the fact that the ZO conventional modulation systems such QAM arrange the signal points at constant intervals. There have been no such systems that can change or modulate the arrangement of signal points.
,~jT~iARY' OF THE INVENTIOlY
25 It is an object of the present invention, for solving the foregoing disadvantages, to provide a communication system arranged for compatible use for both the existing rTSC

and introducing HDTV broadcast services, particula:ly via satellite and also, for minimizing signal attenuating or shadow regions of its service area on the grounds.
A communication system according to the present 5 invention intentionally varies signal points, which used to be disposed at uniform intervals, to perform the signal transmission/reception. For example, if applied to a Q.AM
signal, the communication system comprises two major sections: a tranbmitter having a signal input circuit, a modulator circuit for producing m numbers of signal points, in a signal vector field through modulation of a plurality of out-of-phase carrier waves using an input signal supplied from the input circuit, and a transmitter circuit for transmitting a resultant modulated signal; and a receiver 15 having an input circuit for receiving the modulated signal, a demodulator circuit for demodulating one-bit signal points of a qA~i carrier wave, and an output circuit.
In operation, the input signal containing a first data stream of n values and a second data stream is fed to the 20 modulator circuit of the transmitter where a modified m-bit QAM carrier wave is produced representing m signal points in a vector field. The m signal points are divided into n signal point groups to which the n values of the first data stream are assigned respectively. Also, data of the second data 25 stream are assigned to m/r_ signal poin~s or sub groups of each signal point group. Then, a resultant transmission signal is transmitted from the transmitter circuit.

Similarly, a third data stream can be propagated.
At the p-bit demodulator circuit, p>m, of the receiver, the first data stream of the transmission signal is first demodulated through dividing p signal points in a signal 5 space diagram into n signal point groups. Then, the second ~ data stream is demodulated through assigning p/n values to p/n signal paints of each corresponding signal point group for reconstruction of both the first and second data streams.
If the receiver is at P=n, the n signal point groups are 10 reclaimed and assigned the n values for demodulation and reconstruction of the first data stream.
Upon receiving the same transmission signal from the transmitter, a receiver equipped with a large sized antenna and capable of large-data modulation can reproduce both the 1b first and second data streams. A receiver eQuipped with a small sized antenna and capable of small-data modulation can reproduce the first data stream only. Accordingly, the compatibility of the signal transmission system will be ensured. When the first data stream is an NTSC TV signal or 20 low frequency band component of an HDTV signal and the second data stroam is a high frequency baud component of the HDTV
signal, the small-data modulation receiver can reconstruct the NTSC TV signal and the large-data modulation receiver can reconstruct the HDTV signal. As understood, a digital 25 NTSC/HDT'f simultaneously broadcast service will be feasible using the compatibility of the signal transmission system of the present invention.

_T
More specifically, the communication system of the present invention comprises: a transmitter having a Signal input circuit, a modulator circuit for producing m signal points, in a signal vector field through modulation of a plurality of out-of-phase carrier waves using an input signal supplied from the input, and a transmitter cirr.uit for transmitting a resultant modulated signal, in which the main procedure includes receiving an input signal containing a first data stream of n values and a second data stream, dividing the m signal points of the signal into n signal point groups, assignirg the n values of the first data stream to the n signal point groups respectively, assigning data of tha second data stream to the signal points of each signal point group respectively, and transmitting the resultant modulated signal; and a receiver having an input circuit for receiving the modulated signal, a demodulator circuit for demodulating p signal points of a QA.M carrier wave, and an output circuit, in which the main procedure includes dividing the p signal points into n signal point groups, demodulating the first data stream of which n values are assigned to the n signal point ,groups respectively, and demodulating the secor_d data stream of which p/n values are assigned to p/n signal points of each signal point group respectively. For example, a transmitter 1 produces a modified m-bit SAM signal of which first, second, and third data streams, each carrying n values, are assigned to relevant signal point groups with a modulator 4. The signal can be intercepted and reproduced the first data stream only by a first receiver 23, both the first and second data streams by a second receiver 33, and all the first, second, and third streams by a third receiver 43.
More particularly, a receiver capable of demodulation of n-bit data can reproduce n bits from a multiple-bit modulated carrier Wave carrying an m-bit data where m>n, thus allowing the communication system to have compatibility and capability of future extension. Also, a mufti-leval signal transmission will be possible by shifting the signal points of QAM so that a nearest signal point to the origin point of I-axis and Q-axis coordinates is spaced of from the origin where f is the distance of the nearest point from each aria and n is more than 1.
Accordingly, a compatible digital satellite broadcast service for both the NTSC and HDTV systems will be feasible when the first data stream carries an NTSC signal and the second data stream carries a difference signal between NTSC
and HDTV. Hence, the capability of corresponding to an increase in the data amount to be transmitted will be ensured. Also, at the ground, its service area will be increased while signal attenuating areas are decreased.
RRrFr' nF~('RTPTTnN OF THE DRAWINGS
Fig. 1 is a schematic view of the entire arrangement of a signal transmission system showing a first embodiment of the present invention;

. . ..z. ...
Fig. Z is a block diagram of a transmitter of the first embodiment;
Fig. 3 is a vecto: diagram showing a transmission signal of the first embodiment;
5 Fig. 4 is a vector diagram showing a transmission signal of the first embodiment;
Fig. 5 is a view showing an assignment of binary codes to signal points according to the first embodiment;
Fig. 6 ie a view showing an assignment of binary codes to signal point groups according to the first embodiment;
Fig. 7 is a view showing an assignment of binary codes to signal points in each signal point group according to the first embodiment;
Fig. 8 is a view showing another assignment of binary 15 codes to signal point groups and thei: signal points according to the first embodiment;
Fig. 9 is a view showing threshold values of the signal point groups according to the first Qmbodiment;
Fig. 10 is a vector diagram of a modified 16 6~AM signal of the first embodiment;
Fig. 11 is a graphic diagram showing the relation between antenna radius rZ and transmission energy ratio n according to the first embodiment;
Fig. 12 is a view stowing the signal points of a modified 84 QAM signal. of the first embodiment;
Fig. 13 is a graphic diagram showing the relation betwean antenna radius r3 and transmission energy ratio n according to the first embodiment;
Fig. 24 is a vector diagram showing signal point groups and their signal points of the modified 6:1 WA.M signal of the first embodiment.;
Fig. 15 is an explanatory view showing the relation between A1 and A~ of the modified 64 QAf~f signal of tt~e first embodiment;
Fig. 16 is a graph diagram showing the relation between antenna radius rZ, r3 and transmission energy ratio nls, n~
respectively according to the first embodiment;
Fig. 17 is a block diagram of a digital transmitter of the first embodiment;
Fig. 18 is a signal space diagram of a 4 PSK modulated signal of the first embodiment;
Fig. 19 is a block diagram of a first receiver of the first embodiment;
Fig. 20 is a signal space diagram of a 4 PSK modulated signal of the first esbodiment;
Fig. 21 is a block diagram o~ a second receiver of the first embodiment;
Fig. 22 is a vector diagram of a modified I6 Q.AM signal of the first embodiment;
Fig. 23 is a vector diagram of a modified 64 Q.AM signal of the first embodiment;
Fig. 24 is a flow chart showing an action of the first embodiment;
Figs. 25(a) and 25(b) are vector diagrams showing an 8 and a 16 QAM signal of the first embodiment respectively;
Fig. 26 is a block diagrem of a third receiver of the first embodiment;
Fig. 27 is a view showing signal points of the modified 64 QAM signal of the first embodiment.;
Fig. 28 is a flow chart showing another action of the first embodiment;
Fig. 29 is a schematic view of the entire arrangement o~
a signal transmission system showing a third embodiment of 10 the present invention;
Fig. 30 is a block die.gram of a first video encoder of the third embodiment;
Fig. 31 is a block diagram of a first video decoder of the third embodiment;
Fig. 32 is a block diagram of a second video decoder of the third embodiment;
Fig 33 is a block diagram of a third video decoder of the third embodiment;
Fig. 34 ie an explanatory view showing a time 20 multiplexing of Di, DZ, and D3 signals according to the third embodiment;
Fig. 35 is an explanatory view showing another time multiplexing of the D1, DZ, and D3 signals according to the third embodiment;
25 Fig. 36 is an explanatory viev: showing a further time multiplexing of the Dl, D2, and D3 signals according to the third embodiment;

Fig. 37 is a schematic view of the entire arrangement of a signal transmission system showing a fourth embodiment of the present invention;
Fig. 38 is a vector diagram of a modified 16 QAM signal of the third embodiment;
Fig. 39 is a vector diagram of the modified 16 QAM
signal of the third embodiment;
Fig. 40 is a vector diagram of a modified 64 QAM signal of the third embodiment;
10 Fig. 41 is a diagram o! assignment of data components en a time base according to the third embodiment;
Fig. 42 is a diagram of assignment of data components on a time base in TDMA action according to the third embodiment;
Fig. 43 is a block diagram of a carrier reproducing circuit of the third embodiment;
Fig. 44 is a diagram showing the principle of carrier wave reproduction according to the third embodiment;
Fig. 45 is a block diagram of a carrier reproducing circuit for reverse modulation of the third embodiment;
20 Fig. 46 is a diagram showing an assignment of signal points of the 16 QAM signal of the third embodiment;
Fig. 47 is a diagram showing an assignnment of signal points of the B4 QAM signal of the third embodiment;
Fig. 48 is a block diagram of a c~srrier reproducing 25 eircu~t for l6x multiplication of the third embodiment;
Fig. 49 is an explanatory view showing a time multiplexing of DVI, D~1, D~2, Due, DV3, and D~ signals according to the third embodiment;
Fig. 50 is an explanatory view showing a TD:~.A time multiplexing of Dyl, Dd" Dy2, Due, Dy3, and D~ signals according to the third embodiment;
Fig. 51 is an explanatory view showing another TDMA time multiplexing of the Dyl, Dgl, Due, Due, Dy3, and D~ signals according to the third embodiment;
Fig. 52 is a diagram showing a signal interference region in a known transmission method according to the fourth embodiment;
Fig. 53 is a diagram showing signal interference regions in a multi-level signal transmission method according to the fourth embodiment;
Fig. 54 is a diagram showing signal attenuating regions in the known transmission method according to the fourth embodiment;
Fig. 55 is a diagram showing signal attenuating regions in the mufti-level signal transmission method according to the fourth embodiment;
Fig. 56 is a diagram showing a signal interference region between two digital TV stations according to the fourth embodiment;
Fig. 57 is a diagram showing an assignment of signal points of a modified 4 ASK signal of the fifth embodiment;
Fig. ~8 is a diagram showing another assign.~nent of signal points of the modified 4 ASK signal oi' the fifth embodiment;

__CA 02331203 2001-02-05 .:.._ . ,_:- . ~.. ';,.W_ -~-'~'.. ..-_ :. - ~.-_ Figs. 59(a) and 59(b) are diagrams showing assignment of signal points of the modified 4 ASK signal of the fifth embodiment;
Fig. 60 is a diagram showing another assignment of signal points of the modified 4 ASK signal of the fifth embodiment when the C/N rate is low;
Fig. 61 is a block diagram of a transmitter of the fifth embodiment;
Figs. 62(a) and 62(b) are diagre.ma showing frequency distribution profiles of an ASK modulated signal of the fifth embodiment;
Fig. 63 is a block diagram of a receiver of the fifth embodiment;
Fig. 64 is a block diagram of a video signal transmitter of the f fifth embodiment;
Fig. 65 is a block diagram of a TV receiver of the fifth embodiment;
Fig. 66 is a block diagram of another iV :eceiver of the fifth embodiment;
Fig. 67 is a block diagram of a satellite-to-ground Tel receiver ef the fifth embodiment;
Fig. 68 is a diagram showing an assignment of signal points of an 8 ASK signal of the fifth embodiment;
Fig. 6g is a block diagram of a L-ideo encoder of the fifth embodiment;
Fig. 70 is a block diagram of a video encoder of the fifth embodiment coni;aining one d=eider circuit;

., , _ _ _ . ' F~ _,. 'n:,.''v ~~ o-c~ y , __7. .. _ Fig. 71 is a block diagram of a video decoder of the fifth embodiment;

Fig. 72 is a block diagram of a video decoder or the fifth embodiment containing one mixer circuit;

Fig. 73 is a diagram showing a time assignment of data.

components of a transmission signalaccording to the fifth embodiment;

Fig. 74(a) is a block diagram f a video decoder o of the fifth embodiment;

Fig. 74(b) is a diagram showing anothQr time assignment of data components of the transmission signal according to the fifth embodiment;

Fig. 75 is a diagram showing a time assignment of data comgonente of a transmission signalaccording to the fifth.

embodiment;

Fig. 76 ie a diagram showing a time assignment of data components of a transmission signalaccording to the fifth embodiment;

Fig. 77 is a diagram showing a time assignment of data components of a transmission signalaccording to the fifth embodiment;

Fig. 78 is a block diagram of a video decoder of the fifth embodiment;

Fig. ?9 is a diagram showing a time assignment of data components of a three-level transmission signal according to the fifth embodiment;

Fig. 80 is a block diagram of nother video decoder a of . . _ . . , _ . - . r _ _ - '~: ~ _ ~ :~-"=o'F= . . . z . . . . . . .
the fif~h embodiment;
Fig. 8i is a diagram showing a time assignment of da!u components of a transmission signal according to the fifth embodiment;
Fig. 8? is a block diagram of a video decoder for D~
. signal of the fifth embodiment;
Fig. 83 is a graphic diagram showing the relation between frequ~ancy and time of a frequency modulated signal according to the fifth embodiment;
Fig. 84 is a block diagram of a magnetic record/playback apparatus of the fifth embodiment;
Fig. 85 is a graphic diagram showing thQ relation between C/N and level according to the second embodiment;
Fig. 86 is a graphic diagram showing the relation between C/N and transmission distance according to the second embodiment;
Fig. 87 is a block diagram of a transmission of the second embodiment;
Fig. 88 is a black diagram of a receiver of the second embodiment;
Fig. 89 is a graphic diagram showing the relation between C/H and error rate according to the second embodiment;
Fig. 90 is a diagram showing signal attenuating regions in the three-level transmission of the fifth embodiment;
Fig. 91 is a diagram showing signal attenuating regions in the four-level transmission of a sixth embodiment;

..:.- . ;_:. ~:__.. '~-.~'._ -:~-.~:_-: . . :.
Fig. 92 is a diagram showing the four-level transmission of the sixth embodiment;
Fig. 93 is a block diagram of a divider of the sixth embodiment;
Fig. 94 is a block diagram of a mixer of the sixth embodiment;
Fig. 95 is a diagram showing ar_otner tour-level transmission of the sixth embodiment;
Fig. 96 is a view of signal propagation of a known digital TV broadcast system;
Fig. 97 is a view of signal propagation of a digital TV
broadcast slstem according to the sixth embodiment;
Fig. 98 is a diagram showing a four-level transmission of the sixth embodiment;
Fig. 89 is a vector diagram of a lfi SRQAM signal of the third embodiment;
Fig. 100 is a vector diagram of a 32 SRQAM signal of the third embodiment;
Fig. I01 is a graphic diagram showing the relation between C/N and error rate according to the third embodiment;
Fig. 102 is a graphic diagram showing the relation between C/h .and error rate according to the third embodiment;
Fig. 103 is a graphic diagram showing tile relation between s'si ft distance n and C!N needed for tr s.nsmission according to the third embodiment;
Fig. 104 is a graphic diagram showing the relation between shift distance n and C/r needed for transmission .... . ,_.. . -.__ ~~,_ _.--.__ - - - ~._. . .. ..: -. .. ...
according to the third embodiment;
Fig. 105 is a graphic diagram showing the relation between signal ievel and distance from a transmitter antenna in terrestrial broadcast service according to the third embodiment;
Fig. 106 is a diagram showing a service area of the 32 SRQAM signal of the third embodiment;
Fig. 107 is a diagram showing a service area of the 32 SRQAM signal of the third embodiment;
Fig. 108 is a diagram showing a frequency distribution profile of a TV signal of the third emhediment;
Fig. 109 is a diagram showing a time assignment of the TV signal of the third embodiment;
Fig. 110 is a diagram showing a principle of C-CDM of the third embodiment;
Fig. 111 is a view showing an assignment of codes according to the third embodiment;
Fig. 112 is a view showing an assignment of an extended 38 QA.M according to the third embodiment;
Fig. 113 is s view showing a frequency assignment of a modulation signal according to the fifth embodiment;
Fig. I14 is a black diagram showing a magne~ic recording/piayback apparatus according tc the fifth embodiment;
Fig. 115 is a block diagram showing a transmitter/receiver of a portable telephone according to the eig5th embodiment;

._:_T .._._ . :~_..- .._ 3=;,t T-Fig. llo is a black diag:am showing base stations according to the eighth embodiment;
Fig. 117 is a view illustrating communication capacities and traffic distribution of a conventional system;
Fig. 118 is a view illustrating communication capacities and traffic distribution according to the eighth embodiment;
Fig. 119(x) is a diagram showing a time slot assignment of a conventional system;
Fig. 119(b) is a diagram showing a time slot assignment according to the eighth embodiment;
Fig. 120(a) is a diagram showing a time slot assignment of a conventional TDMA system;
Fig. 120(b) is a diagram showing a time slot assignment according to a TDMA system of the eighth embodiment;
Fig. 121 is a block diagram showing a one-level transmitter/receiver according to the eighth embodiment;
Fig. 122 is a block diagram showing a two-level transmitter/receiver according to the eighth embodiment;
Fig. 123 is a block diagram showing an OFDM type transmitter/receiver according to the ninth embodiment;
Fig. 124 is a view illustrating a principle of the OFDM
system according to the ninth embodiment;
Fig. 125(a) is a view showing a frequency assignment of a modulation signal of a conventional system;
Fig. 125(b) is a view showing a frequency assignment of a modulation signal according to the ninth embodiment;
Fig. 126(a) is a view showing a frequency assignment of ._._ .._ _ - -t ~ N,.~ C'.,'-o:'.Z . .. _.._ .. -. __.
a transmisbion signal of the ninth embodiment;
Fig. 126(b) is a view showing a frequency assignment of a receiving signal according to the ninth embodiment;
Fig. 127 is a block diagram showing a - 5 transmitter/receiver according to the ninth embodiment;
Fig. 128 is a block diagram showing a Trellis encoder according to the fifth embodiment;
Fig. 129 is a view showing a time assignment of effective symbol periods and guard intervals according to the ninth embodiment;
Fig. 130 is a graphic diagram showing a relation between -C/N rate and error rate according to the ninth embodiment;
Fig. 131 is a block diagram showing a magnetic recording/playback apparatus according to the fifth embodiment;
Fig. 132 ie a view showing a recording format of track on the magnetic tape and a travelling of a head;
Fig. 133 is a block diagram showing a transmitter/receiver according to the third embodiment;
Fig. 134 is a diagram showing a frequency assignment of a conventional broadcasting;
Fig. 135 i5 a diagram showing a relation between service area and picture quality in a three-level signal transmission system according to the third embodiment;
Fig. 136 is a diagram showing a frequency assignment in case the multi-level signal transmission system according to the third embodiment is combined with an FDM;

.... .,.._ . ... ,..~._ w-:~~.-. . . . z_ Fig. 137 is a block diagram showing a transmitter/receiver according to the third embodiment, in which Trellis encoding is adopted; and Fig. 138 is a block diagram showing a transmitter/receiver according to the ninth embodimer_t, in which a part of low frequency band s~.gnal is transmitted by OFDM.
n~~~TFr DESCRIPTION QF TIiF PREFER ED EMBODTMEVTS
Embodiment 1 One embodiment of the present invention will be described referring to the relevant drawings.
Fig. 1 shows the entire arrangement of a signal transmission system according to the present invention. A
transmitter 1 comprises an input unit 2, a divider circuit 3, a modulator 4, and a transmitter unit 5. In action, each input multiples signal is divided by the divider circuit 3 into three groups, a first data stream D1, a second data stream D2, a third data stream D3, which are then modulated by the modulator 4 before transmitted from the transmitter unit 5. The modulated signal is sent up from an antennal 6 through ax uplink 7 to a satellite 10 where it is intercepted by an uplink antenna 11 and amp'_ified by a transponder 12 before transmitted from a downlink antenna 13 towards the ground.
The transmission signal is then sent down through three downlinks 21, 32, and 41 to a first 23, a second 33, and a third re~eivor 43 respectively. In the first receiver 23, the signal intercepted by an antenna ?2 is fed through an input unit 24 to a demodulator 25 where its first data s;.ream only is demodulated, while the second and third data st~eams are not recovered, before transmitted further from an outpu: unit 26.
Similarly, the second receiver 33 allows the first and second data streams of the signal intercepted by an antenna 32 and fed from an input unit 34 to be demodulated by a demodulator 35 and then, summed by a summer 37 to a single data straam which is then transmitted further from an output unit 3E.
The third receiver 43 allows all the first, second, and third data streams of the signal intercepted by an antenna 42 and fed from an input unit 44 to be demodulated by a demodulator 45 and then, summed by a summer 47 to a single data stream which is then transmitted further from an output unit 46.
As understood, the three discrete receivers 23, 33, and 43 have their respective demodulators of different characteristics such that their outputs demodulated from the same frequency band signal of the transmitter 1 contain data of different sizes. More particularly, three different but compatible data can simultaneously be carried on a given frequency band signal to their respective receivers. For example, each of three, existing NTSC, HDTV, and super ATV, digital signals is divided into a low, s high, and a super ..:. .~__- . .._, 'L~t_ Cue' high frequency band components which represent the first, the second, and the third data stream respectively. Accordingly, the three different TV signals can be transmitted on a one-channel frequency band carrier for simultaneous rep~oduc.tion of a medium, a high, and a super high resolution TV image respectively.
In service, the NTSC TV signal is intercepted by a receiver accompanied with a small antenna for demodulation of a sma~i-sized data, the HDTV signal is intercepted by a receiver accompanied with a medium antenna for demodulation of medium-sized data, and the super HDTV signal is intercepted by a receiver accompanied with a large antenna for demodulation of large-sized data. Also, as illustrated in Fig. 1, a digital NTSC TV signal containing only the first data stream for digital NTSC TY broancastinE service is fed to a digital transmitter 51 where it is received by an input unit 52 and modulated by a demodulator 54 before transmitted further from a transmitter unit 55. The demodulated signal is then sent up from an antennal 56 through an uplil:k 57 to the satellite 10 which in turn transmits the same through a downlink 58 to the first receiver 23 on the ground.
The first receiver 23 demodulates with its demodulator the modulated digital signal supplied from the digital transmitter~ 51 to the original first data stream signal.
25 Similarly, the same modulated digital signal can be intercepted and demodulated by the second 33 or third receiver 42 to the first data stream or N'fSC TV signal. In ..__ _._.- . r__. 't~~~ _'--.°'F=~ .. _... '. _. .._ summary, the three discrete receivers 23, 33, and 43 a31 can intercFpt and process a digital signal of the existing T~' system for reproduction.
The arrangement of the signal transmission. system will he described in more detail.
Fig. 2 is a block diagram of the transmitter 1, in which an input signal is fed across the input unit 2 and divided by the divider circuit 3 into three digital signals containing a first, a second, and a third data stream respectively.
Assuming that the input signal is a video signal, its lov frequency bard component is assigned to the first data stream, its high frequency band component to the second data stream, its super-high frequency band component to the third data stresm. The three different frequency band signals are fed to a modulator input 61 of the modulator ~. Here, a signal point modulatiug/changing circuit 6T modulates or changes the positions of the signal points according to an externally given signal. The modulator 4 is arranged for amplitude modulation on two 90°-out-of-phase carriers respectively which are then summed to a multiple QAM signal.
More specifically, the signal Prom the modulator input 61 is fed to both a first 62 and a szcond AM modulator 63. Alsu, a carrier wave of cos(2nfct) produced by a carrier generator 64 is directly fed to the first AM modulator 62 and also, to a a/2 phase shifter 6E where it is 90° shifted in phase to a sin;2nfct) Porm prior to transmitted to the second AM
modulator 63. The two amplitude modulated signals from the :.._ _~_:_ . ~:,._- ~-~.~_ ___~_~:_ _ first and second A.'i modulators 62, 63 e:e summed by a summer 65 to a transmission signal which is then transferred to the transmitter unit 5 for output. The procedure is well known and will no further be explained.
The QA.H signal will now be described in a common Bx8 or 16 state constellation referring to th~a first quadrant of a space diagram in Fig. 3. Th.e output signal of the modulator 4 is expressed by a sum vector of two, Acos2nfct and Bcos2ttfct, vectors 81, 82 which represent the two 90°-out-of-phase carriers respectively. When the distal point of a sum vector from the aero point represents a signal point, the 16 QAM signal has 16 signal points determined by a combination of four horizontal amplitude values a~, a2, a3, a4 and four vertical amplitude values bl, b2, b3, b4. The first quadrant in Fig. 3 contains four signal points 83 at Cu, 84 at C12, 85 at CZ2, and 86 at C~.
Cll is a sum vector of a vector 0-al and a vector 0-bl and thus, expressed as Cll - alcos2nfct-blsin2nfet -Acos(2nfct+dn/2).
It is now assumes that the dista:zce betweer. 0 and al in the orthogcnal coordinates of Fig. 3 is Al, between al and a~
is AZ, between 0 and bl is B1, and between bl and bl is BZ.
As shown in Fig. 4, the 16 signal points are allocated in a vector coordinate, in which each point represents a four-bit pattern thus to allow the transmission of four bit data per period or time slot.
Fig. 5 illustrates a common assignment of two-bit . _ . . ... _ . . . F~ .. 'fj.~'_ =:-"o-W , . . _ _ " : . _ . . . .
patterns Lo the i6 signal points.
When the distance between twa adjacent signal points is great, it will be identified by the receiver with much ease.
hence, it iE desired to space the signal points at greater intervals. If two particular signal points are allocated near to each other, they are rarely distinguished and error rate will be increased. Therefore, it is most preferred to have the signal points spaced at equal intervals as shown in Fig.
5, in which t;he 16 QAM signal is defined by AI=AZ/2.
The transmitter 1 of the embodiment is arranged to divide an input digital signal into a first, a second, and a third data or bit stream. The i6 signal points or groups of signal points are divided into four groups. Then, 4 two-bit patterns of the first data stream are assigned to the four signal point groups respectively, as shown in Fig. 6. More particularly, when the two-bit pattern of the first data stream is 11, one of four signal points of the first signal point group 81 in the first quadrant is selected depending or~
the content of the second data stream for transmission.
Similarly, when 01, one signal point of the second signal point grot:p 92 in the second quadrant is selected and transmitted. When 00, one signal point of the third signal point group 93 in the trird quadran~ is transmitted and when 10, one signal point of the fourth signal point group 94 in the fourth q~sadrant is transmitted. Also, 4 two-bit patterns in the second data stream of the 16 QAM signal, or e.g. 16 four-bit patterns in the second data stream of a 64-state GRAM

