CA2029284C - Relay communication system - Google Patents
Relay communication systemInfo
- Publication number
- CA2029284C CA2029284C CA002029284A CA2029284A CA2029284C CA 2029284 C CA2029284 C CA 2029284C CA 002029284 A CA002029284 A CA 002029284A CA 2029284 A CA2029284 A CA 2029284A CA 2029284 C CA2029284 C CA 2029284C
- Authority
- CA
- Canada
- Prior art keywords
- signals
- frequency
- signal
- radio frequency
- phase
- 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 - Fee Related
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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
- H04B7/204—Multiple access
- H04B7/216—Code division or spread-spectrum multiple access [CDMA, SSMA]
Abstract
The invention is a relay communications system which uses a single reference frequency signal generator to produce a plurality of precisely frequency synchronized code division multiple access radio frequency signals. A transmitter transmits the synchronized signals to a remote satellite based retransmitter which includes a slave oscillator precisely synchronized to the reference signal generator for down-linking the multiple radio frequency signals to a common radio frequency with all of thedown-linked signals being in precise phase synchronism. The relative phase of the down-linked signals can be preserved or altered and the signals combined and amplified by a high-power amplifier operating in the saturation mode. The output from the high power amplifier is applied to a beamforming network to form an overlapping beam signal comprised of multiple code division multiple access information signals.
Description
2~292~
RELAY COMMUNICATION SYSTEM
BACKGROUND
The present invention relates to radio relay llal~ l;a~;ull systems, and more particularly to a satellite relay IIAII~II' '~;IIII system that utilizes a saturated amplifier system to amplify and retransmit ayll~,hlulluualy transmitted CDMA signals derived from a ground station.
Satellite ~u,,,,,,,l,,i- A~ill.lC systems are now well known. In such systems, sig-nals are transmitted from a ground station to a satellite where they are received, am-plified, and l~;LIallallli~L~l to remotely located receivers. Power n~ncllmr~i~n, weight, and physical ~lim~-nci~mc of the satellite-borne circuitty are of critical importance.
A significant application of satellite .,-""", -;. ~I;onc systems is for mobile 0 ~,"" " "~ I ;onC In this Arpli(''l~i~')n, in addition to the critical parameters mentioned above, it is also essential to provide a means to address individual remote users. To this end, CDMA LIA..~.II;~;IIII~ provide a viable solution. This type of secure trans-mission may be effected utilizing orthogonal signals or signal groups which can be combined into overlapping beam trAncmicci~nc The signals are separable by reason15 of the ullald~tcliaLics of the orthogonal signals.
In conventional applications, a plurality of orthogonal signals are transmitted to a satellite relay system, where they are combined into the u.~,.lalJ,u;llg beam signal using linear amplifiers. While it is well known that linear amplifiers are not the most efficient form of amplifier with respect to power . particularly in digital 20 tlallalll;aa;ull A~ , the need to preserve both phase and amplitude information of the individual CDMA signals has typically required their use.
2 202~2g4 SUMMARY OF THE INVENTION
In order to overcome the limitations of .,wl~,..(iul.dl systems addressed above, the present invention provides a relay n~ TIiCc;r)n or ~ system in which the relay L~ .ll of CDMA signals is effected utilizing amplifiers op-erating in a saturation mode. The system is comprised of a ground-based signal gen-erating circuit which includes circuitry which generates a reference frequency signal, a plurality of orthogonal coded binary phase modulated information signals, and a transmitter circuit which generates and transmits a radio frequency signal for each of the h.rull..alioll signals. Each of the radio frequency signals are at a different fre-lû quency and each signal is modulated by one of the inffmnotirln signals. The informa-tion signals, radio frequency signals, and bit rates of the information signals are based upon the frequency of the reference signal.
A remotely located relay transmitter, typically a satellite relay, includes a re-ceiver which is adapted to receive the modulated radio frequency signals and a mas-15 ter oscillator unit connected to the receiver that is configured to translate these uplinkradio frequency signals to a common 11 a~ ;ùn frequency. The master oscillator unit is slaved to the frequency of the uplink reference signal. Mixers are connected to the master oscillator and the receiver and are adapted to syn.,hlulluu~ly translate each of the received signals rl~4u~,.lcir,s such that they have a common carrier fre-20 quency subsequent to Ir~
A summing circuit is coupled to the mixers that is configured to adjust thephase relationship of the signals and sum them. The summing circuit is coupled to a power amplifier operating in a saturated mode that in turn feeds a bealllru~ g net-work. The ~ ~."r.."";.,g network is configured to form several overlapping beamswhich include all of the hlrOIIIIa~iull signal ",~l ~ from the plurality of infor-mation signals. Because the signals are ~yll11llulluui~, they are precisely phase-relat-ed, which results in controlled distortion in the saturating amplifier. Subsequent sep-aration of the multiple overlapping hlrullllaliuu signals may be achieved in accor-dance with known methods for separating CDMA signals.
It is therefore an advantage of the invention to provide an improved relay . .. ", ., -; ~ l ;.~.~ system. It is another advantage of the invention to provide a relay .., .", .; ~ I ;. ,., system that utilizes a single reference frequency signal to generate ~yll~Llun;~ i radio frequency signals and a relay transmitter that utilizes the same reference frequency signal to produce ~yll~,L.ull;~.,d downlink signals having a single 35 frequency that are phase adjusted, combined and amplified with amplifiers operating in a saturation mode to form an c ~ ,9 beam signal. Yet another advantage of the invention is to provide a relay communication system in which precisely phase related illfullll , signals are amplified with amplfflers operating in a saturated mode preserving the phase . . ,~I ,ip without the need for amplitude i,,~u,.. ..
Other aspects of this invention are as follows:
A communication system cc.",u,i~;"y.
signal generating means for generating a reference frequency signal and a plurality of code division multiple access modulated radio frequency signals sy. ,.1 ,.vni~ed therewith;
means for l,.."~", ~y the radio frequency and reference frequency signals;
a remote ,.~r~ ,~."illt, including receiving means for receiving the radio frequency and reference frequency signals, and means connected to the receiving means for reproducing the reference frequency signal;common frequency generating means responsive to the reproduced reference frequency signal for synchronously frequency-altering the radio frequency signals to generate a common frequency;
phase adjusting means coupled to the common frequency generating means adapted to receive the frequency-altered radio frequency signals for adjusting the phase of each of the frequency-altered radio frequency signals to have a ,u, ~d~:t~" "i"ecl phase . . ,;,l ,i~, with respect to the others;
bea",f~"",i"g means connected to the phase adjusting means and including at least one saturation mode amplifier for forming and ..~r~ ,:.", ~9 an c.~.la,u,ui"g beam signal comprised of the phase-adjusted, frequency-altered radio frequency signals.
