CA1211524A - Receiver for a data transmission modem, comprising an echo canceller and an equalizer - Google Patents
Receiver for a data transmission modem, comprising an echo canceller and an equalizerInfo
- Publication number
- CA1211524A CA1211524A CA000438874A CA438874A CA1211524A CA 1211524 A CA1211524 A CA 1211524A CA 000438874 A CA000438874 A CA 000438874A CA 438874 A CA438874 A CA 438874A CA 1211524 A CA1211524 A CA 1211524A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- circuit
- echo
- equalizer
- receiver
- 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
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
- H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers
- H04B3/235—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers combined with adaptive equaliser
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
- H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers
- H04B3/238—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers using initial training sequence
Abstract
ABSTRACT:
A receiver for a data transmission modem pro-cesses the baseband signal of the receive path and com-prise an echo canceller and an equalizer which have a common subtracting circuit for subtracting from the re-ceived signal the synthetic echo and synthetic interference signals generated in the echo canceller and the equalizer.
The output signal of the subtracting circuit is sampled for application to a circuit forming the respective error signals are used to adjust the filters of the echo can-celler and the equalizer. This output signal of the sub-tracting circuit is further applied to a circuit for re-covering the clock of the received data after having been sampled at a frequency which satisfies the Shannon theo-rem with regard to the signal transmitted by the modem, while the synthetic echo signal is generated at this sampling frequency.
A receiver for a data transmission modem pro-cesses the baseband signal of the receive path and com-prise an echo canceller and an equalizer which have a common subtracting circuit for subtracting from the re-ceived signal the synthetic echo and synthetic interference signals generated in the echo canceller and the equalizer.
The output signal of the subtracting circuit is sampled for application to a circuit forming the respective error signals are used to adjust the filters of the echo can-celler and the equalizer. This output signal of the sub-tracting circuit is further applied to a circuit for re-covering the clock of the received data after having been sampled at a frequency which satisfies the Shannon theo-rem with regard to the signal transmitted by the modem, while the synthetic echo signal is generated at this sampling frequency.
Description
Lowe 82.587 1 1.9.1983 "Receiver for a elate transmission modern, comprising an echo canceler and an equalizer".
The invention relates to a receiver used in a data transmission modem for recovering, from the base band signal of the receive path, the data signal transmitted by the remote modem, this receiver comprising an echo canceler incorporating an adjustable processing arrange-mint comprising at least one transversal filter and no-ceiling a signal from the transmit path, a self-adaptive equalizer comprising a transversal filter receiving the data signal recovered by the decision circuit of the no-sever, and a subtracting circuit for subtracting from the base band signal of the receive path the synthetic echo and synthetic interference signals generated in the echo canceler and the equalizer, the output signal of the sub-treating circuit being sampled for application to a air-cult forming the error signals used to adjust the filter coefficients of the echo canceler and of the equalizer.
Receivers processing base band signals are direct-lye utilized in the base band data transmission modems. But it is alternatively possible to use these receivers in data transmission modems employing carrier modulation, by applying to these receivers the base band signals resulting from the demodulation of the received signal.
In the receiver under consideration, an echo canceler and a self-adaptive equalizer reemployed six multaneously for a correct recovery of the received data.
The function of the echo canceler is to cancel automatic gaily -the unwanted echo signal produced in the receive path of a local modem by the transmitted signal of this modem and superposed on the useful signal originating from the remote modem in the case of full duplex trays mission. The function of` the equalizer is to cancel auto-matica1ly the unwanted interfererlce signal superposed on Lo so Pluck 2 1.9.1983 equal roused data present at -the input of tune receiver and produce by tile previously received data.
A receiver employing at the same time an echo canceler and an equalizer is described in an article by s lo Mueller, entitled: "Combining Echo Cancellation and Decision eddy Jack equalization" and published in Tut BELL
SWEPT T~`C~rlCAL JOIJRNAL~ Vol. 58, No. 2, February 1979, paves OWE. In this receiver, the coefficients of the transversal filters of the echo canceler and of' the lo equalizer are adjusted simultaneously by using the same error signal formed by the difference between -the output signal of the subtracting circuit and the data signal no-covered by the decision circuit of the receiver, the an-tenon utilized for -this control being the minimization IS of the mean-scluare value of the error signal In this known receiver, sampling the error signal is effected at the baud frequency and the synthetic echo and synthetic inter-furriness signals to be subtracted from the received signal are generated with the same sampling frequency, also equal -to the baud frequency. However, the above-mentioned en-tide does not deal with the important practical problem of recovering the clock of the received data, this clock supplying the said sampling frequency and determining to a large extent the quality of the echo cancellation and -the equalization.
United States Patent No. Isle also disk closes a receiver comprising an echo canceler and an equalizer, these two arrangements operating with the same error signal formed in the same manner as in the above-mentioned article by Mueller. However, in that patent equalization is effected in a different way, that is to say by means of a transversal filter arranged in the received path before the subtracting circuit and -thus 'before echo cancellation is effected. Recovering the clock signal is effected in a circuit connected to the input of the no-chive path, that is -to say starting from the received sign net which has not 'been subjected to any echo cancellation Ill 82.`)87 3 1.9.19~3 and equalization process. It; seems difficult with this structure to obtain a clock which is really in synchronism with the received data and free from noise, and therefore difficult to cancel correctly the unwanted echo and inter-furriness signals.
The present invention has for its object to provide a receiver by means of which it is possible to obtain simultaneously, with an adequate quality, echo cancellatioII~ equalization and clock recovery lo According to the invention, in a receiver come prosing an echo canceler and an equalizer generating sync Thetis echo and synthetic interference signals which are applied -to a subtracting circuit to be subtracted from the base band signal of the receive path, -the output signal of lo the subtracting circuit is further applied -to a circuit for recovering the clock of -the received data after having been sampled a-t a sampling frequency derived from this clock recovery circuit and satisfying the Shannon theorem with regard to the signal transmitted by the modem, while the synthetic echo signal is generated at said sampling frequency.
ilk such a receiver it has been found in pray-lice that -the convergence of the assembly is obtained rapidly, which results in a stable recovered clock and in the cancellation of the echo and interference signals, which is a rather surprising result, -taking into account the close dependence of the operations of the clock no-covey correct, the echo canceler and the equalizer, which are controlled in this receiver starting from the same signal.
How the invention can be put into effect will be more fully appreciated from the following description given by way of example with reference to the accompanying drawings, in which:
Fig. l shows a block diagram of a data trays-mission modem in which the receiver according to the in-mention is incorporated; and 1'~11;"~2.)~7 I 1.9.1983 jig 2 Slows a block diagram of an embodiment of the receiver according to -the invention jig 1 shows the structure of a base band data transmission modem whose receiver includes an echo can-cello and an equalizer. This modem comprises a one-way transmit path 1 and a one receive path 2, which are coupled to a two-way transmission line 3 by means ox a ho-brim coupling circuit 4.