. . _ . . _ . . _ .. ., _ ~~~'o'~z . . _ . ~ : : . _ . _ .
signal, are assigned to four signal points or sub signal point groups o~ each of the four signal point groups 91, 92, 93, 94 respectively, as shown in Fig. 7. It should be understood that the assignment is symtaetrical between any two quadrants. The assignment of the signal points to the four groups 91, 92, 93, 94 is determined by priority to the two-bit data of the first data stream. As the result, two-bit data of the first data stream and two-bit data of the second data stream can be transmitted independently. Also, the first data stream will be demodulated with the use of a common 4 PSK receiver having a given antenna saasitivity. If the antenna sensitivity is higher, a modified type of the 16 qAM
receiver of the present invention will intercept and demodulate both tha first and second data stream with equal success.
Fig. 8 shows an example of the assignment of the first and second data streams in two--bit patterns.
When the low frequency band component of an HDTV video signal is assigned to the first data stream and the high frequency component to the second data stream, the 4 PSK
receiver can produce an NTSC-level picture from the first data stream and the 16- or 64-slate QAM receiver can produce an HDTV picture from a composite reproduction signal of the first and second data streams.
Since the signal points are allocated at equal intervals, there is developed is the 4 P5K receiver a threshold distance between the coordinate axes and the shaded ..._- . ___ . '. . '~.~_ -.:a,-_. . z ., _.
area of the first quadrant, as shown in Fig. 9. If the threshold distances is .~,1, a FSh signal having an amplitude of A,~ will successfully be intercepted. Howeve:, the amplitude has to be ir_creased to a three times greater value or 3A,1,~ for transmission of a 16 QAM signal while the threshold distance A,1.U being maintained. More particularly, the energy for transmitting the 16 Q,AM signal is needed nine times greater than than for sending the 4 PSK signal. Also, when the 4 PSH signal is transmitted in a 16 ~i mode, energy waste will be high and reproduction of a carrier signal will be troublesome. Above all, the energy available for satellite transmitting is not abundant but strictly limited to minimum use. Hence, no large-energy-consuming signal transmitting system will be put into practice until more energy for satellite transmission is available. It is expected that a great number of the 4 FSK receivers are introduced into the market as digital TV broadcasting is soon in service. After introduction to the market, the 4 PSK receivers will hardly be shifted to higher sensitivity models because a signal intercepting characteristic gap between the two, old and new, models is high. Therefore, the transmission of the 4 PSK
signals must not be abandoned.
In this respect, a new system is desperately needed for transmitting the signal point data of a quasi 4 PSK signal in the 16 fj.AM mode with the use of less energy. Otherwise, the limited energy at a satellite station will degrade the entire transmission system.

_. ..._ _ .o ~._ _.z.
The present invention resides in a multiple signal level arrangement in which the four signal point groups 91, 92, 93 94 are allocated at a greater distance from each other, as shown in Fig. 10, for minimizing the energy consumption required for 16 GiAM modulation of quasi 4 PSg signals.
For clearing Lhe relation between the signal receiving sensitivity and the transmitting energy, the arrangement of the digital transmitter 51 and the Pirst receiver 23 will be described in more detail referring to Fig. 1.
Both the digital transmitter 51 and the first receiver 23 are formed of known types for data transmission or video signal transmission e.g. in TV broadcasting service. As shown in Fig. 17, the digital transmitter 51 is a 4 P5E transmitter equivalent to the multiple-bit QA.M transmitter 1, shown in Fig. 2, without AM modulation capabllity. In operation, an input signal ie fed through an input unit 52 to a modulator 54 where it is divided by a modulator input 12i to two components. The two components are then transferred to a first two-phase modulatcr circuit 122 for phase modulation of 2D a base carrier and a second two-phase modulator circuit 123 for phase modulation of a carrier which is 90' out of phase with the base carrier respective: y. Two uutputs of the first and second two-phase modulator circuits 122, 123 are then summed by' a summer 65 to a composite modulated signal which is further transmitted from a transmitter unit 55.
The resultant modulated signal is shaven in the space diagram of Fig. 18.

_ - - ~ -; N.~ ~ =v .~ - .. . , It is known that the four signal points are allocated at equal distances for achievlr_g optimum energy utilization.
Fig. 18 illustrates an example where the four signal points 125, 126, 127, 128 rep..~esent 4 two-bit patterns, I1, O1, 00, and 10 respectively. It is also desired for successful data ., transfer from the digital transmitter 51 to the first receiver 23 than the 4 PSh signal from the digital transmitter 51 has an amplitude of not less than a given level. More specifically, when the minimum amplitude of the 4 PSK signal needed for transmission from the digital transmitter 51 to the first receiver 23 of 4 PSK mode, or the distance between 0 and al in Fig. 18 is A,j,~, the f first receiver 23 successfully intercept any 4 PSX signal having an amplitude of more than A,~.
The first receiver 23 ie arranged to receive at its small-diameter antenna 22 a desired or 4 PSg signal which is transmitted from the tra.nemitter 1 or digital transmitter 51 respectively through the transponder 12 of the satellite 10 and demodulate it with the demodulator 24. In more particular, the first receiver 23 is substantially designed for interception of a digital TV or data communications signal of 4 PSg or 2 PSK mode.
Fig. 19 is a block diagram of the first receiver 23 in which an input signal received by the antenna 22 from the satellite 12 is fed through the input unit 24 to a carrier reproducing circuit 131 where a carrier wave is dEmodulated and to a ~/2 phase shifter 132 where a 90' phew carrier wave __. :~_:_ _. -F" . . .:~_ .. .. .__ is demodulated. Also, two 90°-out-of-phase components of the input signal are detected by a first 133 and a second phase detector circuit 134 respectively and transferred tG a first 136 and a secoad discrimination/demcdulation circuit 137 respectively. Two demodulated components from their respective discrimination/demodulation circuits I36 and 137, which have separately been discriminated at units of time slot by means of timing signals from a timing wave extracting circuit 135, are fed to a first data stream reproducing unit 232 where they are summed to a first data stream signal which is then delivered as nn output from the output unit 26.
The input signal to the first receiver 23 will now be explained in more detail referring to the vector diagram of Fig. 20. The 4 PSK signal received by the first receiver 23 from the digital transmitter 51 is expressed in an ideal form without transmission distortiou and noise, using four signal points 151, I52, 153, 154 shown in Fig. 20.
In practice, the real four signal points appear in particular extended areas about the ideal signal positions 151, 152, 153, 154 respectively due to noise, amplitude distortion, and phase error developed during transmission. If one signal point is unfavorably displaced from its original position, it will hardly be distinguished from its neighbor signal point and the error rate will thus be increased. As the error rate increases to a critical raves, zne reproduction of data becomes less accurate. F'or euabling the data reproduction at a maximum acceptable level of the error - - ,,.,- _.--.o ~ : : . . . . . - _ . . _ . _ rate, the distance between any two signal points should be far enough to be distinguished from each other. If the distance is LAS, the signal point 15I of a 4 PSR signal at close to a critical error level has to stay in a first discriminating area 155 denoted by the hatching of Fig. 20 and determined by ~0-a~'?A~ and ~G-b~~?A~. This allows the signal transmission system to reproduce carrier waves and thus, demodulate a wanted signal. When the minimum radius of the antenna 22 is set to r~, the transmission signal of more than a given level can be intercepted by any receiver of the system. The amplitude of a 4 PSK signal of the digital transmitter 51 shown in Fig. 18 is minimum at A.1,Q and thus, the minimum amplitude A~ of a 4 PSK signal to be received by the first receiver 23 is determined equal to A,ro. As the result, the first receiver 23 can intercept and demode~late the 4 PSK signal from the digital transmitter 51 at the maximum acceptable level of the error rate When the radius of the antenna 22 is more than r~. Tf the transmission signal is of modified 16- or 64-state QAM mode, the first receiver 23 may find difficult to reproduce its carrier wave. For compensation, the signal points are increased to eight which are allocated at angles of (n/4+n~/2) ae shown in Fig. 25(a) and its carrier wave will be reproduced by a 16x multiplication technique. Also, if the signal points are assigned to 16 locations at angles of n~/8 as shown in F'ig.
25(b), the carrier of a quasi 9 PSK mode 16 9AM modulated signal can be reproduced with the carrier reproducing circuit _ CA 02331203 2001-02-05 '. 'i~ _' ~ ~' ~~ .~ .. . . 7 _ .. _ _ . _ .
131 which is modified for performing 16x frequency multiplication. At the rime, the signal points in the transmitter 1 should be arranged to satisfy Al/(A1+A2)=tan(n/8) .
Here, a case of receiving a QPSB signal will be considered. Similarly to the maser performed by the signal point modulating/changing circuit 6? in the transmitter shown in Fig. 2, it is also possible to modulate the positions of the signal points of the QPSH sfgnal shown in Fig. 18 (amplitude-modulation, pulse-modulation, or the like). In this case, the signal point demodulating unit 138 ir_ the first receiver 23 demodulates the position modulated or position changed signal. The demodulated signal is outputted together with the first data stream.
The 16 PSB signal of the transmitter 1 will now be explained referring to the vector diagram of Fig. 8. When the horizontal vector distance Al of the signal point 83 is greater than A,jfl of the minimum amplitude of the 4 PSK signal of the digital transmitter 51, the four signal points 83, 84, 85, 86 in the first quadrant of Fig. 9 stay in the shaded or first 4 PSg signal receivable area 8?. When received by the first receiver 23, the four points of the signal appear in the first discriminating area of the vector field shown in Fie. 20. Hence, any of Lhe signal points 83, 84, 85, 86 of Fig. 9 can be translated into the signal level 151 of Fig. ZO
by the first receiver 23 so that the two-bit pattern of 11 is assigned to a corresponding time slot. The two-bit pattern of 11 is identical to 11 of the first signal point group 91 or first data stream of a signal from the transmitter 1.
Equally, the first data stream will be reproduced at the second, third, or fourth quadrant. As t:~e result, the first receiver 23 reproduces two-bit data of the first data stream out of the plurality of data streams in a 16-, 32-, or 64-state QA.M signal transmitted from the transmitter 1. The second and third data streams are contained in four segments of the signal point group 91 and thus, will not affect on the demodulation of the first data stream. They may however affect the reproduction of a carrier wave and an adjustment, described later, will be needed.
If the transponder of a satellite supplies an abundance of energy, the forgoing technique of 16 to 64-state 8AM mode transmission will be feasible. However, the transponder of the satellite in any existing satellite transmission system is strictly limited in the power supply due to its compact size and the capability of solar batteries. If the transponder or satellite is increased in size thus weight, ZO its launching cost will soar. This disadvantage will rarely be eliminated by traditional techniques unless the cost of launching a satellite rocket is raduced to a considerable level. In the existing system, a common communications satellite provides as low as 20 W of power supply and a common broadcast satellite offers 100 W' to 200 W at best. For transmission of such a 4 PSK signal in the symmetrical 16-state 9ar1 mode as shown in Fig. 9, the minimum signal paint .._:- .._._ :. - ~:~_ _.-. ~..
_ _ - r. ~y'o... _ distance is needed 3A,~ as the 16 QA:At amplitude is expressed by 2A1=A2. Thus, the energy needed far the purpose is nine times greater than that for transmission of a common 4 PSK
signal, in order to maintain compatibility. Also, any conventional satellite transporder can hardly provide a power for enabling such a small antenna of the 4 PSK first receiver to intercept a transmitted signal therefrom. For example, in the existing 40W system, 360W is needed for appropriate signal transmission and will be unrealistic in the respect of cost.
It would be under stood that the symmetrical signal state QAM technique is most effective when Lhe receivers equipped with the same sized antennas are employed corresponding to a given transmitting power. Another novel technique will however be preferred for use with the receivers equipped with different sized antennas.
In more detail, while the 4 PSg signal can be intercepted by a common low cost receiver system having a small antenna, the 16 QA..~i signal is intended to be received by a high cost, high quality, multiple-bit modulating receiver system with a medium or large sized antenna which is designed for prowriding highly valuable services, e.g. ADTV
entertainments, to a particular person who invests more money. This allows both 4 PSK and 16 G7AM signals, if desired, with a 64 DMA, to be transmitted simultaneously with the help of a small incree.se in the transmitting power.
For example, the transmitting power can be maintained ,, _ : - ~: ~~_ ~~..o.
low when the signal points are allocated at Al= AZ as shown in Fig. 10. The amplitude A(4) for transmission of 4 PSK data is a:pressed by a vector 96 equivalent to a square root of (AZ+AZ)Z+(B1+B2)2. Then, ~ A ( 4 ) ( Z=A1Z+$lZATpZ+A'1'pZ=2A,~.32 ' p ( 16 ) ~ ~ (Al+A') Z+ (Bl+BZ ) ~4A,j,~2+4A,~~=B.~Z
~A(16)~/~A(4)~=2 Accordingly, the 16 QAM signal can be transa:itted at a two times greater amplitude and a four times greater transmitting energy than those needed for the 4 PSK signal.
A modified 16 QAM signal according to the present invention will not be demodulated by a common receiver designed for symmetrical, equally distanced signal point QJ~uu'~i. However, it can be demodulated with, the second receiver 33 when two threshold A1 and AZ are predetermined to appropriate values.
At Fig. 10, the minimum distance between two signal points in the first segment of the signal point group 91 is A1 and AZ/2A1 is established as compared with the distance 2A1 of 4 PSH. Then, as A1=A~, the distance becomes 1/2. This explains that the signal receiving sensitivity hss to be two times greater for the same error ra~e and four times greater for the same signal level. For having a four timed greater value of sensitivity, the rt~dius r2 of the antenna 32 of the second receiver 33 has to be two times greater than the radius rl of the antenna 2Z of the first receiver 23 thus satisfying rZ=2r1. For example, the antenna 32 of the second receiver 33 is 60 cm diameter when the antenna 22 if the first receiver . . _ _ _ . . . _ ~- ~ -. :_~: . . .. . . . z . . .
23 is 30 cm. In this manr_er> the second 3ata stream representing the high frequency component of an HDTV will be carried on a signal channel and demodulated successfully. As the second receiver 33 intercepts the second data stream or a higher data signal, its owner can enjoy a return of high investment. Hence, the second receiver 33 of a high price may be accepted. Ac the minimum energy far transmission of 4 PSg data is predetermined, the ratio nlfi of modified 1B APSK
transmitting energy to 4 PSK transmitting energy will be lU calculated to the antenna radius rZ of the second receiver 33 using a ratio between A1 and A2 shown in ~'ig. 10.
in particular, nis is expressed by ((A1+AZ)/Al)Z which is the minimum energy for transmission of 4 PSK data. As the signal point distance suited for modified 16 6?AM interception is AZ, the signal point distance for 4 PSS interception is 2A1, and the signal point distance ratio is AZ/2A1, the antenna radius rZ is determined as shown in Fig. 11, in which the curve 101 represents the relation between the transmittinE energy ratio nls and the radius r2 of the antenna 22 of the second receiver 23.
Also, the point 102 indicates transmission of common 16 QAM at the equal distance signal state mode where the transmitting energy is nine times greater and thus will no more be practi cal . As apparent from the graph of Fi g . 11 , the antenna radius rZ of the seoond receiver 23 cannot be reduced further even if nlfi is increased more than 5 times.
The transmitting energy at the satellite is limited to . . . ~ . . _ . . '. . _ i. "_ _..'-'e ~_'. .. . . . . -a small value and thus, nl6 preferably stays not more than 5 times the value, as denoted by the hatching of Fig. 11. The point 104 within the hatching area 103 indicates, for example, that the antenna radius r2 of a two times greater value is matched with a 4x value of the transmitting energy.
Also, the point 105 represents that the transmission energy should be doubled when rZ is about 5x greater. Those values are alI within a feasible range.
The value of nlfi not greater than 5x value is eapresced us i ng A1 and AZ as nls = ( ( Al~A2 ) /Al ) 2 ~ 5 Hence, AZ<_1.23A1.
If the distance between any two signal point group segments shown in Fig. 10 is 2A(4) and the maximum amplitude is 2A(I6), A(4) and A(18)-A(4) are proportional to Al.and Az respectively. Hence, (A(lfi))~5(A(14))2 is established.
The action of a modified 64 ASPK transmission will be described as the third receiver 43 can perform 64-state QAM
demodulation.
Fig. 12 is a vector diagram in which each signal point group segment contains 16 signal points as compared with 4 signal. points of Fig. 10. The first signal point group segment 91 in Fig. 12 has a 4x4 matrix of 16 signal points allocated at equal interval6 including the point 170. For providing compatibility with 4 PSK, Al?A,1,~ has to be satisfied. If the radius of the antenna 42 of tre third receiver 43 is r3 and the transmitting energy is n~, the _ F ~ _ _ , _ ;_. . ._ 'i~..~i_ c'=". .~.. ..-: _.
equation is eapressed as:
r3Z = ~6Z/~n-1) ~r;2 This relatian between r3 and n of a 64 Q~''f signal is also shown in the graphic representation of Fig. 13.
It is under stood that the signal point assignment shown in Fig. 12 allows the second receiver 33 to demodulate only ~wo-bit patterns of 4 PSK data. Hence, it is desired for having compatibility between the first, second, and third receivers that the second receiver 33 is arranged capable of demodulating n modified 16 QAM form from the 64 AAM modulated signal.
The compatibility between the three discrete receivers can be implemented by three-level grouping of signal points, as illustrated in Fig. 14. The description will be made referring to the first quadrant in which the first signal point group segment 91 represents the two-bit pattern 11 of the first data stream.
In particular, a first sub segment 181 in the first signal point group segment 91 is assigned the two-bit pattern 11 of the second data stream. Equally, a second 182, a third 183, and a fourth sub segment 184 are assigned O1, 00, and 10 of the same respectively. This assignment is identical to that shown in Fig. 7.
The signal point allocation of the third data stream will now be explained referring to the vector diagram of Fig.
15 which shows the first quadrant. As shown, the four signal points 201, 205, 209, 213 represent the two-bit pattern of :_- .,_.. . .:._ ~=~_ -.-:~-~
11, the signal paints 202, 206, 210, 214 represent O1, the signal points 203, 207, 211, 215 represent 00, and signal points 204, 208, 212, 216 represent 10. Accordingly, the two-bit patterns of the third data stream can be transmitted separately of the first and second data streams. In other words, two-biz data of the three different signal levels can be transmitted respectively.
As understood, the present invention permits not only transmission of six-bit data but also interception of three, two-bit, four-bit, and six-bit, different bit length data with their respective receivers while the signal compatibility remains between three levels.
The signal point allocation for providing compatibility between the three levels will be described.
As shown in Fig. 15, Al?A,l,~ is essential for allowing the first receiver 23 to receive the first data stream.
It is needed to space any two signal points from each other by such a distance that the sub segment signal points, e.g. 182, 183, 184, of the second dnta stream shown in Fig.
15 can be distinguished from the signal point 91 saown in Fig. 10.
Fig. 15 shows that they are spaced by 2/3A2. In this case, the distance between the two signal points 201 and 202 in the first sub segment 181 is AZ/6. Tre transmitting energy needed for signal interception with the third receiver 43 is now calculated. If the radius of the antenna 32 is r3 and the needed transmitting energy is n~ Limes the 4 PSK transmitting . . . , . 7 _ : _ . F _ ~' 'j:,~ ' C t.=o'~~ . , . . _ . : . . . . _ .
energy, the equation is expressed as:
r3Z= ( 12r1)Z/ (il-1 ) This relation is also denoted by the curve 211 in Fig. 16.
For example, if the transmitting energy is 6 0~ 9 times greater than that for 4 PSK transmission at the point 223 or 222, the antenna 32 having a radius of 8x or 6x value respectively can intercept the first, second, and third data streams for demodulation. As the signal point distance of the Second data stream ie close to 2/3A2, the relation between rl and r2 is expressed by:
rZ~= ( 3r1) ~/ (n~l ) Therefore, the antenna 32 of the second receiver 33 has to be a little bit increased in radius as denoted by the curve 223.
As understood, whsle the first and second data streams are transmitted trough a traditional satellite which provides a small signal transmitting energy, the third data stream can also be transmitted through a future satellite which provides a greater signal transmitting energy without interrupting the action of the first and second receivers 23, 33 or with no need of modification of the same sad thus, both the compatibility and the advancement will highly be ensured.
The signal receiving action of the second receiver 33 will first be described. As compared with the first receiver 23 arranged for interception with a small radius rl antenna and demodulation of the 4 P5K modulated signal of the digital transmitter 51 or the first data stream of the signal of the transmitter 1, the second receiver 33 is adopted for . . . . . _ . . . . ~ -:a- .
perfectly demodulating the lti signal state two-bit data, shown in Fig. 10, or second data stream of the 1B QAM signal from the transmit:er I. In total, fou~-bit data including also the first data stream can be demodulated. The ratio between Ai and AZ is however different in the two transmitters. The two different data are loaded to a demodulation controller 231 of the second receiver 33, shown in Fig. 21, which in turn supplies their respective threshold values to the demodulating circuit for AM demodulation.
The block diagram of the second receiver 33 in Fig. 21 is similar in basic construction to that of the first receiver 23 shown in Fig. 18. The difference is that the radius rZ of the antenna 32 is greater than ry of the antenna 22. This allows the second receiver 33 to identify a signal component involving a smaller signal point distance. The demodulator 35 of the second receiver 33 also contains a first 232 and a second data stream reproducing unit 233 in addition to the demodulation controller 231. There is provided a first discrimination/reproduction circuit 13fi for 2U AM demodulation of modified 16 QA~'~ signals. As understood, each carrier is a four-bit signal having two, positive and negative, threshold values about the zero level. As apparent from the vector diagram, of Fig. 22, the threshold values are varied depending on the transmitting energy of a transmitter since the transmitting signal of the embodiment i~ a modified 16 QAM signal. When the reference threshold is TH16, it is determined by, as shown in Fig. 22:

.:::_ _-._._ . :-_-; r-.-_ ~-f.:-'.. "., .-. . -.. __.
THIo = f Al+A~ / 2 ) / C A1+AZ ) The various data for demodulation including A1 and A2 or TH_5, and the value m for multiple-bit modulation are also transmitted from the transmitter 1 as carried in the first data stream. The demodulation controller 231 may be arranged for recovering such demodulation data through statistic process of the received signal.
A way of determining the shift factor A1/AZ will described with reference to Fig. 26. A change of the shift factor A~/AZ causes a change of the threshold value. Increase of a difference of a value of AljAz set at the receiver side from a value of Al/AZ set at the transmitter side will increase the error rate. Referring to Fig. 26, the demodZ:lated signal from the second data stream reproducing 1~ unit 233 may be fed back to the demodulation controller 231 to change the shift factor Al/A2 in a direction to increase the error rate. Hy this arrangement, the third receiver 43 may not demodulate the shift factor Al/AZ, so that the circuit constriction can be simplified. Further, the transmitter may not transmit the shift factor Ai/AZ, so that the transmission capacity can be increased. This technique can be applied also to the second receiver 33.
'The demodulation. controller 231 has a memory 231a for storing therein different threshold values (i.e., the shift factors, ti:e number of signal points, the synchronization rules, etc.) which correspond to different channels of TV
broadcas~. Wi:en receiving one of the channels again, the _. ~ _ _ _ .
_ _.
_ . .._ _ . . . . . , _ . . F .. ... ~ cT";o'~-n. ..-. -. -.: ._.
values corresponding to the receiving channel will be read out of the memory to therebs~ stabi 1 ize the reception quickly.
If the demodulation data is lost, the demodulation of the second data stream will hardly be executed. This kill be explained referring to a flow chart shown in Fig. 24.
Even if the demodulation data is not available, demodulation of the 4 PSH at Step 313 and of the first data stream at Step 301 can be implemented. At Step 302, the demodulation data retrieved by the first data stream reproducing :,trait 232 is transferred to the demodulation controller Z31. if m is 4 or 2 at Step 303, the demodulation controller 231 triggers demodulation of 4 PSg or 2 PSg at Step 313. If not, the procedure moves to Step 310. At Step 305, two threshold values THe and TH16 are calculated. The threshold value THlb for A_M demodulation is fed at Step 306 from the demodulation controller 231 to both the first 136 and the second discri:nination/reproduction circuit 137.
Hence, demodulation of ~he modified 16 QAM signal and reproduction of the second data stream can be carried out at Steps 307 and 315 respectively. At Step 308, the error rate is examined and if high, the procedure returns to Step 313 for repeating the 4 PSK demedulaticn.
As shown in Fig. 22, the signal points 85, 83, are aligned on E line at an angle of cos(c~t+nn/2) while 84 and 86 are off the line. Hence, the feedback of a second data stream transmitting carrier wave data from the second data stream .reproducing unit 233 to a carrier reproducing circuit .__.- _ ;_.. . ~:._: ;.~_ ~-=y__ ..:
131 is carried out so that no carrier needs to he extracted nt the timing of the signal points 84 and 86.
The transmitter 1 is arranged to transmit carrier timing signals at intervals of a given time with the first data stream for the purpose of compensation for no demodulation of the second data stream. The carrier timing signal enables to identify the signal points 83 and 85 of the first data stream regardless of demodulation of the second data stream. Hence, the reproduction of carrier wave can be triggered by the transmitting carrier data to the carrier reproducing circuit 131.
It is then examined at Step 304 of the flow chart of Fig. 24 whether m is 16 or not upon receipt of such a modified 64 QAM signal as shown in Fig. 23. At Step 310, it iB also examined whether m is more than 64 or not. If it is determined at Step 311 that the received signal has no equal distance signal point constellation, the procedure goes to Step 312. The signal point distance THE of the modified 64 QAM signal is calculated from:
THE _ (A1+AZ/2 ) / (Al+AZ ) This calculation is equivalent to that of THl6 but its resultant distance between signal points ie smaller.
If the signal paint distance in the first sub segment 181 is A3, the distance between the first 181 and the second sub segment 182 is expressed by (AZ-2A~) . Then, the average distance is (AZ-2A3)/(Al+AZ) whi ch is designated as due. When d~ is smaller than TZ which represents the signal point .._.- . ;_.. . :-._: -.- =--.o-:; . .. .. . -~- z ..
discrimination capability of the second receiver 33, any two signnl points ir. the. segment will hardly be distinguished from each other. This judgement is executed at Step 313. If d~ is out of a permissive range, the procedure moves back to Step 313 for 4 PSK mode demodulation. If d~ ie within the range, the procedure advances to Step 305 for allowing the demodulation of 16 QAM at Step 307. If it is determined at Step 308 that the error rate is too high, the procedure goes back to Step 313 for 4 PSK mode demodulation.
When the transmitter 1 supplied a modified 6 pAM signal such es shown in Fig. 25(x) in which all the signal points are at angles of cos(2~f+n~u/4), the carrier waves of the signal are lengthened to the same phase and will thus be reproduced with much ease. At the time, two-bit data of the first data stream are demodulated with the 4-PSK receiver while oue-bit data of the second data stream is demodulated with the second receiver 33 and the total of three-bit data can be reproduced.
The third receiver 43 will be described i.n more detail.
Fig. 26 shows a block diagram of the third receiver 43 similar to that of the second receiver 33 in Fig. 21. The difference is that a third data stream reproducing unit 234 is added anti also, the discrimination;reproduction circuit has a capabi.Iity of identifying eight-bit data. The antenna 42 of the third receiver 43 has a rndius r3 greater than r2 thus allowing smaller distance state signals, e.g. 32- or 64-state 4AM signals, to be demodulated. For demodulation of the ..:.= . :__. . --_.,- ~:...l_ _--:,-~- .... ..:. ., -64 4Ah! signal, the first discrimination/reproduction circuit 13~ has to identify 8 digital levels of the detected signal in which seven different threshold levels are involved. As one of the threshold values is zero, three are contained in the first quadrant.
Fig. Z7 shows a space diagram of the signal in which the first quadrant contains three diffQrent threshold values.
As shown in Fig. 27, when the three normalized threshold values are TH1~, TH2~, and TH3~, they are expressed by:
TH1~ _ (A1+A3/ 2 ) / (Al+A2 ) TH2~ _ (Al+AZ/2 ) / (Al+A2 ) and TH3~ _ (Al+AZ-A3/2 ) / (Al+AZ) .
Through AM demodulation of a phase detected signal using the three threshold values, the third data stream can be reproduced like the first and second data stream ezplained with Fig. 21. The third data stream contains e.g. four signal points 201, 202, 203, 204 at the first sub segment 181 shown in Fig. 29 which represent 4 values of two-bit pattern.
Hence, sia digits or modified 64 Q.AM signals can be demodulated The demodulation controller 231 detects the value m, Ai, AZ, and Az Prom the demodulation data contained in the first data stream demodulated at the first data stream reproducing unit 232 ar.d calculates the three threshold values TH1~, TH2~, amd TH3~ which are then fed to the first 136 and the second dis~rimination/reproduction circuit 137 so that the modified 64 QAM signal is demodulated with certaint;r. Also, .. . _ _.7... . f'. , '~";_ cW:aW~: . . . . . . ..
if the demodulation data have beer_ scrambled, the modified 64 QAI~i signal can be demodulated only with a specific or subscriber receiver. Fig. 28 is a flow chart showing the action of the demodulation controller 23i for modified 6Q CdAM
signals. The difference from the flow chart for demodulation of 16 QA.'~ shown in Fig. 24 will be explained. The procedure moves from Step 304 to Step 320 where it is examined whether m=32 or not. If m=32, demodulation of 32 Q~'I signals is executed at Step 322. If not, the procedure moves to Step 321 IO where it is examined whether m=84 0: not. If yes, A3 is examined at Step 323. If A3 is sms.lier than a predetermined value, the procedure moves to Step 306 and the sane sequence as of Fig. 24 is implemented. If It is judged at Step 323 that A3 is not smaller than the predetermined value, the procedure goes to Step 324 where the threshold values are calculated. At Step 325, the calculated threshold values are fed to the first and second discrimination/reproduction circuits and at Step 326, the demodulation of the modified 64 QAM signal is carried out. Then, the first, second, and third data streams are reproduced at Step 32 i . At Step 32$, the error rate is examined. If the error rate is high, the procedure moves to Step 305 khere the lE 6L~M demodulation is repeated and if Iow, the demodulation of the 64 GlAM is continued.
The action of carrier wave reprodu~Lion needed for execution of a satisfactory demod~:lating procedure v.il1 now be described. The scope of the present invention includes 4~

. _ _ . ' _ 1. _ _ . ~. ~ . V.~._ v.- p ~ ~ .~ .. . . : . v . _ _ reproduction of the first data stream of a modified 16 or 64 QpM signal with the use of a 4 PSb receiver. However, a common 4 PSB receiver rarely reconstructs carrier waves, thus failing to perform a correct demodulation. For compensation, some arrangements are necessary at ooLh the transmitter and recQiver sides.
Two techniques for the compensation are provided according to the present invention. A first technique relates to transmission of signal points aligned at angles of (2n-1)a/4 at intervals of a given time. A second technique offers transmission of signal points arranged at intervals of an angle of nn/8.
According to the first technique, the eight signal points including 83 and 85 are aligned at angles of ~/4, 3n/4, 5a/4, and ?n/4, as shown in Fig. 38. In action, at least one of the eight signal points is transmitted during sync time slot periods 452, 453, 454, 455 arranged at equal intervals of a time in a time slot gap 451 shown in the time chart of Fig. 38. Any desired signal points are transmitted during the other time slots. The transmitter 1 is also arranged to assign a data for the time slot interval to the sync timing data region 499 of a sync data block, as shown in Fig. 41.
The content of a transmitting signal will be ezplained in more detail referring tv Fig. 41. The time slot group 451 containing the sync time slots 452, 4~3, 454, 455 represents a unit data stream or block 491 carrying a data of Dr_.

- . ; _ . . . :_ . _ - w.= ~ ~=:~w_. . .. . . z . _ _ ~ .
The sync time slots in the signal are arranged at equal intervals of a given time determined by the time slot interval or sync timing data. Herce, when the arrangement of the sync time slots is detected, reproduction of carrier S waves will be executed slot by slot through extracting the sync timing data from their respective time slots.
Such a sync timing data S is contained in a sync block d93 accompanied at the front end of a data frame 492, which is consisted of a number of the sync time slots denoted by the hatching in Fig. 41. Accordingly, the data to be extracted for carrier wave reproduction are increased, thus allowing the 4 PSK receiver to reproduce desired carrier waves at higher ac.:uracy and efficiency.
The sync block 493 comprises sync data regions 496, 497, 498,---containing sync data S1, S2, 83,---respectivel}~ which include unique wards and demodulation data. The phase sync signal assignment region 499 is accompanied at the end of the sync block 493, which holds a data of I? including information about interval arrangement and assignment of the sync time slots.
The signal point data in the phase sync time slot has a particular phasz and can thus be reproduced by the 4 PSK
receiver. Accordingly, IT in the phase sync signal assignment region 499 car. be retrieved w;thout error thus ensuring the reproduction of carrier waves at accuracy.
As shown in Fig. 41, the sync block 493 is followed by a demodulation data block 501 which contains demodulation .:. __ . ._:. . 'r. _' 'i.:..'_ ~~':i'.'": . . :. .. . . _ ..
data aboLt threshold voltages needed for demodulation of the modified multiple-bit 9.A.M signal. This data is essential for demodulation of the multiple-bit 41AM signal and may preferably be coraained in a region 502 which is a part of the sync block 493 for ease of retrieval.
Fig. 42 shows the assignment of signal data for transmission of burst form signals through a TDMA method.
The assignment is distinguished from that of Fig. 41 by the fact that a guard period 521 is inserted between any two adjacent Dn data blocks 491, 491 for interruption of the signal transmission. Also, each data block 491 is accompanied at front end a sync region 522 thus forming a data block 492. During the sync region 522, the signal points at a phase of (2n-1)n/4 are only transmitted.
Accordingly, the carrier Wave reproduction will be feasible with the 4 PSg receiver. More specifically, the sync signal an3 carrier waves can be reproduced through the TDMA method.
The carrier wave reproduction of the first receiver 23 shown ir. Fig. 19 will be explained in more detail referring 2C to Figs. 43 and 44. As shown in Fig. 43, an input signal is fed through the input unit 24 t.o a sync detector circuit 541 where it ie sync detected. A demodulated signal from the sync dete~LOr 541 is transferred to an output circuit 542 for reproduction of the first data stream. A data of the phase sync signal assignment data region 499 (shown in Fig. 41) is retrievEd with an ektracting timing controller circuit 543 so that the timing of sync signals of (2n-1)n/4 data can be _ .. . . : i _ _ . . . ' 'F:._ _ _'- ~o-". . .. . _ . . : . _ _ " ~ .
acknowledged and transferred as a phasE sync control pulse 561 shown ir. Fig. 44 to a carrier reproduction controlling circuit 544. Also, the demodulated signsl ,of the sync detector circuit 541 is fed to ~ frequency multiplier circuit 545 where it is 4x multiplied prior to transmitted to the carrier reproduction ;.ontrolling circuit 544. The resultant signal denoted by 562 in Fig. 44 contains a true phase data 563 and other data. As illust~ated i.n s time chart 564 of Fig. 44, the phase sync time slots 452 carrying the (2n-1)n;4 ld data are also contained at equal intervals. At the carrier reproducing controlling circuit 544, the signal 562 is sampled by the phase sync control pulse 561 to produce a phase sample signal 565 which is then converted through sample-hold action to a phase signal 566. The phase signal 566 of the carrier reproduction controlling circuit 544 is fed across a loop filter 546 to a VCO 547 where its relevant carrier wave is reproduced. The reproduced carrier is then seat to the sync detector circuit 541.
In this manner, the signal point data of the (2n-1)x/4 phase denoted by the shaded areas in Fig. 34 is recovered and utilized so that a correct carrier wave can be reproduced by 4x or 16a frequency multil:iication. Although a plurality of phases are reproduced at the tiwe, the absolute phases of the carrier can be successfully be identified with the used of a 23 unique word assigned t~ the sync region 496 shown in Fig. 41.
For transmlssion of a modified 64 GRAM signal such as shown in Fig. 40" signal points ire the phase sync areas 471 I'::.. 'i-~_ ,_~''~'~_ ~~.. _.z. .. ...
at the (2n-1)n/4 phase denoted by the hatching are assigned to the sync time slots 452, 452b, etc. Its carrier can be reproduced hardly with a common 4 PSK receiver but successfully with the first receiver 23 of 4 PSR mode provided with the carrier reproducing circuit of the embodiment.
The foregoing carrier reproducing circuit is of COSTAS
type. A carrier reproducing circuit of reverse modulation type will now be explained according to the embodiment.
Fig. 45 shows a reverse modulation type carrier reproducing circuit according to the present invention, in which a received signal is fed from the input unit 24 to a sync detector circuit 541 for producing a demodulated signal.
Also, the input signal is delayed by a first delay circuit 591 to a delay eignal_ The delay signal is then transferred to a quadrature phase modulator circuit 592 where it is reverse demodulated by the demodulated signal from the sync detector circuit 541 to a carrier signal. The carrier signal is fed through a carrier reproduction controller circuit 544 to a phase comparator 593. A carrier wave produced by a VCO
547 is delayed by a second delay circuit 594 to a delay signal which is also fed to the phase comparator 593. At the phase comparator 594, the reverse demodulated carrier signal is compared in phase with the delay signal thus producing a phase difference signal. The phase difference signal sent through 8 loop filter 546 to the VCO 547 which in turn produces a carrier wave arranged in phase with the received . . _ . . n ~ a - . . . i ~- . ~ ~ C T'~.0 ~
.. . . T . . . . .
carrier wave. In the same manner as of the GOS1'AS carrier reproducing circuit shown W Fig. 43, an extracting timing controller circuit 543 performs sampling of signal points contained in the hatching areas of Fig. 39. Accordingly, the carrier wave of a 16 or 64 G1AM signal can be reproduced with the 4 PSH demodulator of the first receiver 23.
The reproduction of a carrier wave by 16x frequency multiplication will be explained. The transmitter 1 shown in Fig. 1. is arranged to modulate and transmit a modified 16 QAM
signal with assignment of its signal points at nn/8 phase as shown in Fig. 46, At the Pirst receiver 23 shown in Fig. 19, the carrier wave ca.n be reproduced with its COSTAS carrier reproduction controller circuit containing a I6: multiplier circuit 661 shown in Fig. 48. The signal points at each nu/8 phase shown in Fig. 46 are processed at the first quadrant b the action of the 16x multiplier circuit 661, whereby the carrier will be reproduced by the combination of a loop filter 546 and a VCO 541. Also, the absolute phase may be determined from 16 different phases by assigning a unique word to the sync region.
Tho arrangement of the 16x multiplier circuit will be explained referring to Fig. 48. w sum signal and a difference signal are produced from the demodulated signal by an adder circuit 662 and a subtracter circuit 663 respectively and then, multiplied each other by a multiplier 664 to a cps 26 signal. Also, a multiplier 665 produces a sin 28 signal. The two signals are then multiplied by a multiplier 668 to a sin _ A, : Cr -Q !-.;:.- .-_:- . :.-...' ' .~_ --.--~~-. . .
48 signal.
Similarly, a sin 88 signal is produced from the two, sin 28 and cos 28, signals by the combination of an adder circuit 687, a subtracter circuit 668, and a multiplier 670.
Furthermore, a sin 166 signal is produced by the combination of an adder circuit 671, a subtracter circuit 672, and a multiplier 673. Then, the 16a multiplication is completed.
Through the foregoing 16z multiplication, the carrier wave of all the signal points of zhe modified iB QA.ht signal shown in Fig. 46 will successfully be reproduced without extracting particular signal points.
Eowever, reproduction of the carrier wave of the modified 64 flAM signal shown in Fig. 47 can involve an increase in the error rate due to dislocation of some signal pints from the sync areas 471.
Two techniques are known for compensation for the consequences. One is inhibiting transmission of the signal points dislocated from the sync areas. This causes the total amount of transmitted data to be reduced but allows the arrangement to be facilitated. The other is providing the sync time slots as described in Fig. 38. In more particular, the signal points in the nn/8 sync phase areas, e.g. 471 and 4?la, are transmitted during the period of the corresponding sync time slots in ~he time slot group 451, This triggers an 26 accurate synchronizing action during the period thus minimizing phase error.
As row understood, the 16x multiplication allows the simple 4 PSA receiver to reproduce the carrier wave of a modified 16 or o4 pAM signal. Also, the ir_sertion of the sync time slots causes the phasic accuracy to be increased during the reproducticn of carrier waves from a modified 64 QAM signal.
As set forth above, the signal transmission system of the present invention is capable of transmitting a plurali~y of data on a single carrier wave simultaneously in the multiple signal level arrangement.
More specifically, three different level receivers which have discrete characteristics of signal intercepting sensitivity and demodulating capability are provided in relation to one single transmitter so that any one of them can be selected depending on a wanted data size to be demodulated which is proportional to the price. When the first receiver of low resolution quality and low price is acquired together with a small antenna, its owner can intercept and reproduce the first data stream of a transmission signal. When the second recaiver of medium resolution quality and medium price is acquired together with a medium antenna, its owner can intercept and reproduce both the first and second data streams of the signal. When the third receiver of high resolution quality and high price is acquired with a large antenna, its owner can into~cept and reproduce all the first, second, and third data s~reams of the signal.
If the first receiver is a home-use digital satellite ._..- .!-._ . r-.,. 'f_.~'_ C.!-:o.':- .,.. ..-. ., . .
broadcast receiver of low price, it will overwhelmingly be welcome by a majority Of viewers. The second receiver accompanied with the medium antenna costs more and will be accepted by not common viewers but particular people who wants to enjoy HDTV services. The third receiver accompanied with the large antenna at least before the satellite output is increased, is not appropriated for home use and will possibly be used in relevant industries. For example, the third data stream carrying super HDTV signals is transmitted via a satellite to subscriber cinemas which can thus play video tapes rather than traditional movie films and run movies business at low cost.
When the present invention is applied to a TV signal transmission service, trree different quality pictures are carried on one signal channel wave and will offer compatibility with each other. Although the first embodiment refers to a 4 PSK, a modified 8 QAM, a modified 16 QAM, and a modified 64 QAM signal, other signals will also be employed with equal success including a 32 QAbI, a 256 QAL~I, an 8 PSK, a 16 PSK, a 32 PSK signal. It would be understood that the present invention is not limited to a satellite transmission system and will be applied to a terrestrial communications system or a cable transmission system.
Embodiment 2 A second embodiment of the present invention is featured in which the physical multi-level arrangement of the first embodiment is divided into small levels though e.g.

