CA2154180C - Multiple-modulation communication system - Google Patents
Multiple-modulation communication systemInfo
- Publication number
- CA2154180C CA2154180C CA002154180A CA2154180A CA2154180C CA 2154180 C CA2154180 C CA 2154180C CA 002154180 A CA002154180 A CA 002154180A CA 2154180 A CA2154180 A CA 2154180A CA 2154180 C CA2154180 C CA 2154180C
- Authority
- CA
- Canada
- Prior art keywords
- modulation technique
- modulated
- communication signals
- communication
- transmitter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0008—Modulated-carrier systems arrangements for allowing a transmitter or receiver to use more than one type of modulation
Abstract
A multiple-modulation communication system includes a transmitter (201, 203, 205, 207, 209, 211, 213, 215, 217, 219) that modulates and transmits communication signals modulated by a first modulation technique (201, 203, 205, 207) and communication signals modulated by a second modulation technique (211, 213, 215, 217). The first modulation technique and the second modulation technique are different. The communication system also includes a receiver (221, 223, 225, 227, 229, 231) capable or receiving the communication signals modulated by the first modulated technique and the communication signals modulated by the second modulation technique and demodulating the communication signals.
Description
WO 94119892 2 t .~ ~18 0 PCT/US94/00~80 "., 1 MULTIPLE-MODULATION COMMUNICATION SYSTEM
Field of the Invention This invention relates to radio frequency si{~n~lc~ including but not limiterl to tr~n.cmi~~ion and r~c~tion of amplitude modulated (AM) and frequency modulated (FM) ,ci~nsllc.
Back~rou.ld of the Invention A radio commllniç~tion system permits tr~mcmicfiion of inform~tior be~,wee,l a tr~nsmitter and a ,eceivel. A radio frequency (RF) channel permits tr~n~micsion of inform~tion ao between the tr~nsmitter and the r~ceiver. By combining the inform~tion with an RF ele~o...~netic wave of a particular frequency, i.e., modlll~t.ing the information signal onto a carrier frequency, the resultant modulated information signal may be tr~ncmitted through free space to a leceiver. Various mod~ tion 25 techniques (e.g., amplitude (AM), frequency (FM), phase, and composite modulation) are known to combine the information signal with an electroIn~gnetic wave. Comml~nic~tion units, such as portable radios, mobile radios, and base st~tionc, contain transmitters and/or receivers.
3~ A linear AM transmitter does not have as much coverage area, i.e., the signal does not travel as far, as an FM transmitter at the same peak transmit power level bec~ c-e the average envelope size of an AM tr~ncmicsion varies below the m~ mum output level, whereas the average envelope size of an FM tr~ncmic.cion is 35 constant at the m~rimum output level. An FM transmitter, -
Field of the Invention This invention relates to radio frequency si{~n~lc~ including but not limiterl to tr~n.cmi~~ion and r~c~tion of amplitude modulated (AM) and frequency modulated (FM) ,ci~nsllc.
Back~rou.ld of the Invention A radio commllniç~tion system permits tr~mcmicfiion of inform~tior be~,wee,l a tr~nsmitter and a ,eceivel. A radio frequency (RF) channel permits tr~n~micsion of inform~tion ao between the tr~nsmitter and the r~ceiver. By combining the inform~tion with an RF ele~o...~netic wave of a particular frequency, i.e., modlll~t.ing the information signal onto a carrier frequency, the resultant modulated information signal may be tr~ncmitted through free space to a leceiver. Various mod~ tion 25 techniques (e.g., amplitude (AM), frequency (FM), phase, and composite modulation) are known to combine the information signal with an electroIn~gnetic wave. Comml~nic~tion units, such as portable radios, mobile radios, and base st~tionc, contain transmitters and/or receivers.
3~ A linear AM transmitter does not have as much coverage area, i.e., the signal does not travel as far, as an FM transmitter at the same peak transmit power level bec~ c-e the average envelope size of an AM tr~ncmicsion varies below the m~ mum output level, whereas the average envelope size of an FM tr~ncmic.cion is 35 constant at the m~rimum output level. An FM transmitter, -
2 2 ~ 54 ~ 8Q
however, uses more energy to transmit at the same power level as an AM transmitter, and hence the FM transmitted will more quickly drain the battery of a portable transmitter.
Accordingly, there is a need for a transmitter which has the low power characteristic of an AM transmitter while retaining the advantage of coverage area of an FM transmitter.
SUMMARY OF THE INVENTION
According to one embodiment of the invention, it is provided a communication system characterized by: a transmitter arranged and constructed totransmit communication signals modulated by a first modulation technique when low power consumption by the transmitter is desired and communication signals modulated by a second modulation technique when greater signal coverage by the transmitter is desired, wherein the first modulation technique and the second modulation technique are dirre~ell~; and a receiver for receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demod~ ting the communication signals using a single demodulator having a single demodulation path, wherein both the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique are demodulated using the single demodulation path.
According to another embodiment of the invention, it is provided a radio frequency communication unit, characterized by a receiver, arranged and constructed to receive at least two modes of communication of communication signals, and a transmitter, arranged and constructed to transmit the at least two modes of communication of communication signals, wherein the two modes of communication comprise: a first mode of communication comprising tr~n~mi.~ion of a non-constant envelope amplitude modulated signal when tr~n~mi.~ion with more efficient power consumption is desired; and a second mode of communication comprising tr~n~mi~ion of a constant envelope frequency modulated signal when tr~n~mi~ion of higher average power is desired, wherein the non-constant envelope amplitude modulated signal is modulated using a form of phase shift keying or the constant A
envelope frequency modulated signal is modulated using a form of frequency shiftkeying.