A relay communications system co,,,u,;~;r,y.
reference signal generating means for generating a first reference signal:
data signal means coupled to the reference signal generating means for gener-ating a plurality of coded orthogonal binary phase modulated data signals in sy,,.,l,.un:s.,, with the first reference signal;
carrier signal generating means for generating a radio frequency carrier signal for each of the i,lfu,,,, ) signals, each of the radio frequency carrier signalshaving a different frequency derived from and syr,~,l,,u,,;~d with the first reference 3a signal and being modulated by one of the data signals;
transmitter means coupled to the carrier signal generaUng means for transmit-ting the modulated radio frequenCy signals;
a remotely located relay transmitter including receiver means for reoeiving the 5 modulated radio frequency signals, a slave oscillator coupled to the receiver means and adapted to reproduoe the referenoe frequency signal, mixer means coupled to the slave oscillator and to the reoeiver means for synchronously altering each of the reoeived modulated radio frequency signals to have a common carrier frequency, phase adjusting means coupled to the mixer means for prooessing the frequency altered signals and adjusting the phase of the signals to have a dete~ d phase " ' ~hip wHh respect to each other, and summing means coupled to the mixer means for combining the frequency altered radio frequency signals;
a limiter circuit coupled at its input to said summing means, and coupled at its15 output to a high power amplifier operating in a saturation mode for processing and amplifying the combined frequency altered radio frequency signals; and a bealllfullllill9 network coupled to the power amplifier adapted to form an c. Ia,uping radio frequency beam signal including the binary phase coded signals.
BRIEF DESCRIPTION OF THE DnA ..!~ 9 The various features and adv~"tàyes of the present invention may be more readily understood with reference to the following detailed description taken in con-junction with the accu"".~",,i.,g drawings, wherein like reference numerals designate like structural elements, and in which:
FIG. 1 is a diagram of a relay communication system in aoe,u~dall~,e with the principles of the present invention;
FIG. 2 is a chart showing the ..' ,~I,i,u of synchronously generated orthogonal binary phase modulated signals output by data signal mixers employed in the system of FIG. 1; and FIGS. 3a and 3b are vector diagrams useful in explaining alternative phase re-lationships of the i"f~,"" , signals in ,.;t,~";"" ' c.~ I~,u,ui,,9 beam signalsproduoed by the system of FIG. 1.
DETAILED DESCRIPTION
Referring to FIG. 1, there is shown a relay communications system 10 in ac-cordanoe with the principles of the present invention. The system 10 comprises a35 ground based signal generating circuit 12 and a remotely located ._t~anslll or 3b relay circuH 14. Typically, but not necoss .ily, the leb~ lll or relay circuit 14 is a satellite based circuit.
The ground based circuit 12 includes a master reference frequency oscillator 16 that is adapted to generate a single, fixed trequency clock or reference 5 frequency signal that is provided at its output 18. The reference frequency signal is coupled simultaneously to inputs of three data generating circuits 20, 22, and 24. The data generating circuits 20, 22, and 24 are each adapted to generate an input data signal in the form of binary coded data signals. The data generating drcuits 20, 22, 24 are well known in the art, the particular circuitry employed is dependent upon the particular application of the system 10. The binary coded data signals are typical binary I and 0, or +I, -1, inf~.".. ~ bits. It is significant that the data bit rate is derived from the reference frequency signal generated by the oscillator 16.
The binary coded data signals are coupled from the circuits 20, 22, 24 to re-spective ones of a first plurality of mixers 26, 28, and 30. Simultaneously, therefer-4 2~2Q2~
ence frequency signal provided by the oscillator 16 is coupled to a plurality of code sequence generating circuits 32, 34, and 36. The code sequence generating circuits 32, 34, and 36 are keyed or 5~ ..V..;~l by the reference frequency signal from the oscillator 16. Each of the code sequence generating circuits 32, 34, 36 is adapted to generate a different digital code in the forrn of a specific or variable bit sequence.
The code sequence signals are coupled to the mixers 26, 28, 30 respectively, which is configured to mix the code sequence signals with the data signals provided by the data signal generators 20, 22, 24 to generate a plurality of coded signals. Significant to the invention, the signals provided from the mixers 26, 28, 30 are onhogonal sig-nals. A typical sequence of onhogonal signals is shown in FIG. 2. Such signals ex-hibit the ~hold~,~G~ . A A = A; A-(-A) = -A; A-B = O, for A ~ B; and A- (A+B) =
A.
The reference frequency signal provided by the oscillator 16 is simultaneous-ly coupled to three radio frequency carrier generating circuits 38, 40, 42. Such radio frequency carrier generating circuits are well known in the art and generate radio fre-quency signals of desired frequency suitable for u, ~ ", of information. Signifi-cant to the invention, the three radio frequency carrier generating circuits 38, 40, 42 are each adapted to generate a radio frequency signal that is derived from combina-tions of sums and multiples of the reference frequency signal. The mixers 26, 28, 30 and the radio frequency carrier generating circuits 38, 40, 42 are respectively coupled to a second plurality of mixers 44, 46, 48. The coded data signals provided by the first plurality of mixers 26, 28, 30 are ~;.,,,,1l ~v ~ly coupled to the second plurality of mixers 44, 46, and 48 with the radio frequency carrier signals from the radio fre-quency carrier generating circuits 38, 40, 42. This achieves mr)l1n~ n of the radio frequency carrier signals with the coded data signals.
It should be recognized that the output signals from the second plurality of mixers 44, 46, 48 comprise a group of signals A, B, C as shown in FIG. 2 that are suitable for code division multiple access (CDMA) n d" ~. "~ " These three signals are ~ y coupled to a summing circuit 50 where they are combined and coupledthroughahighpoweramplifier52andanantenna54fornd"~",; ~;.", Typ-ically, the antenna 54 is a directional antenna that directs the combined signal to a re-ceiving antenna 56 of the IGlldl~ t~,~ or relay circuit 14.