The transmit path 1 is connected to a data source 5 which produces data at a frequency F = l/T deter-mined by the clock signal H. These data may be of the two-level or the multi-level type, that is to say having more than trio levels. They are generally applied, as shown in Fig. 1, to an encoder 6 which produces a signal with a spectrum which is better suited to transmission and to recovery of` the clock signal in the remote modem -than -the initial data signal. In the case of two-level data, the en-coding operation effected in the encoder 6 may be buffs encoding, according -to which the data having -the value "1"
are represented by the clock signal H having -the fret quench F and the data having -the value "O" are represented by the complement of this clock signal. Such a two-level, buffs encoded signal does not comprise zero frequency components and the major part of its energy is concentrated in the frequency band extending to OF. The encoding operate ion effected in the encoder 6 may alternatively be a pseudo-ternary encoding causing a signal having a positive, a Vega-live and a zero level to correspond to a two-level data signal. In the case of a signal encoded in the bipolar code of the order 1, which is a specific case of pseudo-ternary encoding, -the major part of the energy is concentrated in the band extending to the frequency F. Ire signal origin noting from encoder 6 is amplified in a -transmit amplifier 7 before application to the transmit port of coupling circuit I. The data signal thus processed in transmit path 1 is transmitted to the remote modem, not shown, via trays-mission line 3.
I
Ply 2.-)87 1 9.19c3 The elate signal transmitted in bye same way by the remote modem is received in the focal modern shown in the jig. 1 and is conveyed by coupling circuit 4 to the input of receive path 2 of this modem. In tilts receive path, the received signal is first amplified in a receive amplifier 8 and thereafter conveyed to a decision circuit 9 of the receiver, which operates at tile clock frequency F = 1/T to recover a data signal depencLing on the data -transmitted by the remote modem. Thus, decision circuit 9 lo can recover a multilevel signal or a two-level buffs encoded signal if a-t the transmission the data have been encoded in buffs, or a two-level non-coded signal if at transmission the two-level data have not been encoded or have been encoded pseudo-ternari]yO The data signal no-covered by decision circuit 9 may optionally be decoded in a decoder 10 before it is used.
Two unwanted signals which may pause an imp permissible error rate in the data recovered by decision circuit 'I may be superposed on the useful data signal so originating from the remote modem and appearing at the out-put of amplifier 8 of the receive path. One of these sign nets is an echo signal I which is produced by the signal transmitted by the local modem and is due to us-avoidable imperfections of coupling circuit 4 and/or -to signal reflections in transmission line 3. The other us-wanted signal is a signal known as (inter symbol) interior-once signal I which is produced by the data symbols oft-jointing from the remote modem and transmitted before each data symbol appearing in the receive path, this inter-I furriness signal being due to amplitude and/or phase distortions by which transmissiorl line 3 may be affected In order to eliminate in the receive path these two unwanted signals f and It an echo canceler and a self-adaptive equalizer having a common subtracting circuit 11 are used simultaneously, as described in the above mentioned article by Mueller. The signal supplied by amplifier 8 of the receive path 2 which may be written lull I 7 6 1.9.'l9~3 so + I + I its applied it) the (-I) input of this subtracting circuit 11. applied to the (~) input of air-cult 11 -is the signal f -I It which it the sum of the synthetic echo signal I genera-ted by the echo canceler and the synthetic -interference signal I generated by Thea elsewhere. Inn the convergence of the assembly formed by the echo canceler and the eqllalizer has 'been chic d, the signals to and I are almost equal to the unwanted signals I and I and the useful data lo signal so originating from -the remote modem and hying capable of correct processing 'by decision circuit for recovering the data is obtained a-t the output of sub-tracking circuit 11.
The echo canceler comprises an adjustable dip vital processirlg arrangement 12 including a-t least one -transversal filter which receives the signal supplied by data source and produces the synthetic echo signal in digital forln. Let it be assumed for the present that arrangement 12 comprises one single digital transversal MU filter which is operative at the sampling instants nut (or n for the sake ox simplicity) having the frequency 1/T of the data produced by source I. The samples of the data applied at the instants n to the input of the filter constituting arrangement 12 are designated c. This filter is arranged in -the usual way so as to store at each instant n, N samples awn - i) applied to its inputter i its an integer extending from O to N - 1) and to calculate the samples of the synthetic echo signal I in accord-ante with the expression:
N
f Jo Sweeney - i) (1) i = O
where Of represents -the coefficients of the filter.
The coefficients Of are adjustable and are ad-jousted in a control circuit 13 so as to minimize the mean-square value of an error signal eta which is elaborated in digital form in a calculating circuit 14. In precuts, 1'~l,1~' ,~2,-)~7 7 1.9.19~3 this can ye obtained by iteratively adjusting the Coffey-clients Of in accordance with the conventional recursion formula:
Sweeney + 1) = Of awn eta (2) In -this formula, eta is -the error signal a-t -the instant n of an iteration n and is a fixed coefficient having a small value relative to 1 and determining the magnitude of the modifications to be applied to -the coefficients lo Of at the iteration n to obtain the coefficients Sweeney + 1) at the iteration (n -I 1).
The self-adaptive equalizer comprises a trays vernal filter 15 which receives the signal recovered by decision circuit 9 and produces the synthetic inter-furriness signal in digital form. Let it be assumed for -the present that digital filter 15 is operative at the sampling instants nut having -the frequency 1/T of the data recovered by decision circuit 9. The samples of the data applied at the instants n to -the input of transversal filter 15 are designated by This filter is arranged so as to store at each instant n, M samples bun - j) applied to its input (where i is an integer extending from 1 to M) and -to calculate the samples of the synthetic interference signals I in accordance with the expression:
M
I = G by - j) (3 j = 1 J
where Go represents the coefficients of the filter.
The coefficients Go are adjustable and are iteratively adjusted in a control circuit 16 in accord-ante with a recursion formula similar to the above formula
The invention relates to a receiver used in a data transmission modem for recovering, from the base band signal of the receive path, the data signal transmitted by the remote modem, this receiver comprising an echo canceler incorporating an adjustable processing arrange-mint comprising at least one transversal filter and no-ceiling a signal from the transmit path, a self-adaptive equalizer comprising a transversal filter receiving the data signal recovered by the decision circuit of the no-sever, and a subtracting circuit for subtracting from the base band signal of the receive path the synthetic echo and synthetic interference signals generated in the echo canceler and the equalizer, the output signal of the sub-treating circuit being sampled for application to a air-cult forming the error signals used to adjust the filter coefficients of the echo canceler and of the equalizer.
Receivers processing base band signals are direct-lye utilized in the base band data transmission modems. But it is alternatively possible to use these receivers in data transmission modems employing carrier modulation, by applying to these receivers the base band signals resulting from the demodulation of the received signal.
In the receiver under consideration, an echo canceler and a self-adaptive equalizer reemployed six multaneously for a correct recovery of the received data.
The function of the echo canceler is to cancel automatic gaily -the unwanted echo signal produced in the receive path of a local modem by the transmitted signal of this modem and superposed on the useful signal originating from the remote modem in the case of full duplex trays mission. The function of` the equalizer is to cancel auto-matica1ly the unwanted interfererlce signal superposed on Lo so Pluck 2 1.9.1983 equal roused data present at -the input of tune receiver and produce by tile previously received data.