According to a further embodiment of the invention, it is provided a S communication unit characterized by: a first modulator, arranged and constructed to modulate communication signals by a first modulation technique, producing a first modulated signal; a second modulator, arranged and constructed to modulate communication signals by a second modulation technique, producing a second modulated signal, wherein the first modulation technique and the second modulation technique are different, and wherein the first modulated signal is modulated using a form of phase shift keying or the second modulated signal is modulated using a form of frequency shift keying; a selector, arranged and constructed to select the first modulated signal when tr~n~mi~ion with more efficient power consumption is desired and the second modulated signal when tr~n~mi.c~ion of higher average power is desired, producing a selected signal; and a transmitter for transmitting the selected slgnal.
According to a still further embodiment of the invention, it is provided A
communication unit characterized by: a transmitter that transmits communication signals modulated by an amplitude modulation technique and communication signalsmodulated by a frequency modulation technique; and a receiver comprising a single demodulator, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein the single demodulator has a single demodulation path and wherein both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
According to a further embodiment of the invention, it is provided a communication unit characterized by: a transmitter that transmits communication signals modulated by an amplitude modulation technique when low power consumption by the transmitter is desired, and transmits communication signals modulated by a frequency modulation technique when greater signal coverage by the A~
8 ~ i transmitter is desired; and a receiver comprising a single demodulator having a single demodulation path, a~anged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the S communication signals modulated by the frequency modulation techni~ue, wherein both the communication signals modulated by the amplitude modulation technique and the comrnunication signals modulated by the ~e~uency modulation technique are demodulated using the single demodulation path.
Brief Description of the Drawings FIG. 1 shows an FM transmitter, an AM transmitter, and a common receiver in accordance with the invention.
FIG. 2 shows a detailed FM transmitter, a detailed AM
transmitter, and a detailed common receiver in accordance with 16 the invention.
Description of a Preferred Embodiment The following describes an apparatus for and method of transmitting communication si~n~l~ with a single transmitter and receiving the same si~n~l.q with a single receiver. Additional communication range is obtained when transmitting FM ~i n~lq More efficient battery performance is achieved when transmitting linear AM_si~l~. A single transmitter transmits both AM and FM si~ . A single~receiver capable of differenti~tin~ phase differences demodulates either AM or FM si~n~liq. Only one receiver is necessary, and there is no need to inform the receiver of what type of mcdulation was performed on the transmitted signal.
In the preferred embodiment, FM modulators have 12.5 kHz channels and linear AM modulators have 6.25 kHz channels. The receiver can be the same in either case. The form of modulation used in the present invention is called QPSK-c. This modulation technique is discussed in detail in U.S. Patent No. Sj377,229
however, uses more energy to transmit at the same power level as an AM transmitter, and hence the FM transmitted will more quickly drain the battery of a portable transmitter.
Accordingly, there is a need for a transmitter which has the low power characteristic of an AM transmitter while retaining the advantage of coverage area of an FM transmitter.
SUMMARY OF THE INVENTION
According to one embodiment of the invention, it is provided a communication system characterized by: a transmitter arranged and constructed totransmit communication signals modulated by a first modulation technique when low power consumption by the transmitter is desired and communication signals modulated by a second modulation technique when greater signal coverage by the transmitter is desired, wherein the first modulation technique and the second modulation technique are dirre~ell~; and a receiver for receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demod~ ting the communication signals using a single demodulator having a single demodulation path, wherein both the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique are demodulated using the single demodulation path.
According to another embodiment of the invention, it is provided a radio frequency communication unit, characterized by a receiver, arranged and constructed to receive at least two modes of communication of communication signals, and a transmitter, arranged and constructed to transmit the at least two modes of communication of communication signals, wherein the two modes of communication comprise: a first mode of communication comprising tr~n~mi.~ion of a non-constant envelope amplitude modulated signal when tr~n~mi.~ion with more efficient power consumption is desired; and a second mode of communication comprising tr~n~mi~ion of a constant envelope frequency modulated signal when tr~n~mi~ion of higher average power is desired, wherein the non-constant envelope amplitude modulated signal is modulated using a form of phase shift keying or the constant A
envelope frequency modulated signal is modulated using a form of frequency shiftkeying.
According to a further embodiment of the invention, it is provided a S communication unit characterized by: a first modulator, arranged and constructed to modulate communication signals by a first modulation technique, producing a first modulated signal; a second modulator, arranged and constructed to modulate communication signals by a second modulation technique, producing a second modulated signal, wherein the first modulation technique and the second modulation technique are different, and wherein the first modulated signal is modulated using a form of phase shift keying or the second modulated signal is modulated using a form of frequency shift keying; a selector, arranged and constructed to select the first modulated signal when tr~n~mi~ion with more efficient power consumption is desired and the second modulated signal when tr~n~mi.c~ion of higher average power is desired, producing a selected signal; and a transmitter for transmitting the selected slgnal.
According to a still further embodiment of the invention, it is provided A
communication unit characterized by: a transmitter that transmits communication signals modulated by an amplitude modulation technique and communication signalsmodulated by a frequency modulation technique; and a receiver comprising a single demodulator, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein the single demodulator has a single demodulation path and wherein both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
According to a further embodiment of the invention, it is provided a communication unit characterized by: a transmitter that transmits communication signals modulated by an amplitude modulation technique when low power consumption by the transmitter is desired, and transmits communication signals modulated by a frequency modulation technique when greater signal coverage by the A~
8 ~ i transmitter is desired; and a receiver comprising a single demodulator having a single demodulation path, a~anged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the S communication signals modulated by the frequency modulation techni~ue, wherein both the communication signals modulated by the amplitude modulation technique and the comrnunication signals modulated by the ~e~uency modulation technique are demodulated using the single demodulation path.
Brief Description of the Drawings FIG. 1 shows an FM transmitter, an AM transmitter, and a common receiver in accordance with the invention.
FIG. 2 shows a detailed FM transmitter, a detailed AM
transmitter, and a detailed common receiver in accordance with 16 the invention.
