CA1314079C - Time shared very small aperture satellite terminals - Google Patents
Time shared very small aperture satellite terminalsInfo
- Publication number
- CA1314079C CA1314079C CA000600820A CA600820A CA1314079C CA 1314079 C CA1314079 C CA 1314079C CA 000600820 A CA000600820 A CA 000600820A CA 600820 A CA600820 A CA 600820A CA 1314079 C CA1314079 C CA 1314079C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- storage means
- data
- carrier
- data signal
- 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
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
- H04B7/18517—Transmission equipment in earth stations
Abstract
TIME SHARED VERY SMALL APERTURE SATELLITE TERMINALS
ABSTRACT OF THE DISCLOSURE
A time shared power amplifier for amplifying first and second modulated carrier signals for transmission. The carrier signals are modulated by first (35) and second (21) data signals, respectively. The first and second signals are characterized by bursts of data separated by periods of silence. If either of the data signals is presented for transmission while the other is being transmitted, the later one is stored in a storage buffer (11, 13) until the earlier one has been transmitted. Thus, each signal is transmitted during the other's silent periods, and since only one carrier is being transmitted at any given time a much smaller amplifier (19) can be used to amplify the carriers to a given power level than would be required if both carriers had to be transmitted at once.
ABSTRACT OF THE DISCLOSURE
A time shared power amplifier for amplifying first and second modulated carrier signals for transmission. The carrier signals are modulated by first (35) and second (21) data signals, respectively. The first and second signals are characterized by bursts of data separated by periods of silence. If either of the data signals is presented for transmission while the other is being transmitted, the later one is stored in a storage buffer (11, 13) until the earlier one has been transmitted. Thus, each signal is transmitted during the other's silent periods, and since only one carrier is being transmitted at any given time a much smaller amplifier (19) can be used to amplify the carriers to a given power level than would be required if both carriers had to be transmitted at once.
Description
-1- 1 3 1 ~079 TIME SHARED y~ERy SMALL APERTURE
SATELLIT~ TERMINALS
BACKGROUND OF_THE INVENTION
Field o~ The Irl~rention Thi~ invent$on is in the general field of radio transmitter power amplifiers for satellite communications, and more particularly in the ~ield of voice and communications power ampli~ier~ which simultaneously amplify for transmission two different signals on different carrier fre~uencies for communication via very small aperture terminals.
Description of the Related Art rt is often necessary to transmit two different data signals by means of a single transmitter. For example, an earth station for transmitting in~ormation fro~ a rem~te computer terminal to a central computer via satellite must at various times transmit voice and computer daka signals. Each data signal must be transmitted on a different carrier frequency, and a power amplifier for use in such a tran~mitter must be capable o~ amplifying a carrier signal of either frequancy to a sufficient level of power ~or t~rans~i ~ion.
One application for tra~smitters of this type is atellite communication terminals in which concurrent communications of voice and data is desired. It is highly desireable that the transmitter be co-located with each antenna at a user site to reduce the overall cost of such systems. However, such use places severe 30 demands on the complexity, cost and performance of such systemsO
For instance, if both voice and computer data signals are ready for transmission at the same time, the power amplifier must simultaneously amplify a carrier signal carrying the compuker data signal and a carrier signal carrying ths voice signal to a sufficient level o~ power for transmission. If the required power level is the same ~or each carrier ~ignal, the amplifier must be able to provide a total power output o~ twice the maximum power which would have been raquired to transmit either carrier signal alone, a di~ference of three dB.
Moreover, when two carrier signals are being 10 amplified simultaneously it is necessary to operate the amplifier some three to six dB below its maximum power level in order to avoid unacceptable intermodulation distortion between ths two signals. Accordingly, a powar ampli~ier which can simulataneously amplify two 15 different carrier signals to a required level o~ power must have a maximum power rating six to nlne dB higher than would be required to amplify only one signal to the same power level.
The power ampli~ier represents a significant 20 part of the cost of a transmitter and, in a relatively small inskallation such as an earth station for a remote computer terminal, may represent a major ~raction of the cost of lthe sntire station. If it were pos~ible to transmit bst~ voice and computer data 25 carrier signal~ by means o~ a power amplifier no more powerful than would be required to trans~it only one signal, signi~icant cost savLngs and increased efficiency o~ operation could be achieved.
Accord mgly, there i5 a need for a way to 30 transmit two different carrier signals, each carrying different data signals such as voice and computer data, without using a power ampli~ier more powerful than would be needed to transmit one such signal by itsel~.
35S~MMARY OF THE INVENTIQN
This inventiorl particularly relates to the field of voice and data communication via very small -3_ 131~079 aperture terminals (VSATs), but is of general utility to a variety of satellite communication systems.
Through this invention, a single transmitter e~uipment is made to function as the equivalent of two such systems supporting concurrent communications of voice and data, thus sub~tantially reducing the cost of such services.
In the newly daveloped field of Ku-band satellite communications, very small aperture terminals ~SATs) are installed directly on the customer premises to reduce the overall cost of a communications system.
Such terminals are usually required to support one voice and one data channel concurrently. With differ2nt destinations for each circuit, the termLnal 15 has to generate and transmit two independent carriers, one for voice and one for the data channel. This, in effect, re~uires the equivalenk of two transmitters, although some components may be combined where practical to save costs.
In the transmit direction, the two carrier signals share a common up-converter and a common power amplifier. While this does not impos~ too much burden on the up-converter, the implications for the power amplifier ars substant~al. These implications are due - 25 to the fact that a power amplifier, which has to simultaneously ampli~y two di~ferent carri~r signals to a required level of power, must have a maximum power rating o~ six to nine dB higher than that required to amplify only one signal to the same power level.
The power amplifier portion of a VSAT represents about 20% of the total VSAT cost and each of the modems represents about 25% of the cost. Since the total cost of a VSAT has a great bearing on the final cost of the communications services to the end users, any reduction 35 of the number of subsystemA or lowering of the design performance re~uirements of the major components of the VSAT would result in substantial savings in VSAT based communications networks.
The pre~ent invention uses the concept of time sharing and makes it pos6ible for each of the voice and computer data signals at a VSAT to share one modulator (~n~tead of each channal having a dediaated modulator) and thereby re~uires the transmission of only one RF
carrier signal at any instant. Al~o, since the system of the present invention only requires the 10 up-conver~ion and amplification of one carrier signal, instead of two in the traditional situation, substantial reductions in the required amplifier power rating (on the order of six to nine dB) is possible.
~hus, by use of the present invention it is estimated 15 that the cost of the amplifier may be cut at least in half. The overall cost reduction ln the VSAT system as a result of the present invention could thus easily reach 25~ or more.
The present invention resides in a time shared 20 power amplifier which amplifies two different carrier slgnals, each carrying different data signals, to a power level equal to that to which a ccnventional amplifier having similar powerhandling capability could amplify a single carrier signal.