The reference frequency signal is also ~ I,y transmitted with the CDMA signals. This transmitted reference frequency signal may be derived from the bit rate of the data signals generated by the data circuits 20, 22, 24, all of which are derived from the reference frequency signal. Alternatively, it may be obtained by 2~292~4 coupling the output signal from reference frequency oscillator 16 to the summing cir-cuit 50, as indicated by dashed line 57, where it is combined and transmitted with the CDMA signals.
The Ir,l ~ 1 11. . or relay circuit 14 includes a tracking reference frequency oscillator 58 connected to the receiving antenna 56. The tracking reference frequen-cy oscillator 58 includes circuitry for detecting the reference frequency signal from the data bit rate as discussed above, and crrcuitry for generating or duplicating the reference frequency signal.
The CDMA signals received at the receiving antenna 56 are coupled to and amplified in a low-noise stage (not shown) separated by filters (not shown), and ap-plied to three mixing circuits 60, 62, 64. The output from the tracking reference fre-quency oscillator 58 is coupled to the inputs of three local oscillators 66, 68, 70.
Each of the local oscillators 66, 68, 70 is adapted to generate a mixing signal derived from the reference frequency signal that is ~yll~,Llvll;~d therewith. The frequencies provided by each of the local oscillators 66, 68, 70 are further selected such that when mixed with the radio frequency carrier signals generated by the radio frequency carrier generating circuits 38, 40, 42, produce output signals from each of the three mixer circuits 60, 62, 64 that have a single frequency. That is, the output signals from the mixers 60, 62, 64 are at the same frequency and are in syn.,l.lu~
The output signals from the mixers 60, 62, 64 are ~imllltan~ollcly coupled to a phase adjusting circuit 72 where a precise phase I~I~Liull~ between the three sig-nals is f ~r~hli~h~1 One optimum ~ llg~,lll~lll for the phase adjusted signals is that the phase vectors of two of the signals are aligned while the third signal has a phase orthogonal to the first two. Such an ~., ,...g.. "~ is adapted to minimize the dynamic 25 range of the amplitudes of the signals.
The phase adjusting circuit 72 is coupled to a summing crrcuit 74, wherein the three phase adjusted signals are combined. Thee summing circuit 74 is coupled byway of a limiter circuit 76 to a high power amplifier 78. The high power amplifier 78 is then coupled to a bealllrvllllil~g network 80. The 1~ ru~ network 80 is a de-30 vice well known in the art, and typically includes a plurality of radiating elementsand wherein the relative phase of the output signals provided by individual elements of a l~.lll~ullllhlg array are precisely controlled to fomm a beam directed in a particu-lar direction or a group of drrections.
In uull~ lLiu~:il systems, both the phase and amplitude of the signals provided 35 to the l~llllrulluillg network 80 must be preserved to form the required overlapping signal beam. Further, due to the I~Uil ;illl~ that the output beam include up to 2~92~
three signals, the high-powered amplifiers 78 may have to carry signals for up to three beams. These signals are BPSK modulated with different ;'lr.~ n ..,. carried by each signal. Accordingly, the signals will have a different phase Id~lLiull~L;lJ over time. The direct and most obvious way to conserve both the amplitude of phase re-lationship is, as taught in the prior art, to oversize the amplifiers 78 and operate them in the quasi-linear operating mode. It is well known that linear operation of the am-plifiers 78 is wasteful of the power in the DC mode.
However, in accordance with the present invention, and with reference to the combining of two signals only, the relative phase of the radio frequency carrier sig-nals downlinked in the mixers 60, 62, for example, are adjusted so that the vectors of the signals are orthogonal. The composite signal provided by the summing circuit 74 has a constant envelope and is QPSK modulated. Accordingly, the amplifiers 78 are operated at saturation with maximum efficiency. The amplifiers 78 have twice therated power of cull~ Lio~la'i amplif ers which carry only one signal of one beam, and are also operated in the saturated mode.
When three signals are combined, there are eight combinations of phase .
states, each associated with different ~mpli~ c In accordance with the present in-vention, because of the limiter 76, phase i.5u. ~ iu.. is conserved while the ampli-tude information is lost. However, the precise ~ ul~ Liull of the signals enables 20 a desired phase relationship to be established between the three signals such that the amplitude information is not required.
In ~ ...c where multiple signals are amplified with a common saturat-ing amplifier 78, several phasing 1 . 1 l ;. " ,~1. ;1.,, shown by vectors A, B, C in FIGS . 3a and 3b, allow operation of the amplifier 78 with high efficiency. In FIG 3a, two sig-25 nals A, B are aligned, and signal C has its phase orthogonal to the two signals A, B.In FIG. 3b, the three signals A, B, C are adjusted to have a relative phase shift of 120 degrees with respect to each other. As a result of simulation studies, it has been found that when the three CUI~IIJU..~ are extracted from the output signal, the useful power from each of the signals is down about 6.1 dB from the total output power in-30 stead of an ideal 4.8 dB ~ullc~i~On~'iing to one-third of the total power. Accordingly, the amplifier 78 may be increased in power to about a 35 percent higher power rat-ing, rather than requiring three times the power rating of the amplifier 78 amplifying one beam. This is contrasted with significantly higher losses in efficiency for either the case of a linear amplifier, ûr in the case of a saturating amplifier with uncon-35 trollied phases among the signal set.
202S28~
For the CU Iv~ ; of the system designer, the reference frequency signal forthe coherent ~ ,s of the signals may be derived from the specific reference frcquency signal from the circuit 12, or derived from the envelope of the bit rate of one of the carriers. In either case, the system is configured so that all rl~4u.,l.ci~ are derived from a, ~h",.. 1~ of the bit rate.
From the above description of the present invention, the use of a single refer-ence frequency signal to generate the coded information signals and downlink thesignals, enables the use of high power amplifiers operating in a saturated mode. The amplifiers efficiently amplify three or more signals ~ l .. u~ ~ly while operating in 10 saturation mode without the need for preserving amplitude ;, r. " ~ in the signals.
This is possible because of the ~y~,Lluni~_liu~ of, or phase ~ iull~ between, the signals, and by the use of a single reference frequency signal to generate and frequen-cy alter the frequency signals.