Description of a Preferred Embodiment The following describes an apparatus for and method of transmitting communication si~n~l~ with a single transmitter and receiving the same si~n~l.q with a single receiver. Additional communication range is obtained when transmitting FM ~i n~lq More efficient battery performance is achieved when transmitting linear AM_si~l~. A single transmitter transmits both AM and FM si~ . A single~receiver capable of differenti~tin~ phase differences demodulates either AM or FM si~n~liq. Only one receiver is necessary, and there is no need to inform the receiver of what type of mcdulation was performed on the transmitted signal.
In the preferred embodiment, FM modulators have 12.5 kHz channels and linear AM modulators have 6.25 kHz channels. The receiver can be the same in either case. The form of modulation used in the present invention is called QPSK-c. This modulation technique is discussed in detail in U.S. Patent No. Sj377,229
3~ titled "Multi-Modulation Scheme Compatible Radio" filed on behalf J~
A
of Alan L. Wilson et al. on December 19, 1990.
QPSK stands for Quaternary Phase Shift Keying. QPSK-c, where the c stands for compatible, is a linear differential form of QPSK that is AM and FM compatible.
It is possible to transmit with a higher average power using FM, and hence increased coverage area is obtained for the signal than when AM is used. An AM transmitter, however, consumes less power and hence is a more efficient user of a portable radio's battery charge or power than an FM transmitter. When using QPSK-c modulation, 4-level FSK (Frequency Shift Keying) is used in FM tr~n~mi.q.~ions and D-QPSK (Differential QPSK) is used in AM tr~nsmissions. Switching from AM to FM yields higher average power, and hence increased coverage area for the si~
at the cost of battery charge. Thus range is enhanced and greater coverage is obtained for the same radio, or commllnic~tion unit, when such coverage is desired. Conversely, switching from FM to AM when e~tended range is not necessary conserves battery charge. In the present invention, the commllnic~tion unit changes its type of modulation and thus is more quickly responsive ~0 to such a change. This is accomplished by, inter alia, an ~/(sin x) filter, where x = ~ f~ in the preferred embodiment, and a phase angle integrator for the exponential function.
One part of FIG. 1 shows a conventional four-level FM
transmitter. Information to be transmitted enters a digital signal processor_(DSP) 101. The DSP 101 processes the information and sends it to frequency modulator 103 which passes the information to power amplifier (PA) 105 which is rated class C. As shown in FIG. 1, a class C four-level FM transmitter transmits a constant envelope.
A conventional linear A~ transmitter is also shown in FIG.
1. Information to be transmitted is processed in DSP 107 and output to a conventional linearizer 109, the output of which is input to a class AB power amplifier 111. As seen in the diagram, an AM
signal has a non-constant envelope. The average signal power of f~4 WO 94/lg892 ~ 215 ~18 0 PCT/US94/00580 an AM signal is less than the average signal power of an FM
signal having the same peak envelope size.
Also shown in FIG. 1 is a common receiver which may receive information from both four-level FM transmitter and linear AM transmitters. The common receiver has a front-end receiver 113, a digital ~eceiver 115, and a digital signal processor 117 that ~,oce~ses the inform~tion into data or audible speech. A
linear AM transmitter has a time-varying amplitude that is reduced for high frequency deviation. Note that D~P 101, DSP 107, and DSP 117 also perform functions other than those shown.
Throughout the specific~ion and drawings, the DSP as shown may be a DSP 56001 av~ hle from Motorola, Inc.
FIG. 2 shows a flet~ile~l implementation of the transmitters and r~C~iv~:r of FIG. 1. An FM transmitter, yielding 4-level FSK
data, iB shown by blocks 201, 203,205 and 207. 4-level data is input to a raised-cosine filter 201 which is a splMtter filter of the Nyquist raised-cosine finite impulse response type with splatter filter tr~n~ition ratio alpha = 0.2, as is known in the art. The FM
transmitter includes a differential encoder comprised of blocks 203 aD and 205. A ~ fT/sin(J~ fT) filter 203 and an integrator 205 comprise the differential encoder. In the preferred embodiment, the integrator 205 is a simple integrator that uses the modulo 27~
property of the phase to avoid overflowing, as is known in the art.
The output of integrator 205 is the phase 0 of the 4-level input sigT-~l. A detailed description of one implementation of the raised-cosine filter 201 and rt fT/sin(7~ fT) filter 203 follows in the next paragraph. Phase modulator 207 takes the phase 0 and modulates it, creating a complex-valued result that is ~l~sign~te~l ej0. The output, ej0, of phase modulator is input to switch 209.
The cascaded filter implementation of the Nyquist raised-cosine filter 201 and the r~ fT/sin(~ fT) filter 203 may be implemented as follows. Let H((d) equal the frequency response of an ideal Nyquist raised cosine filter. The norm~li7.e~ corner frequency is 1 radian/second, and the norrn~li7e~ symbol time (denoted by T) is 7~ seconds, and ._ 5 H(~)=1 forl-a>l~l H(L") = 1 + lcos~7~(l '')12 1 + a)~ for 1 - a < 1~1 s 1 + a H(~) = 0 for 1 + a < 1~1 . - ' 5 The impulse response, h(t), of the filter is found with the inverse Fourier transform, and noting that H(~) is an even function:
~0 ~0 h(t) = 21 H(~)ej~tdL~) = 1 H(~) cos(c~t) d~
~_0 .10 ~l-a ~l+a ~l+a = 1 cos(c~)t) d~ + 21 cos(~t) d~ + 21 cos~ 21+a)~ cos(~t) d~
~lo ,l-a ~1-a Using the identity cos(x) c08(y) = 0.5 CoS(X+y) + 0.5 cOS(X-y) and performing the integration:
h(t) sin[(1-a)t] + sin[(l+a)t] - sin[(l-a)t]
7~t 2~t 16 + sin[Jt+(1+a)t] - sin[(l-a)t] + sin[~-(l+a)t] + sin[(1-a)t] 41 + t) 4~2a - t) Using the identity sin(~+x) = -sin(x), regrouping terms, and then using the identity sin(x+y) + sin(x-y) = 2 sin(x) cos(y):
h(t) 7~ sin[(l+a)t] + sin[(l-a)t] ~ sin(t) cos(at) 8a2~ l2~a)2 a2 The filter function h(t) can be sampled at discrete time intervals to realize the Nyquist raised-cosine finite impulse response filter 201.