A time shared power ampli~ier embodying the invention includes first and second data storage means, control means to initiate transfer of stored data signals out of the storage means, modulation means to provide a carrier signal modulated with any stored data 30 signals out of the storage means, modulation means to provide a carrier signal modulated with any stored data signal being transferred out of either storage means, and a power amplifier to amplify the modulated carrier signal. The carrier signal has a first frequency when 35 modulated with a signal from the ~irst storage means and a second frequency when modulated wi~h a signal from the second storage means.
W hile a signal is being transferred out of th~
first storage means, initiation of any transfer o~
signals out of the second storage means is inhibited.
Similarly, while a signal is being transferred out of the second storage means, mitiation of any transfer of signals out of the ~irst ~torage means is inh~bited.
The power amplifier is never called on to amplify more than one carrier signal at any one time because only one data signal can be transferred out of stor~ at a 10 time and therefors only one modulated carrier signal can be provided at a time. The storage means may comprise first~in, first-out serial storage means.
Conversion means may be provided to convert an analog signal into digital form. Means may be provided to 15 sense the presencs of a signal and to cause one of the data storage means to store the sensed signal.
The modulation means may comprise two separate modulators, each with its own carrier signal generator, and means to prevent the amplifier from receiving more 20 than one carrier signal at a time. Alternatively, the modulation means may comprise a sLngle modulator and a carrier signal generator which provides a carrier signal having a first frequency when being modulated with a data signal ~ro~ the first storage mean~ and a 25 s2cond fr~uency when being modulated with a data ~ignal from the second storage mea~s. In another embodim~nt, the modulation means may comprise means to modulate an lntermediate signal with any data signal from either storage means and means to provide the 30 carrier signal by shifting the frequency of the modulated intermediate signal to either of two desired frequencies according to whether the intermediate signal is being modulated with a data signal from the first storage means or from the second storage means.
35 The carrier signal may be provided by a conventional osc;llator, a digital ~requency synthesizer, or other ~uitable frequency generation means.
t ~ 1 407q In a time shared power amplifier according to the invention, any data signal being held in the second storage means for transmission must wait while any data signal already in ths fir~t storage means is being transmitted, and vice versa. In many applications, the first and second data signals occur in bursts sufficiently brief that any delays introduced by this time sharing will not have adverse effects. For example, speech bursts average about one second and packet data bursts average less than 0.1 second.
Delaying a speech burst by 0.1 second would not be noticeable to the listener at the receiving end of the system. Similarly, delaying a data burst by one second would not adversely affect real-time transaction processing, which normally involves computer processing and transmission delays of several seconds. Thus, in such applications, a much smaller power ampli~ier can be used than would be required to transmit both data signals simultaneously, thereby inparting the benefits described above.
An aspect of the invention is as follows:
A time shared power amplifier comprising:
first data storage means, operative to store a first data signal;
second data storage means, operative to store a second data signal;
control means, responsive to the first storage means to initiate transfer of a stored data signal out of the first storage means and during the transfer to inhibit initiation of transfer of any signal out of the second storage mean~, and responsive to the second storage means to initiate transfer of a stored data signal out of the second storage means and during the trans~er to inhibit initiation of transfer of any signal out of the first storage means;
.~
6a ~ 31 40~q modulation means, operative to provide a carrier signal, to receive a data signal being transferred out of either storage means, and to modulate the carrier signal with the received data signal, said carrier signal comprising a first frequency when modulated with a data signal from said first storage means and a second frequency when modulated with a data signal from said second storage means; and a power amplifier, operative to receive any modulated carrier signal from the modulation means and to amplify the same to a desired power level.
Other objects and advantages of the present invention will become apparent from the following detailed description taken together with the drawings which illustrate by way of example the principles and teachings of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of a voice-data VSAT
according to the prior art.
Figure 2 is a block diagram o~ the basic system of the present invention as applied to a VSAT system.
Figure 3 is a more detailed block diagram of the general arrangement of the system providing input to the power amplifier according to the invention.
B
Figure 4 is a block diagram of an embodiment OI
the modulation means of Figure 3 wherein two separate modulators are employed.
Figure 5 is a block diagram of a ~irst embodiment of the modulation means of Figure 3 wherein a single modulator i8 employed.
Figure 6 is a block diagram of a ~econd embodiment o~ the modulation mean~ of Figure 3 wherein a single modulator and an up-converter are employed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A time shared power amplifier according to the invention amplifies ~or transmi~sion two carrier 15 signals, each carrying di~erent data signals, to a power level as great a~ the maximum power level to which a conventional amplifier could amplify a single carrier signal by separately amplifying eaah carrier ~ignal when a data signal to be carried by that carrier 20 signal i8 ready ~or transmission. If data to be carried by both carrier~ are ready for transmission at the same time, the data are transmitted sequentially rather than simultaneously. In order to provide for this eventuality, data or voice transmissions may be stored 25 in memory until transmission capability i8 available.
It is often neces6ary to amplify and transmit two di~erent radio carri2r signals by means o~ a single power amplifier. and transmitter. For example, an earth station which transmits in~ormation ~rom a 3 0 remote terminal to a central computer via satelli~e sends a voice signal on one carrier and a computer data signal on another. Simultaneous amplification of both signals to a given power level requires a power amplifier having a maximum power capaci~y as much as 35 nine dB greater than would be required to amplify only one of the signals to the same power level.
A typical voice channel is quiet about 60% of the time, and its actual information content occurs in relatively short bursts of not more than a few seconds duration. A typical computer data channel i~ likewise silent more than hal~ the time with its actual information content al80 occurring in relatiYely brie~
bursts. A time shared power amplifier according to the invention takes advantage of these silent periods by tran~mitting a burst of computer data when the ~oice 10 channel is silent and a burst of voice data when the computer channel is silent~ If computer data is presented for transmission while voice data is being sent, the computer data i~ held in temporary storage unt~l tha voice channel becomes quiet, and vice versa.
15 ~hus, only one carri~r need be transmitted at any one time, and a much smaller and less expensive amplifier can be used than would be required to amplify both carriers simultaneously.
An example of a prior art VSAT system is 20 ~lu~trated in Figure 1. As may be seen from the figure, the voice processing channel is entirely separate from the data interface and processing until the two are summed, prior to up-conversion, and input to the power ampli~ier. In the prior art system, the 2 5 two carrier signals in the kransmit direction share a common up-converter and a com~on power ampli~ier. The implications of this arrangemant on the power amplifier are quite ~ubstantial, although other portions of the system such as the up-converter are not a~ drastically 30 effected. Since the power ampliPier in this arrangement ha~ to simultaneously amplify two di~ferent carrier signals to an ouput raquir2d ~or transmission, the power ampli~ier must have a maximum power rating of approximately 6 to 9 dB greater power output than that 35 which would be required to ampli~y a single signal at the same power level. Since the power amplifier for the VS~T system repres2nts a substantial portion of the total cost o~ th~ sy~tem (typically about 2 0% of the cost of a VSAT system) and since the total cost of the VSAT has a substantial bearing on the total cost of a communication system due to a large number of VSATs used in such a system, any redllction in the cost of the VSAT subsyste~ will have a strong mfluence on the total cost of VS~T based satellite communications networks. The present invention thus provides an important improvement on the prior art systems of Figure 1.