Thus there has been described a new and improvcd relay ~ ion~
15 system that utilizes a saturated amplifier system to amplify and retransmit synchro-nously transmitted CDMA signals derived from a ground station. It is to be under-stood that the above-described ~ hl Nl i l l l. . . l is merely illustrative of some of the many specific rl l lho~ l; l l l~ . . l~ which represent a~ of the principles of the present invention. Clearly, numerous and other A. I A n~ can be readily devised 20 by those skilled in the art without departing from the scope of the invention.
RELAY COMMUNICATION SYSTEM
BACKGROUND
The present invention relates to radio relay llal~ l;a~;ull systems, and more particularly to a satellite relay IIAII~II' '~;IIII system that utilizes a saturated amplifier system to amplify and retransmit ayll~,hlulluualy transmitted CDMA signals derived from a ground station.
Satellite ~u,,,,,,,l,,i- A~ill.lC systems are now well known. In such systems, sig-nals are transmitted from a ground station to a satellite where they are received, am-plified, and l~;LIallallli~L~l to remotely located receivers. Power n~ncllmr~i~n, weight, and physical ~lim~-nci~mc of the satellite-borne circuitty are of critical importance.
A significant application of satellite .,-""", -;. ~I;onc systems is for mobile 0 ~,"" " "~ I ;onC In this Arpli(''l~i~')n, in addition to the critical parameters mentioned above, it is also essential to provide a means to address individual remote users. To this end, CDMA LIA..~.II;~;IIII~ provide a viable solution. This type of secure trans-mission may be effected utilizing orthogonal signals or signal groups which can be combined into overlapping beam trAncmicci~nc The signals are separable by reason15 of the ullald~tcliaLics of the orthogonal signals.
In conventional applications, a plurality of orthogonal signals are transmitted to a satellite relay system, where they are combined into the u.~,.lalJ,u;llg beam signal using linear amplifiers. While it is well known that linear amplifiers are not the most efficient form of amplifier with respect to power . particularly in digital 20 tlallalll;aa;ull A~ , the need to preserve both phase and amplitude information of the individual CDMA signals has typically required their use.
2 202~2g4 SUMMARY OF THE INVENTION
In order to overcome the limitations of .,wl~,..(iul.dl systems addressed above, the present invention provides a relay n~ TIiCc;r)n or ~ system in which the relay L~ .ll of CDMA signals is effected utilizing amplifiers op-erating in a saturation mode. The system is comprised of a ground-based signal gen-erating circuit which includes circuitry which generates a reference frequency signal, a plurality of orthogonal coded binary phase modulated information signals, and a transmitter circuit which generates and transmits a radio frequency signal for each of the h.rull..alioll signals. Each of the radio frequency signals are at a different fre-lû quency and each signal is modulated by one of the inffmnotirln signals. The informa-tion signals, radio frequency signals, and bit rates of the information signals are based upon the frequency of the reference signal.
A remotely located relay transmitter, typically a satellite relay, includes a re-ceiver which is adapted to receive the modulated radio frequency signals and a mas-15 ter oscillator unit connected to the receiver that is configured to translate these uplinkradio frequency signals to a common 11 a~ ;ùn frequency. The master oscillator unit is slaved to the frequency of the uplink reference signal. Mixers are connected to the master oscillator and the receiver and are adapted to syn.,hlulluu~ly translate each of the received signals rl~4u~,.lcir,s such that they have a common carrier fre-20 quency subsequent to Ir~
A summing circuit is coupled to the mixers that is configured to adjust thephase relationship of the signals and sum them. The summing circuit is coupled to a power amplifier operating in a saturated mode that in turn feeds a bealllru~ g net-work. The ~ ~."r.."";.,g network is configured to form several overlapping beamswhich include all of the hlrOIIIIa~iull signal ",~l ~ from the plurality of infor-mation signals. Because the signals are ~yll11llulluui~, they are precisely phase-relat-ed, which results in controlled distortion in the saturating amplifier. Subsequent sep-aration of the multiple overlapping hlrullllaliuu signals may be achieved in accor-dance with known methods for separating CDMA signals.
It is therefore an advantage of the invention to provide an improved relay . .. ", ., -; ~ l ;.~.~ system. It is another advantage of the invention to provide a relay .., .", .; ~ I ;. ,., system that utilizes a single reference frequency signal to generate ~yll~Llun;~ i radio frequency signals and a relay transmitter that utilizes the same reference frequency signal to produce ~yll~,L.ull;~.,d downlink signals having a single 35 frequency that are phase adjusted, combined and amplified with amplifiers operating in a saturation mode to form an c ~ ,9 beam signal. Yet another advantage of the invention is to provide a relay communication system in which precisely phase related illfullll , signals are amplified with amplfflers operating in a saturated mode preserving the phase . . ,~I ,ip without the need for amplitude i,,~u,.. ..
Other aspects of this invention are as follows:
A communication system cc.",u,i~;"y.
signal generating means for generating a reference frequency signal and a plurality of code division multiple access modulated radio frequency signals sy. ,.1 ,.vni~ed therewith;
means for l,.."~", ~y the radio frequency and reference frequency signals;
a remote ,.~r~ ,~."illt, including receiving means for receiving the radio frequency and reference frequency signals, and means connected to the receiving means for reproducing the reference frequency signal;common frequency generating means responsive to the reproduced reference frequency signal for synchronously frequency-altering the radio frequency signals to generate a common frequency;
phase adjusting means coupled to the common frequency generating means adapted to receive the frequency-altered radio frequency signals for adjusting the phase of each of the frequency-altered radio frequency signals to have a ,u, ~d~:t~" "i"ecl phase . . ,;,l ,i~, with respect to the others;
bea",f~"",i"g means connected to the phase adjusting means and including at least one saturation mode amplifier for forming and ..~r~ ,:.", ~9 an c.~.la,u,ui"g beam signal comprised of the phase-adjusted, frequency-altered radio frequency signals.