The shaping filter, f(t), is derived as follows, where F(L~) is the 25 frequency response of the shaping filter, T is the symbol time which equals 208.333 llsec for 9600 bits per second which equals r~
seconds for the norrn~ e-l system used in H above, and S 4~80 6 sin(~Ti2) The frequency range of interest for F(~) is -1.2~1 < ~T < 1.2J~, which is the frequency range covered by the Nyquist filter H(~) when the 5 roll-off factor a = 0.2. In order to find a suitable impulse response, the function F will be apprnyim~tetl with a Fourier series of cosine terms, and the result will be transformed to the time flom~in.
A time interval to approYim~te F is first selected to be ~1.33333~, bec~llse it must ~Y~ee~ :~1.2~c and be less than ~2J~
10 bec~ e there is a singularity in F at ~T=2~. The Fourier series eYp~n~iQn follows, where x is the norm~ e~l frequency:
sin(7~) ~ k~ fkcos(l2 kX )Wherex=fT= T
r2/3 fo = 0.75 F(_) dx, and ~2/3 fk = 1.5 F(x) cos(1233333) dx for k ~ 0.
These integrals are easily evaluated numerically. The first twelve terms appear in the following table.
ao k fk k fk 0 1.35697 6 0.0281791 -0.4839 7 -0.0210304 2 0.189043 8 0.0162746 3 -0.0982102 9 -0.0129571
A
of Alan L. Wilson et al. on December 19, 1990.
QPSK stands for Quaternary Phase Shift Keying. QPSK-c, where the c stands for compatible, is a linear differential form of QPSK that is AM and FM compatible.
It is possible to transmit with a higher average power using FM, and hence increased coverage area is obtained for the signal than when AM is used. An AM transmitter, however, consumes less power and hence is a more efficient user of a portable radio's battery charge or power than an FM transmitter. When using QPSK-c modulation, 4-level FSK (Frequency Shift Keying) is used in FM tr~n~mi.q.~ions and D-QPSK (Differential QPSK) is used in AM tr~nsmissions. Switching from AM to FM yields higher average power, and hence increased coverage area for the si~
at the cost of battery charge. Thus range is enhanced and greater coverage is obtained for the same radio, or commllnic~tion unit, when such coverage is desired. Conversely, switching from FM to AM when e~tended range is not necessary conserves battery charge. In the present invention, the commllnic~tion unit changes its type of modulation and thus is more quickly responsive ~0 to such a change. This is accomplished by, inter alia, an ~/(sin x) filter, where x = ~ f~ in the preferred embodiment, and a phase angle integrator for the exponential function.
One part of FIG. 1 shows a conventional four-level FM
transmitter. Information to be transmitted enters a digital signal processor_(DSP) 101. The DSP 101 processes the information and sends it to frequency modulator 103 which passes the information to power amplifier (PA) 105 which is rated class C. As shown in FIG. 1, a class C four-level FM transmitter transmits a constant envelope.
A conventional linear A~ transmitter is also shown in FIG.
1. Information to be transmitted is processed in DSP 107 and output to a conventional linearizer 109, the output of which is input to a class AB power amplifier 111. As seen in the diagram, an AM
signal has a non-constant envelope. The average signal power of f~4 WO 94/lg892 ~ 215 ~18 0 PCT/US94/00580 an AM signal is less than the average signal power of an FM
signal having the same peak envelope size.
Also shown in FIG. 1 is a common receiver which may receive information from both four-level FM transmitter and linear AM transmitters. The common receiver has a front-end receiver 113, a digital ~eceiver 115, and a digital signal processor 117 that ~,oce~ses the inform~tion into data or audible speech. A
linear AM transmitter has a time-varying amplitude that is reduced for high frequency deviation. Note that D~P 101, DSP 107, and DSP 117 also perform functions other than those shown.
Throughout the specific~ion and drawings, the DSP as shown may be a DSP 56001 av~ hle from Motorola, Inc.
FIG. 2 shows a flet~ile~l implementation of the transmitters and r~C~iv~:r of FIG. 1. An FM transmitter, yielding 4-level FSK
data, iB shown by blocks 201, 203,205 and 207. 4-level data is input to a raised-cosine filter 201 which is a splMtter filter of the Nyquist raised-cosine finite impulse response type with splatter filter tr~n~ition ratio alpha = 0.2, as is known in the art. The FM
transmitter includes a differential encoder comprised of blocks 203 aD and 205. A ~ fT/sin(J~ fT) filter 203 and an integrator 205 comprise the differential encoder. In the preferred embodiment, the integrator 205 is a simple integrator that uses the modulo 27~
property of the phase to avoid overflowing, as is known in the art.
The output of integrator 205 is the phase 0 of the 4-level input sigT-~l. A detailed description of one implementation of the raised-cosine filter 201 and rt fT/sin(7~ fT) filter 203 follows in the next paragraph. Phase modulator 207 takes the phase 0 and modulates it, creating a complex-valued result that is ~l~sign~te~l ej0. The output, ej0, of phase modulator is input to switch 209.