. . . . . _ _ _ r- _, w ::~_ _T~;-~-- , . . . . . . . . . .
discriminatior. in error correction capability, thus forming a logic nult~-level construction. In the first embodiment, each m~:.lti-level channel has different :evels in the electric signal amplitude or physical demodulating capability. The second embodiment offers different levels in the logic reproduction capability such as error correction. For example, the data D1 in a multl-level channel is divided into two, D~_1 and D1_Z, components and D1_1 is more increased in the error correction capability than D~_2 for discrimination.
Accordingly, as the error detection and correction capability is different between Dl_1 and Di_~ at demodulation, D1_1 can successfully be reproduced within a given error rate When the C/N level of an original transmitting signal is as low as disenabling the reproduction of Dl_z. This will be implemented using the logic mufti-level arrangement.
More specifically, the logic mufti--level arrangement is consisted of dividing data of a modulated nulti-level channel and discriminating distances between error correction codes by mixing error correction codes with product codes for varying error correction capability. Hence, a more multi-level signal can be transmitted.
In fact, a D1 channel is divided into two sub channels D1_I and DI_Z and a DZ channe 1 i s d i v i de d i nto two sub channe 1 s DZ_1 and DMZ .
This will be explained in more detail referring to Fig.
87 in whi ch D1_i is reproduced f rim a lowest C/N signal . If the C/N rate is d at minimum, three components D1_~, DZ_1 and D~_Z cannot be reproduced while D:_i is reproduced. If C/N is not less than c, D1_Z can also be reproduced. Equally, when C/N is b, DZ_l is reprodu.~.ed and when C/N is a, D?_Z is reproduced. as the C/N rate increases, the reproducible signal levels are increased in number. The lower the C/N, the fewer the reproducible signal levels. This will be explained in the form of relation between transmitting distance and reproducible C/N value referring to Fig. 86. In common, the C/N value of a received signal is decreased in proportion to the distance of transmission as expressed by the real line 861 in Fig. 86. It is now assumed that the distance from a transmitter antenna to a receiver antenna is La when C/N=a, Lb when C/N=b, Lc when C/N=c, Ld when C/N=d, and Le when C/N=e. If the distance from the transmitter antenna is greater than Ld, D1_i can be reproduced as shown in Fig. 85 where the receivable area 862 is denoted by the hatching. In otlier words, D1_1 can be reproduced within a most extended area. Similarly, Di_Z can be reproduced in an area 863 when the distance is not more than Lc. In this area 863 containing the area 862, Dl_, can with no doubt be reFroduced. In a small area 854, DZ_1 can be reproduced and in a amalleet area 865, DZ_Z can be rep:oduced. As understood, the different data levels of a channel can be reproduced corresponding to degrees of declination in the C/N rate. The logic multi-level arrangement of the signal transmission system of the present invention can provide the sense effect as of a traditional analogue transmission system in which th amount of receivable _ -, _ , _ - ;. J =._._~__._ data is gradually lowered as the C/:V rate decreases.
The constru~tior. of the logic multi-level arrangement will be described in which there are provided t~:o physical levels and two logic levels. Fig. 87 is a block diagram of a transmitter 1 which is substaLtiaily identical in construction to teat shown in Fig. 2 and described previously in the first embodiment a~ci will no further be explained in detail. The only difference is that error correction code encoders are added as abbreviated to ECC encoders. The divider circuit 3 has four outputs 1-1, 1-2, 2-1, and 2-2 through which four signals D~_i, D1_2, D~1, and DZ_Z divided from an input signal are delivered. T'he two signals Dl_1 and D._Z
are fed to two, main ar_d sub, ECC encoders 872a, 873a of a first ECC encoder 871a respectively for converting to error correction code forms.
The main ECC encoder 872a has a h'_gher error correction capability than that of the sub ECC encoder 873x. Hence, D1_1 can be reproduced at a lower rate of C/N than DI_Z as apparent from the CI3-level diagram of F'ig. 80. More particularly, the logic level of Dl_1 is less affected by dEClination of the C/'_Y
than that of D:_2. After error correction code encoding, D1_1 and Dl_L are summed by a summer 874a to a Dl signal whicY. is then transferred tc the modulator 4. The other two signals D~_ and DZ_~ of the divider ci:cui~ 3 are error correction encoded by two, main and sub, ECC encoders 872b, 873b of a second 1_CC encoder 871b respectively and then, summed by s summer 874b to a DZ signs= which i5 transmitted to the ._. _..___ . F-:,- _ c'-'~'.°
modulator 4. The main ECC encoder 872b is higher in the error correction capability than the sub ECC encoder 873b.
The modulator 4 in turn produces from the two, Dl and D2, input signals a multi-level modulated signal which is further transmitted from the transmitter unit 5. As understood, the output signal from the transmitter 1 has two physical levels Dl and DZ and also, four logic levels Dl_l, D1-2' DZ-i' ~d D2-2 based on the two physical levels for providing different error correction capabilities.
The reception of such a multi-level signal will be explained. Fig. 8B is a block diagram of a second receiver 33 which is almost identical in construction to that shown in Fig. 21 and described in the first embodiment. The second receiver 33 arranged for intercepting multi-level signals from the transmitter 1 shown in Fig. 87 further comprises a first 878a and a second ECC decoder 876b, in which the demodulation of QAM, or any of ASK, PSFi, and FSg if desired, is executed.
As shown in Fig. 88, a receiver signal is demodulated by the demodulator 35 to the two, Dl and DZ, signals which are then fed to two dividers 3a and 3b respectively where they are divided into four logic levels Dl_l, Di-2' D2-1' and DZ_Z. The four signals are transferred to the first 878a and the second ECC decoder 876b in which Dl_~ is error corrected by a main ECC decoder 877a, Dl_2 by a sub EC~ decoder 878x, D2_1 by a main ECC decoder 877b, DZ_Z by a sub ECC decoder 878b before all sent to the summer 37. At the summer 37, the four, Dl-1' ._.. . ,_. . F:_- '-r:.~'~ ~--'vo:~. a .. ..z. .. .,. ...
Dl_Z, D~_l, end DZ_Z, error corrected signals are summed to a signal which ie then delivered frcm the output unit 36.
Since Dl_1 and b~_1 are higher in the error correction capability than D1_' a :d DZ_Z respectively, the error rate remains less than a given value although C/N is fairly- low as shown in Fig. 85 and thus, an original signal will be reproduced successfully.
T?1e action of discriminating the error correction capability between the main ECC decoders 877a, 877b and the sub ECC decoders 878a, 878b wi ll now be described in more detail. It is a good idea for having a difference in the error correction capability to use in the sub ECC decoder a common coding technique, e.g. Reed-Solomon or BCH method, having a standard code distance and in the main ECC decoder, another encoding technique in which the distance between correction codes is increased using Reed-Solomon cod s, their product codes, or other long-length codes. A variety of known techniques for increasing the error correction code distance have been introduced and will no more explained, The present invention can be associated with any known technique for having the logic u:ulti-level arrangement.
The logic multi-level arrangement m 11 be explained in conjunction with a diagram of Fig. 89 showing the relation between C/R and error rate after error correction. As shown, the straight line 881 represents Dl_1 at tre C/N and error rate relation and the line 882 represents Dl_2 at same.
As the C/N rate of an input signal decreases, the error _ p ~. _ _. r_: . .. . . . _ . . . .
--.: ' ~; _: how rate increases after error correction. If C/N is lower than a given value, the error rate exceeds a reference value Eth determined by the system design standards and no original cats will normally be reconstructed. When C/N is lawered to lass tl-.an e, the D1 signal fails to be reproduced as expressed by the line 881 of Dl_1 in Fig. 89. When a<_C/N<d, Dl_1 of the Dl signal exhibits a higher error rate than Eth and will not be reproduced.
When C/N ie d at the point Fs85d, D1_1 having a higher Id error correction capability than Dl_~ becomes not higher in the error rate than Eth and can be reproduced. At the time, the error rate of Dl__Z remains higher than Eth after error correction a:ld will no longer be reproduced.
When C/N is increased up to c at the point 885c, Dl_Z
becomes not higher in the error rate than Eth and can be reproduced. At the time, D~1 and DMZ remain in no demodulation state. After the C/N rate is increased further to b', the DZ signal becomes ready to be demodulated.
when C/N is increased to b at the point 885b, DZ_1 of the DZ signal becomes not higher in the error rate than Eth and can be reproduced. At the time, the error rate of DMZ remains higher than Eth and will not be reproduced. When C/N is increased up to a at the point 885a, DZ_2 becomes not higher than Eth and can be reproduced.
As described above, the four different signal logic levels divided from two, D1 and D2, physical levels through discrimination of the error correction capability between the _. t~
- , - _ .__.- _-_. . -~.~ .,_. ___~ _._ _ . _-_ .. ' _ .~ _ _ levels, can be transmitted simultaneously.
Lsing the logic mufti-level arrangement of the present invention in accompany with a mufti-level construction in which at least a part of the original signal is reproduced even if data in a higher level is lost, digital signal transmission will successfully be ezecuted without losing the advantageous effect of an analogue signal transmission in which transmitting data is gradually decreased as the C/N
rate becomes low.
Thanking to up-to-data image data compression techniques, compressed image data can be tranEmitted in the Logic mufti-level arrangement for enabling a receiver station to reproduce a higher quality image than that of an enalogue system and also, with not sharply but at steps declining the signal level for ensuring signal interception in s wider area. The present invention can provide an extra effect of the mufti-layer arrangement which is hardly implemented by a known digital signal transmission system without deteriorating high quality image data.
Embo ~,ment 3 .4 third embodiment of the present invention will be described referring to the relevant drawings.
Fig. 29 is a schematic total view illustrating the third embodiment .n the form of a digital ~f~' broadcasting system.
An input video signal 402 of super high resolution T'' image is fed to an input unit 403 of a first video encoder 401.
Then, the signal is divided by a divider circuit 404 into = . - _ . . . :. _ _ _ ~,,y .,_ _,_.-_-_:- . : . . _ .
three, first, second, and third, data streams which are transmitted to a compressing circuit 405 for data compression before further delivered.
Equally, other three input video signals 406, 40., and 408 are fed to a second 409, a third 410, and a fourth video encoder 411 respectively which all are arranged identical in construction to the first video encoder 401 for data compression.
The four first data streams from their respective encoders 401, 409, 410, 911 are transferred to a first multipleaer 413 of a multiplexer 412 where they are time multiplexed by TD'S process to a first data stream multiples signal which is fed to a transmitter 1.
A part or al l of the four second data streams from their respective encoders 401, 409, 410, 411 are transferred to a second multipleaer 414 of the multiplexer 412 where they are time multiplexed to a second data stream multiplex signal which is then fed to the transmitter 1. Also, a part or all of the lour third data streams are transferred to a third multiplexer 415 where they are time multiplexed to a third data stream multiplez signal which is then fed to the transmitter 1.
The transmitter 1 performs modulation of the three data stream signals with its modulator 4 by the same manner as described in the first embodiment. The modulated signals are sent from a transmitter unit 5 through an antenna 6 and an upiink 7 to a transponder 12 of a satellite 10 which in turn .:__ ..___ .--_, ~..~_ _-:o-___ transmits it to three different receivers including a first recei~~er 23.
The modulated signal transmitted through a downlink 21 is intercepted by a small antenna 22 having a radius r1 and fed to a first data stream reproducing unit 232 of the first receivar 23 where its first data stream only is demodulated.
The demodulated first data stream is then converted by a first video decoder 421 to a traditional 425 or wide-picture NTSC or video output signal 426 of low image resolution.
Also, the modulated signal transmitted through a downlink 31 is intercepted by a medium antenna 32 having a radius r2 and fad to a first Z32 and a second data stream reproducing unit 233 of a second receiver 33 where its first and second data streams are demodulated respectively. The demodulated first and second data streams are then summed and converted by a second video decoder 422 to an HDTV or video output signal 427 of high image resolution and/or to the video output signals 425 and 426.
Also, the modulated signal transmitted through a downlink 41 ie intercepted by a large antenna 4Z having a radius r3 and fed to a first 232, a second 233, and a third data stream reproducing unit 234 of a third receiver 43 where its first, second, and third data streams are demodulated respectively. The demodulated first, second, and third data streams are then summed and converted by a third video decoder 423 to a super HDTV or video output signal 428 of super high image resolution for use in a video theater or ..:.- . v_.- . ::-..;. '~,_ _ _.-.,-- ~ . . ..z. ..
cinema. The video output signals 425, 428, and 427 can also be reproduced if desired. A common digital TV signal is transmitted from a conventional digital transmitter 51 and when intercepted by the first receiver 23, will be converted to the video output signal 426 such as a low resolution NTSC
TV siEnal.
The first video encoder 401 will now be explained in more detail referring to the block diagram of Fig. 30. An input video signal of super high resolution is fed through the input unit 403 to the divider circuit 404 where it is divided into four components by sub-band coding process. In more particular, the input video signal is separated through passing a horizontal lowpass filer 451 and a horizontal highpass filter 452 of e.g. QMF mode to two, low and high, horizontal frequency components which are then subsampled to a half oP their quantities by two subsamplers 453 and 454 respectively. The low horizontal component is filter~d by a vertical lowpass filter 455 and a vertical highpass filter 456 to a low horizontal low vertical component or H~VL signal and a low horizontal high vertical component or HLVg signal respectively. The two, H~VL and HiV9, signals are then subeampled to a half by two subsamplers 457 and 458 respectively and transferred to the compressing circuit 405.
The high horizontal component is filtered by a vertical lowpass filter 459 and a vertical highpass filter 480 to a high horizontal low vertical component or HgVL signal and a high horizontal nigh vertical component or H~Vg signal < ~. _ _ v .
.___ _ .-. . ~.-_. 'L~._~_ ='.. eG, ' . ..z. ., .. .~:
respectively. The two, H~V~ and HdVB, signals are then subsampled to a half by two subsamplers 461 and 462 respectively and transferred to the compressing circuit 405.
HIVt signal is preferably DCT compressed by a first compressor 471 of the compressi.zg circuit-405 and fed to a first output 472 as the first data stream.
Also, HLVg signal is compressed by a second compressor 473 and fed to a second output 464.. HfzJ4 signal is compressed by a third compressor 463 and fed t.o the second output 464.
HaVH signal is divided by a divide: 465 into two, high resolution (HgV81,) and suFer high resolution (H~V~2~, video signals which are then transferred to the second output 464 and a third output 4B8 respectively.
The first video decoder 421 will now be explained in more detail referring to Fig. 31. The first data stream or D1 signal of the first receiver 23 is fed through an input unit 501 to a descrambler 5Q2 of the first video decoder 421 where it is descrambled. The descrambled D1 signal is expanded by an expander 503 to HLVL which is then fed to an aspect ratio changing circuit 504_ Thus, HLVL signal can be delivered through an output unit 505 as a standard 500, letterbox format 507, wide-screen 508, or sidepanel format NTSC signal 509. The scanning format may be of non-interlace or interlace type and its ~iTSC mode lines may be 525 or doubled to 1050 by double tracing. When the received signal from the digital transmitter 51 is a digital T4 signal of 4 PSK mode, it can also be converted by the first receiver 23 and the first _ : - , r _ _,_ :._ . _ . _ . . _ _ _ -- . N.- _. ~ ~, o :, ... .. .. ._ _._ video decoder 421 to a i'll picture. The second video decoder 422 will be explained in more detail referring to the block diagram of Fig. 32. The D1 signal of the second receiver 33 is fed through a first input 521 to a first expander 522 for data expansion and then, transferred to an oversampler 523 where it is sampled at 2a. The oversampled signal is filtered by a vertical lowpass Filter 524 to HLVL. Also, the DZ signal of the second receiver 33 is fed through a second input 530 to a divider 531 where it is divided into three components which are then transferred to a second 532, a third 533, and a fourth expander 534 respectively for data expansion. The three expanded components are sampled at 2x by three oversamplers 535., 536, 537 and filtered by a vertical highpass 538, a vertical lowpass 539, and a vertical high-pass filter 540 respectively. Then, HLVL from the vertical lowpass filter 524 and HLVB Prom the vertical highpaes filter 53B are summed by an adder 525, sampled by an oversampler 541, and filtered by a horizontal lowpass filter 542 to a low frequency horizontal video signal. H~VL from Lhe vertical lowpaes filter 539 and HHVdl from the vertical highpass filter 540 are summed by an adder 526, sampled by an oversampler 544, and filtered by a horizontal highpass filter 545 to a high frequency horizontal video signal . The two, high and low frequency, horizontal video signal are then summed by an adder 543 to a high resolution video signal HD which is further transmitted through an output unit 546 as a video output 547 of e.g. HDTV format. If desired a traditional rT6C

. . . n _ _ _ . . . .. ~ . ;, i~ ~ "f, o l~= [ . . . . _ T . _ video output can be reconstructed with equal success.
Fig. 33 is a block diagram of the third video decoder 423 in which the Di and DZ signals are fed through a first 521 and a second input 530 respectively to a high frequency band video decoder circuit 527 where they are converted to an HD
signal by the same manner as above described. The D3 signal is fed through a third input 551 to a super high frequency band video decoder circuit 552 where it is expanded, descrambled, and composed to HHVg2 signal. The HD signal of the high frequency band video decoder circuit 527 and the H~GB2 signal of the super high frequency band video decoder circuit 552 are summed by a sumeier 553 to a super high resolution TV or S-HD signal which is then delivered through an output unit 554 as a super resolution video output 555.
The action of multiplexing in the multiplexer 412 shown in Fig. 29 will be explained is aoore detail. Fig. 34 illustrates a data assignment in which the three, first, second, and third, data streams Dl, DZ, D3 contain in a period of T six NTSC channel data L1, L2, L3, L4, L5, L6, six HDTV
channe l data !rIl , M2 , M3 , M4 , M5 , M6 and s ix S-HDTV cha.nne i data Hl, H2, iii, H4, H5, H6 respectively. In action, the NTSC
or D1 signal data L1 to L6 are time multiplexed by TDM
process during the period T. More particularly, HLVL of D1 is assigned to a domain 601 for the first channel. Then, a difference date. :41 between HDTV and VTSC or a sum of HLV~, HBVL, and H~VH1 is assigned to a domain 602 for the first channel. Also, a difference data H1 between HDTV and super .C Y . a v . . . ., HDTV or liBV82 (see Fig. 30) is assigned to a domain 503 for the firs: charnel.
The selection of the first channel TV signal will now be described G~'hen intercepted by the first receiver 23 with a small antenna coupled to the first video decoder 421, the first channel signal is converted to s standard or widescreen VTSC TV signal as shown in Fig. 31. When intercepted by the second receiver 33 with a medium antenna coupled to the second video decoder 422, the signal is converted by summing L1 of the first data stream D1 assigned to the domnin 601 and M1 of the second data stream DZ assigned to the domain 602 to ar. HDTV signal of the first channel equivalent in program to the NTSC signal.
When intercepted by the third receiver 43 with a large antenna coupled to the third video decoder 423, the signal is convdrted by summing L1 of Di assigned to the domain 601, M1 of DZ assigned to the domain 602, and lh of D3 assigned to the domain 603 to a super HDTV signal of the first channel equivalent in program to the NTSC signal. The other channel ' signals can be reproduced in an equal manner.
Fig. 35 shows another data assignment L1 of a first channel NTSC signal is assigned to a first domain 601. The domain BO1 which is allocated at the front end of the first data stream Dl, also contains at front a data 511 including a descrambling data and the demodulation data described in the first embodiment. A first channel HDTV signal is transmitted as L1 and ~I1. M1 which is thus a difference data .... . ,_._ :.,_- ;:.~ _._.~_~._ between NTSC and HDT1~' is assigned to two domains 602 and 611 of DZ. If L1 is a compressed NTSC component of 6 Mbps, M1 is as two times higher as 12 Mbps. Hence, the total of L1 and M1 can be demodulated at 18 Mbps with the second receiver 33 and the second video decoder 423. According to current data compression techniques, HDTV compressed signals can be reproduced at about 15 Mbps. This allows the data assignment shown in Fig. 35 to enable simultaneous reproduction of an NTSC and HDTV first channel signal. However, this assignment allows no second channel HDTV signal to be carried. S21 is a descrambling data in the HDTV signal. A first channel super HDTV signal component comprises L1, M1, and H1. The difference data H1 is assigned to three domains 603, 612, and 613 of D,~. If the NTSC signal is 6 Mbps, the super HDTV is carried aL as high as 36 Mbps. When a compressed rate is increased, super HDTV video data of about 2000 scanning line for reproduction of a cinema size picture for commercial use can be Transmitted with an equal manner.
Fig. 36 shows a further data assignment in which HI of a super HDTV signal is assigned to eia times domains. If a NTSC compressed signal is 6 Mbps, this assignment can carry as nine times higher as 54 Mbps of D3 data. Accordingly, super HDTV data of higher picture quality can be transmitted.
The foregoing data assignment maces the use of one of two, horicontal and vertical, polarizatior_ planes of a transmission wave. When both the hcrizontai and vertical poiari2ation planes are used, the frequency utilization will ?1 . . : _- _ ; _ . - . -:-. _,: '~~.~,_ -.-_~____ _ : . _ _ be doubled. This will be explained below.
Fig. 49 shows a data assignment in which DV1 and D81 are a vertical and a horizontal polarization signal of the first data stream respectively, DMZ and D~ era a vertical and s horizontal polarisation signal of the second data stream respectively, and Dy3 and D~ are a vertical and a horizontal polarization signal of the third data stream respectively.
The vertical polarization signal DYl of the first data stream carries a low frequency band or NTSC TV data and the horizontal polarization signal D81 carries a high frequency band or HDTV data. When the first receiver 23 is equipped with a. vertical polarization antenna, it can reproduce only the NTSC signal. When the first receiver 23 is equipped with an antenna for both horizontally and vertically polarised waves, it can reproduce the HDTV signal through summing L1 and M1. More specifically, the first receiver 23 can provide compatibility between NTSC and HDTV with the use of a particular type antenna.
Fig. 50 illustrates a TDMA method in which each data burst 721 is accompanied at front a sync data 731 and a card data 741. Also, a frame sync data 720 is provided at the front of a fame. Like chaanels are assigned to like time slots. For example, a first tine slot 750 carries NTSC, HDTV, and super HDTV data of the first channel simultaneously. The six time slots 750, 750a, 750b, 750c, 750d, 750e are arranged independent from each other. Hence, each station can offer NTSC, HDTV, and/or supper HDTV services independently of the - Y- _ _ ~ ,r=:-c.
~~-.~'.c .o ._ .~,. ._:. .. ~- .;_ other stations through selecting a pa:ticular channel of the time slots. Also, the first receiver 23 can reproduce an NTSC
signal when equipped with a horizontal polarization antenna and both NTSC e.nd HDTV signals when equipped with a compatible polarization antenna. In this respect, the second receiver 33 can reproduce a super HDTV at lower resolution while the third receiver 43 can reproduce a full super f~TV
signal. According to the third embodiment, a compatible signal transmission system will be constructed. It is understood that the data assignment is not limited to the burst mode TDMA method shown in Fig. 50 and another method such as time division multiplexing of continuous signals as shown in Fig. 49 will be employed with equal success. Also, a data assignment shown in Fig. 51 will permit a HDTV signal to be reproduced at high resolution.
As set forth above, the compatible digital TV signal transmission system of the third embodiment can offer three, super HDTV, HDTV, and conventional NTSC> TV broadcast services simultaneously. In addition, a video signal intercepted by a commercial station or cinema can be electronized.
The modified WAM of the embodiments is now termed as SR,QAM and its error rate will be examined.
First, the error rate in 16 SR.pA~I will be calculated.
Fig. 99 shows a vector diagram of 16 SRQAM signal points. As apparent from the first quadrant, the 16 signal points of standard 16 QA.'~! including 83a, 83b, 84a, 83a are allocated at T .- - ~;_ fir.
equal intervals of 28.
The signal point 83a is spaced 8 from both the I-axis and the Q-axis of the coordinate. It. is now assumed that n is a shift value of the 16 SRQAM. In 16 SRG~AM, the signal point 83a of 16 QAM is shifted to a signal point B3 where the distance from each axis is ns. The shift value n is thus expressed as:
0<n<3.
The other signal points 84a and B6a are also shifted to two points 84 and 88 respectively.
If the error rate of the first data stream is Pel, it is obtained from:
Peg-ib= 4 { erfc { 2 ~ ) -+- erfc ( ~ ) crfC ( ) 9+n~
Also, the error rate Pe2 of the second data stream is obtained from:
3n Pt:-t s = 2 erfc ( ~ ) crfc ( 3'" ) 4 2 9-~n~
The error rata of 36 or 32 SRWA.'~i will be calculated.
Fig. 100 is a vector diagram of a 38 SRQAM signal in which the distance between any two 36 QAM signal points is 28.
The signal point 83a of 36 QA.'~ is spaced b from each axis of the coordinate. It is now assumed that n is a shift value of the 16 SRQA.'H. In 36 SRQAM, the signal point 83a is shifted to a signal point 83 where the distance from each ._._= . _:. . :.__- ~.!' ,~-=-y;- -:. . ...
axis is n8. Similarly, the nine 36 Q~1M signal points in the first quadrant are shifted to points 83; 84, 85, B6, 97, 98, 89, 100, 101 respectively. If a signal point group 90 comprising the nine signal points is regarded as a single signal point, the error rate Pel in reproduction of only the first data stream D. with a modified 4 PSX receiver and the errcr rate PeZ in reproduction of the second data stream DZ
after discriminating the nine signal points of the group 90 from each other, are obtained respectively from:
nd Pe ~-32 = i erfc ( ~ ) 6 erfC ( 5 ~ x n 2n T 25 ) 5-n b Pc2-3Z = Z trfc Z 3 a S-n 1 erfc ~ 40 X n +2n+?5 ) Fig. 101 shows the relation between error rate Pe and C/N rate in transmission in which the curve 900 represents a conventional or not modified 32 QAM signal. The straight line 905 represents a signal having 101'5 of the error rate. The curve 901a represents a DI level 32 SRn~,AM signal of the present invention at the shift rate n of 1.5. As shown, the C/N rate of the 32 SRQAM slgnal is 5 dB lower at the error rate of 101' than that of the conventional 32 QA.'yI. This means that the present invention allows a D1 signal to be 2~ reproduced at a given error rate when its C/N rate is relatively low.
The curve 9U2a represents a DZ level SRQAN signal ai .... _.._._ . °:.,. '~:..=',"_C:-'-oF= . ..z: :. "__ _ r a=1.5 which can be reproduced at the error rate of 10 1"' only when its C/N rate is 2.5 d8 higher than that of the conventional 32 QA.~S of the curve 900. Also, the curves 901b and 902b represent D, and DZ SRG~AM siEnals at n=2.0 respectively. The curves 902c represents a DZ SRQAM signel at n=2.5. It is apparent that the C/N rate of the SRQ.AM signal at the error rate of 10 1'S is 5d8, 8d8, and lOdB higher at n=1.5, 2.0, and 2.5 respectively in the DI Ievel and 2.5 dB
lower in the DZ level than that of a common 32 QAM signal.
Shown in Fig. 103 is the C/N rate of the first and second data streams DI, BZ of a 32 SRQAM signal which is needed for maintaining a constant error rate against variation of the shift n. As apparent, when the shift n is more than 0.8, there is developed a clear difference between two C/N rates of their respective Dl and DZ levels so that the mufti-level signal, namely first and second data, transmission can be implemented successfully. In brief, n>0.85 is essential for mufti-level data transmission of thQ
32 SRQAM signal of the present invention.
Fig. lU2 shows the relation between the C/N rate and the error rate for 16 SRQAM signals. The curve 900 represAnts a common 16 QAM signal. The curves 901x, 901b, 901c and Dl level or first data stream 16 SRQAM signals at n=1.2, I.5, and I.B respectively. The curves 902a, 902b, 902c are DZ
level or second data stream 16 SHGIAM signals at n=1.2, 1.5, and 1.8 respectively.
The C/N rate of the first and second data streams Dl, D2 ._.. .l_~_ . F: " ';:.J"_ Gt-=o';-Z , , ..z. :. _ .u_ of a 16 SRQAM signal is shown in Fig. 104, which is needed for maintaining a constant error rate against variation of the shift n. As apparent, when the shift n is more than 0.9 (n>0.9), the multi-level data transmission of the 16 SRQAM
signal will be eaocuted.
Une example of propagation of SRQAM signals of the present invention will now be described for use with a digital TV terrestrial broadcast service. Fig. 105 shows the relation between the signal level and the distance between a transmitter antenna and a receiver antenna in the terrestrial broad cast service. The curve 911 represents a transmitted signal from the transmitter antenna of 1250 feet high. It is assumed that the error rate essential for reproduction of an applicable digital TV signal is 10 1'S. The hatching area 912 represents a noise interruption. The point 910 represents a signal reception limit of a conventional 32 QAM signal at C/N=15 dB where the distance L is 60 miles and a digital HDTV
signal can be intercepted at minimum.
The C/N rate varies 5 dB under a worse receiving condition such as bad weather. If a change in the relevant condition, e.g. weather, attenuates the C/N rate, the interception of an HDTV signal will hardly be ensured. Also, geographical conditions largely affect the propagation of signals and a decrease of about 10 dB at least will be unavoidable. Hence, successful signal interception ~.ithin BO
miles will never be guaranteed and above all, a digital signal will be propagated harder zhazl an analogue signal. It . .. _ _ l-W . 'F. ,. '~%.~L ~'Y'~'c~ v~ .. . _ . . .. . ..
would be understood that the service area of a conventional digital TY broadcast service is less dependable.
In case of the 32 SRQAM signal of the present invention, three-level signal transmission system is constituted as shown in Figs. 133 and I37. This permits a low resolution NTSC signal of M1'EG level to be carried on the 1-1 data stream D1_~, a medium resolution TV data of e.g. NTSC system to be carried on the 1-2 data stream D1_Z, and a high frequency component of F~TV data to be carried on the second data stream D2. Accordingly, the service area of the 1-2 data stream of the SRG1AM signal is increased to a 70 mile point 910a while of the second data stream remains Within a 55 mile point 910b, as shown in Fig. 105. Fig. 108 illustrates a computer simulation result of the service area of the 32 SRC~AM signal of the present invention, which is similar to Fig. 53 but ezplaina in more detail. As shown, the regions 708, 703c, 703a, 703b, '112 represent a conventional 32 QAM
receivable area, a 1-1 data level D1_1 receivable area, a 1-2 data level D1_Z receivable area, a second data level DZ
recei~~able area, and a service area of a neighbor analogue TV
station respectively. The conventional 32 GRAM signal data used in this drawing is based on a conventionally disclosed one.
For common 32 QAM signal, the 60-mile-radius service area can be established theoretically. The signal level will however be attenuated by geographical or weather conditions and particularly, considerably declined at near the limit of . . . . . i - ~ . . . . _ ~ t~:. $ ,- G'~. a ~' . . . . . . . " _ the service area.
If the low frequency band TV component of MPEG1 grade is carried on the 1--1 level D1_l data and the medium frequency band TV component of NTSC grade on the 1-2 level Dl_Z data an3 high ~requency band TV component of HDTV on the second level DZ data, the service area of the 32 SRQAM signal of the present invention ie increased by 10 miles in radius for reception of an EDTV signal of medium resolution grade and 18 miles for reception of an LDTV signal of low resolution grade although decreased by 5 miles for reception of an HDTV signal of high resolution grade, as shown in Fig. 106. Fig. 107 shows a service area in case of a shift factor n or s = 1.8.
Fig. 135 shows the service area of Fig. 107 in terms of area.
More particularly, the medium resolution component of a digital TV broadcast signal of the SRQAM mode of the preset invention can successfully be intercepted in ar_ unfavorable service rtgion or shadow area where a conventional medium frequency band TV signal is hardly propagated and avtenuated due ~o obstacles. Within at least the predetermined service ZO area, the NTSC TV signal of the SRQAIvi mode can be intercepted by any traditional TV receiver. As the shadow or signal attenuating area developed by building structures and other obstacles or by interference of a neighbor analogue TV signal or produced in a low land is decreased to a minimum, TV
viewers or subscribers will be increased in number.
Also, the HDTV service can be appreciated by only a few viewers who afford to have a set cf high cost HDTV receiver _ CA 02331203 2001-02-05 . . _ _ - _ _ _ . ~~ _ _.. '~ , . _ C' _. _ _I -_ .
and display, according io the conventional system. The system of the present invention allows a traditional NTSC, PAL, or SECAM receiver to intercept a medium resclution component of the digital HDTZ signal with the use of an additional digital tuner. A majority of TV viewers can hence enjoy the service at less cost and will be increased in number. This will encourage the TV broadcast business and create an extra social benefit.
Furthermore, the signal receivable area for medium resolution or hTSC TV service according to the present invention is increased about 36X at n=2.5, as compared with the conventional system, As the service area thus the number of TV viewers is increased, the TV broadcast business enjoys an increasing profit. This reduces a risk in the development 1~ of a new digital TV business which will thus be encouraged to put into practice.
Fig. 107 shows the service area of a 32 SR~QAM signal of the present invention in which the same effect will be ensured at n=1.8. Two service areas 703x, ~03b of Dl and DZ
signals respectively can be determined in extension for optimum signal propagation by varying the shift n considering a profile of HDTV and NTSC receiver distribution or geographical features. Accordingly, TV viewers will satisfy the service and a supplier station will enjoy a maximum of viewers.
This advantage is given when:
n>1.0 Hence, if the 32 SRQAM signal is selected, the shift n is determined by:
1<n<5 Also, if the 16 SRQAM signal is employed, n is determined by:
1<n<3 In the SRQAM mode signal terrestrial broadcast service in which the first and second data levels are created by shifting corresponding signal points as shown in Fige. 99 and 100, the advantage of the present invention will be given when the shift n in a 16, 32, or 64 SROA.M signal is more than 1Ø
In the above embodiments, the low and high frequency band components of a video signal are transmitted as the first c~nd second data streams. However, the transmitted signal may be an audio signal. In this case, low frequency or low resolution components of an audio signal may be transmitted as the first data stream, and high frequency or high resolution components of the audio signal may be transmitted as the second data stream. Accordingly, it is possible to receive high C/N portion in high sound quality, and low C/I~ portion in low sound quality. This can be utilized in PCM broadcast, radio, portable telephone end the like. In this case, the broadcasting area or communication distance can be expanded as compared with the conventional systems.
Furthermore, the third embodiment can incorporate a time division multiplexing (TDM) systeu~ as ehown in Fig. 133.