Figure 2 illustrates a generalized block diagram of a VSAT according to the present invention which uses time . haring in the transmit direction. Time sharing is nok desireable in the receive direction, since 15 receive data iB normally contained in a continuous transmission broadcast from a hub terminal to a number of VSATs. Thus, the primary savings and effienciences of t.he present invention are directed to the time sharing o~ transmission of voice and data informationO
20 The primary difference between the prior art systems of Figure 1 and the present invention is related to the tran~mit interfac~ and processing function, in that i~
swi~ches the modulator input between the voice and data transmit int~rfaces to time share the output prior to 25 up-conversion and input to the power amplifier. Thus, the ~eparate voice and data interface processing of the ~r$or art is replaced by an i~tergrated voice data processing block that dif~ers Ln the transmi~ direction only and, as will be explained in more detail below, 30 provides for the time sharing of voice and data Lnformation prior to input to the power ampliiier. The following detailed description describes various preferr2d embodiments of the portion of the present invention indicated by the upper portion o~ this 35 diagram enclosed in the dotted lines and representing the voice/data processing and amplification system.
-lo- 1 31 ~079 A pre~erred embodiment of a time shared power ampli~ier as illustrated in Figure 3 includes first data storage means 11 operative to store a first data signal; second data storage means 13, operative to store a second data signal; and control means 15, responsiYe to tha first storage means 11 to ini~iate transfer o~ a stored data signal out o~ the first storage means 11 and during the transfer to inhibi~
initiation of trans~er of any signal out of the second storage means 13, and responsive to the second storage means 13 to initiate transfer of a stored data signal out of the second storage means 13 and during the transfer to inhibit initiation of transfer o~ any signal out of the ~irst storage means 11.
Also included i5 modulation means 17, operative to provide a carrier signal, to receive a data signal being transferred out oP either storage means, and to modulate the carrier signal with the received data signal, the carrier signal having a first frequency 20 when modulated with a data signal ~rom the first storage means 11 and a second fre~uency when modula~ed with a ~ignal from the ~econd storage means 13. A
power amplifier 19 is operative to rec~ive any modulated earrier signal from the modulation means and 25 to amplify the same to a desired power level.
A tim~ shared power amplifier according to the invention ~ay ba used, ~or example, in a remotely looated earth stakion to transmit a .computer data signal and a voice signal to a central location or 30 perhaps to two dif~erent locations. In such an application, the ~irst storage means 11 may be adapted to receive and store the computer data signal and the second storage means 13 may be adapted to receive and store the voice signal.
More particularly, the first storage means 11 may comprise first-in, first QUt serial storage means such as a serial shift register of random access 131~079 memory. The storage ~eans 11 receives the computer data signal from a computer source 21 through a line 23. The computer source 21 provides a control signal to indicate when it is ready to send a computer data signal to the ~torage means 11. This control signal is sent i~rom the source 21 through a linQ 25 to a fir~t input of an AND gate 27. A computer clock source 29 provides clock pu182s to the computQr source 21 and to a second input of the AND gate 27 through a line 31.
The control signal carried by the line 25 enables the AND gate 27. When the AND gate 27 is enabled, clock pulses from the clock source 29 pass from the AND gate 27 to a "write" input of the storage means 11 by a line 33, clocking the computer data 15 signal from the source 21 into the storage means 11.
Sim~arly, the second storage means 13 receives the voice signal from a voice source 35. The voice source 35 provides a voice signal in analog form.
Voice conv~rsion m~ans 37, such as an analog-to-digital 20 converter, converts the analog voice signal into digital form for storage. The conversion means 37 receives the analog voice signal from the source 35 thrsugh a llne 39 an provides the voice signal in digital form to the storage means 13 throllgh a line 41.
Mean~ 43 such as a voice detector sens~s the pre ence of a voice ignal on the line 41 and causes ~he storagQ ~eans 13 to store the sensed voice signal by providing a control signal through a line 45 to a first input o~ an AND gate 47. A ~oice clock source 49 30 provides clock pulses to the conversion means 37 and to a second input of tha AND gate 47 through a line 51.
The control signal carried by the line 4 5 enables the AND gate 47. When the AND gate 47 is enabled, clock pulses ~rom the voice clock source 49 35 pass from the AND gate 47 to a "write" lnput of the storage ~eans 13 through a line 53, clocking the t 31 4079 dlgi~al voice signal from the conversion m~ans 37 into ~he storage m ans 13.
When a computer data signal has been stored in the storage means 11, the storage maans 11 provides a "computer data ready" signal to the control means 15 through ~ line 55. The control ~eans 15 may comprise, ~or exampls, logic such a first and ~econd AND gatPs 57 and 59. The "computer data ready" ~ignal carried by the line 55 i8 applied to a non-inverting input of the first AND gate 57. The "computer data ready" signal passes through the AND gate 57 and is applied to a first input of an AND gate 61 through a line 63, thereby enabling the gate 61. The gate 61 receives computer clock pulses ~rom the computer clock source 29 through the line 31, and when the yate 61 has been enabled by the "computer data ready" signal it pa~ses the clock pulses through a line 65 to a "read" input of the storage means 11 to clock the stored computer data signal out of the storage means 11.
Similarly, when a voice signal has ~een stored in the voice storage means 13, a "voice data ready"
signal is provided to the control mean. 15 through a line 67. The "voice data ready" signal carried by the line 67 i~ applied to a non-inverting input of the second AND gate 59. ~ The "voice da~a ready" signal passes through the AND gat~ 59 and i~ applied to a first input o~ an AND gate 69 through a line 71, thereby enabling the gate 69 T~e gate 69 receives ~oice clock pulses ~rom the voice clock ~ource 49 30 through the line 51, and when the gate 69 has been en~bled by the "voice data ready" signal it passes the clock pulses through a line 73 to a "read" input of the storage means 13 to clock the stored voice signal out of the storage means 13.
The "computer data ready" signal ~rom the AND
gate 57 on the line 63 is applied to an inverting input of the gate 59. When present a~ this inverting input -13- 131~079 of the gate 59, the "computer data ready" signal inhibits any "voice data ready" signal rom passing through the gate 59 and thereby prevents voic:e clock pulses from clocking any signal out of the storage means 13. Llkewi e, the "voice data ready" signal from the AND gats 59 on thQ line 71 i9 applied to an inverting input of the gate 57, and, when present at thi9 inverting input o~ the gate 57, the "voice data ready" signal inhibi~s any "computer data ready" signal from passing through th~ gate 57 and thereby prevents computer clock pulses ~rom clocking any signal out of the storage means 11 Thus, if a computer data signal is ready for transmission prior to the time a voice siqnal is ready, 15 ~h~ computer data signal gets transmitted first and, if a voice signal is ready ~or transmission at ~his time, the voice signal is kept in the storage means 13 until the computer data signal has been transmi~ted, and vice versa. Since computer data (e.g. transaction or pacXer 20 data), and voice signals both occur in short bursts, neither signal ever has to wait very long to be transmitted.