The cascaded filter implementation of the Nyquist raised-cosine filter 201 and the r~ fT/sin(~ fT) filter 203 may be implemented as follows. Let H((d) equal the frequency response of an ideal Nyquist raised cosine filter. The norm~li7.e~ corner frequency is 1 radian/second, and the norrn~li7e~ symbol time (denoted by T) is 7~ seconds, and ._ 5 H(~)=1 forl-a>l~l H(L") = 1 + lcos~7~(l '')12 1 + a)~ for 1 - a < 1~1 s 1 + a H(~) = 0 for 1 + a < 1~1 . - ' 5 The impulse response, h(t), of the filter is found with the inverse Fourier transform, and noting that H(~) is an even function:
~0 ~0 h(t) = 21 H(~)ej~tdL~) = 1 H(~) cos(c~t) d~
~_0 .10 ~l-a ~l+a ~l+a = 1 cos(c~)t) d~ + 21 cos(~t) d~ + 21 cos~ 21+a)~ cos(~t) d~
~lo ,l-a ~1-a Using the identity cos(x) c08(y) = 0.5 CoS(X+y) + 0.5 cOS(X-y) and performing the integration:
h(t) sin[(1-a)t] + sin[(l+a)t] - sin[(l-a)t]
7~t 2~t 16 + sin[Jt+(1+a)t] - sin[(l-a)t] + sin[~-(l+a)t] + sin[(1-a)t] 41 + t) 4~2a - t) Using the identity sin(~+x) = -sin(x), regrouping terms, and then using the identity sin(x+y) + sin(x-y) = 2 sin(x) cos(y):
h(t) 7~ sin[(l+a)t] + sin[(l-a)t] ~ sin(t) cos(at) 8a2~ l2~a)2 a2 The filter function h(t) can be sampled at discrete time intervals to realize the Nyquist raised-cosine finite impulse response filter 201.
The shaping filter, f(t), is derived as follows, where F(L~) is the 25 frequency response of the shaping filter, T is the symbol time which equals 208.333 llsec for 9600 bits per second which equals r~
seconds for the norrn~ e-l system used in H above, and S 4~80 6 sin(~Ti2) The frequency range of interest for F(~) is -1.2~1 < ~T < 1.2J~, which is the frequency range covered by the Nyquist filter H(~) when the 5 roll-off factor a = 0.2. In order to find a suitable impulse response, the function F will be apprnyim~tetl with a Fourier series of cosine terms, and the result will be transformed to the time flom~in.
A time interval to approYim~te F is first selected to be ~1.33333~, bec~llse it must ~Y~ee~ :~1.2~c and be less than ~2J~
10 bec~ e there is a singularity in F at ~T=2~. The Fourier series eYp~n~iQn follows, where x is the norm~ e~l frequency:
sin(7~) ~ k~ fkcos(l2 kX )Wherex=fT= T
r2/3 fo = 0.75 F(_) dx, and ~2/3 fk = 1.5 F(x) cos(1233333) dx for k ~ 0.
These integrals are easily evaluated numerically. The first twelve terms appear in the following table.
ao k fk k fk 0 1.35697 6 0.0281791 -0.4839 7 -0.0210304 2 0.189043 8 0.0162746 3 -0.0982102 9 -0.0129571
4 0.0594481 10 0.0105541 -0.0396059 11 -0.00875928 Performing the inverse Fourier transform on the series as follows:
WO 94/19892 ~ 1 ~ 418 0 PCT/US94/00580 k ej~t d~ ' f(t) =1 F(~)ej~l)td~=l (fo + ~ fkCos~l33333)) =1 fo~t)+ ~ 0.75kT) +k~l 2 where ~(t) represents the Dirac delta function. Sampling at 8 6 samples per symbol yields non-zero samples and 0.75 x 8 = 6 sample intervals. The middle or 0th sample has amplitude fo, and the rem~inin~ samples have amplitudes fk/2 for k=:t1, i2, i3, C~cs~tlinf~ the previously computed h(t) with f(t) yields the filters neceS~ry for an FM ~/4 DQPSK-c tr~n~mitter~ as used in the preferred emho~liment of the present invention. Although the above implementation is shown in band-limite~ form, band-limiting is optional and is not required for the ~lesellt invention.
The AM transmitter, yiel~lin~ D-QPSK data, is comprised of blocks 211, 213,215, and 217. Four level data having levels of i ~J4 and i 3~14 enters a differential encoder comprised of a summer 211 and a delay 213. The output of this di~re,~lltial encoder enters a phase modulator 215, where the output of the phase modulator 215 has complex components I and Q at one sample per symbol. I
represents the in-phase component, and Q represents the a~ quadrature component. The output of modulator 215 is input to raised cosine filter 217 with alpha = 0.2 where raised cosine filter 217 is simil~r to raised cosine filter 201. The output of raised cosine filter 217 is input to switch 209. Whichever form of tr~n~mi~sion is selected, either FM or AM, the output of that part 2~ of the transmitter is input to modulator 219, which modulates the signal to the carrier frequency ~.
Blocks 211,213, and 215 each operate at the rate of one sample/symbol or 4800 symbols/second. Blocks 201 and 217 interpolate from 1 sample/symbol to N samples/symbol at the WO 94/198g2 PCTIUS94/00580 output, where N is usually 10 or more, but at least greater than one. Blocks 203, 206, and 207 esch operate at N samples/symbol.
For efficiency and to elimin~te redundant parts in the preferred embodiment, only one class AB PA is used in the
WO 94/19892 ~ 1 ~ 418 0 PCT/US94/00580 k ej~t d~ ' f(t) =1 F(~)ej~l)td~=l (fo + ~ fkCos~l33333)) =1 fo~t)+ ~ 0.75kT) +k~l 2 where ~(t) represents the Dirac delta function. Sampling at 8 6 samples per symbol yields non-zero samples and 0.75 x 8 = 6 sample intervals. The middle or 0th sample has amplitude fo, and the rem~inin~ samples have amplitudes fk/2 for k=:t1, i2, i3, C~cs~tlinf~ the previously computed h(t) with f(t) yields the filters neceS~ry for an FM ~/4 DQPSK-c tr~n~mitter~ as used in the preferred emho~liment of the present invention. Although the above implementation is shown in band-limite~ form, band-limiting is optional and is not required for the ~lesellt invention.
