CA1215745A - Transmitter power control circuit - Google Patents

Transmitter power control circuit

Info

Publication number
CA1215745A
CA1215745A CA000441679A CA441679A CA1215745A CA 1215745 A CA1215745 A CA 1215745A CA 000441679 A CA000441679 A CA 000441679A CA 441679 A CA441679 A CA 441679A CA 1215745 A CA1215745 A CA 1215745A
Authority
CA
Canada
Prior art keywords
control signal
amplitude
transceiver
frequency
magnitude
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
Application number
CA000441679A
Other languages
French (fr)
Inventor
Adolf J. Giger
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Western Electric Co Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Western Electric Co Inc filed Critical Western Electric Co Inc
Application granted granted Critical
Publication of CA1215745A publication Critical patent/CA1215745A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W52/00Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04TPC
    • H04W52/52TPC using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

TRANSMITTER POWER CONTROL CIRCUIT
Abstract In a radio communication system, an adaptive transmitter power control system is described wherein the signal level at each receiver is monitored and a control signal, which is a function of the signal level, is transmitted back to the transmitting station to adjust the transmitter output power, as required. By transmitting the lowest power level consistent with system objectives, the repeater circuits operate in a highly linear mode, and cochannel interference is significantly reduced.

Description

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Transmitter_power control circuit Tech_ical Field This invention relates to radio communication systems and, more particularly, ~o arrangements for controlling the transmitter output power.
Background of the Invention The output power of a transmitter in a radio communic~tion system is based upon the transmission objectives set forth for the system. These are derived from grade-of-service analyses of the results of subjective and objective tests. In digital radio systems, for instance, the problem is that in order to meet system objectives under adverse propogation conditions the power level required is considerably greater than the level needed during more normal conditions. In particular, it is only during the short periods of deep fading that high transmitter output p~wer is required~ This characteristic is peculiar ~o digital radio systems which can satisfac-torily op2rate (at low error rates) very close to theix threshold of operation where the erxor rate exceeds a certain limit. In contrastt analog FM and AM radio systems require high transmitter power at all times because of the cumulative nature of its thermal noise contribution.

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~. , It is, accordingly, the broad objective o~ the invention to control the transmitter output power in digital radio communication systems.
Summary of the Invention In accordance with the present invention, the received signal power of the digital signal is monitored at the recelver and a control signal is transmitted back to the transmitter to adjust the transmitter output power, as required.
The advantages of transmitting at reduced power levels are many in digital radio systems. First, the lower transmitted powers under normal propagating conditions allow operation of the repeater circuits in a highly linear mode~ ~his is very important for the high level (i.e, 64QAM) modulation schemes used today or contemplated in the future. Such modulation methods contain a high degree of amplitude modulation which could be adversely affected by nonlinear repeater circuits. The two degradations of importance are eye degradation and spectrum spreading.
The former affects bit error ra~e. The latter affects interference into adjacent channels. During the rare events of very deep fads the transmitter power will be maximum and the nonlinear distortion will increase.
Fortunately at this ex~reme point, where the error rate reaches a very high value (10 3)~ the nonlinear distortions are considerably less destructive.
A second benefit of transmitter power control is that cochannel and adjacent channel interferences are significantly reduced. This will permit the coexistence of digital and analog systems sharing the same frequency band without resorting to such measures as space diversity antenna systems.
A third advantage of transmitter power control is the possibility of operating digital radio systems without using regeneration in every repeater station. The low J ~