A receiver employing at the same time an echo canceler and an equalizer is described in an article by s lo Mueller, entitled: "Combining Echo Cancellation and Decision eddy Jack equalization" and published in Tut BELL
SWEPT T~`C~rlCAL JOIJRNAL~ Vol. 58, No. 2, February 1979, paves OWE. In this receiver, the coefficients of the transversal filters of the echo canceler and of' the lo equalizer are adjusted simultaneously by using the same error signal formed by the difference between -the output signal of the subtracting circuit and the data signal no-covered by the decision circuit of the receiver, the an-tenon utilized for -this control being the minimization IS of the mean-scluare value of the error signal In this known receiver, sampling the error signal is effected at the baud frequency and the synthetic echo and synthetic inter-furriness signals to be subtracted from the received signal are generated with the same sampling frequency, also equal -to the baud frequency. However, the above-mentioned en-tide does not deal with the important practical problem of recovering the clock of the received data, this clock supplying the said sampling frequency and determining to a large extent the quality of the echo cancellation and -the equalization.
United States Patent No. Isle also disk closes a receiver comprising an echo canceler and an equalizer, these two arrangements operating with the same error signal formed in the same manner as in the above-mentioned article by Mueller. However, in that patent equalization is effected in a different way, that is to say by means of a transversal filter arranged in the received path before the subtracting circuit and -thus 'before echo cancellation is effected. Recovering the clock signal is effected in a circuit connected to the input of the no-chive path, that is -to say starting from the received sign net which has not 'been subjected to any echo cancellation Ill 82.`)87 3 1.9.19~3 and equalization process. It; seems difficult with this structure to obtain a clock which is really in synchronism with the received data and free from noise, and therefore difficult to cancel correctly the unwanted echo and inter-furriness signals.
The present invention has for its object to provide a receiver by means of which it is possible to obtain simultaneously, with an adequate quality, echo cancellatioII~ equalization and clock recovery lo According to the invention, in a receiver come prosing an echo canceler and an equalizer generating sync Thetis echo and synthetic interference signals which are applied -to a subtracting circuit to be subtracted from the base band signal of the receive path, -the output signal of lo the subtracting circuit is further applied -to a circuit for recovering the clock of -the received data after having been sampled a-t a sampling frequency derived from this clock recovery circuit and satisfying the Shannon theorem with regard to the signal transmitted by the modem, while the synthetic echo signal is generated at said sampling frequency.
ilk such a receiver it has been found in pray-lice that -the convergence of the assembly is obtained rapidly, which results in a stable recovered clock and in the cancellation of the echo and interference signals, which is a rather surprising result, -taking into account the close dependence of the operations of the clock no-covey correct, the echo canceler and the equalizer, which are controlled in this receiver starting from the same signal.
How the invention can be put into effect will be more fully appreciated from the following description given by way of example with reference to the accompanying drawings, in which:
Fig. l shows a block diagram of a data trays-mission modem in which the receiver according to the in-mention is incorporated; and 1'~11;"~2.)~7 I 1.9.1983 jig 2 Slows a block diagram of an embodiment of the receiver according to -the invention jig 1 shows the structure of a base band data transmission modem whose receiver includes an echo can-cello and an equalizer. This modem comprises a one-way transmit path 1 and a one receive path 2, which are coupled to a two-way transmission line 3 by means ox a ho-brim coupling circuit 4.
The transmit path 1 is connected to a data source 5 which produces data at a frequency F = l/T deter-mined by the clock signal H. These data may be of the two-level or the multi-level type, that is to say having more than trio levels. They are generally applied, as shown in Fig. 1, to an encoder 6 which produces a signal with a spectrum which is better suited to transmission and to recovery of` the clock signal in the remote modem -than -the initial data signal. In the case of two-level data, the en-coding operation effected in the encoder 6 may be buffs encoding, according -to which the data having -the value "1"
are represented by the clock signal H having -the fret quench F and the data having -the value "O" are represented by the complement of this clock signal. Such a two-level, buffs encoded signal does not comprise zero frequency components and the major part of its energy is concentrated in the frequency band extending to OF. The encoding operate ion effected in the encoder 6 may alternatively be a pseudo-ternary encoding causing a signal having a positive, a Vega-live and a zero level to correspond to a two-level data signal. In the case of a signal encoded in the bipolar code of the order 1, which is a specific case of pseudo-ternary encoding, -the major part of the energy is concentrated in the band extending to the frequency F. Ire signal origin noting from encoder 6 is amplified in a -transmit amplifier 7 before application to the transmit port of coupling circuit I. The data signal thus processed in transmit path 1 is transmitted to the remote modem, not shown, via trays-mission line 3.
I
Ply 2.-)87 1 9.19c3 The elate signal transmitted in bye same way by the remote modem is received in the focal modern shown in the jig. 1 and is conveyed by coupling circuit 4 to the input of receive path 2 of this modem. In tilts receive path, the received signal is first amplified in a receive amplifier 8 and thereafter conveyed to a decision circuit 9 of the receiver, which operates at tile clock frequency F = 1/T to recover a data signal depencLing on the data -transmitted by the remote modem. Thus, decision circuit 9 lo can recover a multilevel signal or a two-level buffs encoded signal if a-t the transmission the data have been encoded in buffs, or a two-level non-coded signal if at transmission the two-level data have not been encoded or have been encoded pseudo-ternari]yO The data signal no-covered by decision circuit 9 may optionally be decoded in a decoder 10 before it is used.
Two unwanted signals which may pause an imp permissible error rate in the data recovered by decision circuit 'I may be superposed on the useful data signal so originating from the remote modem and appearing at the out-put of amplifier 8 of the receive path. One of these sign nets is an echo signal I which is produced by the signal transmitted by the local modem and is due to us-avoidable imperfections of coupling circuit 4 and/or -to signal reflections in transmission line 3. The other us-wanted signal is a signal known as (inter symbol) interior-once signal I which is produced by the data symbols oft-jointing from the remote modem and transmitted before each data symbol appearing in the receive path, this inter-I furriness signal being due to amplitude and/or phase distortions by which transmissiorl line 3 may be affected In order to eliminate in the receive path these two unwanted signals f and It an echo canceler and a self-adaptive equalizer having a common subtracting circuit 11 are used simultaneously, as described in the above mentioned article by Mueller. The signal supplied by amplifier 8 of the receive path 2 which may be written lull I 7 6 1.9.'l9~3 so + I + I its applied it) the (-I) input of this subtracting circuit 11. applied to the (~) input of air-cult 11 -is the signal f -I It which it the sum of the synthetic echo signal I genera-ted by the echo canceler and the synthetic -interference signal I generated by Thea elsewhere. Inn the convergence of the assembly formed by the echo canceler and the eqllalizer has 'been chic d, the signals to and I are almost equal to the unwanted signals I and I and the useful data lo signal so originating from -the remote modem and hying capable of correct processing 'by decision circuit for recovering the data is obtained a-t the output of sub-tracking circuit 11.