The modulation means 17 receives a stored computer data signal from the 6torage means 11 through 25 a line 75 and a ~tored voice signal from th2 storage mean3 13 through a line 77. ~he modulation means 17 provides a carrier ~ignal modulated with any data signal being transferred out of either storage means, the carrier signal having a first frequency when 30 ~odulated with a computer data ~ignal from the storage maans 11 and a second frequency when modulated with a voice signal from the storage means 13. The modulated carrier signal is provided to the power amplifier 19 through a line 79.
In one embodiment, illustrated in Figure 4, the modulation means 17 may comprise a first modulator 81~
operative to provide a carrier signal having the ~irst 1 31 ~079 frequency and to modulate ths same with a data signal being trans~erred out of the firs1: storage means 11 through the line 751 and the second modulator 83, operative to provide a carrier signal having the second frequPncy and to modulate the same with a data signal being transferred out of the second storage mean~ 13 through the llne 77. Neans to prevent the power amplifier 19 from receivLng more than one ~ the carrier signals at any given time, such as first and 10 second carrier ~witches 85 and 87, may also be provided. The ~irst carrier swi~ch 85 receives the modulated ~irst carrier signal from the ~irst modulator 81 through a line 89. The ~irst carrier switch 85 enables ~he modulated first carrier signal to be 15 provided to the power amplifier 19 through the line 79 only when the switch 85 is activated by a "computer data ready" signal carried by the line 63. Similarly, the second carrier switch 87 receives the modulated second carrier signal from the second modulator 83 through a line 91 and passes the same to the power amplifier 19 through the line 79 onl~ when enabled by a "voice data ready" signal carried by the line 71.
In another embodiment, illustrated Ln Figure 5, the modulation means 17 compri.ses a carrier generator 93, operative to provide a carrier signa~ having the ~irs~ frequency when a data signal is being transferred fro~ the ~irst storage means 11, and the second frequency when a data signal is being transferred from the second storage means 13; and a modulator 95, 30 operative to modulate the carrier signal with any data signal bem g transfsrred out of either storage means 11 or 13. The modulator 95 receives the carrier signal from the carrier generator 93 through a line 97. A
data selector 99 may also be provided to select a data 35 signal from one or the other of the storage means 11 or 13. The data signal as selected by the data selector 99 is provided to the modulator 95 through a line 101.
1 31 llrO79 The data selector and the carrier generakor both receiv~ the "computer data ready" and "voice data ready" signals through the lines 63 and 71, respectively. The data selector 99 may be omitted if the storage means 11 and 13 are equipped with tri-state outputs or with som~ other means to insure that neither will ~nterfere with data being provided by the other at any time.
Another embodiment of the modulation means 17 is 10 shown in Figure 6. This embodiment comprises means such as a modulator 103 to generate an intermediate signal and modulate the same with any data 6ignal being transferred out of either storage means; and means such as an up-converter 105 to provide the modulated carrier ~ignal by shifting the frequency of the modulated intermediate signal to the first carrier freguency when the intermediate signal is being modulated with a data signal ~rom the first storage means 11 and to the second carrier frequency when the intermediate signal is being modulated with a data signal from the second ~torage mean3 13. The up-converter 105 receives the modulated intermediate signal from the modulator 103 through a line 107~ The modulator 103 receives the data signal from the data selector 99 as previously 25 de~cribed through the line 101, or directly form the toraga means 11 and 13 if a data selector is not used. A frequency selsctor 109 receives the "computer data ready" and "voice data ready" signals from the control means 15 through the lines 63 and 71, 30 respectively, and selects the appropriate carrier frequency accordLngly. The fre~uency selector 109 may comprise an oscillator which provides a signal to be combined wi~h the intermediate signal in the up-converter 105 to produce the carrier signal, or it 35 may comprise means to select a frequency control signal to be ~pplied to the up-converter 105. In the latter case, the up-converter 105 includes frequency generation means such as, Por example, a digital frequency synthesizer to provide a signal to be combined with the intermediate ~ignal. The frequency selector ignal is applied to the up-converter 105 from ~he freguency selector 109 through a lm e lll.
A time shared power ampli~ier according to the invention can amplify two different modulated carrier signal~ to a level o~ power equal to that to which a conventional amplifier could amplify a single modulated carrier signal. Two signals can thus be transmitted by a transmitter having no more power than would be required to transmit only one such signal, resulting in a signi~icantly smaller, less axpensive and more e~*icient transmi~ter than would otherwise be required.
Although certain specific embodiments of the invention have been disclosed, the scope of the invsntion is not to be limited to the particular forms and parts 80 described and illustrated. Accordingly, except as limited by the claims, the invention may be 20 practiced otherwise than a~ specifically set forth herein.
SATELLIT~ TERMINALS
BACKGROUND OF_THE INVENTION
Field o~ The Irl~rention Thi~ invent$on is in the general field of radio transmitter power amplifiers for satellite communications, and more particularly in the ~ield of voice and communications power ampli~ier~ which simultaneously amplify for transmission two different signals on different carrier fre~uencies for communication via very small aperture terminals.
Description of the Related Art rt is often necessary to transmit two different data signals by means of a single transmitter. For example, an earth station for transmitting in~ormation fro~ a rem~te computer terminal to a central computer via satellite must at various times transmit voice and computer daka signals. Each data signal must be transmitted on a different carrier frequency, and a power amplifier for use in such a tran~mitter must be capable o~ amplifying a carrier signal of either frequancy to a sufficient level of power ~or t~rans~i ~ion.
One application for tra~smitters of this type is atellite communication terminals in which concurrent communications of voice and data is desired. It is highly desireable that the transmitter be co-located with each antenna at a user site to reduce the overall cost of such systems. However, such use places severe 30 demands on the complexity, cost and performance of such systemsO
For instance, if both voice and computer data signals are ready for transmission at the same time, the power amplifier must simultaneously amplify a carrier signal carrying the compuker data signal and a carrier signal carrying ths voice signal to a sufficient level o~ power for transmission. If the required power level is the same ~or each carrier ~ignal, the amplifier must be able to provide a total power output o~ twice the maximum power which would have been raquired to transmit either carrier signal alone, a di~ference of three dB.
Moreover, when two carrier signals are being 10 amplified simultaneously it is necessary to operate the amplifier some three to six dB below its maximum power level in order to avoid unacceptable intermodulation distortion between ths two signals. Accordingly, a powar ampli~ier which can simulataneously amplify two 15 different carrier signals to a required level o~ power must have a maximum power rating six to nlne dB higher than would be required to amplify only one signal to the same power level.
The power ampli~ier represents a significant 20 part of the cost of a transmitter and, in a relatively small inskallation such as an earth station for a remote computer terminal, may represent a major ~raction of the cost of lthe sntire station. If it were pos~ible to transmit bst~ voice and computer data 25 carrier signal~ by means o~ a power amplifier no more powerful than would be required to trans~it only one signal, signi~icant cost savLngs and increased efficiency o~ operation could be achieved.