The AM transmitter, yiel~lin~ D-QPSK data, is comprised of blocks 211, 213,215, and 217. Four level data having levels of i ~J4 and i 3~14 enters a differential encoder comprised of a summer 211 and a delay 213. The output of this di~re,~lltial encoder enters a phase modulator 215, where the output of the phase modulator 215 has complex components I and Q at one sample per symbol. I
represents the in-phase component, and Q represents the a~ quadrature component. The output of modulator 215 is input to raised cosine filter 217 with alpha = 0.2 where raised cosine filter 217 is simil~r to raised cosine filter 201. The output of raised cosine filter 217 is input to switch 209. Whichever form of tr~n~mi~sion is selected, either FM or AM, the output of that part 2~ of the transmitter is input to modulator 219, which modulates the signal to the carrier frequency ~.
Blocks 211,213, and 215 each operate at the rate of one sample/symbol or 4800 symbols/second. Blocks 201 and 217 interpolate from 1 sample/symbol to N samples/symbol at the WO 94/198g2 PCTIUS94/00580 output, where N is usually 10 or more, but at least greater than one. Blocks 203, 206, and 207 esch operate at N samples/symbol.
For efficiency and to elimin~te redundant parts in the preferred embodiment, only one class AB PA is used in the
5 transmitter, thus the linear AM transmitter configuration of FIG.
1 is used to embody the entire tr~n~mitter of FIG. 2, blocks 201 through 219 inclusive. Bec~ e the preferred embodiment of the present invention uses a DSP, tr~n.cmitter blocks 201,203, 205, 207, 209, 211, 213, 215, 217, and 219 are easily implemented in the DSP
107 of the linear AM tr~nRmitter. Bec~nRe blocks 201 through 219 are included in the DSP 107, it is unneces~ to duplicate DSP 101, frequency mo~ ~r 103, and PA 105. The modulator 219 is also implemented in the DSP 107, and the output of the mo-illl~tQr 219 is input to the linearizer 109 prior to tr~n~miRgion.
A ~etqile~ common l~ceiver is also shown in FIG. 2. In the l~le~ ed embodiment, the ~ceiv~:r blocks 221,223, 225, 227, 229, and 231 are all implemented in the DSP 117. When the rfCeiv~r and transmitter are in the same commllnic~tion unit or radio, one or more DSPs may be used to support the functions of DSP 107 and DSP 117. A loose IF (intermediate frequency) filter 221, first receives a modulated siEn~l. The output of the loose IF filter 221 is input to inverse tangent function 223, which is part of a frequency demodulator including blocks 223, 225 and 227. Blocks 225 and 227 are also part of a differential encoder also including integrate and 25 dump filter 229, the function of which is described in detail in the following paragraph. The output of block 223 is input to summer 227 and the ~o~itive form of the delayed component is subtracted from block 227 as output from block 225. The output of integrate and dump filter 229 is input to stochastic gradient bit l~uv~r~
30 block 231 the output of which is four level data as transmitted initially. Stochastic gradient bit r~~vel ~ is well known in the art.
Because the receiver is sensitive only to phase, the envelope does not matter and both FM and AM tr~nsmi~sion may be received and properly decoded by this common receiver. Thus, because a 35 more powerful AM PA is required than for an FM PA for the same WO 94/19892 215 ~18 0 PCT/US94/00580 range, a switch of the two modulations temporarily although draining more power gains extra (greater) coverage area.
The impulse response for the integrate and dump filter 229 is derived below, in a closed-form solution that is expressed in terms 5 of the sine integral function Si(x), which is well known in the art.
A band-limited integrate and dump filter is achieved when a portion of the side lobes are filtered out of the frequency response.
The portion of the frequency response that is necess~ry for good fidelity in the symbol recove~ ~ is in the range -(1 + a)/(2T) Hz to 10 (1 + a)/(2T) Hz. Because of a spectral null at l/T Hz, the response is restricted to l/T Hz cutoff. Where H(x) is the frequency response of a band-limited integrate and dump filter:
H(x) ~x for I x I c 1 H(x) = O forlxl > 1.
Where h(t) is the impulse ~e~ se of the filter H(x), ~ = 2~, and H(~) is an even function:
.~ ~27~
ao h(t)=l H(~)e~ td~=1 sin(~/2) ~td~"
,2 = 1 2 sin(~/2) cos(~t) d~
.o = 1 ~( sin[(t+l/2)~] - sin[(t-1/2)~])d~
~2~t+1/2) ~27~(t-l/2) ~,0 sin(y) dy sin(y) dyy .x =l(Si[2~(t+1/2)]- Si[2~(t-1/2)]) whereSi(~)= sin(t)~.
,0 t WO 94/19892 5 ~'18 0 PCT/US94/00~80 Although the above implementation is shown in band-limited form, band-limiting is optional and is not required for the present invention.
Hence in the present invention, wh~en it is desired for any 5 reason by comm~nd or as determined- by the radio, the radio will automatically switch from AM tQ FM to gain extra range for a particular sign~l. The radio or commllnic~tion unit may also lece,ve a sien~l, such as from a base stqtion or other controlling unit including another radio, instructing it to transmit with a 10 particular modulation. Similarly, the radio will automatically switch from FM to AM to gain better battery efficiency. This switching takes place in switch 209, which is controlled by a DSP
in the preferred embodiment.
Although the preferred embodiment uses QPSK-c 15 mod--l~tion, a common receiver can still be used for any mod~ tion that distinguishes data by phase, i.e., where all the con~tell~tion points fall on a circle, such as QPSK, D-QPSK, and CORPSK (Correlated PSK).
Although a DSP is used to perform many of the functions of ao the present invention, discrete elements or other progr~mm~hle logic may also be used and will achieve the same effect.