The echo canceler comprises an adjustable dip vital processirlg arrangement 12 including a-t least one -transversal filter which receives the signal supplied by data source and produces the synthetic echo signal in digital forln. Let it be assumed for the present that arrangement 12 comprises one single digital transversal MU filter which is operative at the sampling instants nut (or n for the sake ox simplicity) having the frequency 1/T of the data produced by source I. The samples of the data applied at the instants n to the input of the filter constituting arrangement 12 are designated c. This filter is arranged in -the usual way so as to store at each instant n, N samples awn - i) applied to its inputter i its an integer extending from O to N - 1) and to calculate the samples of the synthetic echo signal I in accord-ante with the expression:
N
f Jo Sweeney - i) (1) i = O
where Of represents -the coefficients of the filter.
The coefficients Of are adjustable and are ad-jousted in a control circuit 13 so as to minimize the mean-square value of an error signal eta which is elaborated in digital form in a calculating circuit 14. In precuts, 1'~l,1~' ,~2,-)~7 7 1.9.19~3 this can ye obtained by iteratively adjusting the Coffey-clients Of in accordance with the conventional recursion formula:
Sweeney + 1) = Of awn eta (2) In -this formula, eta is -the error signal a-t -the instant n of an iteration n and is a fixed coefficient having a small value relative to 1 and determining the magnitude of the modifications to be applied to -the coefficients lo Of at the iteration n to obtain the coefficients Sweeney + 1) at the iteration (n -I 1).
The self-adaptive equalizer comprises a trays vernal filter 15 which receives the signal recovered by decision circuit 9 and produces the synthetic inter-furriness signal in digital form. Let it be assumed for -the present that digital filter 15 is operative at the sampling instants nut having -the frequency 1/T of the data recovered by decision circuit 9. The samples of the data applied at the instants n to -the input of transversal filter 15 are designated by This filter is arranged so as to store at each instant n, M samples bun - j) applied to its input (where i is an integer extending from 1 to M) and -to calculate the samples of the synthetic interference signals I in accordance with the expression:
M
I = G by - j) (3 j = 1 J
where Go represents the coefficients of the filter.
The coefficients Go are adjustable and are iteratively adjusted in a control circuit 16 in accord-ante with a recursion formula similar to the above formula
(2):
Gun + 1) = Go (n) -I by - jug (4) In this formula, is a mixed coefficient having a small value relative to 1 and erg is the error signal used to adjust the coefficients of the equalizer and eta-borate in calculating circuit 14.
2.)~7 1 9.1983 The digital signals (n) end I are added to-getter it aft adder circuit 17 and -the sum signal obtained is converted into analog form by means of a digit alto analog converter 18, which produces the correction signal Jo t) t) applied to the (-) input of subtracting circuit 11.
In the neural receiver described in the article by lowlier, always -the same error signal is used to con-trot the coefficients of the echo canceler and of the equalizer in accordance with the recursion formulae (2) and (4), respectively. In this known receiver, this common error signal is formed at the frequency F = 1/T as the difference between the data by recovered by decision circuit 9 and the samples f formed by sampling at the frequency 1/T, -the signal f produced by subtracting air cult 11. In -this known receiver, the digital signals (n) end no are calculated with this sampling frequency l;` = 1/T, which is a frequency insufficient for canceling, over their complete frequency band, the echo signal and the interference signal which occupy substantially the same frequency band as the -transmitted signal, that is to say as mentioned in the foregoing, the band extending from O -to OF in the case of a buffs encoding and the band extending from O to F in the case of a bipolar encoding of the order of 1. This wrists in that no information allowing the recovery of the clock of the received data having the frequency IT is obtained in the signal supplied by subtracting circuit 11~ For the rest, in this prior art receiver, there is no circuit for recovering the clock of the received data -to have all the elements of the no-Syria, and more specifically -the echo canceler and -the equalizer, operate and, in -the case of a homochronous transmission system, to activate also local Dow source 5.
If one wants to have the clock recovery air-cult act on the received signal directly coming from coupling circuit I, as is described in the above mentioned Ignited States Pa-tent No. isle, owe, there is of` necessity I
lull ,~'. I 1.9.19$3 obtained a clock signal beset with the noise produced by the echo sigrlal I and the interference signal Iota) and consequerltl~ havillg a quality which is inadequate for eye cancellation and equalization These drawbacks can be obviated by means of the present invention. According -to the invention, the signal f supplied by subtracting circuit 11 is sampled in a sampl.e-and-hold circuit 19 by means of a sampling sign net ha having a frequency foe which substantially satisfies lo the Shannon with regard to the signal transmitted by the modem. For eY.amp].e~ in -the case of a biphase-encoded transmitted signal, the major part of whose energy is lo-acted in the band [0-21~], a sampling frequency pa at least equal to OF can be chosen. To simplify the description, it it its assumed hereinafter that a biphase-encoded transmitted signal is used, with a sampling frequency Ida equal -to 4.1~.
The signal thus sampled and supplied by circuit lo is not only applied -to decision circuit 9 and to error cowlick-feting circuit 14, but also to a clock recovery circuit 20 which produces the recovered clock signal H having a frequency F. This clock recovery circuit 20 is formed in a way which is known per so by means of, for example, a digital phase lock loop, to synchronize a local clock with -the -transitions of the signal rut sampled in sampling circuit 19. In the case of buffs encoding of the trains-milted signal, the signal f has two transitions for each bit period T.
In a -timing circuit 21, different control sign nets and control frequencies for the echo canceler and the equalizer are derived from the recovered clock signal If having the frequency F = 1/T and being supplied by circuit 20. This circuit 21 supplies the signal Lola having the sampling frecluency Fax which controls sample-and-hold circuit 19 and which may be equal -to OF in the case of bit I phase encoding.
In the receiver according to the invention, the synthetic cello signal its generated by digital processillg arrangement 12 with -the ambling frowns lay when a X2.)~7 10 1.9.1983 sampling frowns Fax = Lo is used one knows that it is possible to implement processing arrangemel1t 12 by means of four identical transversal filters, not shown, which act on the kowtow signal c. produced by source 5, using sampling signals IT to :1-13 produced by timing circuit 21.
These sampling signals II to Ho have the same frequency l/T and are shifted over T/4 relative to each other The four transversal jilters which make up processing arrange-mint 12 form, in accordance with formula (1), the Cynthia-tic echo signals (n), on on on respectively which under the control of the signals owe, Ho, ~12, Ho are sampled sequentially at instants shifted over To relative to each other. The synthetic echo signals (n) to on are multiplexed so as -to form at the output of processing I arrangement 12 the synthetic echo signal I sampled at the frequency foe = LO In order to modify the coefficients of` the four transversal filters which make up processing arrangement 12, the error signal eta of the echo canceler is calculated in calculating circuit 14 at the sampling frequency Fax = OF. This error signal is applied to control circuit 13 -to be distributed in time and to form four error signals eta to eat, which are each sampled at the frequent cry F = 1/T. The coefficients of the four transversal lit-lens of arrangement 12 are iteratively adjusted in accordance with the formula (2), by using for these filters the error signals ego to eat, respectively-In the case of a synthetic echo signal formed as described in the foregoing by using a sampling frequency Zoo = OF, the echo signal ( t) can be canceled yin a wide band extending Prom 0 to OF, in which the major part of a buffs encoded data signal having the frequency 1/T is located. As regards -the equalizer, it has been found that it is not absolutely necessary to form -the synthetic interference signal I with a sampling frequency of the same high value as -that used Jo form -the synthetic echo signal. In the example of a buffs encoded signal i-t is possible to use a sampling frequency Fog = I to foreign the
Gun + 1) = Go (n) -I by - jug (4) In this formula, is a mixed coefficient having a small value relative to 1 and erg is the error signal used to adjust the coefficients of the equalizer and eta-borate in calculating circuit 14.