Accord mgly, there i5 a need for a way to 30 transmit two different carrier signals, each carrying different data signals such as voice and computer data, without using a power ampli~ier more powerful than would be needed to transmit one such signal by itsel~.
35S~MMARY OF THE INVENTIQN
This inventiorl particularly relates to the field of voice and data communication via very small -3_ 131~079 aperture terminals (VSATs), but is of general utility to a variety of satellite communication systems.
Through this invention, a single transmitter e~uipment is made to function as the equivalent of two such systems supporting concurrent communications of voice and data, thus sub~tantially reducing the cost of such services.
In the newly daveloped field of Ku-band satellite communications, very small aperture terminals ~SATs) are installed directly on the customer premises to reduce the overall cost of a communications system.
Such terminals are usually required to support one voice and one data channel concurrently. With differ2nt destinations for each circuit, the termLnal 15 has to generate and transmit two independent carriers, one for voice and one for the data channel. This, in effect, re~uires the equivalenk of two transmitters, although some components may be combined where practical to save costs.
In the transmit direction, the two carrier signals share a common up-converter and a common power amplifier. While this does not impos~ too much burden on the up-converter, the implications for the power amplifier ars substant~al. These implications are due - 25 to the fact that a power amplifier, which has to simultaneously ampli~y two di~ferent carri~r signals to a required level of power, must have a maximum power rating o~ six to nine dB higher than that required to amplify only one signal to the same power level.
The power amplifier portion of a VSAT represents about 20% of the total VSAT cost and each of the modems represents about 25% of the cost. Since the total cost of a VSAT has a great bearing on the final cost of the communications services to the end users, any reduction 35 of the number of subsystemA or lowering of the design performance re~uirements of the major components of the VSAT would result in substantial savings in VSAT based communications networks.
The pre~ent invention uses the concept of time sharing and makes it pos6ible for each of the voice and computer data signals at a VSAT to share one modulator (~n~tead of each channal having a dediaated modulator) and thereby re~uires the transmission of only one RF
carrier signal at any instant. Al~o, since the system of the present invention only requires the 10 up-conver~ion and amplification of one carrier signal, instead of two in the traditional situation, substantial reductions in the required amplifier power rating (on the order of six to nine dB) is possible.
~hus, by use of the present invention it is estimated 15 that the cost of the amplifier may be cut at least in half. The overall cost reduction ln the VSAT system as a result of the present invention could thus easily reach 25~ or more.
The present invention resides in a time shared 20 power amplifier which amplifies two different carrier slgnals, each carrying different data signals, to a power level equal to that to which a ccnventional amplifier having similar powerhandling capability could amplify a single carrier signal.
A time shared power ampli~ier embodying the invention includes first and second data storage means, control means to initiate transfer of stored data signals out of the storage means, modulation means to provide a carrier signal modulated with any stored data 30 signals out of the storage means, modulation means to provide a carrier signal modulated with any stored data signal being transferred out of either storage means, and a power amplifier to amplify the modulated carrier signal. The carrier signal has a first frequency when 35 modulated with a signal from the ~irst storage means and a second frequency when modulated wi~h a signal from the second storage means.
W hile a signal is being transferred out of th~
first storage means, initiation of any transfer o~
signals out of the second storage means is inhibited.
Similarly, while a signal is being transferred out of the second storage means, mitiation of any transfer of signals out of the ~irst ~torage means is inh~bited.
The power amplifier is never called on to amplify more than one carrier signal at any one time because only one data signal can be transferred out of stor~ at a 10 time and therefors only one modulated carrier signal can be provided at a time. The storage means may comprise first~in, first-out serial storage means.
Conversion means may be provided to convert an analog signal into digital form. Means may be provided to 15 sense the presencs of a signal and to cause one of the data storage means to store the sensed signal.
The modulation means may comprise two separate modulators, each with its own carrier signal generator, and means to prevent the amplifier from receiving more 20 than one carrier signal at a time. Alternatively, the modulation means may comprise a sLngle modulator and a carrier signal generator which provides a carrier signal having a first frequency when being modulated with a data signal ~ro~ the first storage mean~ and a 25 s2cond fr~uency when being modulated with a data ~ignal from the second storage mea~s. In another embodim~nt, the modulation means may comprise means to modulate an lntermediate signal with any data signal from either storage means and means to provide the 30 carrier signal by shifting the frequency of the modulated intermediate signal to either of two desired frequencies according to whether the intermediate signal is being modulated with a data signal from the first storage means or from the second storage means.
35 The carrier signal may be provided by a conventional osc;llator, a digital ~requency synthesizer, or other ~uitable frequency generation means.
t ~ 1 407q In a time shared power amplifier according to the invention, any data signal being held in the second storage means for transmission must wait while any data signal already in ths fir~t storage means is being transmitted, and vice versa. In many applications, the first and second data signals occur in bursts sufficiently brief that any delays introduced by this time sharing will not have adverse effects. For example, speech bursts average about one second and packet data bursts average less than 0.1 second.
Delaying a speech burst by 0.1 second would not be noticeable to the listener at the receiving end of the system. Similarly, delaying a data burst by one second would not adversely affect real-time transaction processing, which normally involves computer processing and transmission delays of several seconds. Thus, in such applications, a much smaller power ampli~ier can be used than would be required to transmit both data signals simultaneously, thereby inparting the benefits described above.
An aspect of the invention is as follows:
A time shared power amplifier comprising:
first data storage means, operative to store a first data signal;
second data storage means, operative to store a second data signal;
control means, responsive to the first storage means to initiate transfer of a stored data signal out of the first storage means and during the transfer to inhibit initiation of transfer of any signal out of the second storage mean~, and responsive to the second storage means to initiate transfer of a stored data signal out of the second storage means and during the trans~er to inhibit initiation of transfer of any signal out of the first storage means;
.~
6a ~ 31 40~q modulation means, operative to provide a carrier signal, to receive a data signal being transferred out of either storage means, and to modulate the carrier signal with the received data signal, said carrier signal comprising a first frequency when modulated with a data signal from said first storage means and a second frequency when modulated with a data signal from said second storage means; and a power amplifier, operative to receive any modulated carrier signal from the modulation means and to amplify the same to a desired power level.
Other objects and advantages of the present invention will become apparent from the following detailed description taken together with the drawings which illustrate by way of example the principles and teachings of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of a voice-data VSAT
according to the prior art.
Figure 2 is a block diagram o~ the basic system of the present invention as applied to a VSAT system.
Figure 3 is a more detailed block diagram of the general arrangement of the system providing input to the power amplifier according to the invention.
B
Figure 4 is a block diagram of an embodiment OI
the modulation means of Figure 3 wherein two separate modulators are employed.
Figure 5 is a block diagram of a ~irst embodiment of the modulation means of Figure 3 wherein a single modulator i8 employed.