nonlinear distortions, which approach single sideband conditions, may make regeneration only necessary in radio switching stations, a substantial operational benefit.
Finally, there may be the simple power saving that results from operating at lower power levelsO
In accordance with an aspect of the invention there is provided a radio transceiver comprising a receiver section capable of receiving an information signal destined for an end user in a predetermined channel from a remote, immediately preceding, transmitter of a radio system, the receiver section comprising amplifier means including an automatic gain control (AGC) arrangement capable of gen-erating a d-c control signal which has a magnitude that (a) is a function of the ampli~ude of the received infor-mation signal at any instant of time and (b) can varybetween a predetermined range of amplitude levels;
means responsive to the d-c control signal from the AGC
arrangement of the amplifier means in the receiver section for generating an a-c control signal whose frequency is (a) a function of the magnitude of the d-c control signal at any instant of time, and (b) lies within a predetermined band of frequencies within a range of a loop bandwidth of the AGC arrangement of the receiver section; and a trans-mitter section capable of transmitting an information signal destined for a remote end user in a predetermined transmission channel to a remote, next sequential, receiver of the radio system associated with said remote trans-mitter, the transmitter section comprising amplifier means including an AGC arrangement which is responsive to the a-c control signal from the generating means for amplitude modulating (AM) the amplitude of the information signal transmitted in the predetermined transmission channel to the remote, next sequen~ial, receiver in accordance with the frequensy variations of said a-c control signal from the generating means.

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In accordance with another aspect of the invention there is provided a method of providing adaptive trans-mitted power control for transmissions in a radio system comprising a first transceiver and a second remote, next sequential, transceiver along a radio route, the method comprising the steps of (a~ receiving, at the second remote, next sequential, transceiver, an information signal transmitted by the first transceiver in a predeter-mined channel and destined for an end user at the second remote, next se~uential, transceiver; (b) generating a d-c control signal at an automatic gain control ~AGC) arrange-ment in a receiver section of the second, next sequential, transceiver which has a magnitude that (l) is a function of the amplitude of the information signal received in step (a), and (2) can vary between a predetermined range of levels; (c) generating from the d-c control signal from step (b), and a-c control signal whose frequency (l~ is a function of the magnitude of the d-c control signal at any instant of time, and (2) lies within a predetermined band of frequencies which is within a range of a loop bandwidth of an AGC arrangement in a receiver section of the first transceiver; (d) amplitude modulating, with a transmitter AGC arrangement and associated amplifier the amplitude of an information signal transmitted by the second, next sequential, transceiver to the first transceiver in accordance with frequency variations of the a~c control signal generated in step (c); and (e) detecting, with a receiver AGC arrangement and associated amplifier at the first transceiver, the amplitude modulations in the amplitude of the in~ormation signal transmitted in step (d) for generating therefrom a control signal which is a function of said amplitude modulations and is capable of adaptively modifying the amplitude of a transmission from the first transceiver to the second, next sequential, transceiver.

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Brief_Descri~tion of the Drawin~
FIG~ l shows a radio system in accordance wi~h the present invention and FIG. 2 shows an illustrative power control characteristic.
Detailed Description Referring to the drawings, FIG. l shows the relevant components of a two-way radio communication system. Included are portions of a transmitter 10 and receiver ll of a west-to-east communication link and portions of a transmitter 12 and receiver 13 of an east-to-west link. Each of the transmitter portions lO, 12 shown comprises an i.f. amplifier with AGC 14, 17; a frequency up-converter 15, 18; an rOf. power amplifier 16 19; and antennae 35, 36. Receiver portions 11, 13 shown comprise antennae 37, 38; low noise r.f. amplifiers 20, 24; frequency down-converters 21, 25; and i.f. amplifiers with AGC 22, 26.
In accordance with this embodiment of the invention the two links are interconnected by means of feedback circuits 30 and 40 which connect the AGC
circuits of the i~f. amplifiers 22, 26 of receivers ll and 13, to the AGC circuits of the i.f. amplifiers 17, 14 respectively, of transmitters 12 and lO.
In the absence of feedback circui~s 30 and 40, each transmitter is desi~ned to have a constant power output which is sufficiently high to provide a certain level of overall system performance during periods of deep fades. However, as noted above~ this high power level is not required most of the time. Accordingly, the system is modified to transmit at a level that is a function of the existing propagation conditions, as determined by the carrier signal level at the receiver~ Thus~ with respect to transmission in the west-to-east direction, the AGC
voltage developed in i.f . amplif ier 22 in receiver 11, :, -- 6 ~