A relay communications system co,,,u,;~;r,y.
reference signal generating means for generating a first reference signal:
data signal means coupled to the reference signal generating means for gener-ating a plurality of coded orthogonal binary phase modulated data signals in sy,,.,l,.un:s.,, with the first reference signal;
carrier signal generating means for generating a radio frequency carrier signal for each of the i,lfu,,,, ) signals, each of the radio frequency carrier signalshaving a different frequency derived from and syr,~,l,,u,,;~d with the first reference 3a signal and being modulated by one of the data signals;
transmitter means coupled to the carrier signal generaUng means for transmit-ting the modulated radio frequenCy signals;
a remotely located relay transmitter including receiver means for reoeiving the 5 modulated radio frequency signals, a slave oscillator coupled to the receiver means and adapted to reproduoe the referenoe frequency signal, mixer means coupled to the slave oscillator and to the reoeiver means for synchronously altering each of the reoeived modulated radio frequency signals to have a common carrier frequency, phase adjusting means coupled to the mixer means for prooessing the frequency altered signals and adjusting the phase of the signals to have a dete~ d phase " ' ~hip wHh respect to each other, and summing means coupled to the mixer means for combining the frequency altered radio frequency signals;
a limiter circuit coupled at its input to said summing means, and coupled at its15 output to a high power amplifier operating in a saturation mode for processing and amplifying the combined frequency altered radio frequency signals; and a bealllfullllill9 network coupled to the power amplifier adapted to form an c. Ia,uping radio frequency beam signal including the binary phase coded signals.
BRIEF DESCRIPTION OF THE DnA ..!~ 9 The various features and adv~"tàyes of the present invention may be more readily understood with reference to the following detailed description taken in con-junction with the accu"".~",,i.,g drawings, wherein like reference numerals designate like structural elements, and in which:
FIG. 1 is a diagram of a relay communication system in aoe,u~dall~,e with the principles of the present invention;
FIG. 2 is a chart showing the ..' ,~I,i,u of synchronously generated orthogonal binary phase modulated signals output by data signal mixers employed in the system of FIG. 1; and FIGS. 3a and 3b are vector diagrams useful in explaining alternative phase re-lationships of the i"f~,"" , signals in ,.;t,~";"" ' c.~ I~,u,ui,,9 beam signalsproduoed by the system of FIG. 1.
DETAILED DESCRIPTION
Referring to FIG. 1, there is shown a relay communications system 10 in ac-cordanoe with the principles of the present invention. The system 10 comprises a35 ground based signal generating circuit 12 and a remotely located ._t~anslll or 3b relay circuH 14. Typically, but not necoss .ily, the leb~ lll or relay circuit 14 is a satellite based circuit.
The ground based circuit 12 includes a master reference frequency oscillator 16 that is adapted to generate a single, fixed trequency clock or reference 5 frequency signal that is provided at its output 18. The reference frequency signal is coupled simultaneously to inputs of three data generating circuits 20, 22, and 24. The data generating circuits 20, 22, and 24 are each adapted to generate an input data signal in the form of binary coded data signals. The data generating drcuits 20, 22, 24 are well known in the art, the particular circuitry employed is dependent upon the particular application of the system 10. The binary coded data signals are typical binary I and 0, or +I, -1, inf~.".. ~ bits. It is significant that the data bit rate is derived from the reference frequency signal generated by the oscillator 16.
The binary coded data signals are coupled from the circuits 20, 22, 24 to re-spective ones of a first plurality of mixers 26, 28, and 30. Simultaneously, therefer-4 2~2Q2~
ence frequency signal provided by the oscillator 16 is coupled to a plurality of code sequence generating circuits 32, 34, and 36. The code sequence generating circuits 32, 34, and 36 are keyed or 5~ ..V..;~l by the reference frequency signal from the oscillator 16. Each of the code sequence generating circuits 32, 34, 36 is adapted to generate a different digital code in the forrn of a specific or variable bit sequence.
The code sequence signals are coupled to the mixers 26, 28, 30 respectively, which is configured to mix the code sequence signals with the data signals provided by the data signal generators 20, 22, 24 to generate a plurality of coded signals. Significant to the invention, the signals provided from the mixers 26, 28, 30 are onhogonal sig-nals. A typical sequence of onhogonal signals is shown in FIG. 2. Such signals ex-hibit the ~hold~,~G~ . A A = A; A-(-A) = -A; A-B = O, for A ~ B; and A- (A+B) =
A.
The reference frequency signal provided by the oscillator 16 is simultaneous-ly coupled to three radio frequency carrier generating circuits 38, 40, 42. Such radio frequency carrier generating circuits are well known in the art and generate radio fre-quency signals of desired frequency suitable for u, ~ ", of information. Signifi-cant to the invention, the three radio frequency carrier generating circuits 38, 40, 42 are each adapted to generate a radio frequency signal that is derived from combina-tions of sums and multiples of the reference frequency signal. The mixers 26, 28, 30 and the radio frequency carrier generating circuits 38, 40, 42 are respectively coupled to a second plurality of mixers 44, 46, 48. The coded data signals provided by the first plurality of mixers 26, 28, 30 are ~;.,,,,1l ~v ~ly coupled to the second plurality of mixers 44, 46, and 48 with the radio frequency carrier signals from the radio fre-quency carrier generating circuits 38, 40, 42. This achieves mr)l1n~ n of the radio frequency carrier signals with the coded data signals.
It should be recognized that the output signals from the second plurality of mixers 44, 46, 48 comprise a group of signals A, B, C as shown in FIG. 2 that are suitable for code division multiple access (CDMA) n d" ~. "~ " These three signals are ~ y coupled to a summing circuit 50 where they are combined and coupledthroughahighpoweramplifier52andanantenna54fornd"~",; ~;.", Typ-ically, the antenna 54 is a directional antenna that directs the combined signal to a re-ceiving antenna 56 of the IGlldl~ t~,~ or relay circuit 14.
The reference frequency signal is also ~ I,y transmitted with the CDMA signals. This transmitted reference frequency signal may be derived from the bit rate of the data signals generated by the data circuits 20, 22, 24, all of which are derived from the reference frequency signal. Alternatively, it may be obtained by 2~292~4 coupling the output signal from reference frequency oscillator 16 to the summing cir-cuit 50, as indicated by dashed line 57, where it is combined and transmitted with the CDMA signals.
The Ir,l ~ 1 11. . or relay circuit 14 includes a tracking reference frequency oscillator 58 connected to the receiving antenna 56. The tracking reference frequen-cy oscillator 58 includes circuitry for detecting the reference frequency signal from the data bit rate as discussed above, and crrcuitry for generating or duplicating the reference frequency signal.