Figure 6 is a block diagram of a ~econd embodiment o~ the modulation mean~ of Figure 3 wherein a single modulator and an up-converter are employed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A time shared power amplifier according to the invention amplifies ~or transmi~sion two carrier 15 signals, each carrying di~erent data signals, to a power level as great a~ the maximum power level to which a conventional amplifier could amplify a single carrier signal by separately amplifying eaah carrier ~ignal when a data signal to be carried by that carrier 20 signal i8 ready ~or transmission. If data to be carried by both carrier~ are ready for transmission at the same time, the data are transmitted sequentially rather than simultaneously. In order to provide for this eventuality, data or voice transmissions may be stored 25 in memory until transmission capability i8 available.
It is often neces6ary to amplify and transmit two di~erent radio carri2r signals by means o~ a single power amplifier. and transmitter. For example, an earth station which transmits in~ormation ~rom a 3 0 remote terminal to a central computer via satelli~e sends a voice signal on one carrier and a computer data signal on another. Simultaneous amplification of both signals to a given power level requires a power amplifier having a maximum power capaci~y as much as 35 nine dB greater than would be required to amplify only one of the signals to the same power level.
A typical voice channel is quiet about 60% of the time, and its actual information content occurs in relatively short bursts of not more than a few seconds duration. A typical computer data channel i~ likewise silent more than hal~ the time with its actual information content al80 occurring in relatiYely brie~
bursts. A time shared power amplifier according to the invention takes advantage of these silent periods by tran~mitting a burst of computer data when the ~oice 10 channel is silent and a burst of voice data when the computer channel is silent~ If computer data is presented for transmission while voice data is being sent, the computer data i~ held in temporary storage unt~l tha voice channel becomes quiet, and vice versa.
15 ~hus, only one carri~r need be transmitted at any one time, and a much smaller and less expensive amplifier can be used than would be required to amplify both carriers simultaneously.
An example of a prior art VSAT system is 20 ~lu~trated in Figure 1. As may be seen from the figure, the voice processing channel is entirely separate from the data interface and processing until the two are summed, prior to up-conversion, and input to the power ampli~ier. In the prior art system, the 2 5 two carrier signals in the kransmit direction share a common up-converter and a com~on power ampli~ier. The implications of this arrangemant on the power amplifier are quite ~ubstantial, although other portions of the system such as the up-converter are not a~ drastically 30 effected. Since the power ampliPier in this arrangement ha~ to simultaneously amplify two di~ferent carrier signals to an ouput raquir2d ~or transmission, the power ampli~ier must have a maximum power rating of approximately 6 to 9 dB greater power output than that 35 which would be required to ampli~y a single signal at the same power level. Since the power amplifier for the VS~T system repres2nts a substantial portion of the total cost o~ th~ sy~tem (typically about 2 0% of the cost of a VSAT system) and since the total cost of the VSAT has a substantial bearing on the total cost of a communication system due to a large number of VSATs used in such a system, any redllction in the cost of the VSAT subsyste~ will have a strong mfluence on the total cost of VS~T based satellite communications networks. The present invention thus provides an important improvement on the prior art systems of Figure 1.
Figure 2 illustrates a generalized block diagram of a VSAT according to the present invention which uses time . haring in the transmit direction. Time sharing is nok desireable in the receive direction, since 15 receive data iB normally contained in a continuous transmission broadcast from a hub terminal to a number of VSATs. Thus, the primary savings and effienciences of t.he present invention are directed to the time sharing o~ transmission of voice and data informationO
20 The primary difference between the prior art systems of Figure 1 and the present invention is related to the tran~mit interfac~ and processing function, in that i~
swi~ches the modulator input between the voice and data transmit int~rfaces to time share the output prior to 25 up-conversion and input to the power amplifier. Thus, the ~eparate voice and data interface processing of the ~r$or art is replaced by an i~tergrated voice data processing block that dif~ers Ln the transmi~ direction only and, as will be explained in more detail below, 30 provides for the time sharing of voice and data Lnformation prior to input to the power ampliiier. The following detailed description describes various preferr2d embodiments of the portion of the present invention indicated by the upper portion o~ this 35 diagram enclosed in the dotted lines and representing the voice/data processing and amplification system.
-lo- 1 31 ~079 A pre~erred embodiment of a time shared power ampli~ier as illustrated in Figure 3 includes first data storage means 11 operative to store a first data signal; second data storage means 13, operative to store a second data signal; and control means 15, responsiYe to tha first storage means 11 to ini~iate transfer o~ a stored data signal out o~ the first storage means 11 and during the transfer to inhibi~
initiation of trans~er of any signal out of the second storage means 13, and responsive to the second storage means 13 to initiate transfer of a stored data signal out of the second storage means 13 and during the transfer to inhibit initiation of transfer o~ any signal out of the ~irst storage means 11.
Also included i5 modulation means 17, operative to provide a carrier signal, to receive a data signal being transferred out oP either storage means, and to modulate the carrier signal with the received data signal, the carrier signal having a first frequency 20 when modulated with a data signal ~rom the first storage means 11 and a second fre~uency when modula~ed with a ~ignal from the ~econd storage means 13. A
power amplifier 19 is operative to rec~ive any modulated earrier signal from the modulation means and 25 to amplify the same to a desired power level.
A tim~ shared power amplifier according to the invention ~ay ba used, ~or example, in a remotely looated earth stakion to transmit a .computer data signal and a voice signal to a central location or 30 perhaps to two dif~erent locations. In such an application, the ~irst storage means 11 may be adapted to receive and store the computer data signal and the second storage means 13 may be adapted to receive and store the voice signal.
More particularly, the first storage means 11 may comprise first-in, first QUt serial storage means such as a serial shift register of random access 131~079 memory. The storage ~eans 11 receives the computer data signal from a computer source 21 through a line 23. The computer source 21 provides a control signal to indicate when it is ready to send a computer data signal to the ~torage means 11. This control signal is sent i~rom the source 21 through a linQ 25 to a fir~t input of an AND gate 27. A computer clock source 29 provides clock pu182s to the computQr source 21 and to a second input of the AND gate 27 through a line 31.
The control signal carried by the line 25 enables the AND gate 27. When the AND gate 27 is enabled, clock pulses from the clock source 29 pass from the AND gate 27 to a "write" input of the storage means 11 by a line 33, clocking the computer data 15 signal from the source 21 into the storage means 11.
Sim~arly, the second storage means 13 receives the voice signal from a voice source 35. The voice source 35 provides a voice signal in analog form.
Voice conv~rsion m~ans 37, such as an analog-to-digital 20 converter, converts the analog voice signal into digital form for storage. The conversion means 37 receives the analog voice signal from the source 35 thrsugh a llne 39 an provides the voice signal in digital form to the storage means 13 throllgh a line 41.
Mean~ 43 such as a voice detector sens~s the pre ence of a voice ignal on the line 41 and causes ~he storagQ ~eans 13 to store the sensed voice signal by providing a control signal through a line 45 to a first input o~ an AND gate 47. A ~oice clock source 49 30 provides clock pulses to the conversion means 37 and to a second input of tha AND gate 47 through a line 51.