which is essentially a d.c. voltage~ and is a measure of the received signal level, is applied to FM deviator 31 whose output is an a.c. signal whose frequency is a function of the applied AGC voltage. This a.c. signal is coupled to the AGC circuit of i.f~ amplifier 17 of trans-mitter 12 and serves to superimpose a modulation upon the amplitude of the east-to-west transmitted carrier signal.
This modulation, in turn, causes the AGC voltage of i.f.
amplifier 26 in receiver 13 to have an a.c. component, provided that the modulation frequency is within the band-width of the AGC control loop. This AGC component is then applied to the FM discriminator 41 in feedback circuit 40.
The output of discriminator 41 is a d.c. signal whose magnitude is a function of the frequency of the a.c.
signal applied thereto. Thus ? the d.c. voltage forming the AGC. signal of i.f. amplifier 14 in transmitter 10 is a func~ion of the magnitude of the AGC signal in i.f.
amplifier 22. If the latter is large, indicating a strong received carrier signal at receiver 11, a correspondingly large AGC voltage is applied to amplifier 14 in transmitter lO, thus reducing the gain of the amplifier and the magni-tude of the signal applied to r~f. power amplifier 16.
If, on th~ other hand, a signal fade develops, the AGC
voltage in amplifier 22 decreases, thereby decreasing the AGC signal in amplifier 140 This increases the gain of amplifier 14, thereby increasing the output power trans-mitted by r.f. amplifier 16. Thus, an adaptive transmitter power control is provided with the addition of only an FM
deviator at the receiver and an FM discriminator at the transmitter.
As is evident, a similar power control can be provided for the east-to-west channel by the addition of an FM deviator 42 (shown in broken outline) which converts the d.c. component of the AGC signal developed in amplifier 26 to an a.c. signal which modulates the west-to-east carrier, and an FM discriminator 32 (shown in broken outline) which detects the a.c. component of the AGC
signal developed in ampliEier 22 and converts it to a d.c. signal which controls the gain of amplifier 17.
Thus, with a minimum amount of additional circuitry, two-way adaptive transmitter power control is achieved.
An important feature of the invention is the sup-pression of the a.c. components on the radio signal by the AGC circuits in i.f. amplifiers 22 and 26. This assures that no interference i5 being cause by these signals in the adjacent radio hops.
The overall power control characteristic is a function of the FM deviator, the FM discriminator, and the gain characteristics of the respective amplifiers.
By varying any or all of these parameters any control characteristic can be realized. For example, in a control circuit constructed to test the concept, it was decided to maintain a constant output power for downfades up to 20dB
and upfades up to 5dB. This was designated as Region I.
As the fade increases beyond 20db, the transmitter power is increase correspondingly. This second interval was designated Region II. Upfades are relatively fre~uent occurrences which can lead to overdrive conditions in the input stages of receivers 11 and 13. In order to prevent such conditions the transmitter output power i5 ~urther reducted for upfades higher than 5dB. FIG. 2 shows the relationship between transmitter power and fad depth for the example just described. Note that during nor~al and modestly faded conditions, the control system is in effect disconnected and a constant (relatively low) output power is maintained. This contributes to the high reliability of the power control system. The characteristic shown in FIG. 2 can be obtained in various ways by nonlinear shaping of the FM deviator, the FM discriminator and gain and AGC
characteristics of the power control loop as is well-known ," .~

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in the art. Such non-linear shaping means is shown in FIG. 1 within dashed lines designated 33 and 43 at the two transceivers. As stated above, however, it should be understood that such nonlinear shaping means 33 and 43 actually can be part of the FM devia-tor 31, 42, the FM
discriminator 32, 41, and/or the AGC arrangements in elements 22, 17 or 26, 14, respectively, and is not necessarily a separate circuit.
In ~he above-described embodiment of the invention, the power control signals are shown as being transmitted over an FM-AM link, piggy-backed on the broadband digital signal traveling in the opposite direction. It will be recognized, however, that this signal can just as readily be transmitted over a separate service (auxiliary, telemetry) channel, if available.
Stability of the overall control loop can be achieved by using known techniques of control system design.