-, _ r _ ~ ~ ..v.~.._ G'~-.-~ ., . _ . _ . _ .. _ . . . .,. _. _ _ o n . . . . . . . . . . _ Utilization of the TDM makes it possible to increase the number of subchannels. An ECC encoder 743a and an ECC encoder 743b, provided in two subchannels, differentiate ECC code gains so as to make a difference between thresholds of these two subchannels. Whereby, an increase of channel number of the multi-level signal transmission can be realized. In this case, it is also possible to provide two Trellis encoders 743a, 743b as shown in Fig. 137 and differentiate their code gains. The explanation of this block diagram is substantially identical to that of later described block diagram of Fig. 131 which shows the sixth embodiment of the present invention and, therefore, will not described here.
In a simulation of Fig. 106, there is provided 5 dH
difference of a coding gain between 1-1 subchannel Dl_1 and 1 2 sub channe 1 Dl-2' An SRQAM is the system applying a C-CDM (Constellation-Coda Division Multiplex) of the present invention to a rectangle-gAM. A C-CAM, which is a multiplexing method independent of TDM or FDM, can obtain subcharu~els by dividing a constellation-code corresponding a code. An increase of the number of codes will bring au expansion of transmission capacity, which is not attained by TDM or FD~I alone, while maintaining almost perfect compatibility with conventional communication apparatus. Thus C-CDM pan bring excellent effects.
Although above embodiment combines the C-CDM and the TDM, it is also possible to combine :,he C-CDM with the FDM

_ _. _ _._~_ . . _ . _ ~ _ . _ . . x' '~:.~',: _~~_ :o . . . . . . . . _ . . .
(Frequency Division ;Multiplex) to obtain similar modulation effect of threshold values. Such a system can be used for a TV broadcasting, and Fig. 108 shows a frequency distribution of a TV signal. A spectrum 725 represents a frequency distribution of a conventional analogue, e.g. NTSC, broadcasting signal. The largest signal is a video carrier 722. A color carrier 723 and a sound carrier 724 are not so large. There is known a method of using an FDM for dividing a digital broadcasting signal into two frequencies. In this case, a carrier is divided into a first carrier 726 and a second carrier 727 to transmit a first 720 and a second signal 721 respectively. An interference can be lowered by placing °irst and second carriers 726, 727 sufficiently far from the video carrier 722. The first signal ?20 serves to transmit a low resolution TV signal at a large output level, while tr:e second signal 721 serves to transmit a high resolution TZ' signal at a small output level. Consequently, the mufti-level signal transmission making use of an FDM can be realized without being bothered by obstruction.
Fig. 13d shows an example of a conventional method using a 32 QAM system. As the subchannel A has a larger output than the subchannel H, a threshold value for the subchannel A, i.e. a threshold 1, can be set small 4~5 dF3 than a threshold value for the subchannel B, i.e. a threshold 2.
Accordingly, a two-level broadcasting having 4~5 dB t:~reshold difference can be realized. In this case, however, a large reduction of signal reception amount will occur if the . . _ . _ ~ _ ~ _ ~ . _ T . , - . . . . _ , n ... _ _-~'~0 ~~' . , . _ T _ . . ., . .
receiving signal level decreases below the threshold 2.
Because the second signal 721a, having a large information amount as shaded in the draxir~g, can.ot be received in such a case and only the first signal 720x, having a small information amount, is received. Consequently, a picture quality brought by the second level will be extremely worse.
However, thQ present invention resolves this problem.
According to the present invention, the first signal 720 is given by 32 SRQA~I mode which is obtained through C-CDM
modulation so that the subchannel A is divided into two subcha.nnels 1 of A and 2 of A. The newly added subchannel 1 of A, having a lowest threshold value, carries a low resolution component. The second signal 721 is also given by 32 SRQAM made, and a threshold value for the subchannel 1 of B is equalized with the threshold 2.
With this arrangement, the region in which a transmitted signal is not received when the signal level decreases below the threshold 2 is reduced to a shaded portion of the second signal 721a in Fig. 108. As the subchannei 1 of H and the subchannel A are both receivable, the transmission amount is not so much reduced in total. Accordingly, a better picture quality is reproduced even ir_ the second level at the signal level of the threshold 2.
By transmitting a normal resclut~on component in one subchannel, it becomes possible to increase the number of multiple level and expand a low resolution service area.
This low-threshold subchannel is utilised for transmitting ~. - r .~._ -'-'-i ='. .z. . .. _ _.
important information such as sound information, sync information, headers of respective data, because these information carried on this low-threshold subchannel ca.n be surely received. Thus stable reception is feasible. If a subchannel is newly added '_n the second signal 721 in the same manner, the level number of multi-level transmission can be increased in the service area. In the case where an HDTV
signal has 1050 scanning lines, an new service area equivalent to 775 lines can be provided in addition to 525 lines.
Accordingly, the combination of the FDM and the C-CDM
realizes an increase of service area. Although above embodiment divides a subchannel into two, it is needless to say it will also be preferable to divide it into three or more.
Nezt, a method of avoiding obstruction by combining the TDM and the C-CDM will be explained. As shown in Fig. I09, an analogue TV signal includes a horizontal retrace line portion 732 and a video signal portion 731. This method utilizes a low signal level of the rorizontal retrace line portion 732 and non-display of obstruction on a picture plane during this period. By synchronizing a digital TV signal with an analogue TV signal, horizontal retrace line sync slots 733, 733a of the horizontal retrace line portion 732 can be used for transmission of an important, e.g. a sync, signal or numerous data at a high output iavel. Thue, it becomes possible to increase data amount or output level without . : _ . : ~ ~ . _ . r _ :. '~:.~,_ __~:;-~-~ . . . _ . . . . .
increasing obst~uction. The similar effect will be expected even if vertical retrace line sync slots 737, 737a are provided synchronously with vertical retrace line portions 735, 735a.
Fig. 110 shows a principle of the C-CDM. Furthermore, Fig. 111 shows a code assignment of the C-CDM equivalent to an expanded 16 QAM. Fig. 112 shows a code assignment of the C-CDM equivalent to an expanded 36 QAM. As shown in Figs.
110 and 111, a 256 QAI~f signal is divided into four, 740x, 740b, 740c, 740d, levels which have 4, 16, 64, Z56 segments, respectively. A signal code word 742d of 256 QAM on the fourth level 740d is "11111111" of 8 bit. This is split into four code words 741x, 741b, 741c, and 741d of 2-bit ---- i.e.
"11", "11", "11", "11", which are then allocated on signal point regions 742x, 742b, 742c, 742d of first, second, third, fourth levels 740a, 740b, 740c, 740d, respectively. As a result, subchannels 1, 2, 3, 4 of 2 bit are created. This is termed as C-CDM (Constellation-Code Division Multiplex). Fig.
111 shows a detailed code assignment of the C-CDM equivalent to expanded 16 QtI.~I , and Fig. 112 shows a detailed code assignment of the C-CDM equivalent to expanded 36 QAM. As the C-CDM is an independent multiplexing system, it can be combined with the conventional FD~I (Frequency Division Multiplex) or TDM (Time Division Multiplex) to further increase the number of subchannels. In this manner, the C-CDM system realizes a novel multiplexing system. Although the C-CDM is explained by using a rectangle QA.~I, other _..- . ,_.__ . .-._, ~-.;_ __.~ :_ . .
modulation system having signal points, e.g. QAM, PSK, ASK, and even FSK if frequency regions are regarded as signal points, can be also used for this multiplexing in the same manner.
Embodiment 4 A fourth embodiment of the present invention will be described referring to the relevant drawings.
Fig. 37 illustrates the entire arrangement of a signal transmission system of the fourth embodiment, which is lU arranged for terrestrial service and similar in both construction and action to that of the third embodiment shown in Fig. 29. The difference is that the transmitter antenna 6 is replaced with a terrestrial antenna 6a and the receiver antennas 22, 23, 24 are replaced With also three terrestrial antennas 22a, 23x, 24a. The action of the system is identical to that of the third embodiment and will no more be explained. The terrestrial broadcast service un7.iJ~e a satellite service depends much on the distance between the transmitter antenna 6a to the receiver antennas 22x, 32x, 42x. if a receiver is located far from the transmitter, the level of a received signal is low. Particularly, a common multi-Ievel QAM signal can hardly be demodulated by the receiver which thus reproduces no TV program.
The signal transmission system of the present invention allows the first receiver 23 equipped with the antenna 22a, which is located at a far distance as shown in Fig. 37, to intercept aluodified 16 or 64 QAM s~gnai nrrd demodulate at 4 _ CA 02331203 2001-02-05 _ _ . _ _ . . ,. '~:._ t_ G~',c-'- F'- - ..z. ._ ._.
PSK mode the first data stream or D, component of the received signal to an NTSC video signal so that a TV program picture of medium resolution can he displayed even if the level of the received signal is relatively low.
Alse, the second receiver 33 with the antenna 32a is located at a medium distance from the antenna 6a and can thus intercept and demodulate both the first and second data streams or Dl and D2 components of the modified 16 or 64 QAM
signal to an HDTV video signal which in turn produces an HDTV
program picture.
The third receiver 43 with the antenna 42a is located at a near distance and can intercept and demodulate the first, second, and third data streams or Dl, DZ, and D3 components of the modified 16 or 64 QAM signal to a super HDTV video signal which in turn produces a super HDTV picture in quality to a common movie picture.
The assignment of frequencies is determined by the same manner as of the time division multiplexing shown in Fige.
34, 35, and 36. Like Fig. 34, when the frequencies are assigned t first to sixth channels, L1 of the D1 component carries an NTSC data of the first channel, M1 of the D2 component carries an fiDTV difference data of the first channel, and H1 of the D3 component carries a super HDTV
difference data of the first channel. Accordingly, NTSC, HDTV, and super HDTV data all can be carried on the same channel. If DZ and D3 of the other channels are utilized as shown in Figs. 35 and 36, more data of HDTV and super HDTV

- ~ - F- _ _ r _ _ . . - . , _ _ _ . . _ . '~-, ~ ~ C.-'u-C'~ L . . . . _ » . - _ _ _ . .
respectively can be transmitted for higher resolution display.
As understood, the system allows three different but compatible digital TV signals to be carded on a single channel or using DZ and D3 regions of other channels. Also, the medium resolution TV picture data of each channel can be intercepted in a wider service area according to the present invention.
A variety of terrestrial digital TV broadcast systems employing a 16 qAM HDTV signal of 6 MHz bandwidth have been proposed. Those are however not compatible with the existing NTSC system and thus, have to be associated with a simulcast technique for transmitting NTSC signals of the same program on another channel. also, such a common 16 pAM signal limits a service area. The terrestrial service system of the present invention allows a receiver located at a relatively far distance to intercept successfully a medium resolution TY
signal with no use of an additiunal dovice nor an extra channel.
Fig. 52. shows an interference region of tue service area 702 of a conventional terrestrial digital HDTV broadcast station 701. As shown, the service area 702 of the conventional HDTV station 701 is intersected with the service area 712 of a neighbor analogue T~' station 711. At the intersecting region 713, an HDTV signal is attenuated by signal interference from the analogue TV station 711 and will thus be intercepted with less consistency.

:::- .-._.. . ~F. - u,~~ c=:~'~..-, . ..
Fig. 53 shows an interference region associated with the mufti-level signal transmission system of the present invention. The system is low in the energy utilization as compared with a conventional system and its service area 703 for HDTV signal propagation is smaller than the area 702 of the conventional system. In contrary, the service area 704 for digital NTSC or medium resolution TV signal propagation is larger than the conventional area 702. The level of signal interference from a digital TV station 701 of the system to a neighbor analogue TV station 711 is equivalent to that from a conventional digital TV station, such as shown in Fig. 52.
Zn the service area of the digital TV station 701, there are three interference regions developed by signal interference from the analogue TY station 711. Both HDTV and NTSC signals can hardly be intercepted in the first region 705. Although fairly interfered, an NTSC signal may be intercepted at an equal level in the second region ?06 denoted by the left down hatching. The NTSC signal is carried on the first data stream which can be reproduced at a relatively low C!N rate and will thus be minimum affected when the C/r rate is declined by signal interference from the analogue iV station 711.
Al the third region ?07 denoted by the right down hatching, an HDTV signal can also be intercepted when signal interference is absent while the ~VTSC signal can constantly be intercepted at a low level.
Accordingly, the overall signal receivable area of the . : . . . . _ . . . _ : - 'c:.~ ~ _-=Via'=; ~ . . . z : : . . _ system will be increased although the service area of HDTV
signals becomes a little bit smaller than that of the conventional system. Also, at the signal attenuating regions produced by interference from a neighbor analogue TV station, NTSC level signals of an HDTV program can successfully be intercepted as compared with the conventional system where no HDTV program is viewed in the same area. The system of the prasent invention much reduces the size of signal attenuating area and when increases the energy of signal transmission at a transmitter or transponder station, can extend the HDTV
signal service area to an equal size to the conventional system. also, ~ITSC level signals of a TV program can be intercepted more or less in a far distance area where no service is given by the conventional system or a signal interference area caused by an adjacent analogue TV station.
Although the embodiment employs a two-level signal transmission method, a three-level method such as shown in Fig. 78 will be used with equal success. If an IiDTV signal is divided into three picture levels-HDTV, NTC, and low resolution NTSC, the service area shown in Fig. 59 will be increased from two levels to three levels where the signal propagation is extended radially and outwardly. Also, low resolution NTSC signals can be received at an acceptable level at the first signal interference region 705 where NTSC
signals are hardly be intercepted in the two-level system. As understood, the signal interference is also involved from a digital TV station to an analogue TV station.

._r_T .r,~.La .I~~.. 'I\-...~.. ~.T'yl~ In.. _ _T. .. __ _._ The description will now be continued, provided that no digital TV station should pause a signal interference to any neighbor analogue TV station. According to a novel system under consideration in U.6.A., no-use channels of the existing service channels are utilized for HDTV and thus, digital signals must not interfere with analogue signals.
For the purpose, the transmitting level of a digital signal has to be decreased lower than that shown in Fig. 53. If the digital signal ie of conventional 16 QAM or 4 PSg mode, its HDTV service area 708 becomes decreased as the signal interference region 713 denoted by the cross hatching is fairly Large as shown in Fig. 54. This results in a less numbar of viewers and sponsors, whereby such a digital system will have much difficulty to operate for profitable business.
Fig. 55 shows a similar result according to the system of the present invention. As apparent, the iiDTV signal receivable 7u3 is a little bit smaller than the equal area 708 of the conventional system. However, the lower resolution or NTSC TV signal receivable area ?04 will be increased as compared with the conventional system. The hatching area represents a region where the NTSC level signal of a program can be received while the HDTV signal of the same is hardly intercepted. At the first interference region 705, both F~TV
and NTSC signals cannot be intercepted due to signal interference from an analogue station 7I1.
When the level of signals is equal, the multi-level transmission system of the present invention provides a t . . _ . _ , _ _ _ _ . _, vr.~ ;: ~=-~o'=~: .
.. .._ smaller HDTV service area and a greater NT~C service area for interception of an HDTV program at an NTSC signal level.
Accordingly, the overall service area of each station is increased and more viewers can enjoy its TV broadcasting service. Furthermore, HDTV/NTSC compatible TV business can be operated with economical advantages and consistency. It is also intended that the level of a transmitting signal is increased when the control on averting signal interference to neighbor analogue TV stations is lessened corresponding to a IO sharp increase in the number of home-use digital receivers.
Hence, the service area of HDTV signals will be increased and in this respect, 'the two different regions for interception of HDTV/~YTSC and ~TSC digital TV signal levels respectively, shown in Fig. 55, can be adjusted in proportion by varying the signal point distance in the first and/or second data stream. As the first data stream carries information about the signal point distance, a multi-level signal can be received with more certainty.
Fig. 56 illustrates signal interference between two digital TV stations in which a neighbor TV station 701a also provides a digital TV broadcast service, as compared with nn analogue station iu Fig. 52. Since the level of a transmitting signal becomes high, the HDTV service or high resolution TV signal receivable area 703 in increased to an extension equal to the service area 702 of ar. analogue TV
system.
At the intersecting region 714 between two service areas . - . ~, . . ~.~ _ ~'.-',0 . .~ . . . T . . . _ . _ of their respective stations, the received signal can be reproduced not to an IiT;TV level picture with the use of a common directional antenna due to signal interference but to an NTSC level picture with a particular directional antenna directed towards a desired TV stat.iiz. If a highly directional antenna is used, the received signal from a target station will be reproduced to an HDTV picture. The low resolution signal receivable area 704 is increased larger than the analogue T'J system service area 702 and a couple of intersecting regions 715, 716 developed by the two low resolution signal receivable areas 704 and ~04a of their respective digital TV stations 701 and 701a permit the received signal from antenna directed one of tre two stations to be reproduced to an NTSC level picture.
The HDTV service area of the multi-level signal transmission system of the present invention itself will be much increased when applicable signal restriction rules are withdrawn in a coming digital TV broadcast service maturity time.
At the time, the system of the present invention also provides as a wide HDTV signal receivable area as of the conventional system and particularly, allows its transmitting signal to be reproduced at an NTSC level in a further distance or intersecting areas where TV signals of the conventional system are hardly intercepted. Accordingly, signal attenuating or shadow regions in the service area will be minimized.

Embodiment 5 A first embodiment of the present invention resides in amplitude modulation or ASfi procedure. Fig. 57 illustrates the assignment of signal points of a 4-level ASB signal according to the fifth embodiment, in which four signal points are denoted by 721, ?22, 723, and 724. The four-level transmission permits a 2-bit data to be transmitted in every cycle period. It is assumed that the four signal points 721, 722, 72~, 724 represent two-bit patterns 00, O1, 10, 11 respectively.
For ease ~f four-level signal transmission of the embodiment, the two signal points 721, 722 are designated as a first signal point group 725 and the other two 723, 724 are designated as a second signal point group 726. The distance between the two signal point groups 725 and ?26 is then determined wider than that between any two adjacent signal points. More specifically, the distance LG between the two signals 722 and 723 is arranged wider than the distance L
between the two adjacent points 721 and 722 or 723 and 724.
Thie is expressed as:
L~> L
Hence, the mufti-level signal transmission system of the embodiment is based on L~>L. The embodiment is however not limited to L~>L and L=L~ will be employed temporarily or 2n permanently depending on the requirements Uf design, condition, and setting.
Tile two signal point groups are assigned one-bit patterns of the first data stream D1, as shown in Fig. 59(aj.
More particularly, a bit 0 of binary system is assigned to the first signal point group 725 and another bit 1 to the second signal point group 726. Then, a one-bit pattern of the second data stream DZ is assigned to each signal point. For example,the two signal points ?21, 723 are assigned D2=0 and the other two signal points 722 and 724 are assigned DZ=1.
Those are thus expressed by two bits per symbol.
The multi-level signal transmission of the present invention can be implemented in an ASK mode with the use of the foregoing signal point assignment. The system cf the present invention xorks in the same manner as of a conventional equal signal point distance technique when the signal to noise ratio or C/N rate is high. If the C/N rate becomes low and no data can be reproduced by the conventional technique, the present system ensures reproduction of the first data stream Dl but not the second data stream Dl. In more detail, the state at a low C/N is shown in Fig. 60. The signal points transmitted are displaced by a Gaussian distribution to ranges ?21a, 722a, 723a, 724a respectively at the receiver side due to noise and transmission distortion.
Therefore, the distinction between the two signals 721 and 722 or 723 and 724 will hardly be executed. In other words, the error rate in the second data stream DZ will be increased. As apparent from Fig. 60, the two signal points 721, 722 are easily distinguished from the other two signal points 723, 724. The distinction between the two signal point groups 725 and 726 can thus be carriec out with ease. As the result, the first data stream D1 will be reproduced at a low error rate.
Accordingly, the two different leval data Dl and DZ can be transmitted simultaneously. More particularly, both the first and second data streams Dl and DZ of a given signal transmitted through the multi-level transmission systen can be reproduced at the area where the C/h rate is high and the first data streaa D1 only can be reproduced in the area where the C/N rate is low.
Fig. 61 is a block diagram of a transmitter 741 in which an input unit 742 comprises a first data stream input 743 and a second data s~ream input 744. A car: ier wave from a carrier generator 64 is amplitude modu~ated by a multiplier 74t3 using an iaput signal fed across a processor 745 from the input unit 743. The mo~3uiated signal is then band limited by a filter 747 to an ASH signal of e.g. VSB mode which is then delivered from an output unit 748.
The waveform of the AS$ r~ignal after filtering will now be examined. Fig. 62(a) shows a frequency spectrum of the ASK
modulated signal in which two sidebands are provided on both sides of the carrier frequency band. Dne of the two sidebands is eliminated with the filter 474 tc~ produce a signal 749 which contains a carrier component as shown in Fig. 62(b).
The signal 749 is a VSB signal and if the modulation frequency band is fp, will be transmitted in a frequency band of about fa/2. Hence, the frequency utilization becomes high.