The control signal carried by the line 4 5 enables the AND gate 47. When the AND gate 47 is enabled, clock pulses ~rom the voice clock source 49 35 pass from the AND gate 47 to a "write" lnput of the storage ~eans 13 through a line 53, clocking the t 31 4079 dlgi~al voice signal from the conversion m~ans 37 into ~he storage m ans 13.
When a computer data signal has been stored in the storage means 11, the storage maans 11 provides a "computer data ready" signal to the control means 15 through ~ line 55. The control ~eans 15 may comprise, ~or exampls, logic such a first and ~econd AND gatPs 57 and 59. The "computer data ready" ~ignal carried by the line 55 i8 applied to a non-inverting input of the first AND gate 57. The "computer data ready" signal passes through the AND gate 57 and is applied to a first input of an AND gate 61 through a line 63, thereby enabling the gate 61. The gate 61 receives computer clock pulses ~rom the computer clock source 29 through the line 31, and when the yate 61 has been enabled by the "computer data ready" signal it pa~ses the clock pulses through a line 65 to a "read" input of the storage means 11 to clock the stored computer data signal out of the storage means 11.
Similarly, when a voice signal has ~een stored in the voice storage means 13, a "voice data ready"
signal is provided to the control mean. 15 through a line 67. The "voice data ready" signal carried by the line 67 i~ applied to a non-inverting input of the second AND gate 59. ~ The "voice da~a ready" signal passes through the AND gat~ 59 and i~ applied to a first input o~ an AND gate 69 through a line 71, thereby enabling the gate 69 T~e gate 69 receives ~oice clock pulses ~rom the voice clock ~ource 49 30 through the line 51, and when the gate 69 has been en~bled by the "voice data ready" signal it passes the clock pulses through a line 73 to a "read" input of the storage means 13 to clock the stored voice signal out of the storage means 13.
The "computer data ready" signal ~rom the AND
gate 57 on the line 63 is applied to an inverting input of the gate 59. When present a~ this inverting input -13- 131~079 of the gate 59, the "computer data ready" signal inhibits any "voice data ready" signal rom passing through the gate 59 and thereby prevents voic:e clock pulses from clocking any signal out of the storage means 13. Llkewi e, the "voice data ready" signal from the AND gats 59 on thQ line 71 i9 applied to an inverting input of the gate 57, and, when present at thi9 inverting input o~ the gate 57, the "voice data ready" signal inhibi~s any "computer data ready" signal from passing through th~ gate 57 and thereby prevents computer clock pulses ~rom clocking any signal out of the storage means 11 Thus, if a computer data signal is ready for transmission prior to the time a voice siqnal is ready, 15 ~h~ computer data signal gets transmitted first and, if a voice signal is ready ~or transmission at ~his time, the voice signal is kept in the storage means 13 until the computer data signal has been transmi~ted, and vice versa. Since computer data (e.g. transaction or pacXer 20 data), and voice signals both occur in short bursts, neither signal ever has to wait very long to be transmitted.
The modulation means 17 receives a stored computer data signal from the 6torage means 11 through 25 a line 75 and a ~tored voice signal from th2 storage mean3 13 through a line 77. ~he modulation means 17 provides a carrier ~ignal modulated with any data signal being transferred out of either storage means, the carrier signal having a first frequency when 30 ~odulated with a computer data ~ignal from the storage maans 11 and a second frequency when modulated with a voice signal from the storage means 13. The modulated carrier signal is provided to the power amplifier 19 through a line 79.
In one embodiment, illustrated in Figure 4, the modulation means 17 may comprise a first modulator 81~
operative to provide a carrier signal having the ~irst 1 31 ~079 frequency and to modulate ths same with a data signal being trans~erred out of the firs1: storage means 11 through the line 751 and the second modulator 83, operative to provide a carrier signal having the second frequPncy and to modulate the same with a data signal being transferred out of the second storage mean~ 13 through the llne 77. Neans to prevent the power amplifier 19 from receivLng more than one ~ the carrier signals at any given time, such as first and 10 second carrier ~witches 85 and 87, may also be provided. The ~irst carrier swi~ch 85 receives the modulated ~irst carrier signal from the ~irst modulator 81 through a line 89. The ~irst carrier switch 85 enables ~he modulated first carrier signal to be 15 provided to the power amplifier 19 through the line 79 only when the switch 85 is activated by a "computer data ready" signal carried by the line 63. Similarly, the second carrier switch 87 receives the modulated second carrier signal from the second modulator 83 through a line 91 and passes the same to the power amplifier 19 through the line 79 onl~ when enabled by a "voice data ready" signal carried by the line 71.
In another embodiment, illustrated Ln Figure 5, the modulation means 17 compri.ses a carrier generator 93, operative to provide a carrier signa~ having the ~irs~ frequency when a data signal is being transferred fro~ the ~irst storage means 11, and the second frequency when a data signal is being transferred from the second storage means 13; and a modulator 95, 30 operative to modulate the carrier signal with any data signal bem g transfsrred out of either storage means 11 or 13. The modulator 95 receives the carrier signal from the carrier generator 93 through a line 97. A
data selector 99 may also be provided to select a data 35 signal from one or the other of the storage means 11 or 13. The data signal as selected by the data selector 99 is provided to the modulator 95 through a line 101.
1 31 llrO79 The data selector and the carrier generakor both receiv~ the "computer data ready" and "voice data ready" signals through the lines 63 and 71, respectively. The data selector 99 may be omitted if the storage means 11 and 13 are equipped with tri-state outputs or with som~ other means to insure that neither will ~nterfere with data being provided by the other at any time.
Another embodiment of the modulation means 17 is 10 shown in Figure 6. This embodiment comprises means such as a modulator 103 to generate an intermediate signal and modulate the same with any data 6ignal being transferred out of either storage means; and means such as an up-converter 105 to provide the modulated carrier ~ignal by shifting the frequency of the modulated intermediate signal to the first carrier freguency when the intermediate signal is being modulated with a data signal ~rom the first storage means 11 and to the second carrier frequency when the intermediate signal is being modulated with a data signal from the second ~torage mean3 13. The up-converter 105 receives the modulated intermediate signal from the modulator 103 through a line 107~ The modulator 103 receives the data signal from the data selector 99 as previously 25 de~cribed through the line 101, or directly form the toraga means 11 and 13 if a data selector is not used. A frequency selsctor 109 receives the "computer data ready" and "voice data ready" signals from the control means 15 through the lines 63 and 71, 30 respectively, and selects the appropriate carrier frequency accordLngly. The fre~uency selector 109 may comprise an oscillator which provides a signal to be combined wi~h the intermediate signal in the up-converter 105 to produce the carrier signal, or it 35 may comprise means to select a frequency control signal to be ~pplied to the up-converter 105. In the latter case, the up-converter 105 includes frequency generation means such as, Por example, a digital frequency synthesizer to provide a signal to be combined with the intermediate ~ignal. The frequency selector ignal is applied to the up-converter 105 from ~he freguency selector 109 through a lm e lll.