2.)~7 1 9.1983 The digital signals (n) end I are added to-getter it aft adder circuit 17 and -the sum signal obtained is converted into analog form by means of a digit alto analog converter 18, which produces the correction signal Jo t) t) applied to the (-) input of subtracting circuit 11.
In the neural receiver described in the article by lowlier, always -the same error signal is used to con-trot the coefficients of the echo canceler and of the equalizer in accordance with the recursion formulae (2) and (4), respectively. In this known receiver, this common error signal is formed at the frequency F = 1/T as the difference between the data by recovered by decision circuit 9 and the samples f formed by sampling at the frequency 1/T, -the signal f produced by subtracting air cult 11. In -this known receiver, the digital signals (n) end no are calculated with this sampling frequency l;` = 1/T, which is a frequency insufficient for canceling, over their complete frequency band, the echo signal and the interference signal which occupy substantially the same frequency band as the -transmitted signal, that is to say as mentioned in the foregoing, the band extending from O -to OF in the case of a buffs encoding and the band extending from O to F in the case of a bipolar encoding of the order of 1. This wrists in that no information allowing the recovery of the clock of the received data having the frequency IT is obtained in the signal supplied by subtracting circuit 11~ For the rest, in this prior art receiver, there is no circuit for recovering the clock of the received data -to have all the elements of the no-Syria, and more specifically -the echo canceler and -the equalizer, operate and, in -the case of a homochronous transmission system, to activate also local Dow source 5.
If one wants to have the clock recovery air-cult act on the received signal directly coming from coupling circuit I, as is described in the above mentioned Ignited States Pa-tent No. isle, owe, there is of` necessity I
lull ,~'. I 1.9.19$3 obtained a clock signal beset with the noise produced by the echo sigrlal I and the interference signal Iota) and consequerltl~ havillg a quality which is inadequate for eye cancellation and equalization These drawbacks can be obviated by means of the present invention. According -to the invention, the signal f supplied by subtracting circuit 11 is sampled in a sampl.e-and-hold circuit 19 by means of a sampling sign net ha having a frequency foe which substantially satisfies lo the Shannon with regard to the signal transmitted by the modem. For eY.amp].e~ in -the case of a biphase-encoded transmitted signal, the major part of whose energy is lo-acted in the band [0-21~], a sampling frequency pa at least equal to OF can be chosen. To simplify the description, it it its assumed hereinafter that a biphase-encoded transmitted signal is used, with a sampling frequency Ida equal -to 4.1~.
The signal thus sampled and supplied by circuit lo is not only applied -to decision circuit 9 and to error cowlick-feting circuit 14, but also to a clock recovery circuit 20 which produces the recovered clock signal H having a frequency F. This clock recovery circuit 20 is formed in a way which is known per so by means of, for example, a digital phase lock loop, to synchronize a local clock with -the -transitions of the signal rut sampled in sampling circuit 19. In the case of buffs encoding of the trains-milted signal, the signal f has two transitions for each bit period T.
In a -timing circuit 21, different control sign nets and control frequencies for the echo canceler and the equalizer are derived from the recovered clock signal If having the frequency F = 1/T and being supplied by circuit 20. This circuit 21 supplies the signal Lola having the sampling frecluency Fax which controls sample-and-hold circuit 19 and which may be equal -to OF in the case of bit I phase encoding.
In the receiver according to the invention, the synthetic cello signal its generated by digital processillg arrangement 12 with -the ambling frowns lay when a X2.)~7 10 1.9.1983 sampling frowns Fax = Lo is used one knows that it is possible to implement processing arrangemel1t 12 by means of four identical transversal filters, not shown, which act on the kowtow signal c. produced by source 5, using sampling signals IT to :1-13 produced by timing circuit 21.
These sampling signals II to Ho have the same frequency l/T and are shifted over T/4 relative to each other The four transversal jilters which make up processing arrange-mint 12 form, in accordance with formula (1), the Cynthia-tic echo signals (n), on on on respectively which under the control of the signals owe, Ho, ~12, Ho are sampled sequentially at instants shifted over To relative to each other. The synthetic echo signals (n) to on are multiplexed so as -to form at the output of processing I arrangement 12 the synthetic echo signal I sampled at the frequency foe = LO In order to modify the coefficients of` the four transversal filters which make up processing arrangement 12, the error signal eta of the echo canceler is calculated in calculating circuit 14 at the sampling frequency Fax = OF. This error signal is applied to control circuit 13 -to be distributed in time and to form four error signals eta to eat, which are each sampled at the frequent cry F = 1/T. The coefficients of the four transversal lit-lens of arrangement 12 are iteratively adjusted in accordance with the formula (2), by using for these filters the error signals ego to eat, respectively-In the case of a synthetic echo signal formed as described in the foregoing by using a sampling frequency Zoo = OF, the echo signal ( t) can be canceled yin a wide band extending Prom 0 to OF, in which the major part of a buffs encoded data signal having the frequency 1/T is located. As regards -the equalizer, it has been found that it is not absolutely necessary to form -the synthetic interference signal I with a sampling frequency of the same high value as -that used Jo form -the synthetic echo signal. In the example of a buffs encoded signal i-t is possible to use a sampling frequency Fog = I to foreign the
3 I.
PI 82.587 11 sunnily In that case, traversal ton 15 of the equalizer receives -the signal H having the frequency F
supplied by timing circuit 21 to sample at this frequency the data signal by recovered by decision circuit 9. In filter 15, the samples of the synthetic interference sign net I are calculated at this frequency Fog = foe in accordance with a formula which is similar to the formula (3). To modify the coefficients of filter 15, the error signal erg of the equalizer is calculated in calculating circuit 14 at the sampling frequency F OF. This error signal erg is applied to control circuit 16, in which the coefficients of filter 15 are iteratively adjusted in accordance with the recursion formula (4).
With a receiver of this construction, in which the signal produced by subtracting circuit 11 is sampled at the Shannon frequency before being applied simultane-ouzel to clock recovery circuit 20 and to circuit 14 form-in the error signal for the echo canceler and the equal-sizer, and in which at least the echo canceler operates at this Shannon sampling frequency, the rather surprising result appeared in practice that the convergence of the assembly is obtained rapidly, which finds expression in a stable recovered clock and the cancellation of the unwanted echo and interference signals A particularly satisfactory operation is obtained when, to adjust the coefficients of the trays-vernal filters of the echo canceler and the equalizer error signals are used which are formed in the wanner described in Canadian Patent application No. 438,539 relating to an echo canceler and in Canadian Patent Application Nod 438,538 relating to an equalizer. Accord-in to these Patent Applications filed on October 6, 1983 by Applicants, the filter coefficients of an echo can-celled or an equalizer are modified with the aid of an error signal determined at an actual sampling instant by forming the difference between the value of the corrected received signal (the echo signal or 1'~l1 YO-YO 12 1.9.1983 the interference signal) at that sampling instant and the value of this corrected signal at a previous sampling in-slant, this last-mentioned value of the corrected signal having teen multiplied prcviollsly by tile ratio between the value of` the rccov*red data signal at the actual sampling install and the value of -the recovered data signal at the previous sampling instant; modifying the Coffey-c ens is effected or not effected depending on whether the said two values of the recovered data signal differ lo from zero or whether at least one of -these values is equal to Nero. If the actual sampling instant and -the previous sampling instant, which is used to calculate the error signal and which is not of necessity the immediately pro-ceding instant, are separated by the period T of the data, the error signal c at the actual sampling instant nor n -to simplify the description) may be written:
c = f - run (5) f and run - 1) being the values of the corrected no-ceiled signal at the sampling instants n and (n - 1), by and bun - 1) being the values of the data signal no-covered at the sampling instants n and (n - 1).