What is claimed is:
1 is used to embody the entire tr~n~mitter of FIG. 2, blocks 201 through 219 inclusive. Bec~ e the preferred embodiment of the present invention uses a DSP, tr~n.cmitter blocks 201,203, 205, 207, 209, 211, 213, 215, 217, and 219 are easily implemented in the DSP
107 of the linear AM tr~nRmitter. Bec~nRe blocks 201 through 219 are included in the DSP 107, it is unneces~ to duplicate DSP 101, frequency mo~ ~r 103, and PA 105. The modulator 219 is also implemented in the DSP 107, and the output of the mo-illl~tQr 219 is input to the linearizer 109 prior to tr~n~miRgion.
A ~etqile~ common l~ceiver is also shown in FIG. 2. In the l~le~ ed embodiment, the ~ceiv~:r blocks 221,223, 225, 227, 229, and 231 are all implemented in the DSP 117. When the rfCeiv~r and transmitter are in the same commllnic~tion unit or radio, one or more DSPs may be used to support the functions of DSP 107 and DSP 117. A loose IF (intermediate frequency) filter 221, first receives a modulated siEn~l. The output of the loose IF filter 221 is input to inverse tangent function 223, which is part of a frequency demodulator including blocks 223, 225 and 227. Blocks 225 and 227 are also part of a differential encoder also including integrate and 25 dump filter 229, the function of which is described in detail in the following paragraph. The output of block 223 is input to summer 227 and the ~o~itive form of the delayed component is subtracted from block 227 as output from block 225. The output of integrate and dump filter 229 is input to stochastic gradient bit l~uv~r~
30 block 231 the output of which is four level data as transmitted initially. Stochastic gradient bit r~~vel ~ is well known in the art.
Because the receiver is sensitive only to phase, the envelope does not matter and both FM and AM tr~nsmi~sion may be received and properly decoded by this common receiver. Thus, because a 35 more powerful AM PA is required than for an FM PA for the same WO 94/19892 215 ~18 0 PCT/US94/00580 range, a switch of the two modulations temporarily although draining more power gains extra (greater) coverage area.
The impulse response for the integrate and dump filter 229 is derived below, in a closed-form solution that is expressed in terms 5 of the sine integral function Si(x), which is well known in the art.
A band-limited integrate and dump filter is achieved when a portion of the side lobes are filtered out of the frequency response.
The portion of the frequency response that is necess~ry for good fidelity in the symbol recove~ ~ is in the range -(1 + a)/(2T) Hz to 10 (1 + a)/(2T) Hz. Because of a spectral null at l/T Hz, the response is restricted to l/T Hz cutoff. Where H(x) is the frequency response of a band-limited integrate and dump filter:
H(x) ~x for I x I c 1 H(x) = O forlxl > 1.
Where h(t) is the impulse ~e~ se of the filter H(x), ~ = 2~, and H(~) is an even function:
.~ ~27~
ao h(t)=l H(~)e~ td~=1 sin(~/2) ~td~"
,2 = 1 2 sin(~/2) cos(~t) d~
.o = 1 ~( sin[(t+l/2)~] - sin[(t-1/2)~])d~
~2~t+1/2) ~27~(t-l/2) ~,0 sin(y) dy sin(y) dyy .x =l(Si[2~(t+1/2)]- Si[2~(t-1/2)]) whereSi(~)= sin(t)~.
,0 t WO 94/19892 5 ~'18 0 PCT/US94/00~80 Although the above implementation is shown in band-limited form, band-limiting is optional and is not required for the present invention.
Hence in the present invention, wh~en it is desired for any 5 reason by comm~nd or as determined- by the radio, the radio will automatically switch from AM tQ FM to gain extra range for a particular sign~l. The radio or commllnic~tion unit may also lece,ve a sien~l, such as from a base stqtion or other controlling unit including another radio, instructing it to transmit with a 10 particular modulation. Similarly, the radio will automatically switch from FM to AM to gain better battery efficiency. This switching takes place in switch 209, which is controlled by a DSP
in the preferred embodiment.
Although the preferred embodiment uses QPSK-c 15 mod--l~tion, a common receiver can still be used for any mod~ tion that distinguishes data by phase, i.e., where all the con~tell~tion points fall on a circle, such as QPSK, D-QPSK, and CORPSK (Correlated PSK).
Although a DSP is used to perform many of the functions of ao the present invention, discrete elements or other progr~mm~hle logic may also be used and will achieve the same effect.
What is claimed is:
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A communication system characterized by:
a transmitter arranged and constructed to transmit communication signals modulated by a first modulation technique when low power consumption by the transmitter is desired and communication signals modulated by a second modulation technique when greater signal coverage by the transmitter is desired, wherein the first modulation technique and the second modulation technique are different; and a receiver for receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demodulating the communication signals using a single demodulator having a single demodulation path, wherein both the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique are demodulated using the single demodulation path.
a transmitter arranged and constructed to transmit communication signals modulated by a first modulation technique when low power consumption by the transmitter is desired and communication signals modulated by a second modulation technique when greater signal coverage by the transmitter is desired, wherein the first modulation technique and the second modulation technique are different; and a receiver for receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demodulating the communication signals using a single demodulator having a single demodulation path, wherein both the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique are demodulated using the single demodulation path.
2. The communication system of claim 1, further characterized in that the first modulation technique is a form of phase shift keying and the second modulation technique is a form of frequency shift keying.