A time shared power ampli~ier according to the invention can amplify two different modulated carrier signal~ to a level o~ power equal to that to which a conventional amplifier could amplify a single modulated carrier signal. Two signals can thus be transmitted by a transmitter having no more power than would be required to transmit only one such signal, resulting in a signi~icantly smaller, less axpensive and more e~*icient transmi~ter than would otherwise be required.
Although certain specific embodiments of the invention have been disclosed, the scope of the invsntion is not to be limited to the particular forms and parts 80 described and illustrated. Accordingly, except as limited by the claims, the invention may be 20 practiced otherwise than a~ specifically set forth herein.
Claims (10)
1. A time shared power amplifier comprising:
first data storage means, operative to store a first data signal;
second data storage means, operative to store a second data signal;
control means, responsive to the first storage means to initiate transfer of a stored data signal out of the first storage means and during the transfer to inhibit initiation of transfer of any signal out of the second storage means, and responsive to the second storage means to initiate transfer of a stored data signal out of the second storage means and during the transfer to inhibit initiation of transfer of any signal out of the first storage means;
modulation means, operative to provide a carrier signal, to receive a data signal being transferred out of either storage means, and to modulate the carrier signal with the received data signal, said carrier signal comprising a first frequency when modulated with data signal from said first storage means and a second frequency when modulated with a data signal from said second storage means; and a power amplifier, operative to receive any modulated carrier signal from the modulation means and to amplify the same to a desired power level.
first data storage means, operative to store a first data signal;
second data storage means, operative to store a second data signal;
control means, responsive to the first storage means to initiate transfer of a stored data signal out of the first storage means and during the transfer to inhibit initiation of transfer of any signal out of the second storage means, and responsive to the second storage means to initiate transfer of a stored data signal out of the second storage means and during the transfer to inhibit initiation of transfer of any signal out of the first storage means;
modulation means, operative to provide a carrier signal, to receive a data signal being transferred out of either storage means, and to modulate the carrier signal with the received data signal, said carrier signal comprising a first frequency when modulated with data signal from said first storage means and a second frequency when modulated with a data signal from said second storage means; and a power amplifier, operative to receive any modulated carrier signal from the modulation means and to amplify the same to a desired power level.
2. A time shared power amplifier according to Claim 1 wherein the modulation means further comprises:
means to generate an intermediate signal and to modulate the same with any data signal being transferred out of either storage means; and means to provide the carrier signal by shifting the frequency of the modulated intermediate signal to the first frequency when the intermediate signal is being modulated with a data signal from the first storage means and to the second frequency when the intermediate signal is being modulated with a data signal from the second storage means.
means to generate an intermediate signal and to modulate the same with any data signal being transferred out of either storage means; and means to provide the carrier signal by shifting the frequency of the modulated intermediate signal to the first frequency when the intermediate signal is being modulated with a data signal from the first storage means and to the second frequency when the intermediate signal is being modulated with a data signal from the second storage means.
3. A time shared power amplifier according to Claim 1 wherein the first data storage means comprises first-in, first-out serial storage means.
4. A time shared power amplifier according to Claim 1 and further comprising conversion means to convert an analog signal into digital form for storage in one of the storage means.
5. A time shared power amplifier according to Claim 1 and further comprising means to sense the presence of a data signal for storage and to cause one of the data storage means to store the sensed signal.
6. A time shared power amplifier according to Claim 1 wherein the modulation means further comprises:
a first modulator, operative to provide a carrier signal having the first frequency and to modulate the same with a data signal being transferred out of the first storage means, and a second modulator, operative to provide a carrier signal having the second frequency and to modulate the same with a data signal being transferred out of the second storage means.
a first modulator, operative to provide a carrier signal having the first frequency and to modulate the same with a data signal being transferred out of the first storage means, and a second modulator, operative to provide a carrier signal having the second frequency and to modulate the same with a data signal being transferred out of the second storage means.
7. A time shared power amplifier according to Claim 6 and further comprising means to prevent the amplifier from receiving more than one of the carrier signals at any given time.
8. A time shared power amplifier according to Claim 1 wherein the modulation means further comprises:
a carrier generator, operative to provide a carrier signal having the first frequency when a data signal is being transferred from the first storage means and the second frequency when a data signal is being transferred from the second storage means; and a modulator, operative to modulate the carrier signal when any data signal being transferred out of either storage means.
a carrier generator, operative to provide a carrier signal having the first frequency when a data signal is being transferred from the first storage means and the second frequency when a data signal is being transferred from the second storage means; and a modulator, operative to modulate the carrier signal when any data signal being transferred out of either storage means.
9. A time shared power amplifier according to Claim 8 wherein the carrier generator comprises a digital frequency synthesizer.
10. A time shared power amplifier according to Claim 2 wherein the means to provide the carrier signal comprises a digital frequency synthesizer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US207,425 | 1988-06-16 | ||
| US07/207,425 US4995055A (en) | 1988-06-16 | 1988-06-16 | Time shared very small aperture satellite terminals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1314079C true CA1314079C (en) | 1993-03-02 |
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ID=22770497
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000600820A Expired - Lifetime CA1314079C (en) | 1988-06-16 | 1989-05-26 | Time shared very small aperture satellite terminals |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4995055A (en) |
| EP (1) | EP0346868B1 (en) |
| JP (1) | JPH06103861B2 (en) |
| AU (1) | AU597200B1 (en) |
| CA (1) | CA1314079C (en) |
| DE (1) | DE68912971T2 (en) |
| ES (1) | ES2048788T3 (en) |
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-
1988
- 1988-06-16 US US07/207,425 patent/US4995055A/en not_active Expired - Lifetime
-
1989
- 1989-05-26 CA CA000600820A patent/CA1314079C/en not_active Expired - Lifetime
- 1989-05-30 AU AU35812/89A patent/AU597200B1/en not_active Expired
- 1989-06-14 DE DE68912971T patent/DE68912971T2/en not_active Expired - Lifetime
- 1989-06-14 ES ES89110794T patent/ES2048788T3/en not_active Expired - Lifetime
- 1989-06-14 EP EP89110794A patent/EP0346868B1/en not_active Expired - Lifetime
- 1989-06-16 JP JP1152444A patent/JPH06103861B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109328290A (en) * | 2016-06-21 | 2019-02-12 | 艾威普科公司 | Complete secondary air-cooled type industrial steam condensing unit |
Also Published As
| Publication number | Publication date |
|---|---|
| ES2048788T3 (en) | 1994-04-01 |
| EP0346868A2 (en) | 1989-12-20 |
| JPH06103861B2 (en) | 1994-12-14 |
| JPH0239641A (en) | 1990-02-08 |
| US4995055A (en) | 1991-02-19 |
| DE68912971T2 (en) | 1994-08-25 |
| DE68912971D1 (en) | 1994-03-24 |
| AU597200B1 (en) | 1990-05-24 |
| EP0346868B1 (en) | 1994-02-09 |
| EP0346868A3 (en) | 1991-08-07 |
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