In the case in which the data signal transmitted by the remote modem is a -two-level signal or results from a pseudo -ternary encoding of -two-level data, the data sign net required by the decision circuit has a positive and a negative level, characterized by the sign of the corrected signal. So in that case by = Sgn[r(n)~ and bun - 1) =
Sgn[r(n - 1)], where Sun r ] means sign of L ]" In that case the above formula (5) may be written:
c = f - run - 1).Sgn[r(n)].Sgn run - I) (~) Fig. 2 shows an embodiment of a receiver accord-in to the invention which, to adjust the coefficients of the filter of -the echo canceler and -the equalizer, Utah-I ~1'11F 82.,)X7 13 1.9.1983 lives an error signal formed in accordance with -the pro-Syria described in the -two above-rnentionec~ Patent Apply-cations. yo-yo of example, fig. 2 illustrates -the case in which the recovered data signal has a positive level and a negative level, so that the formula (6) is vapid and the modificatior1s of the coefficients are Avis effected, as the recovered data signal never has the zero level. In Fig. 2, elements having the same function as those in it 1 are given the same reference signs.
Let it be assumed for the example illustrated by Fig. 2 that in sampling circuit 19 the received correct-Ed signal f is sampled at a frequency pa which is equal -to 4 times the frequency l/T of' the data, so that the sampling instants to may be written: to = n (1 q/L~?T, n being an integer extending from - Jo to + GO and q assuming the values O, 1, 2, 3. In decision circuit 9, the data by are recovered at the frequency 1/T at the in-slant nut, in the form of the quantities Sgn[r(n)~. The error signal c must be calculated at the frequency Fax at all sampling instants tax Circuit 14 comprises a portion 25 which cowlick-fates this error signal c. This circuit portion 25 come proses a delay circuit 26 producing a delay T and being connected to the output of sampling circuit 19, so that at an instant characterized by n the values f and run - 1) of' the signal f are obtained a-t -the two terminals of de-lay circuit 26. The circuits 27 and 28 are connected to the input and to the output of delay circuit 26, respect lively and are formed just like decision circuit 9 with I the aid, for example, of a comparator circuit whose in-venting input terminal is at the Nero potential, so that they produce the quantities Sgn[r(n)] and Sgn[r(n 1)], respectively. on Exclusive Circuit 29 forms the product Sgn[r(n)~.Sgn[r(n - I A multiplying circuit JO forms the product run - 1). Sgn[-r(n)]. Sgn[r(n - Andy a sub-treating circuit 31, whose (+) input is connected to the input of delay circuit 26 and whose (-) input it con-netted to the 01ltpUt of` mul-ti,plyir1g circuit JO, produces PHI 82~587 14 the error signal c in accordance with the formula I
In the embodiment of the receiver shown in Yoga 2, the error signal c thus formed is not directly used for the adjustment of the filter coefficients of the echo canceler and the equalizer. First, in accordance with a known method by means of which it is possible to simplify the calculation of the coefficients only the sign of the error signal is used, that is to say the quantity Sun [ennui which is formed in a circuit 32.
lug As regards the equalizer, to adjust the Coffey-clients of filter 15, use is made or a signal erg formed by only retaining every other of the quantities Sun no formed at the sampling frequency Fax this operation being effected by means of a flip-flop 33, which is connected to the output of circuit 32 and whose clock input receives the signal H which has the frequency Fog = Foe.
Thus the signal erg used to adjust the coefficients of transversal filter 15 in accordance with the formula (4) is generated with the same frequency Fog as that of the synthetic interference signal I.
For the echo canceler in which the synthetic echo signal I is generated at the frequency Fax by means of the four transversal filters forming processing arrange-mint 12 as described in the foregoing, the signal Sun Sweeney formed with the sampling frequency Fax could be used directly to adjust the coefficients of these filters but, in accordance with an embodiment of the echo canceler described in the above-mentioned Canadian Patent Apply-cation 438,539 a signal eta formed in the following way in a logic circuit 34 is used to adjust these coefficients in accordance with the formula (2). This logic circuit 3 receives at one input the signal Sun Cot supplied by circuit 32 and at another input the signal Sun [f]
supplied by circuit 27. Logic circuit 34 is arranged to provide a two-bit signal eta r the number represented by these two hits being equal to zero when the quantities Sun [en and Sun run have different values and hying PHI 82~587 15 equal to I or -1 when the quantities Sgn[e(n)~and Sgnrr(n~ have the same values Al or I As demon-striated in said Canadian Patent Application No. 438,539, -the action of the signal Sgn[r(n)] for reducing the residual echo signal is dominant when the echo signal I has a higher level than the received useful signal so that is to say in practice at the beginning of the convergence of the echo counselor The action of the signal SgnLe(n)] is dominant when the echo signal o Jo t) has a lower level than the received useful signal so and results in practice in the residual echo signal being fully canceled.
PI 82.587 11 sunnily In that case, traversal ton 15 of the equalizer receives -the signal H having the frequency F
supplied by timing circuit 21 to sample at this frequency the data signal by recovered by decision circuit 9. In filter 15, the samples of the synthetic interference sign net I are calculated at this frequency Fog = foe in accordance with a formula which is similar to the formula (3). To modify the coefficients of filter 15, the error signal erg of the equalizer is calculated in calculating circuit 14 at the sampling frequency F OF. This error signal erg is applied to control circuit 16, in which the coefficients of filter 15 are iteratively adjusted in accordance with the recursion formula (4).