Claims (18)

Claims:
1. A radio transceiver comprising:
a receiver section capable of receiving an information signal destined for an end user in a pre-determined channel from a remote, immediately preceding, transmitter of a radio system r the receiver section comprising amplifier means including an automatic gain control (AGC) arrangement capable of generating a d-c control signal which has a magnitude that (a) is a function of the amplitude of the received information signal at any instant of time and (b) can vary between a predetermined range of amplitude levels;
means responsive to the d-c control signal from the AGC arrangement of the amplifier means in the receiver section for generating an a-c control signal whose frequency is (a) a function of the magnitude of the d-c control signal at any instant of time, and (b) lies within a predetermined band of frequencies within a range of a loop bandwidth of the AGC arrangement of the receiver section; and a transmitter section capable of transmitting an information signal destined for a remote end user in a predetermined transmission channel to a remote, next sequential, receiver of the radio system associated with said remote transmitter, the transmitter section comprising amplifier means including an AGC arrangement which is responsive to the a-c control signal from the generating means for amplitude modulating (AM) the amplitude of the information signal transmitted in the predetermined transmission channel to the remote, next sequential, receiver in accordance with the frequency variations of said a-c control signal from the generating means.
2. A transceiver according to claim 1 where the information signal received from the remote, immediately preceding, transmitter also includes variations in its amplitude which correspond to frequency variations in an a-c control signal generated at the remote, im-mediately preceding, transmitter, which frequency variations are a function of the amplitude of the information signal received at the associated remote, next sequential, receiver from the transmitter section at any instant of time, wherein the AGC arrangement in the receiver section is responsive to frequency variations in the amplitude of the received information signal for generating an a-c control signal which is superimposed on the d-c control signal and corresponds to the frequency of said amplitude variations;
the generating means is further responsive to the frequency of the a-c control signal superimposed on said d-c control signal from the AGC arrangement of the ampli-fier means of the receiver section for generating there-from a separate d-c control signal which is a function of the frequency of said a-c control signal; and the AGC arrangement of the amplifier means in the transmitter section is responsive to the separate d-c control signal from said generating means for adaptively changing the amplitude of the transmitted information signal as a functon of the magnitude of said separate d-c control signal generated by the generating means.
3. A transceiver according to claim 2 wherein the amplifier means including the AGC arrangement in the receiver section includes means which provides a feedback gain which is sufficient to prevent frequency variations in the amplitude of the received information signal from propagating beyond said amplifier means to the destined end user.
4. A transceiver according to claim 1 wherein the transceiver further includes:
means, responsive to the d-c control signals generated by the AGC arrangement in the amplifier means of the receiver section, for causing the generating means to generate a constant frequency a-c control signal when said d-c control signal is within a predetermined range of magnitudes, representing a predetermined range of acceptable amplitude levels of a received information signal, and for adaptively changing the frequency of the a-c control signal when the magnitude of said d-c control signal is above or below said predetermined range of magnitudes.
5. A transceiver according to claim 2 wherein the transceiver further includes:
means, responsive to the a-c control signal super-imposed on the d-c control signal generated by the AGC
arrangement of the amplifier means in the receiver section, for causing the separate d-c control signal, transmitted to the AGC arrangement of the amplifier means in the transmitter section, to maintain a constant magnitude when said superimposed a-c control signal is within a predetermined frequency band representing a predetermined range of acceptable amplitude levels of a received information signal, and for adaptively changing the magnitude of the separate d-c control signal when the frequency of the superimposed a-c control signal is above or below said predetermined frequency band.
6. A transceiver according to claim 1 wherein the generating means comprises an FM deviator capable of converting the magnitude of the input d-c control signal into an output a-c control signal comprising a frequency which is a function of the magnitude of said d-c control signal.
7. A transceiver according to claim 2 wherein the generating means comprises:
an FM deviator capable of converting the magnitude of the input d-c control signal into an output a-c control signal comprising a frequency which is a function of the magnitude of said d-c control signal; and an FM discriminator capable of converting the a-c control signal, superimposed on the d-c control signal, into the separate output d-c control signal for transmission to the AGC arrangement of the amplifier means in the transmitter section.
8. A transceiver capable of receiving an information signal which is destined for an end user in a predetermined channel from a remote, immediately preceding, transmitter of a radio system, where the information signal includes frequency variations on its amplitude which cor-respond to frequency variations in an a-c control signal generated at the remote, immediately preceding, transmitter which is a functon of the amplitude of an information signal received from the present transceiver at a remote, next sequential, receiver of the radio system associated with said remote transmitter, the transceiver comprising:
a receiver section capable of receiving the information signal and comprising amplifier means including an automatic gain control (AGC) arrangement capable of generating an a-c control signal whose frequency is a function of the frequency variations in the amplitude of the received information signal;
means, responsive to the frequency of the a-c control signal from the AGC arrangement of the amplifier means in the receiver section for generating therefrom a d-c control signal including a magnitude which is a function of the instantaneous frequency of the a-c control signal, and a transmitter section capable of transmitting an information signal which is destined for a remote end user in a predetermined transmission channel to the remote, next sequential, receiver, the transmitter section comprising amplifier means including an AGC arrangement which is responsive to the d-c control signal from the generating means for adaptively changing the amplitude of the transmitted information signal as a function of the instantaneous magnitude of said d-c control signal.
9. A transceiver according to claim 8 wherein the AGC arrangement of the amplifier means in the receiver section is further capable of generating a d-c control signal, on which said a-c control signal is super-imposed, which has a magnitude that (a) is a function of the amplitude of the received information signal at any instant of time, and (b) can vary between a predetermined range of levels;
the generating means is also responsive to the d-c control signal from the AGC arrangement of the amplifier means in the receiver section for generating a separate a-c output control signal whose frequency is (a) a function of the instantaneous magnitude of the d-c control signal from the AGC arrangement, and (b) lies with-in a predetermined frequency band within a range of a loop bandwidth of the AGC arrangement; and the AGC arrangement of the amplifier means in the transmitter section is responsive to the separate a-c out-put control signal from the generating means for amplitude modulating (AM) the amplitude of the information signal being transmitted in the predetermined transmission channel to the remote, next sequential, receiver in accordance with the instantaneous frequency of said a-c output control signal.
10. A transceiver according to claim 8 wherein the transceiver further comprises:
means, responsive to the a-c control signal generated by the AGC arrangement in the amplifier means of the receiver section, for causing the generating means to generate a constant magnitude d-c output control signal when said a-c control signal is within a predetermined band of frequencies, representing a predetermined range of acceptable amplitude levels of a received information signal at the remote, next sequential, receiver, and for adaptively changing the magnitude of the d-c control signal when the frequency of said a-c control signal is above or below said predetermined band of frequencies.
11. A transceiver according to claim 8 wherein the amplifier means including an AGC arrangement in the receiver section further includes means which provides a feedback gain which is sufficient to prevent frequency variations in the amplitude of the received information signal from propagating beyond said amplifier means to the destined end user.
12. A transceiver according to claim 8 wherein the generating means comprises:
an FM discriminator capable of converting the a-c control signal into the d-c control signal for transmission to the AGC arrangement of the amplifier means in the transmitter section.
13. A transceiver according to claim 9 wherein the generating means comprises:
an FM discriminator capable of converting the a-c control signal into the d-c control signal for transmission to the AGC arrangement of the amplifier means in the trans-mitter section; and an FM deviator capable of converting the magnitude of the d-c control signal into the separate a-c output control signal.
14. A method of providing adaptive transmitted power control for transmissions in a radio system com-prising a first transceiver and a second remote, next sequential, transceiver along a radio route, the method comprising the steps of:
(a) receiving, at the second remote, next sequential, transceiver, an information signal trans-mitted by the first transceiver in a predetermined channel and destined for an end user at the second remote, next sequential, transceiver;