The CDMA signals received at the receiving antenna 56 are coupled to and amplified in a low-noise stage (not shown) separated by filters (not shown), and ap-plied to three mixing circuits 60, 62, 64. The output from the tracking reference fre-quency oscillator 58 is coupled to the inputs of three local oscillators 66, 68, 70.
Each of the local oscillators 66, 68, 70 is adapted to generate a mixing signal derived from the reference frequency signal that is ~yll~,Llvll;~d therewith. The frequencies provided by each of the local oscillators 66, 68, 70 are further selected such that when mixed with the radio frequency carrier signals generated by the radio frequency carrier generating circuits 38, 40, 42, produce output signals from each of the three mixer circuits 60, 62, 64 that have a single frequency. That is, the output signals from the mixers 60, 62, 64 are at the same frequency and are in syn.,l.lu~
The output signals from the mixers 60, 62, 64 are ~imllltan~ollcly coupled to a phase adjusting circuit 72 where a precise phase I~I~Liull~ between the three sig-nals is f ~r~hli~h~1 One optimum ~ llg~,lll~lll for the phase adjusted signals is that the phase vectors of two of the signals are aligned while the third signal has a phase orthogonal to the first two. Such an ~., ,...g.. "~ is adapted to minimize the dynamic 25 range of the amplitudes of the signals.
The phase adjusting circuit 72 is coupled to a summing crrcuit 74, wherein the three phase adjusted signals are combined. Thee summing circuit 74 is coupled byway of a limiter circuit 76 to a high power amplifier 78. The high power amplifier 78 is then coupled to a bealllrvllllil~g network 80. The 1~ ru~ network 80 is a de-30 vice well known in the art, and typically includes a plurality of radiating elementsand wherein the relative phase of the output signals provided by individual elements of a l~.lll~ullllhlg array are precisely controlled to fomm a beam directed in a particu-lar direction or a group of drrections.
In uull~ lLiu~:il systems, both the phase and amplitude of the signals provided 35 to the l~llllrulluillg network 80 must be preserved to form the required overlapping signal beam. Further, due to the I~Uil ;illl~ that the output beam include up to 2~92~
three signals, the high-powered amplifiers 78 may have to carry signals for up to three beams. These signals are BPSK modulated with different ;'lr.~ n ..,. carried by each signal. Accordingly, the signals will have a different phase Id~lLiull~L;lJ over time. The direct and most obvious way to conserve both the amplitude of phase re-lationship is, as taught in the prior art, to oversize the amplifiers 78 and operate them in the quasi-linear operating mode. It is well known that linear operation of the am-plifiers 78 is wasteful of the power in the DC mode.
However, in accordance with the present invention, and with reference to the combining of two signals only, the relative phase of the radio frequency carrier sig-nals downlinked in the mixers 60, 62, for example, are adjusted so that the vectors of the signals are orthogonal. The composite signal provided by the summing circuit 74 has a constant envelope and is QPSK modulated. Accordingly, the amplifiers 78 are operated at saturation with maximum efficiency. The amplifiers 78 have twice therated power of cull~ Lio~la'i amplif ers which carry only one signal of one beam, and are also operated in the saturated mode.
When three signals are combined, there are eight combinations of phase .
states, each associated with different ~mpli~ c In accordance with the present in-vention, because of the limiter 76, phase i.5u. ~ iu.. is conserved while the ampli-tude information is lost. However, the precise ~ ul~ Liull of the signals enables 20 a desired phase relationship to be established between the three signals such that the amplitude information is not required.
In ~ ...c where multiple signals are amplified with a common saturat-ing amplifier 78, several phasing 1 . 1 l ;. " ,~1. ;1.,, shown by vectors A, B, C in FIGS . 3a and 3b, allow operation of the amplifier 78 with high efficiency. In FIG 3a, two sig-25 nals A, B are aligned, and signal C has its phase orthogonal to the two signals A, B.In FIG. 3b, the three signals A, B, C are adjusted to have a relative phase shift of 120 degrees with respect to each other. As a result of simulation studies, it has been found that when the three CUI~IIJU..~ are extracted from the output signal, the useful power from each of the signals is down about 6.1 dB from the total output power in-30 stead of an ideal 4.8 dB ~ullc~i~On~'iing to one-third of the total power. Accordingly, the amplifier 78 may be increased in power to about a 35 percent higher power rat-ing, rather than requiring three times the power rating of the amplifier 78 amplifying one beam. This is contrasted with significantly higher losses in efficiency for either the case of a linear amplifier, ûr in the case of a saturating amplifier with uncon-35 trollied phases among the signal set.
202S28~
For the CU Iv~ ; of the system designer, the reference frequency signal forthe coherent ~ ,s of the signals may be derived from the specific reference frcquency signal from the circuit 12, or derived from the envelope of the bit rate of one of the carriers. In either case, the system is configured so that all rl~4u.,l.ci~ are derived from a, ~h",.. 1~ of the bit rate.
From the above description of the present invention, the use of a single refer-ence frequency signal to generate the coded information signals and downlink thesignals, enables the use of high power amplifiers operating in a saturated mode. The amplifiers efficiently amplify three or more signals ~ l .. u~ ~ly while operating in 10 saturation mode without the need for preserving amplitude ;, r. " ~ in the signals.
This is possible because of the ~y~,Lluni~_liu~ of, or phase ~ iull~ between, the signals, and by the use of a single reference frequency signal to generate and frequen-cy alter the frequency signals.
Thus there has been described a new and improvcd relay ~ ion~
15 system that utilizes a saturated amplifier system to amplify and retransmit synchro-nously transmitted CDMA signals derived from a ground station. It is to be under-stood that the above-described ~ hl Nl i l l l. . . l is merely illustrative of some of the many specific rl l lho~ l; l l l~ . . l~ which represent a~ of the principles of the present invention. Clearly, numerous and other A. I A n~ can be readily devised 20 by those skilled in the art without departing from the scope of the invention.