With a receiver of this construction, in which the signal produced by subtracting circuit 11 is sampled at the Shannon frequency before being applied simultane-ouzel to clock recovery circuit 20 and to circuit 14 form-in the error signal for the echo canceler and the equal-sizer, and in which at least the echo canceler operates at this Shannon sampling frequency, the rather surprising result appeared in practice that the convergence of the assembly is obtained rapidly, which finds expression in a stable recovered clock and the cancellation of the unwanted echo and interference signals A particularly satisfactory operation is obtained when, to adjust the coefficients of the trays-vernal filters of the echo canceler and the equalizer error signals are used which are formed in the wanner described in Canadian Patent application No. 438,539 relating to an echo canceler and in Canadian Patent Application Nod 438,538 relating to an equalizer. Accord-in to these Patent Applications filed on October 6, 1983 by Applicants, the filter coefficients of an echo can-celled or an equalizer are modified with the aid of an error signal determined at an actual sampling instant by forming the difference between the value of the corrected received signal (the echo signal or 1'~l1 YO-YO 12 1.9.1983 the interference signal) at that sampling instant and the value of this corrected signal at a previous sampling in-slant, this last-mentioned value of the corrected signal having teen multiplied prcviollsly by tile ratio between the value of` the rccov*red data signal at the actual sampling install and the value of -the recovered data signal at the previous sampling instant; modifying the Coffey-c ens is effected or not effected depending on whether the said two values of the recovered data signal differ lo from zero or whether at least one of -these values is equal to Nero. If the actual sampling instant and -the previous sampling instant, which is used to calculate the error signal and which is not of necessity the immediately pro-ceding instant, are separated by the period T of the data, the error signal c at the actual sampling instant nor n -to simplify the description) may be written:
c = f - run (5) f and run - 1) being the values of the corrected no-ceiled signal at the sampling instants n and (n - 1), by and bun - 1) being the values of the data signal no-covered at the sampling instants n and (n - 1).
In the case in which the data signal transmitted by the remote modem is a -two-level signal or results from a pseudo -ternary encoding of -two-level data, the data sign net required by the decision circuit has a positive and a negative level, characterized by the sign of the corrected signal. So in that case by = Sgn[r(n)~ and bun - 1) =
Sgn[r(n - 1)], where Sun r ] means sign of L ]" In that case the above formula (5) may be written:
c = f - run - 1).Sgn[r(n)].Sgn run - I) (~) Fig. 2 shows an embodiment of a receiver accord-in to the invention which, to adjust the coefficients of the filter of -the echo canceler and -the equalizer, Utah-I ~1'11F 82.,)X7 13 1.9.1983 lives an error signal formed in accordance with -the pro-Syria described in the -two above-rnentionec~ Patent Apply-cations. yo-yo of example, fig. 2 illustrates -the case in which the recovered data signal has a positive level and a negative level, so that the formula (6) is vapid and the modificatior1s of the coefficients are Avis effected, as the recovered data signal never has the zero level. In Fig. 2, elements having the same function as those in it 1 are given the same reference signs.
Let it be assumed for the example illustrated by Fig. 2 that in sampling circuit 19 the received correct-Ed signal f is sampled at a frequency pa which is equal -to 4 times the frequency l/T of' the data, so that the sampling instants to may be written: to = n (1 q/L~?T, n being an integer extending from - Jo to + GO and q assuming the values O, 1, 2, 3. In decision circuit 9, the data by are recovered at the frequency 1/T at the in-slant nut, in the form of the quantities Sgn[r(n)~. The error signal c must be calculated at the frequency Fax at all sampling instants tax Circuit 14 comprises a portion 25 which cowlick-fates this error signal c. This circuit portion 25 come proses a delay circuit 26 producing a delay T and being connected to the output of sampling circuit 19, so that at an instant characterized by n the values f and run - 1) of' the signal f are obtained a-t -the two terminals of de-lay circuit 26. The circuits 27 and 28 are connected to the input and to the output of delay circuit 26, respect lively and are formed just like decision circuit 9 with I the aid, for example, of a comparator circuit whose in-venting input terminal is at the Nero potential, so that they produce the quantities Sgn[r(n)] and Sgn[r(n 1)], respectively. on Exclusive Circuit 29 forms the product Sgn[r(n)~.Sgn[r(n - I A multiplying circuit JO forms the product run - 1). Sgn[-r(n)]. Sgn[r(n - Andy a sub-treating circuit 31, whose (+) input is connected to the input of delay circuit 26 and whose (-) input it con-netted to the 01ltpUt of` mul-ti,plyir1g circuit JO, produces PHI 82~587 14 the error signal c in accordance with the formula I
In the embodiment of the receiver shown in Yoga 2, the error signal c thus formed is not directly used for the adjustment of the filter coefficients of the echo canceler and the equalizer. First, in accordance with a known method by means of which it is possible to simplify the calculation of the coefficients only the sign of the error signal is used, that is to say the quantity Sun [ennui which is formed in a circuit 32.
lug As regards the equalizer, to adjust the Coffey-clients of filter 15, use is made or a signal erg formed by only retaining every other of the quantities Sun no formed at the sampling frequency Fax this operation being effected by means of a flip-flop 33, which is connected to the output of circuit 32 and whose clock input receives the signal H which has the frequency Fog = Foe.
Thus the signal erg used to adjust the coefficients of transversal filter 15 in accordance with the formula (4) is generated with the same frequency Fog as that of the synthetic interference signal I.
For the echo canceler in which the synthetic echo signal I is generated at the frequency Fax by means of the four transversal filters forming processing arrange-mint 12 as described in the foregoing, the signal Sun Sweeney formed with the sampling frequency Fax could be used directly to adjust the coefficients of these filters but, in accordance with an embodiment of the echo canceler described in the above-mentioned Canadian Patent Apply-cation 438,539 a signal eta formed in the following way in a logic circuit 34 is used to adjust these coefficients in accordance with the formula (2). This logic circuit 3 receives at one input the signal Sun Cot supplied by circuit 32 and at another input the signal Sun [f]
supplied by circuit 27. Logic circuit 34 is arranged to provide a two-bit signal eta r the number represented by these two hits being equal to zero when the quantities Sun [en and Sun run have different values and hying PHI 82~587 15 equal to I or -1 when the quantities Sgn[e(n)~and Sgnrr(n~ have the same values Al or I As demon-striated in said Canadian Patent Application No. 438,539, -the action of the signal Sgn[r(n)] for reducing the residual echo signal is dominant when the echo signal I has a higher level than the received useful signal so that is to say in practice at the beginning of the convergence of the echo counselor The action of the signal SgnLe(n)] is dominant when the echo signal o Jo t) has a lower level than the received useful signal so and results in practice in the residual echo signal being fully canceled.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. A receiver used in a data transmission modem for recovering, from the baseband signal of the receive path, the data signal transmitted by the remote modem, this receiver comprising an echo canceller incorporating an adjustable processing arrangement comprising at least one transversal filter and receiving a signal from the transmit path, a self-adaptive equalizer comprising a transversal filter receiving the data signal recovered by the desicion circuit of the receiver, and subtracting cir-cuit for subtracting from the baseband signal of the receive path the synthetic echo and synthetic interference signals generated in the echo canceller and the equalizer, the output signal of the subtracting circuit being sampled for application to a circuit forming the error signals used to adjust the filter coefficients of the echo canceller and the equalizer, characterized in that the output signal of the subtracting circuit is further applied to a circuit for recovering the clock of the received data after having been sampled at a sampling frequency derived from this clock re-covery circuit and satisfying the Shannon theorem with re-gard to the signal transmitted by the modem, while the syn-thetic echo signal is generated at said sampling frequency.
2. A receiver as claimed in Claim 2, characterized in that the synthetic interference signal is generated at a sampling frequency which is at least equal to half the sampling frequency at which the synthetic echo signal is ge-nerated.