(b) generating a d-c control signal at an auto-matic gain control (AGC) arrangement in a receiver section of the second, next sequential, transceiver which has a magnitude that (1) is a function of the amplitude of the information signal received in step (a), and (2) can vary between a predetermined range of levels;
(c) generating from the d-c control signal from step (b), and a-c control signal whose frequency (1) is a function of the magnitude of the d-c control signal at any instant of time, and (2) lies within a predetermined band of frequencies which is within a range of a loop bandwidth of an AGC arrangement in a receiver section of the first transceivers (d) amplitude modulating, with a transmitter AGC
arrangement and associated amplifier the amplitude of an information signal transmitted by the second, next sequential, transceiver to the first transceiver in accordance with frequency variations of the a-c control signal generated in step (c) and (e) detecting, with a receiver AGC arrangement and associated amplifier at the first transceiver, the amplitude modulations in the amplitude of the information signal transmitted in step (d) for generating therefrom a control signal which is a function of said amplitude modulations and is capable of adaptively modifying the amplitude of a transmission from the first transceiver to the second, next sequential, transceiver.
A method of providing adaptive transmitted power control in accordance with claim 14 wherein for step (e), performing the steps of:
(e1) detecting, with a receiver AGC arrangement the amplitude modulations in the amplitude of the received information signal;
(e2) generating an a-c control signal, from the receiver AGC arrangement which includes an instantaneous frequency that is a function of the detected amplitude modulations in step (e1) and lies within a range of a loop bandwidth of said receiver AGC arrangement;
(e3) generating from the a-c control signal generated in step (e2), a d-c control signal which has a magnitude that is a function of the frequency of the a-c control signal; and (e4) adaptively changing the amplitude of trans-mitted information signals to the second, next sequential, transceiver as a function of the instantaneous magnitude of the d-c control signal generated in step (e3).
16. A method of providing adaptive transmitted power control in accordance with claim 15 wherein concur-rent with performing step (e2), performing the step of:
(e5) suppressing the modulations in the amplitude of the received information signal with elements in the receiver AGC arrangement prior to transmission of the information signal to a destined end user.
17. A method of providing adaptive transmitted power control in accordance with claim 14 wherein the method comprises the further steps of:
(f) concurrent with step (e), generating, in the receiver AGC arrangement at the first transceiver, a d-c control signal including a magnitude that (1) is a function of the amplitude of the information signal received in step (e), and (2) can vary between a predetermined range of levels;
(g) generating from the d-c control signal from step (f) an a-c control signal whose frequency is (1) a function of the magnitude of the d-c control signal at any instant of time, and (2) lies within a predetermined band of frequencies within a range of a loop bandwidth of the AGC arrangement in the receiver secton of the second remote transceiver;