._. _ ~_._ _:F._,. 'f~,:_ ~'~o.'r: ..._ . _ .._ Using VSB mode transmission, the ASK signal of two bit per symbol shown in Fig. 6G can thus carry in the frequency band an amount of data equal to that of 16 tZAM mode at four bits per symbol.
Fig. 63 ie a block diagram of a receiver 751 in which an input signal intercepted by~ a terrestrial antenna 32a is transferred through an input unit 752 to a mixer 753 where it is mixed with a signal from a variable oscillator 754 controlled by channel selection to a lower medium frequency signal. The signal from the mixer 753 is then detected by a detector 75~ and filtered by an LPF 756 to a baseband signal which is transferred to a discriminating/reproduction circuit 757. The diserimination/reproduction circuit 757 reproduces two, first D1 and second D2, data streams from the baseband signal aad transmit them further through a first 758 and a second data stream output 759 respectively.
The transmission of a TV signal using such a transmitter and a receiver will be explained. Fig. 64 is a block diagram of a video signal transmitter 774 in which a high resolution TV signal, e.g. an HDTV signal, is fed through an input unit 403 to a divider circuit 404 of a first video encoder 401 whore it is divided into four high/low frequency TV signal components denoted by e.g. HLVt, HtVH, H~Vt, and HHVb. This action is identical to that of the third embodiment previously described referring to Fig. 30 and will no more be explained in detail. The four separate TV signals are ancoded respectively by a compressor 405 using a known _._. ..l-__ .:~r'~__,. 'r-.~~ cr'T';a'" . . .... :. ... ...
DPCMDCT Variable length code encoding technique which is commonly used e.g. in MPEG. Meanwhile, the motion compensation of the signal is carried out at the input unit 403. The compressed signals are summed by a summer 77i to two, first and second, data streams Dl, D2. The low frequency video signal component or HyV1 signal is contained in the first data stream Dl. The two data stream signals D1, DZ are then transferred to a first 743 and a second data stream input ?44 of a transmitter unit 741 where they are amplitude modulated and summed to an ASg signal of e.g. VSB mode which is propagated from a terrestrial antenna for broadcast service.
Fig. 65 is a block diagram o; a TV receiver for such a digital TV broadcast system. A digital TV signal intercepted by a terrestrial antenna 32a is fed to an input 752 of a receiver 781. The signal is then transferred to a detection/demodulation circuit 760 where a desired channel signal is selected and demodulated to two, first and second, data streams Dl, DZ which are then fed to a first 758 and a second data stream output 758 respectively. The action in the receiver unit 751 is similar to that described previously and will no more be explained in detail. The two data streams Dl, DZ are sent to a divider unit 776 in Which Dl is divided by a divider 777 into two components; one or compressed HLVL
is transferred to a first input 521 of a second video decoder d22 ana the other is fed to a summer 778 where it is summed with DZ prior to transfer to a second input 531 of the second .:. .= . ;_.. . _:-. _:. %..~L _--:~-,-:; ., . . :. . .. . . ..
video decoder 422. Compressed HLVL is then sent from the first input 521 to a first expander 523 where it is expanded to H~V~
of the original length which is then transferred to a video mixer 548 and an aspect ratio changing circuit 779. When the input TV signal is an HDTV signal, HLV~ represents a wide-screen NTSC signal. When the same is an NTSC signal, H~VL
represents a lower resolution. video signal, e.g. MPEGl,,that an NTSC level.
The input TV signal of the embodiment is an HDTV signal and HLVI becomes a wide-screen NTSC signal. If the aspect ratio of an availabie display is 16:9, H~Vt is directly delivered through an output unit as a 16:9 video output 426.
If the display has an aspect ratio of 4:3, HLVI is shifted by the aspect ratio changing circuit 779 to a letterbox or sidepanel format and then, delivered from the output unit 780 as a corresponding format video output 425.
The second data stream DZ fed from the second data stream output 759 to the summer 778 is summed with the output of the divider 777 to a sum signal which is then fed to the second input 531 of the second video decoder 4Z2. The sum signal is further transferred to a divider circuit 531 while it is divided into three compressed forms of HLVb, HHVL, and HHV~. The three compressed signals are then fed to a second 535, a third 536, and a fourth expander 537 respectively for converting by expansion to HLVg, HHV~, and HBVg of the original length. The three signals are summed with HLVL by the video mixer 548 to a composite HDTV signal which is fed through an _ _ - _ _. L =_~T
:__- . __- _~-__, ' ,- ~... ..
~° u.. __Y_ .. .__ ___ output 546 of the second video decoder to the output unit 780. Finally, the HDTV signal is delivered from the output unit ?80 as an HDTV video signal 427.
The output unit 780 is arranged for detecting ar error rate in the second data stream of the second data stream output ?59 through an error rate detector 7$2 and if the error rate is high, delivering H~VL of low resolution video data systematically.
Accordingly, the multi-level signal transmission system for digital TV signal transmission and reception becomes feasible. For example, if a TV signal transmitter statinn is near, both the first and second data streams of a received signal can successfully be reproduced to exhibit an HDTV
quality picture. If the transmitter station is far, the first data stream can be reproduced to RLVL which is converted to a low resolution TV picture. Hence, any TV program will be intercepted in a wider area and displayed at a picture dual i ty ranging from ITV to NTSC leve 1 .
Fig. 66 is a block diagram showing another arrangement of the TV receiver. As shown, the receiver unit 751 contains only a first data stream output 768 and thus, the processing of the second data stream or HDTV data is not needed so that the overall construction can be minimized. It is a good idea to have the first video decoder 421 shown in Fig. 31 as a video decoder of the receiver. Accordingly, an NTSC level picture will be reproduced. The receiver is fabricated at much less cost as having no capability to receive any HDTV

.... . . n..r_ ..~ . w.~v v'-' C~..'. . . . .T. .. , .. .. _ level signal and will widely be accepted in the market. In brief, the receiver can be used as an adapter tuner for interception of a digital TV signal m th gm ng no modification to the ezisting T1' system including a display.
The TV receiver 781 may have a further arrangement ehown in Fig. 67, which serves as both a satellite broadcast receiver for demodulation of PSK signals and a terrestrial broadcast receiver for demodulation of ASK signals. In action, a PSH signal received by a satellite s.ntenna 32 ie mixed by a mixer 786 with a signal from an oscillator 787 to a low frequency signal which is then fed through an input unit 34 to a mixer 753 similar to one shown in Fig. 63. The low frequency signal of PSK or GLOM mode in a given channel of the satellite TV system is transferred to a modulator 35 where two data streams D1 and D2 are reproduced from the signal. Dl and DZ are sent through a divider 788 to a second video decoder 422 where they are converted to a video signal which is then delivered from an output unit 780. Also, a digital or analogue terrestrial TV signal intercepted by a terrestrial antenna 32a is fed through an input unit 752 to the miter 753 where une desired channel is selected by the same manner as described in Fig. 63 and detected to a low frequency base band signal. The signal of analogue form is sent directly to the demodulator 35 for demodulation. The signal of digital form is then test zo a discrimination/reproducing circuit 757 where two data streams D1 and D2 are reproduced from the signal. D1 and D2 nre . : : : - . -. _ . - , ~-.~ . .. '-..: _ ~.~;'2'. ~ . _ - . . . . : _ _ .
converted by the second video decoder 422 to a video signal which is then delivered further. A satellite analogue TV
signal is transferred to a video demodulator 788 where it is AN modulated to an analogue video signal which is then delivered from the output unit 780. As understood, the mixer 753 of the TV receiver 781 shown in rig. 67 is arranged compatible between two, satellite and terrestrial, broadcast services. Also, a receiver circuit including a detector 765 and an LPF 756 for AM modulation of an analogue signal can be utilized compatible with a digital ASH signal of the terrestrial TV service. The ma3or part of the arrangement shown in Fig. 67 is arranged for compatible use, thus minimizing a circuitry construction.
According to the embodiment, a 4-level ASK signal is divided into two, D1 and DZ, level components for execution of the one-bit mode multi-level signal transmission. If an 8-level ASK signal is used as shown in Fig. 68, it can be transmitted in a one-bit mode three-level, D1, DZ, and D3, arrangement. A shown in Fig. 68, D1 is assigned to eight signal points 721x, 721b, 722a, 722b, 723x, 723b, 724x, 724b, each pair representing a two-bit pattern, DZ is assigned to four small signal point groups 721, 722, 723, 724, each two groups representing a two-bit pattern, and D3 is assigned to two large sig~:la1 point groups 725 and 726 representing a two-bit pattern. More particularly, this is equivalent to a form in which each of the four signal points 721, 722, 723, 724 shown in Fig. 57 is divided into two components thus . . . _- _ ~ _ _ _ . _ ~~ _ T. ~1~. ; ~._ G~~ p ~- . . _ _ : - . . . _ .
producing three different level data.
The three-level signal transmission is identical to that described in the third embodiment and will no further be explained in detail.
In particular, the arrangement of the video encoder 401 of the third embodiment shown in Fig. 30 is replaced with n.
modification of which block diagram is Fig. 69. The operation of the modified arrangement is similar and will no longer be explained in detail. Two video signal divider circuits 404 and 404a which may be sub-band filters are provided forming a divider unit 794. The divider unit 794 may also be arranged more simple a shown in the block diagram of Fig. 70, in which a signal passes across one signal divider circuit two times at time division mode. More specifically, a video signal of e.g. HDTV or super HDTV from the input unit 403 is time-base compressed by a time-base compressor 795 and fed to the divider circuit 404 where it is divided into four components, H$Vg-H, H~V~ H, and H~VB H, and HLVL-H at a first cycle. At the time, four switches 765, 765x, 765b, 765c remain turned to the position 1 so that H~Vg-H, HdVL--H, and HLV~-H are trausmittsd to a compressing circuit 405. Meanwhile, Ii~V~-H
is fed back through the terminal 1 of the switch 765c to the time-base compressor 795. At a second cycle, the four switches ?65, 765x, 765b, 785c turned to the position 2 and all the four components of tLe divider circuit 404 are simultaneously transferred to the compressing circuit 405.
Accordingly, the divider unit 796 of Fig. 70 arranged for time division processing of an input signal can be constructed in a simpler dividir_g circuit form.
At the receiver side, such a video decoder as described in the third embodiment and shown in Fig. 30 is needed for three-level transmission of a video signal. More particularly, a third video decoder 423 is provided which contains two mixers 556 and 556a of different processing capability as shown in the block diagram of Fig. 71.
Also, the third video decoder 423 may be modified in which the same action is executed with one single mixer 556 as showr. in Fig. 72. At the first timing, five switches ?65, 765x, 765b, 765c, 765d remains turned to the position 1.
Hence, HLVL, H~VH, H~VI, and HgVB are fed from a first 522, a second 522e, a third 522b and a fourth expander 522c to through their respective switches to the mixer 556 where they are mixed to a single video signal. The video signal which represents H~VL-H of an input high resolution video signal is then fed back through the terminal 1 of the switch 765d to the terminal 2 of the switch ?BSc. At the second timing, the four switches 785, 765x, 765b, 765c are turned to the point 2. Thus, H~VH-H, H~V~ H, H~Vd-H, and HLV~-H are transferred to the mixer 556 where they are mined to n single video signal which is then sent across the terminal 2 of the switch 785d to the output unit 554 for further delivery.
In this meaner of time division processing of a three-level signal, two mixers can be replaced with one mixer.
More part i cul ar 1 y , f our component s HtV~ , HLV~, H~Vi, HBV~

are fed to producQ HtVL H at the first timing. Then, HLVg-H, HgVL-H, and H~Vd H are fed at the second timing delayed from th first timing and mixed with HLVL-H to a target video signal. It is thus essential to perform the two actions at an imter~al of time.
If the four components are overlapped each other or supplied in a variable sequence, they have to be time-base adjusted to a given sequence through ubing memories accompanied with their respective switches 765, 765a, 765b, 765c. In the foregoing manner, a signal is transmitted from the transmitter at two different timing periods as shown in Fig. 73 so that no time-base controlling circuit is needed in the receiver which is thus arranged more compact.
As shown in Fig. 73, D1 is the first data stream of a transmitting signal and HtVt, HLVg, HgVL, and HgVH are transmitted on D1 channel at the period of first timing.
Then, at the period of second timing, HLVH, HgVL, and FigVa are transmitted on DZ channel. As the signal is transmitted in a time division sequence, the encoder in the receiver can be arranged more simple.
The technique of reducing the number of the expanders in the decoder will now be explained. Fig. 74(b) shows a time-base assignment of four data components 810, 810x, 810b, 810c of a signal. When other four data components 811, 811a, 811b, 811c are inserted between the four data components 811, 811a, Bllb, 811c respectively, the latter can be transmitted at intervals of time. In action, the second video decoder 422 . . . . _ . ; _ . - . ::: . _ r ';.,Y _ ~.--;_r.~ . .. . . - . .
shown in Fig. 74(a) receives the four components of the first data stream D1 at a first input 521 and transfers them through a switch 812 to nn ezpander 503 one after another.
More particularly, the component 810 first fed is expanded during the feeding of the component 811 and after completion oP processing the component 810, the succeeding component 810e ie fed. Hence, the expander 503 can process a row of the components at time intervals by the same time division manner as of the mixer, thus substituting the simultaneous action of a number of expanders.
Fig. 75 is n time-base assignment of data components of an HDT'1 signal , in whi ch H1VL( 1 ) of an NTSC component of the first charm~1 signal for a TV program is allocated to a data domain 821 of Dl signal. Also, HiVH, HHVL, and H.~VH carrying HDTV additional components of the first channel signal are allocated to three domains 821x, 821b, 821c of D2 signal respectively. There are provided other data components 822, 822a, 822b, 822c between the data components of the first channel signal which can thus be ezpanded with an expander circuit during transmission of the other data. Hence, all the data components of one channel signal will be processed by a single expander capable of operating at a higher speed.
Similar effects will be ensured by assignment of the data components to other domains 821, 821x, 821b, 821c as shown in Fig. ?6. This becomes more effective in transmission and reception of a common 4 PSK or ASH signal having no different digital levels.

.-- ..-. _ . _ . ::=._ _:: ~~.~r: -~:-er.--..
Fig, 77 shows a time-base assignment of data components during physical two-level transmission of three different signal level data: e.g. NTSC, HDTV, and super HDTV or low resolution NTSC, standard resolution NTSC, and HDTV. For example, for transmission of three data components of low resolution NTSC, standard NTSC, and HDTV, the low resolution NTSC or H~VL is allocated to the data dumain 821 of Dl signal.
Also, HrVg, H$V~, and HgYg of the standard NTSC component are allocated to three domains 821x, 821b, 821c respectively.
HLVe-H, H~Vt-H, and IigVg-H of the HDTV component are allocated to domains 823, 823a, and 823b respectively.
The foregoing assignment is associated with such a logic Ievel arrangement based on discrimination in the error correction capability as described in the second embodiment.
More particularly, HLV~ is carried on D11 channel of the Dl signal. The D1_1 channel is higher in the error correction capability than D1_Z channel, as described in the second embodiment. The DZ_i channel is higher in the redundancy but lower in the error rate than the D1_Z channel and the date 821 can be reconstructed at a Iower C/N rate than that of the other data 821x, 821b, 821c. More specifically, a low resolution NTSC component will be reproduced at a far location from the transmitter antenna or in a signal attenuating or shadow area, e.g. the interior of a vehicle.
In view of the error rate, the data 821 of D1_1 channel is less affected by signal interference than the other data 821a, 821b, 821c of D1_Z channel, while being specifically .. . . .~._ . ~~ _. C,___y_ - . . ~ ..: ...._ . .0 ....
discriminated and stayed in a different logic level, as described in the second embodiment. While D1 and DZ are divided into two physically different levels, the levels determined by discrimination of the distance between error correcting codes are arranged different in the logic level.
The demodulation of DZ data requires a higher C/N rate than that for D1 deter. In action, HLVL or low resolution NTSC
signal can at least be reproduced in a distant or lower C/N
service area. H~Vg, HHV~, and H~V~ can in addition be reproduced at a lower C/N area. Then, at a high C/N area, HLVH-H, H~Vt-H, and HBVB-H components can also be reproduced to develop an HDTV signal. Accordingly, three different ievel broadcast signals can be played back. This method allows the signal receivable area shown in Fig. 53 to increase from a double region to a triple region, as shown in Fig. 90, thus ensuring higher opportunity for enjoying TV programs Figs. 78 i5 a block diagram of the third video decoder arranged for the time-base assignment of data shown in Fig.
77, which is similar to that shown in Fig. 72 except that the third input 551 for D3 signal is eliminated and the arrangement shown in Fig. 74(a) is added.
In operation, both the Dl and DZ signals are fed through two input units 521, 530 respectively to a switch 812 at the first timing. As their components including H~VL are time divided, they are transferred in a bequence by the switch 812 to an expander 503. This sequence will now be explained referring to the time-base assignment of Fig. 77. A

... .1_._ __~°~ ,T v.:.~~~ c~'F.
.:~: _. ... .._ compressed form of H~VL of the first channel is first fed to the expander 503 where it is expanded. Then, HLVS, HHVI, and HgVd are expanded. All the four expanded components are sent through a switch 812a to a miter 556 where they are mixed to produce H~VL-H. H~VL H is then fed back from the terminal 1 of a switch 765a through the input Z of a switch 765 to the H~V~
input of the mixer 556.
At the second timing, HLVH-H, HHVL H, and HaVH-H of the DZ
signal shown in Fig. 77 are fed to the expander 503 where they are expanded before transferred through the switch 821a to the mixer 556. They are mixed by the mixer 556 to an HDTV
signal which is fed through the terminal Z of the switch 765a to the output unit 52I for further delivery. The time-base assignment of data components for transmission, shown in Fig.
77, contributes to the simplest arrangement of the expander and mixer. Although Fig. 77 shows two, Dl and Dz, signal levels, four-level transmission of a TV signal will be feasible using the addition of a D3 signal and a super resolution HDTV signal.
Fig. 79 illustrates a time-base assignment of data components of a physical three-level, Dl, D2, D3, TV signal, in which data components of the same channel are so arranged as not to overlap with one another with time. Fig. BO is a block diagram of a modified video decoder 423, similar to Fig. 78, in which a third input 521a is added. The time-base assignment of data components shown in Fig. 79 also ccntributes to the simple construction of the decoder.

.... _ .___ _. .. '~~.~~, ~',.'~.o:~ . ..
The action of the modified decoder 423 is almost identical to that shown in Fig. 78 and associated with the time-base assignment shown in Fig. ?7 and will no more be explained, It is also possible to multiplex data components on the Dl signal as shown in Fig. 81. HoHever, two data B21 and 822 are increased higher in the error correction capability than other data components 821x, 812b, 812c, thus staying at a higher signal level. More particularly, the data assignment for transmission is made in one physical level but two logic level relationship. Also, each data component of the second chanrnel is inserted between two adjacent data components of the first channel so that serial processing can be. eiecuted at the receiver side and the same effects as of the time-base assignment shown in Fig. 79 will thus be obtained.
The time-base assignment of data components shown in Fig. 81 is based on the logic level mode and can also be carried in the physical level mode when the bit transmission rate of the two data components 821 and 822 is decreased to 1/2 or 1/3 thus t,o lower the error rate. The physical level arrangement is consisted of three different levels.
Fig. 82 is a block diagram of another modified video decoder 423 for decoding of the D1 signal time-base arranged as shown in Fig. 81, which is simpler in construction than that shown in Fig. 80. Its action is identical to that of the decoder shown in Fig. 80 and will be no more explained.
As understood, the time-base assignment of data .. f"

_ . . _ _ _ .,~ _ _ ~. 1.,. .._ _ ,.
components shown in Fig. 81 also contributes to the similar arrangement of the expander and mixer. Also, four data components of the Dl signal are fed at respective time slices to a mixer 556. Hence, the circuitry arrangement of the mixer 556 or a plurality of circuit blocks such as provided in the video mixer 548 of Fig. 32 may be arranged for changing the connection therebetween corresponding to each data component so that they became compatible in time division action and thus, minimized in circuitry construction.
Accordingly, the receiver can be minimized in the overall construction.
It would be understood that the fifth embodiment is not limited to ASH modulation and the other methods including PSK
and QAM modulation, such as described in the first, second, and third embodiments, will be employed with equal success.
Also, FSK modulation will be eligible in any of the embodiments. For example, the signal points of a multiple-level FSB signal consisting of four frequency components fl, f2, f3, f4 are divided into groups as shown in Fig. 58 sad when the distance between any two groups are spaced from each other for ease of discrimination, the multi-Ievel transmission of the FSK signal can be implemented, as i l lustrated in Fib; . 83 .
More particularly, it is assumed that the frequency group B41 of fl and f2 is assigned D1=0 and the group B42 of f3 and f4 is assigned Dl=1. If fl and f3 represent 0 at D2 and f2 and f4 represent 1 rit D2, twa-bit data transmission, one ,s, . ., ....- _-._._ ..~:._.: ___ _-_,_;__ . . ..-. _ bit at Dl or DZ, will be possible as shown in Fig. 83. When the C/N rate is high, a combination of Dl=0 and DZ=1 is reconstructed at t=t3 and a combination of Dl=1 and D~0 at t=t4. When the C/N rate is low, Dl=0 only is reproduced at t=t3 and Dl=1 at t=t4. In this manner, the FSK signal can be transmitted in the multi-level arrangement. Thie multi-state FSK signal transmission is applicable to each of the third, fourth, and fifth embodiments.
The f i f th embodiment may al so be implemented in the form of a magnetic record/playback apparatus of which block diagram shown in Fig. 84 because its ASH mode action is appropriate to magnetic record and playback operation.
Embodiment 6 A sixth embodiment of the present invention is applicable to a magnetic recording and playback apparatus.
Although the above-described fifth embodiment applies the present invention to a multiple-level recording ASK data transmission system, it is also feasible in the same manner to adopt this invention in a magnetic recording and playback apparatus of a multi-level ASK recording system. A multi-level magnetic recording can be realized by incorporating the C-CDM system of the present invention to PSK, FCK, and QAM, as well as ASH.
First of all, the method of realizing a multi-level recording in a 16 QAM or 32 61AM magnetic recording playback apparatus will be explained with reference to the C-CDM
system of the present invention. Fig. 84 is a circuit block ... _ _. ._ .... r ,_ _..o.
diagram showing a QAM system incorporating C-CDM modulator.
Hereinafter, a e~AM system being mul~iplexed by the C-CDM
modulator is termed as SRQAM.
As shown in Flg. 84, an input video signal, e.g. an HDTV
signal, to a magnetic record/playback apparatus 851 is divided and compressed by a video encoder 401 into a low frequency band signal through a first video encoder 401a and a high frequency band signnl through a second video enceder 401b respectively. Then, a low frequency band component, e.g. H~VL, of the video signal is fed to a first data stream input 743 of an input section 742 and a high frequency band component including HHV~ ie fed to a second data stream input 744 of the same. The two components are further transferred to a modulator 749 of a modulator/demadulator unit 852. The first data stream input 743 adds an error correcting code to the low frequency band signal in an ECC 743a. On the othQr hand, the second data strEam fed into the second data stream input ?44 is 2 bit in case of 16 SRQA_M, 3 bit in case of 36 SRQAM, and 4 bit in case of 84 SRQA.~t. After an error correcting code being encoded in an ECC 744a, this signal is supplied to a Trellis encoder 744b in which a Trellis encoded signal having a ratio 1/2 in case of 16 SRQAM, 2/3 in case of 32 SRQAM, and 3/4 in case of 64 SRGAM is produced. A 64 SRQpM signal, for example, ras a first data stream of 2 bit and a second data stream of 4 bit. A Trellis encoder of Fig.
128 allows this fi4 SRQAM signal to perform a Trellis encoding of ratio 3/4 wherein 3 bit data is Converted into 4 bit 3ata.

Thus redundancy increases and a data rate decreases, while error correcting capability increases. This results in the reduction of an error rate in the same data rate.
Accordingly, transmittable information amount of the recording/playback system or transmission system will increase substantially.
It is, however, possible to constitute the first data stream input 743 to exclude a Trellis encoder as shown in Fig. 84 of this sixth embodiment because the first data stream has low error rate inherently. This will be advantageous in view of simplification of circuit configuration. The second data stream, however, has a narrow inter-code distance as compared with the first data stream and, therefore, has a worse error rate. The Trellis encoding of the second data stream improves such a worse error rate.
It is no doubt that an overall circuit configuration becomes simple if the Trellis encoding of the first data stream is eliminated. An operation for modulation is almost identical to that of the transmitter of the fifth embodiment shown in Fig. 64 and will c~e no more a:plained. A modulated signal of the modulator ?49 is fed into a recording/playback circuit 853 in which it is AC biased by a bias generator 856 and amplified by an amplifier 857x. Thereafter, the signa~ is fed to a magnetic head 854 for recording onto a magnetic tape 855.
A format of the recording signal is shown in a recording signal frequency assignment of Fig. 113. A main, e.g. 16 xnr .~_ , a. ~.L

... . _. .. .. -,_ -._,oi-SRQAM, signal 859 having a carrier of frequency fc records information, and also a pilot fF signal 859a having a frequency 2fc is recorded simultaneously. Distortion in the recording operation is lowered as a bias signal 859b having a frequency fHl~ adds AC bias for magnetic recording. Two of three-level signals shown in Fig. 113 are recorded in multiple state. In order to reproduce these recorded signals, two thresholds Th-1-2, Th-2 are givHn. A signal 859 will reproduce all of two levels while a signal 859c will reproduce D1 data only, depending on the C/N level of the recording/playback.
A main signal of 16 SR.QAM will have a signal point assignment shown in Fig. 10. Furthermore, a main signal of 36 SRQAM will have a signal point assignment shown in Fig. 100.
In reproduction of this signal, both the main signal 859 and the pilot signal 859a are reproduced through the magnetic hoed 854 and asplified by an amplifier 857b. An output signal of the amplifier 857b is fed to a carrier reproduction circuit 858 in which a filter 858a separates the frequency of the pilot signal fp having a frequency 2f0 and a 1/2 frequency divider 858b reproduces a carrier of frequency f0 to transfer it to a demodulator 760. This reproduced carrier is used to demodulate the main signal in the demodulator 760.
Assuming that a magnetic recording tape 855, e.g. HDTV tape, ie of high C/h rate, 16 signal points are discriminatable and thus both D; and D2 are demodulated in the demodulator 760.
Subsequently, a video decoder 402 reproduce all the signals.