Claims (18)
1. A communication system comprising:
signal generating means for generating a reference frequency signal and a plurality of code division multiple access modulated radio frequency signals synchronized therewith;
means for transmitting the radio frequency and reference frequency signals;
a remote retransmitter including receiving means for receiving the transmitted radio frequency and reference frequency signals, and means connected to the receiving means for reproducing the reference frequency signal;common frequency generating means responsive to the reproduced reference frequency signal for synchronously frequency-altering the radio frequency signals to generate a common frequency;
phase adjusting means coupled to the common frequency generating means adapted to receive the frequency-altered radio frequency signals for adjusting the phase of each of the frequency-altered radio frequency signals to have a predetermined phase relationship with respect to the others;
beamforming means connected to the phase adjusting means and including at least one saturation mode amplifier for forming and retransmitting an overlapping beam signal comprised of the phase-adjusted, frequency-altered radiofrequency signals.
signal generating means for generating a reference frequency signal and a plurality of code division multiple access modulated radio frequency signals synchronized therewith;
means for transmitting the radio frequency and reference frequency signals;
a remote retransmitter including receiving means for receiving the transmitted radio frequency and reference frequency signals, and means connected to the receiving means for reproducing the reference frequency signal;common frequency generating means responsive to the reproduced reference frequency signal for synchronously frequency-altering the radio frequency signals to generate a common frequency;
phase adjusting means coupled to the common frequency generating means adapted to receive the frequency-altered radio frequency signals for adjusting the phase of each of the frequency-altered radio frequency signals to have a predetermined phase relationship with respect to the others;
beamforming means connected to the phase adjusting means and including at least one saturation mode amplifier for forming and retransmitting an overlapping beam signal comprised of the phase-adjusted, frequency-altered radiofrequency signals.
2. The system of Claim 1 wherein the reference frequency signal generating means comprises a fixed frequency oscillator.
3. The system of Claim 2 wherein the signal generating means includes a code sequence signal generating circuit for generating code sequence signals, aninformation signal generating circuit for generating a plurality of orthogonal information signals, and means for combining code sequence signals and orthogonal information signals to produce coded sequence information for each ofthe plurality of radio frequency signals.
4. The system of Claim 3 wherein the frequency of the reference frequency signal comprises the bit rate frequency.
5. The system of Claim 4 wherein the means for reproducing the reference frequency signal comprises a tracking oscillator responsive to a bit rate envelope of the information signal, which bit rate envelope is employed to reproduce the reference frequency signal.
6. The system of Claim 1 wherein the phase adjusting means further comprises summing circuit means for summing the frequency-altered phase-adjusted radio frequency signals; and signal limiter means connected between the summing means and the beamforming means for limiting the amplitude of signals provided to the saturation mode amplifier.
7. The system of Claim 6 which comprises two radio frequency signals, the phase adjusting means adjusting the relative phases of the two signals to be orthogonal.
8. The system of Claim 6 which comprises three radio frequency signals, the phase adjusting means adjusting the relative phase of two of the signals to be in alignment with each other and adjusting the third of the signals to be orthogonal thereto.
9. The system of Claim 6 which comprises three radio frequency signals, the phase adjusting means adjusting the phase of the three signals to be displaced 120 degrees relative to each other.
10. A relay communications system comprising:
reference signal generating means for generating a first reference signal;
data signal means coupled to the reference signal generating means for generating a plurality of coded orthogonal binary phase modulated data signals in synchronism with the first reference signal;
carrier signal generating means for generating a radio frequency carrier signal for each of the information signals, each of the radio frequency carrier signals having a different frequency derived from and synchronized with the first reference signal and being modulated by one of the data signals;
transmitter means coupled to the carrier signal generating means for transmitting the modulated radio frequency signals;
a remotely located relay transmitter including receiver means for receiving the modulated radio frequency signals, a slave oscillator coupled to the receiver means and adapted to reproduce the reference frequency signal, mixer means coupled to the slave oscillator and to the receiver means for synchronously altering each of the received modulated radio frequency signals to have a common carrier frequency, phase adjusting means coupled to the mixer means for processing the frequency altered signals and adjusting the phase of the signals to have a predetermined phase relationship with respect to each other, and summing means coupled to the mixer means for combining the frequency altered radio frequency signals;
a limiter circuit coupled at its input to said summing means, and coupled at its output to a high power amplifier operating in a saturation mode for processing and amplifying the combined frequency altered radio frequency signals; and a beamforming network coupled to the power amplifier adapted to form an overlapping radio frequency beam signal including the binary phase coded signals.
reference signal generating means for generating a first reference signal;
data signal means coupled to the reference signal generating means for generating a plurality of coded orthogonal binary phase modulated data signals in synchronism with the first reference signal;
carrier signal generating means for generating a radio frequency carrier signal for each of the information signals, each of the radio frequency carrier signals having a different frequency derived from and synchronized with the first reference signal and being modulated by one of the data signals;
transmitter means coupled to the carrier signal generating means for transmitting the modulated radio frequency signals;
a remotely located relay transmitter including receiver means for receiving the modulated radio frequency signals, a slave oscillator coupled to the receiver means and adapted to reproduce the reference frequency signal, mixer means coupled to the slave oscillator and to the receiver means for synchronously altering each of the received modulated radio frequency signals to have a common carrier frequency, phase adjusting means coupled to the mixer means for processing the frequency altered signals and adjusting the phase of the signals to have a predetermined phase relationship with respect to each other, and summing means coupled to the mixer means for combining the frequency altered radio frequency signals;
a limiter circuit coupled at its input to said summing means, and coupled at its output to a high power amplifier operating in a saturation mode for processing and amplifying the combined frequency altered radio frequency signals; and a beamforming network coupled to the power amplifier adapted to form an overlapping radio frequency beam signal including the binary phase coded signals.
11. The system of Claim 10 wherein the binary phased coded signals are CDMA coded signals.
12. The system of Claim 11 wherein the CDMA signals comprise orthogonal signals.
13. The system of Claim 10 wherein the slave oscillator is adapted to derive its frequency from the bit rate of one of the data signals.
14. The system of Claim to wherein the slave oscillator is adapted to derive its frequency from the first reference frequency signal.
15. The system of Claim 10 wherein the remotely located relay transmitter is a satellite-based relay transmitter.
16. The system of Claim 10 which comprises two radio frequency carrier signals, and wherein the slave oscillator and mixer means is adapted to alter the phase of the two radio frequency carrier signals to be orthogonal to each other.