3. A radio frequency communication unit, characterized by a receiver, arranged and constructed to receive at least two modes of communication of communication signals, and a transmitter, arranged and constructed to transmit the at least two modes of communication of communication signals, wherein the two modes of communication comprise:
a first mode of communication comprising transmission of a non-constant envelope amplitude modulated signal when transmission with more efficient power consumption is desired; and a second mode of communication comprising transmission of a constant envelope frequency modulated signal when transmission of higher average power isdesired, wherein the non-constant envelope amplitude modulated signal is modulated using a form of phase shift keying or the constant envelope frequency modulated signal is modulated using a form of frequency shift keying.
a first mode of communication comprising transmission of a non-constant envelope amplitude modulated signal when transmission with more efficient power consumption is desired; and a second mode of communication comprising transmission of a constant envelope frequency modulated signal when transmission of higher average power isdesired, wherein the non-constant envelope amplitude modulated signal is modulated using a form of phase shift keying or the constant envelope frequency modulated signal is modulated using a form of frequency shift keying.
4. The radio frequency communication unit of claim 3, further characterized in that the first mode of communication is utilized when low power consumption by atransmitter of the communication signals is desired.
5. The radio frequency communication unit of claim 3, further characterized in that the second mode of communication is utilized when greater signal coverage by a transmitter of the communication signals is desired.
6. A communication unit characterized by:
a first modulator, arranged and constructed to modulate communication signals by a first modulation technique, producing a first modulated signal;
a second modulator, arranged and constructed to modulate communication signals by a second modulation technique, producing a second modulated signal, wherein the first modulation technique and the second modulation technique are different, and wherein the first modulated signal is modulated using a form of phase shift keying or the second modulated signal is modulated using a form of frequency shift keying;
a selector, arranged and constructed to select the first modulated signal when transmission with more efficient power consumption is desired and the second modulated signal when transmission of higher average power is desired, producing a selected signal; and a transmitter for transmitting the selected signal.
a first modulator, arranged and constructed to modulate communication signals by a first modulation technique, producing a first modulated signal;
a second modulator, arranged and constructed to modulate communication signals by a second modulation technique, producing a second modulated signal, wherein the first modulation technique and the second modulation technique are different, and wherein the first modulated signal is modulated using a form of phase shift keying or the second modulated signal is modulated using a form of frequency shift keying;
a selector, arranged and constructed to select the first modulated signal when transmission with more efficient power consumption is desired and the second modulated signal when transmission of higher average power is desired, producing a selected signal; and a transmitter for transmitting the selected signal.
7. A communication unit characterized by:
a transmitter that transmits communication signals modulated by an amplitude modulation technique and communication signals modulated by a frequency modulation technique; and a receiver comprising a single demodulator, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein the single demodulator has a single demodulation path and wherein both the communication signals modulated by the amplitude modulationtechnique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
a transmitter that transmits communication signals modulated by an amplitude modulation technique and communication signals modulated by a frequency modulation technique; and a receiver comprising a single demodulator, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein the single demodulator has a single demodulation path and wherein both the communication signals modulated by the amplitude modulationtechnique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
8. The communication unit of claim 7, further characterized in that the communication signals modulated by the amplitude modulation technique are transmitted when low power consumption by the transmitter is desired.
9. The communication unit of claim 7, further characterized in that the communication signals modulated by the frequency modulation technique are transmitted when greater signal coverage by the transmitter is desired.
10. A communication unit characterized by:
a transmitter that transmits communication signals modulated by an amplitude modulation technique when low power consumption by the transmitter is desired, and transmits communication signals modulated by a frequency modulation technique when greater signal coverage by the transmitter is desired; and a receiver comprising a single demodulator having a single demodulation path, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
a transmitter that transmits communication signals modulated by an amplitude modulation technique when low power consumption by the transmitter is desired, and transmits communication signals modulated by a frequency modulation technique when greater signal coverage by the transmitter is desired; and a receiver comprising a single demodulator having a single demodulation path, arranged and constructed to receive and demodulate both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique, wherein both the communication signals modulated by the amplitude modulation technique and the communication signals modulated by the frequency modulation technique are demodulated using the single demodulation path.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1858993A | 1993-02-17 | 1993-02-17 | |
| US08/018,589 | 1993-02-17 |
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| CA2154180A1 CA2154180A1 (en) | 1994-09-01 |
| CA2154180C true CA2154180C (en) | 1999-04-06 |
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ID=21788725
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002154180A Expired - Lifetime CA2154180C (en) | 1993-02-17 | 1994-01-14 | Multiple-modulation communication system |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5602868A (en) |
| KR (1) | KR0183143B1 (en) |
| CN (1) | CN1100860A (en) |
| AU (1) | AU677300B2 (en) |
| BR (1) | BR9405728A (en) |
| CA (1) | CA2154180C (en) |
| TW (1) | TW325609B (en) |
| WO (1) | WO1994019892A1 (en) |
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-
1994
- 1994-01-14 CA CA002154180A patent/CA2154180C/en not_active Expired - Lifetime
- 1994-01-14 AU AU62297/94A patent/AU677300B2/en not_active Expired
- 1994-01-14 WO PCT/US1994/000580 patent/WO1994019892A1/en active Application Filing
- 1994-01-14 KR KR1019950703419A patent/KR0183143B1/en not_active IP Right Cessation
- 1994-01-14 BR BR9405728A patent/BR9405728A/en not_active IP Right Cessation
- 1994-01-27 TW TW083100684A patent/TW325609B/en not_active IP Right Cessation
- 1994-01-31 CN CN94101194A patent/CN1100860A/en active Pending
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1995
- 1995-05-22 US US08/445,572 patent/US5602868A/en not_active Expired - Lifetime
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|---|---|
| TW325609B (en) | 1998-01-21 |
| KR960701544A (en) | 1996-02-24 |
| BR9405728A (en) | 1995-11-28 |
| AU677300B2 (en) | 1997-04-17 |
| AU6229794A (en) | 1994-09-14 |
| CN1100860A (en) | 1995-03-29 |
| WO1994019892A1 (en) | 1994-09-01 |
| KR0183143B1 (en) | 1999-05-15 |
| CA2154180A1 (en) | 1994-09-01 |
| US5602868A (en) | 1997-02-11 |
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