(h) amplitude modulating the amplitude of a transmitted information signal destined for the second transceiver in accordance with the frequency variations of the a-c control signal generated in step (g); and (i) concurrent with steps (a) to (d), at the second, next sequential, transceiver, detecting in the receiver section AGC arrangement, amplitude modulations in the amplitude of an information signal received from the first transceiver for generating, from said detected modulations, a control signal capable of adaptively modifying the amplitude of an information signal transmission of the second, next sequential, transceiver to the first transceiver.
18. A method of providing adaptive transmitted power control in accordance with claim 17 where in performing steps (e) and (i), performing the steps of:
(j) detecting the amplitude modulations in the amplitude of a received information signal at the associated transceiver, which amplitude modulations comprise a frequency which lies within a range of a loop bandwidth of the AGC arrangement in the receiver section;
(k) generating an a-c control signal which includes an instantaneous frequency that is a function of the detected amplitude modulations in step (j);
(l) generating from the a-c control signal generated in step (k), a d-c control signal which has a magnitude that is a function of the frequency of the a-c control signal; and (m) adaptively changing, in a transmitter section AGC arrangement and associated amplifier of the associated transceiver the amplitude of transmitted information signals to the other transceiver as a function of the instantaneous magnitude of the d-c control signal generated in step (1).
CA000441679A 1982-12-27 1983-11-22 Transmitter power control circuit Expired CA1215745A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US453,513 1982-12-27
US06/453,513 US4495648A (en) 1982-12-27 1982-12-27 Transmitter power control circuit

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CA1215745A true CA1215745A (en) 1986-12-23

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US (1) US4495648A (en)
EP (1) EP0115139B1 (en)
JP (1) JPS59133739A (en)
CA (1) CA1215745A (en)
DE (1) DE3377887D1 (en)
GB (1) GB2132454B (en)

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DE3377887D1 (en) 1988-10-06
EP0115139B1 (en) 1988-08-31
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US4495648A (en) 1985-01-22
EP0115139A3 (en) 1985-08-28

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