17. The system of Claim 10 wherein the frequency altered radio frequency signals include three data signals that have a relative phase of 120 degrees with respect to each other.
18. The system of Claim 10 wherein the data signals include three data signals, the phase of the data signals in the radio frequencycarrier signals include two information signals in phase alignment and one data signal having a phase orthogonal to the first two.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/444,499 US5038341A (en) | 1989-12-01 | 1989-12-01 | Relay communication system |
| US444,499 | 1989-12-01 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2029284A1 CA2029284A1 (en) | 1991-06-02 |
| CA2029284C true CA2029284C (en) | 1998-07-14 |
Family
ID=23765168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002029284A Expired - Fee Related CA2029284C (en) | 1989-12-01 | 1990-11-05 | Relay communication system |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5038341A (en) |
| EP (1) | EP0430587B1 (en) |
| JP (1) | JPH0799824B2 (en) |
| CA (1) | CA2029284C (en) |
| DE (1) | DE69023206T2 (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI86124C (en) * | 1990-11-15 | 1992-07-10 | Telenokia Oy | RADIOSAENDARMOTTAGARSYSTEM. |
| CA2105710A1 (en) * | 1992-11-12 | 1994-05-13 | Raymond Joseph Leopold | Network of hierarchical communication systems and method therefor |
| US5394120A (en) * | 1993-04-13 | 1995-02-28 | Japan Radio Co., Ltd. | Device for testing an amplifier |
| US5625871A (en) * | 1994-09-30 | 1997-04-29 | Lucent Technologies Inc. | Cellular communications system with multicarrier signal processing |
| US5570350A (en) * | 1994-09-30 | 1996-10-29 | Lucent Technologies Inc. | CDMA cellular communications with multicarrier signal processing |
| JP2718398B2 (en) * | 1995-06-30 | 1998-02-25 | 日本電気株式会社 | CDMA base station transmitter |
| FR2737014B1 (en) * | 1995-07-17 | 1997-10-10 | Centre Nat Etd Spatiales | SYSTEM AND METHOD FOR MEASURING THE TOTAL ELECTRONIC CONTENT OF THE IONOSPHERE |
| US5745839A (en) * | 1995-09-01 | 1998-04-28 | Cd Radio, Inc. | Satellite multiple access system with distortion cancellation and compression compensation |
| DE19603443C1 (en) * | 1996-01-31 | 1997-07-10 | Siemens Ag | Code-modulated transmission method and a transmission system operating according to this transmission method |
| US6223019B1 (en) | 1996-03-14 | 2001-04-24 | Sirius Satellite Radio Inc. | Efficient high latitude service area satellite mobile broadcasting systems |
| DE19633519A1 (en) * | 1996-08-09 | 1998-02-12 | Sylke Dipl Ing Bechstein | Spread=spectrum signal transmission method |
| US6826169B1 (en) | 1996-12-20 | 2004-11-30 | Fujitsu Limited | Code multiplexing transmitting apparatus |
| JP3311951B2 (en) | 1996-12-20 | 2002-08-05 | 富士通株式会社 | Code multiplex transmitter |
| US5903549A (en) * | 1997-02-21 | 1999-05-11 | Hughes Electronics Corporation | Ground based beam forming utilizing synchronized code division multiplexing |
| US6023616A (en) * | 1998-03-10 | 2000-02-08 | Cd Radio Inc. | Satellite broadcast receiver system |
| US6072785A (en) * | 1997-03-04 | 2000-06-06 | At&T Corp | Differential PSK signalling in CDMA networks |
| US6072770A (en) * | 1997-03-04 | 2000-06-06 | At&T Corporation | Method and system providing unified DPSK-PSK signalling for CDMA-based satellite communications |
| US6072769A (en) * | 1997-03-04 | 2000-06-06 | At&T Corporation | Method for multitone division multiple access communications |
| US6148024A (en) * | 1997-03-04 | 2000-11-14 | At&T Corporation | FFT-based multitone DPSK modem |
| US6101168A (en) * | 1997-11-13 | 2000-08-08 | Qualcomm Inc. | Method and apparatus for time efficient retransmission using symbol accumulation |
| US20050223306A1 (en) * | 2004-03-30 | 2005-10-06 | Franca-Neto Luiz M | Communications apparatus, systems, and methods |
| US8165171B2 (en) * | 2009-03-19 | 2012-04-24 | Raytheon Bbn Technologies Corp. | Methods and systems for distributed synchronization |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4232266A (en) * | 1978-09-05 | 1980-11-04 | Bell Telephone Laboratories, Incorporated | Technique for sharing a plurality of transponders among a same or larger number of channels |
| US4494228A (en) * | 1982-08-12 | 1985-01-15 | The United States Of America As Represented By The Secretary Of The Army | Orthogonal code division multiple access communications systems |
| DE3447107A1 (en) * | 1984-12-22 | 1986-06-26 | Philips Patentverwaltung Gmbh, 2000 Hamburg | PROCESS FOR TRANSMITTING MESSAGES IN A DIGITAL RADIO TRANSMISSION SYSTEM |
| US4901307A (en) * | 1986-10-17 | 1990-02-13 | Qualcomm, Inc. | Spread spectrum multiple access communication system using satellite or terrestrial repeaters |
-
1989
- 1989-12-01 US US07/444,499 patent/US5038341A/en not_active Expired - Lifetime
-
1990
- 1990-11-05 CA CA002029284A patent/CA2029284C/en not_active Expired - Fee Related
- 1990-11-22 EP EP90312728A patent/EP0430587B1/en not_active Expired - Lifetime
- 1990-11-22 DE DE69023206T patent/DE69023206T2/en not_active Expired - Fee Related
- 1990-11-28 JP JP2328774A patent/JPH0799824B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE69023206T2 (en) | 1996-04-18 |
| JPH0799824B2 (en) | 1995-10-25 |
| CA2029284A1 (en) | 1991-06-02 |
| JPH03190330A (en) | 1991-08-20 |
| EP0430587A2 (en) | 1991-06-05 |
| US5038341A (en) | 1991-08-06 |
| EP0430587A3 (en) | 1992-04-08 |
| EP0430587B1 (en) | 1995-10-25 |
| DE69023206D1 (en) | 1995-11-30 |
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