A.n HDTV VCR can reproduce a high bit-rate TV signal such as a 15 Mbps HDTV signal. The low the C/N rate, the cheaper the cost of a video tape. So far, a VHS tape in the market is inferior mare than 10 dB in the C/N rate to a full-scale broadcast tape. If a video tape 855 is of low C/N rate, it will not be able to discriminate all the 16 or 32 valued signal points. Wherefore the first data stream D1 can be reproduced, while a 2 bit, 3 bit, or 4 bit data stream ~f tho second data stream DZ cannot be reproduced. Only 2 bit data stream of the first data stream is reproduced. If a two-level HDTV video signal is recorded and reproduced, a low C/N
tape having insufficient capability of reproducing a high frequency band video signal can output only a low rate low frequency band video signal of the first data stream, specifically e.g. a 7 Mbps wide NTSC TV signal.
As shown in s block diagram of Fig. 114, the second data stream output 758, the second data stream input 744, and the second video decoder 402a can be eliminated in order to provide customers one aspect of lower grade products. In this case, a recording/playback apparatus 851, dedicated to a low bit rate, will include a modulator such as a modified QF~SB which modulates and demodulates the first data stream only. This apparatus allows only the first data stream to be recorded and reproduced. Specifically, a wide NTSC grade video signal can be recorded and reproduced, Above-described high C/N rate video tape B55 capable of recording a high bit-rate signal, e.g. HDTV signal, will be _ _._ ._..- . ,_._ .. ._. w.- _. -,.., able to use in such a low bit-rate dedicated magnetic recording/playbac:k apparatus but will reproduce the first data stream D1 only. That is, the wide NTSC signal. is outputted, while the second data stream is not reproduced. In other words, on2 recording/playback apparatus having a complicated configuration can reproduce a HDTV signal and the other recording/playback apparatus having a simple configuration can reproduce a wide hTSC signal if a given video tape 855 includes the same multi-level HDTV signal.
Accordingly in case of two-level multiple state, four combinations will be realized with perfect compatibility among two tapes having different C/N rates and two recording/playback apparatus having different recordlng/playbac.k data rates. This will bring remarkable effect. In this case, an h'TSC dedicated apparatus will be simple in construction as compared with an HDTV dedicated apparatus. In more detail, a circuit scale of EDTV decoder will be 1/6 of that of HDTV decoder. Therefore, a low function apparatus can be realized at fairly low cost.
Realizatic:n of two, ~~TV and EDTV, types recording/playback apparatus having different recording/reproducing capability of picture quality will provide various type products ranging in a wide price range. Lsers can freely select a tape among a plural ity of tapes, from an expensive high C/N rate tape to a cheaper low C/N rate tape, as occasion demands so as to satisfy required picture quality. Not only maintaining perfect comFatibility but obtaining expandable capability a~l,u~"~..~,~

.:._- .-,_.. ._r..: :..~._ ~.~-'-,-=-: . .. ..:. ._. ...
will be attained and further compatibility with a future system will be ensured. Consequently, it will be paseible to establish long-lasting standards for recording/playback apparatus. Other recording methods will be used in the same manner. For example, a multi-level recording will be realized by use csf phase modulation explained in the first and third embodiments. A recording using ASK exglained in the fifth embodiment will also be possible. A multiple state will be realized by converting present recording from two-level to four-level and dividing into two groups as shown in Figs. 59(c) and 59(d).
A circuit block diagram for ASE is identical to that disclosed in Fig. 84. Besides embodiments already described, a multi-levol recording will be also realized by use of multiple tracks on a. magnetic tape. Furthermore, a theoretical multi-level recording will be feasible by differentiating the error correcting capability so as to discriminate respective data.
Compatibility with future standards will be described below. A setting of standards for recording/playback apparatus such as VCR is normally executed by taking account of the most highest C/N rate tape available in practice. The recording characteristics of tapes progresses rapidly. For example, the C/!V rate has been improved more than 10 dB
compared with the tape used 10 years ago. If supposed that new standards will be established after 10 to 20 years due to an advancement of tape property, a conventional method will ~~lr ~o . _"

.._. _,_._ _.... ...._ _-._-_:, encounter with difficulty in maintaining compatibility with older standards. New and old standards, in fact, used to be one-way compatible or non-compatible with each other. (~ tte contrary, in accordance with the present invention, the standards are first of all established for recording and/or reproducing the first data stream and/or second data stream on present day tapes. Subsequently, if the C/N rate is improved magnificently in future, an upper level data stream, e.g. a third data stream, will be added without any difficulty as long as the present invention is incorporated in the system. For examgle, a super HDTV VCR capable of recording or reproducing a three-level 64 SRQAM signal will be realized hhile maintaining perfect compatibility with the conventional standards. A magnetic tape, recording first to third data streams in compliance with new standards, will be able to use, of cause, in the older two-level magnetic recording/playback apparatus capable of recording and/or reproducing only first and second data streams. In this case, first and second data streams can be reproduced perfectly although the third data stream is left non-reproduced.
Therefore, an HDTV signal can be reproduced. For these reasons, the merit of expanding recording data amount while maintaining compatibility between new and old standards is expected.
Returning to the explanation of reproducing operation of Fig. 84, the magnetic head 854 and the magnetic reproduction circuit 853 reproduce a reproducing signal from the magnetic ;;wi~ wct~: -,. .~,~, tape 855 and feeds it to the modulation/demodulation circuit 852. The demodulating operation is almost identical with that of first, third, and fourth embodiments and will no further be explained. The demodulator ?60 reproduces the first and second data streams D1 and D2. The second data stream DZ is error corrected with high code gain in a Trellis-decoder 759b such as a Vitabi decoder, so as to be low error rate. The video decoder 402 demodulates D1 and DZ signals to output an HDTV video signal.
Fig. 131 is a block diagram showing a three-level magnetic recording/playback apparatus in accordance with the present invention which includes one theoretical level in addition to two physical levels. This system is substantially the same as that of Fig. 84. The difference is that the first data stream is further divided into two subchannels by use of a TDM in order to realise a three -level construction.
Aa shown in fig. 131, an HDTV signal is separated first of all into two, medium and low frequency band video signals D1_1 and Dl_Z, through a 1-1 video encoder 401c and a 1-2 video encoder 401d and, thereafter, fed into a first data stream input 743 of an input section 742. The data stream D1_1 having a picture quality of MPEG grade is error correcting coded with high code gain in an ECC encoder 743x, while the data stream Dl_z is error correcting coded with normal code gain in an ACC encoder 743b. D~_I and D1_Z are time multiplexed together in a TDM 743c to be one data stream Dl.
Dl and DZ are modulated into two-level signal in a C-CDM 749 12'.

- _ . ~ .- _ - ._ ..z. _.
and then recorded on the magnetic tape 855 through the magnetic head 854.
In playback operation, a recording signal reproduced through the magnetic head 854 is demodulated into D1 and DZ
by the C-CDM demadulator 760 in the same manner as in the explanation of Fig. 84. The first data stream D1 is demodulated into two, Di_1 and Dl_Z, sub channels through the TDM 758c provided in the first data stream output 758. D~-1 data is error corrected in an ECC decoder 758a having high code gain. Therefare, Dl-1 data can be demodulated at a lower C/N rate as compared with D1_Z data. A 1-1 video decoder 402a decodes the D~_1 data and outputs an LDTV signal. On the other hand, D1_Z data is error corrected in au ECC decoder 75Bb having normal code gain. Therefore, D1_Z data has a threshold value of high C/N rate compared with D1_1 data and thus will not be demodulated when a signal level is not large. Dl-2 aata 1a tnen aemoaulaten in a ~-z video aecvavr -lo8d ena summed with Dl_1 data to output an EDTV signal of wide NTSC
grade.
The second data stream DZ is Vitabi demodulated in a Trellis decoder 759b and error corrected at an ECC decoder 759a. Thereafter, DZ data is converted into a high :.requency band video signal through a second video decoder 402b and, then, summed with Di_1 and Dy_Z data to output an HDTV signal.
In this case, a threshold value of the C/N rate of DZ data is set larger than that of C/N rate of D1_Z data. Accordingly, Dl_1 data, i . c: . an LDTV signal , wi 11 be reproduced from a tape 855 having a smaller C/N rate. Dl_1 and D;_Z data, i.e. an EDTV
signal, will be reproduced from a tape 855 having a normal C/N rate. And, I)1_I, Dl-2' and DZ data, i.e. an HDTV signal, will be reproduced from a tape 855 having a high C/N rate.
Three-level~nagnet.ic recording/playhack apparatus can be realized in this manner. As described in the foregoing description, the tape 855 has an interrelation between C/N
rate and cost. The present invention allows users to select a grade of tape in accordance with a content of TV program they want to record because video signals having picture qualities of three grades can be recorded and/or reproduced in accordance with tape cost.
Next, an effect of multi-level recording will be described with respect to fast feed playback. As shown in a recording track diagram of Fig. 132, a recording track 855a having an azimuth angle A and a recording track 855b having an opposite azimuth angle B are alternately arrayed on the magnetic tape 855. The recording track 855a has a recording region 855c at its central portion and the remainder as D1_Z
recording regions B55d, as denoted in the drawing. This unique recording pattern is provided on at least oae of several recording tracks. The recording region 855c records one frame of LI)'fV signal. A high frequency band signal DZ is recorded on a DZ recording region 855e corresponding to an entire recording region of the recording track 855x. This recording format causes no noz-el effect against a normal speed recording/playback operation.

A fast feed reproduction in a reverse direction does not allow a magnetic head trace 855f having an azimuth angle A to coincide with the magnetic track as shown in the drawing. As the present invention provides the D1_, recording region 855c at a central narrow region of the magnetic tape as shown in FIG. 132, this region only is surely reproduced although it occurs at a predetermined probability. Thus reproduced D1_1 signal can demodulate an entire picture plane of the same time although its picture quality is an LDTV of MPEGl level. In this manner several to several tens LDTV signals per second can be reproduced with perfect picture images during the fast feed playback operation, thereby enabling users to surely confirm picture images during the fast feed operation.
A head trace 855g corresponds to a head trace in the reverse playback operation, from which it is understood only a part of the magnetic track is traced in the reverse playback operation. The recording/playback format shown in FIG. 132 however allows, even in such a reverse playback operation, to reproduce D,_~
recording region and, therefore, an animation of LDTV grade is outputted intermittently.
Accordingly, the present invention makes it possible to record a picture image of LDTV grade within a narrow region on the recording track, which results in intermittent reproduction of almost perfect still pictures with picture quality of LDTV
grade during normal and reverse fast feed playback operations. Thus, the users can easily confirm picture images even in high-speed searching.

Next, another method will be described to respond a higher speed fast. feed playback operation. A D1_1 recording region 855c is provided as shown at lower right of Fig. I32, so that one frame of LDTV signal is recorded thereon.
Furthermore, a narrow Dl_l~D~ recording region 855h is provided at a part of the Dl_1 recording region 855c. A
subchannel D1_y in this region records c, part of information relating to th~ one frame of LDTV signal. The remainder of the LDTV information is recorded on the DZ recording region 855j of the Dl_1~DZ recording region 855h in a duplicated manner. The subchannel DZ has a data recording capacity 3 to 5 times as much as the subchannel D1_l. Therefore, subchannels Dl_1 and DZ can record one frame information of LDTV signal on a smaller, 1/3-1/5, area of the recording tape. As the head trace can be recorded in a further narrower regions,855h, 855j, both time and area are decreased into 1/3"1/5 ns compared with a head trace time T5.1. Even if the trace of head is further inclined by increasing the fast feed speed amount, the probability of entirely tracing this region will be increased. Accordingly, perfect LDTV picture images will be iatermittently reproduced even if the fast feed speed is increased up to 3 to 5 times as fast as the case of the subchanne i D1_l onl y .
In case of a two-level YCR, this method is useless in reproducing the DZ recording region 855j and therefore this region will not be reproduces in a high-speed fast feed playback operation. On the othei hand, a three-level high performance VCR will allow users to confirm a pictu~e image even if a fast feed playback operation is executed at a faster, 3 to 5 ae fast as the two-level VCR, speed. In other words, not only excellent picture quality is obtained in accordance with cost but a maximum fast feed speed capable of reproducing picture images can be increased in accordance with the cost.
Although this embodiment utilizes a multi-level modulation system, it is needless to say that a normal, w.g.
18 QAM, modulation system can also be adopted to realize the fast feed playback operation in accordance with the present invention as long as an encoding of picture images is of multiple type.
A recording method of a conventional non-multiple digital VCR, in which picture images are highly compressed, disperses video data uniformly. Therefore, it was not possible in a fast feed playback operation to reproduce all the picture images on a picture plane of the same time. The picture reproduced was the one consisting of plurality of picture image blacks having non-coincided time bases with each other. The present invention, however, provides a multi-level HDTV VCR which can reproduce gicture image blocks having coincided time bases on an entire picture plane during a fast feed playback operation although its picture quality is o: LD1'V grade.
The three-level recording in accordance with the present invention will be able to reproduce a high resolution TV

signal such as HDTV signal when the recording/playback system has a high C/N rate. Meanwhile, a TV signal of EDTV grade, e.g. a wide NTSC signal, or a TV signal of LDTV grade, e.g.
a low resolution NTSC signal, will be reproduced when the recording/playback system has a low C/N rate or poor function.
As ie described in the foregoing description, the magnetic recording/playback apparatus in accordance with the present invention can reproduce picture images consisting of the same content even if the C/N rate is low or an error rate is high, although the resolution or the picture quality is relatively low.
Embodiment 7 A seventh embodiment of the present invention will be described far execution of four-level video signal transmission. A combination of the four-levol signal transmission and the four-level video data construction will create a four-level sigual service area as shown in Fig. 91.
The four-level service area is consisted of, from innermost, a first 890a, a second 890b, a third 890c, and a fourth signal receiving area 890d. The method of developing such a four-ll.evel service area will be explained in more detail.
The four-level arrangement can be implemented by using four physically different levels determined through modulation or four logic level' defined by data discrimina~ion in the error correction capability. The former provides ,a large difference in the C/N rate between two 1z7 . : : _- . : _ . . , .:.-. .: ~: - ~r~;:., .-. . . . : : .
adjacent levels and Lhe C/N rate has to he increased to discriminate all the four levels from each other. The latter ~s based on the action of demodulation and a difference in the C/N rate between two adjacent levels should stay at minimum. Hence, the four-level arrangement is best constructed using a combination of two physical levels and two logic levels. The division of a video signal into four signal levels will be explained.
Fig. 93 is a block diagram of a divider circuit 3 which comprises a video divider 895 and four compressors 405x, 405b, 405c, 405d. The video divider 895 contains three dividers 404a, 404b, 404c which are arranged identical to the divider circuit 404 of the first video encoder 401 shown in Fig. 30 and will be no more explained. An input video signal is divided by the dividers into four components, HLV~ of IoW
resolution data, HHVH of high resolution data, and HLVa and HgVL for medium resolution data. The resolution of HLVL is a half that of the original input signal.
The input video signal is first divided by the divider 404a into two, high and low, frequency band components, each component being divided into two, horizontal and vertical, segments. The intermediate between the high and low frequency ranges is a dividing point according to the embodiment.
Hence, if the input video signal is an F3DTV signal of 1000 line vertical resolution, HLV~ has a vertical resolution of 500 lines and a horizontal resolution of a half value.
Each of two, hori2ontal and vertical, data of the low .... . _._ . ,- _.~.o,t frequency coaponent H~VL is further divided by the divider 404c into two frequency band segments. Hence, an H~VL segment output is 250 lines in the vertical resolution and 1/4 0: the original horizontal resolution. This output of the divider 404c which is termed as an LL signal is then compressed by the compressor 405a to a D1_1 signal.
The other three higher frequency segments of H~VL are mixed by a miter 772c to an LH signal which is then compressed by the compressor 405b to a D1_Z signal. The compressor 405b may be replaced with three compressors provided between the divider 404c and the miter 772c.
Ii-Vg, H$Vt,and HBVa form the divider 404a are mixed by a mixer 772a to an H~V~ H signal. If the input signal is as high as 1000 lines in both horizontal and vertical resolution, HgVg-H has 500 to 1000 lines of a horizontal and a vertical resolution. H$V~ H is fed to the divider 404b where it is divided agnin into four components.
Similarly, H~V~ from the divider 404b has 500 to ?50 lines of a horizontal and a vertical resolution and transferred as an HL signal to the compressor 405c. The other three components, H~Vg, H~Vt, and H~Vg, from the divider 404b have 750 to 1000 lines of a horizontal and a vertical resolution and are mixed by a mixer 772b to an HH signal which is they. compressed by the compressor 405d and delivered as a ~D~z signal. After compression, the HL signal is delivered as a DZ_1 signal. As the result, LL or D1_1 carries a frequency data of 0 to 250 lines, LH or D1_Z carries a ...- _ n~.- .J~ ...~ H.W_ -'-0~ .'. .~.. ..T. .. ._. ._.
frequency data from more than 250 lines up to 500 lines, HL
or DZ_1 carries a frequency data of more than 500 lines up to 750 lines, and HH or DZ_l carries a frequency data of more than 750 linQS to 1000 lines so that the divider circuit 3 can provide a four-level signal. Accordingly, when the divider circuit 3 of the transmitter 1 shown in Fig. 87 is replaced with the divider circuit of Fig. 93, the transmission oP a four-level signal will be implemented.
The combination of multi-level data and multi-level transmission allows a video signal to be at steps declined in the picture quality in proportion to the C/N rate during transmission, thus contributing to the enlargement of the Tv broadcast service area. At the receiving side, the action of demodulation and reconstruction is identical to that of the Becoud receiver of the second embodiment shown in Fig. 88 and will be no more explained. In particular, the miter 37 is modified for video signal transmission rather than data communications and will now be explained in more detail.
As described in the second embodiment, a received signal after demodulated and error corrected, is fed as a set of four components D1_l, Dl_Z, DZ-1, DZ-2 to the miter 3? of the second receiver 33 of Fig. 88.
Fig. 94 is a block diagram of a modified mixer 33 in which Dl_l, Dl-Z' DZ-1' DZ-2 are explained by their respective expanders 523x, 523b, 523c, 523d to an LL, and LH, an HL, and an HH signal respectively which are equivalent to those described with Fig. 93. If the bandwidth of the input signal is l, LL has a bandwidth of 1/4, LL+LH has a bandwidth of 1/2, LL+LH+HL has a bandwidth of 3/4, and LL+LH+HL+HH has a bandwidth of 1. The LH signal is then divided by a divider 531 a and mixed by a video mixer 548a with the LL signal.
An output of the video mixer 548a is transferred to an HL VL terminal of a video mixer 548c. The video mixer 531 a is identical to that of the second decoder 527 of FIG. 32 and will be no more explained. Also, the HH signal is divided by a divider 531 b and fed to a video mixer 548b. At the video mixer 548b, the HH signal is mixed with the HL signal to an HH VH -H
signal which is then divided by a divider 531c and sent to the video mixer 548c. At the video mixer 548c, HH VH -H is combined with the sum signal of LH and LL to a video output. The video output of the mixer 33 is then transferred to the output unit 36 of the second receiver shown in FIG. 88 where it is converted to a TV signal for delivery. If the original signal has 1050 lines of vertical resolution or is an HDTV signal of about 1000-line resolution, its four different signal level components can be intercepted in their respective signal receiving areas shown in FIG. 91.
The picture quality of the four different components will be described in more detail. The illustration of FIG. 92 represents a combination of FIGS. 86 and 91. As apparent, when the C/N rate increases, the overall signal level of amount of data is increased from 862d to 862a by steps of four signal levels D1-~, D,_z, Dz-,, Dz-z~
Also, as shown in FIG. 95, the four different level components LL, LH, HL, and HH are accumulated in proportion to the C/N :ate. More specifically, the quality of a reproduced picture will be increased as Lhe distance from a transmitter antenna becomes small. When L=Ld, LL component is reproduced. When L=Lc, LL+LH signal is reproduced. When L=Lb, LL+LH+HL signal is reproduced. When L=La, LL+LH+HL+HH signal is reproduced. As the result, if the bandwidth of the original signal is 1, the picture quality is enhanced at 1/4 increments of bandwidth from 1/4 to 1 depending on the receiving area. If the original signal is an HDTV of 1000-line vertical resolution, a reproduced TV signal is 250, 500, '750, and 1000 lines in the resolution at their respective receiving areas. The picture quality will thus be varied at steps depending on the level of a signal. Fig. 96 shows the signal propagation of a conventional digital ITV signal transmission system, in which no signal reproduction will be possible when the C/N rate is Iess than V0. Also, signal interception will hardly be guaranteed at signal interference regions, shadow regions, and other signal attenuating regions, denoted by the symbol x, of the service area. Fig.
97 shows the signal propagation of an HDTV signal transmission system of the present invention. As shown, the picture quality will be a full 1000-line grade at the distance La where C/N=a, a 750-line grade at the distance Lb where C/N=b, a 500-line grade at the distance Lc where C/N=c, and a 250-line grade at the distance Ld where C/N=d. Within the distance La, there are shown unfavorable regions where the C/N rate drops sharply and no HDTV quality picture will be reproduced. As understood, a lower picture quality signal can however be intercepted and reproduced according to the multi-level signal transmission system of the present invention. For example, the picture quality will be a 750-line grade at the point B in a building shadow area, a 250-line grade at the point D in a running train, a 750-line grade at the point F in a ghost developing area, a 250-line grade at the point G in a running car, a 250-line grade at the point L in a neighbor signal interference area. As set forth above, the signal transmission system of the present invention allows a TV signal to be successfully received at a grade in the area where the conventional system is poorly qualified, thus increasing its service area. FIG. 98 shows an example of simultaneous broadcasting of four different TV programs, in which three quality programs C, B, A
are transmitted on their respective channels D1_z, Dz-n Dz-z while a program D
identical to that of a local analogue TV station is propagated on the D~_, channel.
Accordingly, while the program D is kept available at simulcast service, the other three programs can also be distributed on air for offering a multiple program broadcast service.
Embodiment 8 Hereinafter, an eighth embodiment of the present invention will be explained refernng to the drawings. The eighth embodiment employs a multi-level signal transmission system of the present invention for a transmitter/reception in . : .° . . ' '~:. ~ ~ cue-;-F= .. . . . . - . . . . . _ . . _ a cellular telephone system.
Fig. 115 is a block diagram showing a transmitter/receiver of a portable telephone, in which a telephone conversation sound inputted across a microphone 762 is compressed and coded in a compressor 405 into mufti-level, Dl, BZ, and D3, data previously described. These D1, DZ, and D3 data are time divided in a time division circuit 765 into predetermined time slots and, then, modulated in a modulator 4 into a mufti-level, e.g. SRGZAM, signal previously described. Thereafter, an antenna sharing unit ?64 and an antenna 22 transmit a carrier wave carrying a modulated signal, which will be intercepted by a base station later described and further transmitted to other base stations or a central telephone exchanger so as to communicate with other telephones.
On the contrary, the antenna 22 receives transmission radio waves from other base Stations as communication signals from other telephones. A received signal is demodulated in a multiple-level, e.g. SR,QAM, type demodulator 45 into D1, D2, and D3 data. A timing circuit '767 detects timing signals on the basis of demodulated signals. These timing signals are fed into the time division circuit 765. Demodulated signals Dl, DL, and D3 are fed into an expander 503 and expanded into a sound signal, which is then transmitted to a speaker 763 and converted into sound.
Fig. 118 shows a block diagram ezemplarily showing an arrangement of base stations, in which three base stations a : . . . , ; ~ . _ , . ~ - '~:,~ _ ~v'1o''"= . . , _ . . . . . . , . _ 771, 772, and 773 locate at center of respective receiving cells 768, 769, and 770 of hezagon or circle. These base stations 771, 772, and 773 respectively has a plurality of transmitter/receiver units 761a'761j each similar to that of Fig. 115 so as to have data communication channels equivalent to the number of these transmitter/receiver units. A base station controller 774 ie connected to all the base stations and always monitors a communication traffic amount of each base station. Based on the monitoring result, the base station controller 774 carries out an overall system control including allocation of channel frequencies to respective base stations or control of receiving cells of respective base stations.
Fig. 11? is a view showing a traffic distribution of communication amount in a conventional, e.g. QPSK, system.
A diagram d=A shows data 774a and 774b having frequency utilization efficiency 2 bit/Hz, and a diagram d=B shows data 774c having frequency utilization efficiency 2 bit/H2. A
summation of these data 774x, 774b, and ?74c becomes a data 774d, which represents a transmission amount of Ach consisting of receiving cello 7fi8 and 770. Frequency utilization efficiency of 2 bit/Hz is uniformly distributed.
However, density of population in an actual urban area is locally high in several crowded areas 775x, ?75b, and 775c which include buildings concentrated. A data 774e representing a co~.munication traffic amount shows several peaks at locations just corresponding to these crowded areas :_.- . ._.. ._:;._, 'F...~' ~o-~_-' ,.., ..z. .. .. ...
775x, 775b, and 775c, in contrast with other area having small communication amount. A capacity of a conventional cellular telephone was uniformly set to 2 bit/Hz frequency efficiency at entire region as shown by the data 774d irrespective of actual traffic amount TF shown by the data 774e. It is not effective to give the same frequency efficiency regardless of actual traffic amount. In order to compensate this ineffectiveness, the conventional systems have allocated many frequencies to the regions having a large traffic amount, increased channel number, or decreased the receiving cell of the same. However, an increase of channel number is restricted by the frequency spectrum. Furthermore, conventional multi-level, e.g. 18 QAM or 84 QAM, mode transmission systems increase transmission vower. A
reduction of receiving cell will induce an increase in number of base stations, which will increase installation coat.
It is ideal for the improvement of an overall system efficiency to increase the frequency efficiency of the region having a larger traffic amount and decrease the frequency efficiency of the region having a smaller traffic amount. A
multi-level signal transmission system in accordance with the present invention realizes this ideal modification. This will be explained with reference to Fig. 118 showing a communication amount & traffic distribution in accordance with the eighth embodiment of the present invention.
More specifically, Fig. 118 shows communication amounts of respective receiving cells 770b, 768, 769, 770, and 770a . _ _ _ . . _ . .. . ::i : :.. '~.~.'= j=~-;~ ~,_ ~ .. _ . -~ : . . . _ _ _ _ .
takan along a line A-A' . The receiving cells 768 and 770 utilize frequencies of a channel group A, while the receiving cells 770b, 769, and 770a utilize frequencies of a channel group B which does not overlap with the channel group A. The base station controller 774 shown in Fig. 116 increases or decreases chapel number of these channels in accordance with the traffic amount of respective receiving cells. In Fig.
118, a diagram d=A represents a distribution of a communication amount of the A channel. A diagram d=B
represents a distribution of a communication amount of the B
channel. A diagram d=A+B represents a distribution of a communication amount of all the channels. A diagram TF
represents a communication traffic amount, and a diagram P
shows a distribution of buildings and population.
The receiving cells ?68, 769, and 770 employ the multi-level, e.g. SRQAM, signal transmission system. Therefore, it is possible to obtain a frequency utilization efficiency of 6 bit/Hz, three times as large as 2 bit/Hz of QPSK, in the vicinity of the base stations as denoted by data 776x, 776b, and 776c. Meanwhile, the frequency utilization efficiency decreases at steps from 6 bit/H2 to 4 bit/Hz, and 4 bit/Hz to 2 bit/Hz, as it goes to suburban area. If the transmission power is insufficient, 2 bit/Hz areas become narrower than the receiving cells, denoted by dotted lines 777a, 777b, 777c, of pPSK. However, an equivalent receiving cell will be easily obtained by slightly increasing the transmission power of the base stations.

.:._ .~_.- .::-._: ;..~~ W-;o--- .... ._-_ .. ... _..
Transmitting/receiving operation of a mobile station capable of responding to a 64 SRQ,AM signal is carried out by use of modified QPSK, which is obtained by set a shift amount of SRQAM to S=I, at the place far from the base station, by use of 1fi SRQAM at the place not so far from the same, and 64 SRQAM at the nearest place. Accordingly, the maximum transmission power does not increase as compared with f~PSK.
Furthermore, 4 SRQAM type tranemitter/receiver, whose circuit configuration ie simplified as shown in a block diagram of Fig. 121, will be able to communicate with other telephones while maintaining compatibility. That will be the same in lfi SRQAM type transmitter/receiver shown in a block diagram of Fig. 122. As a result, three different type telephones having different modulation systems will be provided. Small in size and light in weight is important for portable telephones. In this regard, the 4 SRQAM system having a simple circuit configuration will be suitable for the users who want a small and light telephone although its frequency utilization efficiency is low and therefore cost of call may increase. In this manner, the present invention system can suit for a wide variety of usage.
As is explained above, the transmission system having a distribution like d=A+B of Fig. 118, whose capacity is locally altered, is accomplished. Therefore, an overall frequency utilization efficiency wi~I be much effectively improved if layout of base stations is determined to tit for the actual traffic amount denoted by TF. Especially, effect - - . ~_- - fi' __ _ - i _ = _ ~.; - ~ ~ ...'_ ~:-t~:?. .-, a . . . _ . . . _ - _ _ . ' of the present invention will be large in a micro cell system, whose receiving cells are smaller and therefore numerous sub base stations are required. Because a large number of sub base stations can be easily installed at the place having a large traffic amount.
Neat, data assignment of each time slot will be explained referring to Fig, 119, wherein Fig. 119(a) shows a conventional time slot and Fig. 119(b) shows a time slot according to the eighth embodiment. The conventional system performs a down, i.e. from a base station to a mobile station, transmission as shown in Fig. 119(a), in which a sync signal S is transmitted by a time slot 780a and transmission signals to respective portable phones of A, B, C channels by time slots 780b, ?80c, 780d respectively at a frequency A. On the other hand, an up, i.e. from the mobile station to the base station, transmission is performed in such a manner that a sync signal S, and transmission signals of a, b, c channels are transmitted by time slots 781x, ?81b, 781c, 781d at a frequency B.
The present invention, which is characterized by a multi-level, e.g. 64 SRQAM, signal transmission system, allows to have three-level data consisting of D1, DZ, D3 of 2 bit/Hz as shown in Fig. 119(b). As both of Al and AZ data are transmitted by 16 SRHAM, their time slats have two times data rate as shown by slots ?SZb, 782c and 783b, 783c. It means the same quality sound can be transmitted by a half time.
Accordingly, a time width of respective time slots 782b, 782c becomes a half. In this manner, two times transmission capacity can be acquired at the two-level region 776c shown in Fig. 11B, i.e. in the vicinity of the base station.
In the same way, time slots 7828, 7838 carry out th~
5 transmission/reception of E1 data by use of a 64 SRQAM
signal. As the transmission capacity is three times, one time slot can be used for three channels of El, E2, E3. Thie would be used for a region further close to the base station.
Thus, up to three times communication capacity can be 10 obtained at the same frequency band. An actual transmission efficiency, however, would be reduced to 80%. It is desirable for enhancing the effect of the present invention to coincide the transmission amount distribution according to the present invention with the regional distribution of the 15 actual traffic amount as perfect as possible.
In fact, an actual urban area consists of a crowded building district and a greenbelt zone surrounding this building area. Even an actual suburb area consists of a residential district and fields or a forest surrounding this 20 residential district. These urban and suburb areas resemble the distribution of the TF diagram. Thus, the application of the present invention will be effective.
Fig. 120 is a diagram showing time slots by the TI1MA
method, wherein Fig. 120(a) shows a conventional method and 25 Fig. 120(b) shows the present invention. The conventional method uses time slots 786a, 786b for transmission to portable phones of A, B channels at the same frequency and _._ _ _._ ._ _. -_. - .: _. :.. .:-~_ . :-_ ..:
time slots 787x, 7R7b for transmission from the same, as shown in Fig. 120(x).
On the contrary, 16 SRQAM mode of the present invention uses a time slot 788a for reception of Al channel and a time slot 788c for transmission to Al channel as shown in Fig.
120(b)_ A width of the time slot becomes approximately 1/2.
In case of 84 SRQAM mode, a time slot 788i is used for reception of D1 channel and a time slot 7881 is used for transmission to Dl channel. A width of the time slot becomes approximately 1/3.
In order to save electric power, a transmission of E1 channel is executed by use of a normal 4 SRQAM time slot 788r while reception of E1 channel is executed by use of a 16 SRQAM time slot 788p being a 1/2 time slot. Transmission power is surely suppressed, although communication cost may increase due to a long occupation time. This will be effective for a small and light portable telephone equipped with a small battery or when the battery is almost warn out.
As is described in the foregoing description, the present invention makes it possible to determine the distribution of transmission capacity so as to coincide with an actual traffic distributipn, thereby increasing substantial transmission capacity. Furthermore, the present invention a110w6 base stations or mobile stations to freely select one among two or three transmission capacities. If the frequency utilization ef:iciency is selected lower, power consumption will be decreased. If the frequency utilization efficiency is selected higher, communication cost will be saved. Moreover, adoption of a 4 SRQAM mode having smaller cspacity will simplify the circuitry and reduce the size and cast of the telephone. Ae explained in the previous embodiments, one characteristics of the present invention is that compatibility is maintained among all of associated stntions. In this manner, the present invention not only increases transmission capacity but allows to provide customers a wide variety of series from a super mini telephone to a high performance telephone.
Embodim Hereinafter, a ninth embodiment of the present invention will be described referring to the drawings. The ninth embodiment employs this invention in an OFDM transmission system. Fig. 123 is a block diagram of an OFDM
transmitter/receiver, and Fig. i24 is a diagram showing a principle of an OFDM action. An OFDM is one of FDM and has a better efficiQncy in frequency utilization as compared with a general FDM, because an OFDM sets adjacent two carriers to be quadrature with each other. Furthermore, an OFDM can bear multipath obstruction such as ghost and, therefore, may be applied in the future to the digital music broadcasting or digital TV broadcasting.
As shown in the principle diagram of Fig. 124, an OFDM
converts an input signal by a serial to parallel converter 791 into a data being disposed on a frequency axis 793 at intervals of 1/ts, so as to produce subchannels 794a-?84e.

... ..T. ., .7T ...
This signal is inversely FFT converted by a modulator 4 having an inverse FFT 40 into a signal on a time axis 799 to produce a transmission signal 785. This inverse FFT signal is transmitted during an effective symbol period 796 of the time 5 period ts. A guard interval 797 having an amount tg is provided between respective symbol periods.
A transmitting/receiving action of an HDTV signal in accordance with this ninth embodiment will be explained referring to the block diagram of Fig. 123, which shows a 10 hybrid OFDM-CCDM system. An inputted HDTV Bignai is separated by a video encoder 401 into three-level, a low frequency band Di_l, a medium-low frequency band Dl_z, and a high-medium-low frequency band DZ, video signals, and fed into an input section 742.
15 In a first data stream input 743, a D1_1 signal is ECC
encoded with high code gain and a D1_2 signal is ECC encoded with normal code gain. A TDM 743 performs time division multiplexing of Dl_1 and Dl_Z signals to produce a Dl signal, which is then fed to a D1 serial to parallel converter 791d 20 in a modulator 852x. The D1 signal consists of n pieces of parallel data, which are inputted into first inputs of n pieces of C-CDM modulator 4a, db,---respectively.
On the other hand, the high frequency band signal DZ is fed into a second data stream input 744 of the input section 25 742, in which the D2 signal is ECC (Error Correction Code) encoded in an ECC 744a and then Trellis encoded in a Trellis encoder 744b. Thereafter, the D., signal is supplied to a Dz - " . ..,. .. . _:.
serial to parallel converter 791b of the modulator 852a and converted into n pieces of parallel data, which are inputted into second inputs of the n pieces of C-CDM modulator 4a, 4b,---respectively.
The C-CDM modulators 4a, 4b, 4c---respectively produces 16 SRQAM signal on the basis of the Di data of the first data stream input and the DZ data of the second data stream input.
These n pieces of C-CDM modulator respectively has a carrier different from each other. As shown in Fig. 124, carriers 794a, 794b, 794c,---are arrayed on the frequency axis 793 so that adjacent two carriers are 90°-out-of-phase with each other. Thus C-CDM modulated n pieces of modulated signal are fed into the inverse FFT circuit 40 and mapped from the frequency axis dimension 793 to the time axis dimension 790.
Thus, time signals 796x, 796b ---, having an effective symbol length ts, are produced. There is provided a guard interval zone ?97a of Tg seconds between the effective symbol time zones 796a and ?96b, in order to reduce multipath obstruction. Fig. 129 is a graph showing a relationship between time axis and eisnal level. The guard time Tg of the guard interval band 797a is determined by taking account of multipath affection and usage of signal. By setting the guard time Tg longer than the multipath affection time, e.g. TV
ghost, modulated signals from the inverse FFT circuit 40 are converted by a parallel to serial converter 4e into one signal and, then, transmitted from n transmitting circuit 5 as an RF signal.

. ._._ ...._. _- _,-'-__ . .: ;Yr .. _ . . . ~ , Y .
Nezt, an action of a receiver 43 will be described. A
received signal, shown as time-base symbol signal 798e of Fig. 124, is fed into an input circuit 24 of Fig. 123. Then, the received signal is converted into a digital signal in a demodulator 852b and further changed into Fourier coefficients in an FFT 40a. Thus, the signal is mapped from the time axis 799 to the frequency axis 793a as shown in Fig.
124. That is, the time-base symbol signal is converted into frequency-base carriers 794a, 794b,-- . As these carriers are in quadrature relationship with each other, it is possible to separate respective modulated signals. Fig.
125(b) shows thus demodulated 18 SR.QAM signal, which is then fed to respective C-CDM demodulators 45a, 45b,--of a C-CDM
demodulator 45, in which demodulated 16 SRQAM signal is demodulate3 into multi-level nub signals D1, Dz. These sub signals D1 and DZ are further demodulated by a D1 parallel to serial converter 852a and a DZ parallel to serial converter 852b into the original D1 and D2 signals.
Since the signal transmission system is of C-CDM multi level shown in 125(b), both D1 and DZ signals will be demodulated under better receiving condition but only D1 signal will be demodulated under worse, e.g. low C/N rate, receiving condition. Demodulated D1 signal is demodulated in an output section 757. As the D1_1 signal has higher ECC code gain as compared with the D1_2 signal, an error signal of the D1_1 signal is reproduced even under worse receiving condition.

_ _ . _: -.:_ ~-..:-_ ~,.. ._- . _ The D1_1 signal is converted by a 1-1 video decoder 402c into a low frequency band signal and outputted as an LDTV, and the D1_Z signal ie converted by a 1-2 video decoder 402d into a medium frequency band signal and outputted as EDTV.
5 The DZ signal is Trellis decoded by a Trellis decoder ?59b and converted by a second video decoder 402b into a high frequency band signal and outpu~ted as an HDTV signal.
Namely, an LDTV signal is outputted in case of the low frequency band signal only. An EDTV signal of wide NTSC
10 grade is outputted if the medium frequency band signal is added to the low frequency band signal, and an HDTV signal is produced by adding low, medium, and high frequency band signals. As well aF the previous embodiment, a TV signal having a picture quality depending on a receiving C/N rate lb can be received. Thus, the ninth embodiment realizes a novel multi-level signal transmission system by combining an OFDM
and a C-CDM, which was not obtained by the OFDM alone.
An OFDM is certainly strong against multipath such as TV
ghost because the guard time Tg can absorb an interference 20 signal of multipath. Accordingly, the OFDM ie applicable to the digital TV broadcasting for automotive vehicle TY
receivers. Meanwhile, no OFDM signal is received when the C/N
rate is less than a predetermined value because its signal transmission pattern is not of a mufti-level type.
25 However the present invention can solve this disadvantage by combining the CFDM with the C-CDM, thus realizing g graditional degradatlon depending on the C/N rate in s video signal reception without being disturbed by multipath.
When a TV signal is received in a compartment of a vehicle, not only the reception is disturbed by multipath but 5 the C/r rate is deteriorated. Therefore, the broadcast service area of a TV broadcast station will not be expanded as expected if the countermeasure is only for multipath.
On the other hand, a reception of TV signal of at least LDTV grade will be ensured by the combination with the multi 10 level transmission C-CDM even if the C/N rate is fairly deteriorated. As a picture plane size of an automotive vehicle TV is normally less than 100 inches, a TV signal of an LDTV grade will provide a satisfactory picture quality.
Thus, the LDTV grade service area of automotive vehicle TV
15 will largely expanded. If an OFDM is used in an entire frequency band of HDTV signal, the present semiconductor technologies cannot prevent circuit scale from increasing so far.
low,. an OFDM method of transmitting only D1_1 of low 20 fr~quency band TV signal will be explained below. As shown in a block diagram in Fig. 138, a medium frequency band component Dl_2 and a high frequency band component DZ of an HDTV signal are multiplexed in a C-CD~I modulator 4a, and then transmitted at a frequency band A through an FDM 40d.
25 On the other hand, a signal received by a receiver 43 is first of all frequency separated by an FDM 40e and, then, demodulated by a C-CDM demodulator 4b of the present invention. Thereafter, thus C-CDM demodulated signal is reproduced into medium and high frequency components of HDTV
in the same way as in Fig. 123. An operation of a video decoder 402 is identical to that of embodiments 1, 2, and 3 5 and will no more be explained.
Meanwhile, the D1_1 signal, a low frequency band signal of MPEG 1 grade of HDTV, is converted by a serial to parallel converter ?91 into a parallel signal and fed to an OFDM
modulator 852c, which executes a QPSK or 16 Q.AM modulation.
10 Subsequently, the Dl_1 signal is converted by an inverse FFT
40 into a time-'base signal and transmitted at a frequency band B through the FDM 40d.
On the other hand, a signal received by the receiver 43 is frequency separated in the FDM 40e and, then, converted 15 into a number of frequency-base signals in an FFT 40a of the OFDM modulator 8524. Thereafter, frequency-base signals are demodulated in respective demodulators 4a, 4b,---and are fed into a parallel to serial converter 8B2a, wherein a D~_1 signal is demodulated. Thus, a Dl_l signal of LDTV grade is 20 outputted from the receiver 43.
In this manner, only an LDTV signal is OFDM modulated in the multi-level signal transmission. The system of Fig. 138 makes it possible t0 provide a complicated OFDM circuit only for an LDTV signal. A bit rate of LDTV signal is 1/20 of that 25 of an HDTV. Therefore, the circuit scale of the OFDM will be reduced to 1/20, which results in an outstanding reduction of overall circuit scale.

An OFDM signal transmission system is strong against multipath and will soon be applied to a mobile station, such as a portable TV, an automotive vehicle TV, or a digital music broadcast receiver, which is exposed under strong and 5 variable multipath obstruction. For such usages a small picture size of less than 10 inches, 4 to 8 inches, is the mainstream. It will be thus guessed that the OFDM modulation of a high resolution TV signal such as HDTV or EDTV will bring less effect. In other words, the reception of a TV
10 signal of LDTV grade would be sufficient for an automotive vehicle TV.
On the contrary, multipath is constant at a fined station such as a home TV. Therefore, a countermeasure against multipath is relatively easy'. Less effect will be 15 brought to such a fiz~d station by OFDM unless it is in a ghost area. Using OFDM for medium and high frequency band components of HDTV is not advantageous in view of present circuit scale of OFDM which is still large.
Accordingly, the method of the present invention, in 20 which OFDM is used only for a low frequency band TV signal as shown in Fig. 138, can widely reduce the circuit scale of the OFDM to less than 1/10 without losing inherent OFDM effect capable of largely reducing multiple obstruction of LDTV when received at a mobile station such as an automotive vehicle.
25 Although the OFDM modulation of Fig. 138 is performed only for D1_l signal, it is also possible to modulate both Dl_1 and Dl_1 by OFDM. In such a csse, a C-CDM two-level signal transmission is used for transmission of Dl_1 and D1_Z. Thus, a mufti-level broadcasting being strong against multipath will be realized for a vehicle such as an automotive vehicle.
Even in a vehicle, the graditional graduation will be 5 realized in such a manner that LDTV and SDTZ signals are received with picture qualities depending on r~rcoiving signal level or antenna sensitivity.
The mufti-level signal transmission according to the present invention is feasible in this manner and produces 10 various effects as previously described. Furthermore, if the mufti-level signal transmission of the present invention is incorporated with an OFDM, it will become possible to provide a system strong against multipath and to alter data transmission grade in accordance with receivable signal level 15 change.
The mufti-level signal tran6mission method of the present invention is intended to increase the utilization of frequencies but nay be suited for not all the transmission systems since causing some type receivers to be declined is 20 the energy utilization. It is a good idea for use with a satellite communications system for selected subscribers to employ most advanced transmitters and receivers designed for best utilization of applicable frequencies and energy. Such a specific purpose signal transmission system will not be 25 bound by the present invention.
The present invention will be advantageous for use with a satellite or terrestrial broadcast service which is _ . _ . . ~. _ _ -. ~ _ - G . ... :~ .. . _ T . . . . . ~. . .
essential to run in the same standards for as long as 50 years. During the service period, the broadcast standards must not be altered but improvements will be provided time to time corresponding to up-to-date technological achievements.
5 Particularly, the energy for signal transmission will surely be increased on any satellite. EacL TV station should provide a compatible service for guaranteeing TV program signal reception to any type receivers ranging from today's common ones to future advanced ones. The signal transmission system 10 of the present invention can provide a compatible broadcast service of both the existing NTSC arid HDTV systems and also, ensure a future extension to match mass data transmission.
The present invention concerns much on the frequency utilization than the energy utilization. The signal receiving 15 sensitivity of each receiver is arranged different depending on a signal state level to be received so that the transmitting power of a transmitter needs not be increased largely. Hence, existing satellites which offer a small energy for reception and transmission of a signal can best be 20 used with the system of the present invention. The system is also arranged for performing the same standards corresponding to an increase in the transmission energy in the future and offering the compatibility between vld and new type receivers. In addition, the present invention will be more 25 advantageous for use with the satellite broadcast standards.
The multi-level signal transmission method of the present invention is more preferably employed for terrestrial _ ~ . ._ _ - _ _ _ .. -- ~ - Y ~ - . . . .. . _ TV broadcast service in which the energy utilization is not crucial, as compared with satellite broadcast service. The results are such that the signal attenuating regions in a servicQ area which are attributed to a conventional digital 5 TiDTV broadcast system are considerably reduced in extension and also, the compatibility of an HDTV receiver or display with the eaieting NTSC: system is obtained. Furthermore, the service area is substantially increased so that program suppliers and sponsors can appreciate more viewers. Although 10 the embodiments of the present invention refer to 18 and 32 G1AM procedures, other modulation techniques including 84, 128, and 256 pAM will be employed with equal success. Also, multiple PSK, ASK, and FSH techniques will be applicable as described with the embodiments.
15 A combination of the TDM with the SRQAM of the present invention has been described in the above. However, the SRpAM
of the present invention can be combined also with any of the FDM, CDMA and frequency dispersal communications systems.

Claims

What is claimed is:

1. A signal transmission apparatus for transmitting a first and a second data stream comprising:
a modulator for assigning said each data stream to a respective constellation in a vector space diagram to produce modulated signals wherein the number of signal points of the constellation for said first data stream is equal to or less than the number of signal points of the constellation for said second data stream, and a transmitter for transmitting the modulated signals, wherein said first data stream has data for demodulation including the number of signal points of the constellation of said second data stream.

2. A signal receiving apparatus comprising:
a receiver for receiving an input signal, said input signal having information of a first and a second data stream, wherein said each data stream is assigned to a respective constellation in a vector space diagram, the number of signal points of the constellation for said first data stream is equal to or less than the number of signal points of the constellation for said data stream, said first data stream having data for demodulation including the number of signal points of the constellation for said second data stream, and a demodulator for demodulating the input signal to produce said first data stream and said second data stream, wherein said second data stream is produced according to said data for demodulation.

3. A signal transmission system comprising signal transmission apparatus according to claim 1, and signal receiving apparatus according to claim 2.

4. A signal transmission method for transmitting a first and a second data stream, comprising:
a modulation step for assigning said each data stream to a respective constellation in a vector space diagram to produce modulated signals wherein the number of signal points of the constellation for said first data stream is equal to or less than the number of signal points of the constellation for said second data stream, and a transmission step for transmitting the modulated signals, wherein said first data stream has data for demodulation including the number of signal points of the constellation for said second data stream.

5. A signal receiving method comprising:
a receiving step for receiving an input signal, said input signal having information of a first and a second data stream, wherein said each data stream is assigned to a respective constellation in a vector space diagram, the number of signal points of the constellation for said first data stream is equal to or less than the number of signal points of the constellation for said second data stream, said first data stream having data for demodulation including the number of signal points of the constellation for said second data stream, and a demodulation step for demodulating the input signal to produce said first data stream and said second data stream, wherein said second data stream is produced according to said data for demodulation.

6. A signal transmitting and receiving method comprising signal transmission method according to claim 4 and signal receiving method according to claim 5.