3. A receiver as claimed in Claim 1 or 2, charac-terized in that the filter coefficients of the echo can-celler and the equalizer are adjusted by means of error signals derived from a signal determined at an actual sampling instant by forming the difference between the value of the output signal of the subtracting circuit at that sampling instant and the value of this signal at a previous sampling instant, previously multiplied by the ratio be-tween the value of the recovered data signal at the actual sampling instant and the value of the recovered data signal at the previous sampling instant, modifying the coefficients being effected or not effected depending on whether the said two values of the recovered data signal differ from zero or at least one of those two values is equal to zero.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8217289 | 1982-10-15 | ||
| FR8217289A FR2534754A1 (en) | 1982-10-15 | 1982-10-15 | RECEIVER FOR A DATA TRANSMITTING MODEM HAVING AN ECHO CANCER AND AN EQUALIZER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1211524A true CA1211524A (en) | 1986-09-16 |
Family
ID=9278307
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000438874A Expired CA1211524A (en) | 1982-10-15 | 1983-10-12 | Receiver for a data transmission modem, comprising an echo canceller and an equalizer |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4531220A (en) |
| EP (1) | EP0107246B1 (en) |
| JP (1) | JPS5994928A (en) |
| AU (1) | AU558758B2 (en) |
| CA (1) | CA1211524A (en) |
| DE (1) | DE3375871D1 (en) |
| FR (1) | FR2534754A1 (en) |
Families Citing this family (26)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2144950A (en) * | 1983-08-10 | 1985-03-13 | Philips Electronic Associated | Data transmission system |
| LU85402A1 (en) * | 1983-12-01 | 1984-09-11 | Siemens Ag | METHOD AND CIRCUIT ARRANGEMENT FOR COMPENSATING CROSS-SPEED AND O. ECHO SIGNALS |
| US4677668A (en) * | 1984-05-01 | 1987-06-30 | North Carolina State University | Echo canceller using parametric methods |
| JPS6173430A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing device of echo |
| JPS6173432A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing device of echo |
| JPS6173429A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing method of echo |
| JPS6173431A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing method of echo |
| GB2164827B (en) * | 1984-09-19 | 1988-04-20 | Nec Corp | Method of cancelling echoes in full-duplex data transmission system |
| JPS6173433A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing method of echo |
| JPS6173435A (en) * | 1984-09-19 | 1986-04-15 | Nec Corp | Removing device of echo |
| NZ214905A (en) * | 1985-01-29 | 1988-09-29 | British Telecomm | Noise cancellation by adaptive filter compensates for timing variations |
| SE447777B (en) * | 1985-04-22 | 1986-12-08 | Ellemtel Utvecklings Ab | PROCEDURE FOR SETTING A DIGITAL EQUIPMENT FILTER AT THE SAME TIME OF ADAPTIVE ECO-ELIMINATION AND ADAPTIVE ELIMINATION OF INTERFACES INCURRED BY INTERSYMBOL INTERFERENCE, AND PROCEDURE FOR IMPLEMENTATION OF PROCEDURE |
| IT1184949B (en) * | 1985-05-14 | 1987-10-28 | Sip | IMPROVEMENT OF BIDIRECTIONAL NUMERIC TRANSMISSION SYSTEMS WITH D ECHO CANCELLATION |
| US4760596A (en) * | 1986-02-25 | 1988-07-26 | Gte Laboratories Incorporated | Adaptive echo cancellation and equalization system signal processor and method therefor |
| US4742510A (en) * | 1986-04-04 | 1988-05-03 | Massachusetts Institute Of Technology | Near and far echo canceller for data communications |
| FR2614484B1 (en) * | 1986-12-30 | 1994-04-08 | Telecommunications Sa | DATA TRANSMISSION TERMINAL ON A BIDIRECTIONAL ANALOGUE CHANNEL WITH ECHO COUPLED AT THE RECEIVING PACE |
| US4970715A (en) * | 1987-03-27 | 1990-11-13 | Universal Data Systems, Inc. | Modem with improved remote echo location and cancellation |
| FR2698502B1 (en) * | 1992-11-25 | 1994-12-23 | Cit Alcatel | Baud rate recovery device in a modem receiver. |
| US5917809A (en) * | 1997-01-08 | 1999-06-29 | Analog Devices, Inc. | Asymmetric digital subscriber loop modem and method |
| JP3097586B2 (en) * | 1997-03-06 | 2000-10-10 | 日本電気株式会社 | Signal detector |
| US6807228B2 (en) | 1998-11-13 | 2004-10-19 | Broadcom Corporation | Dynamic regulation of power consumption of a high-speed communication system |
| US6928106B1 (en) * | 1998-08-28 | 2005-08-09 | Broadcom Corporation | Phy control module for a multi-pair gigabit transceiver |
| US6363129B1 (en) * | 1998-11-09 | 2002-03-26 | Broadcom Corporation | Timing recovery system for a multi-pair gigabit transceiver |
| WO2000065791A1 (en) * | 1999-04-22 | 2000-11-02 | Broadcom Corporation | Gigabit ethernet with timing offsets between the twisted pairs |
| US6643271B1 (en) * | 1999-04-30 | 2003-11-04 | 3Com Corporation | Adjustable gain transmit cancellation in a full-duplex modem data access arrangement (DAA) |
| US20030096935A1 (en) * | 2001-11-16 | 2003-05-22 | Nagpal Vidhu J. | Impact resistant polyureaurethane and method of preparation |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US31253A (en) * | 1861-01-29 | Machine | ||
| US4144417A (en) * | 1975-03-07 | 1979-03-13 | Kokusai Denshin Denwa Kabushiki Kaisha | Echo cancelling system |
| JPS54109720A (en) * | 1978-02-16 | 1979-08-28 | Toshiba Corp | Ghost signal erasing device |
| FR2469837A1 (en) * | 1979-11-07 | 1981-05-22 | Trt Telecom Radio Electr | CARRIER DETECTION DEVICE IN A MODEM PROVIDED WITH AN ECHO CANCER |
| FR2478914B1 (en) * | 1980-03-19 | 1986-01-31 | Ibm France | METHOD AND DEVICE FOR INITIAL ADJUSTMENT OF THE CLOCK OF A SYNCHRONOUS DATA RECEIVER |
| FR2490901A1 (en) * | 1980-09-19 | 1982-03-26 | Trt Telecom Radio Electr | DIGITAL ECHO CANCER WITH ANALOGUE-DIGITAL CONVERTER WITH ADJUSTABLE DYNAMIC |
| US4422175A (en) * | 1981-06-11 | 1983-12-20 | Racal-Vadic, Inc. | Constrained adaptive equalizer |
-
1982
- 1982-10-15 FR FR8217289A patent/FR2534754A1/en active Pending
-
1983
- 1983-10-12 CA CA000438874A patent/CA1211524A/en not_active Expired
- 1983-10-13 DE DE8383201466T patent/DE3375871D1/en not_active Expired
- 1983-10-13 JP JP58190029A patent/JPS5994928A/en active Granted
- 1983-10-13 EP EP83201466A patent/EP0107246B1/en not_active Expired
- 1983-10-14 AU AU20183/83A patent/AU558758B2/en not_active Ceased
- 1983-10-17 US US06/542,837 patent/US4531220A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| FR2534754A1 (en) | 1984-04-20 |
| AU2018383A (en) | 1984-04-19 |
| JPH0310256B2 (en) | 1991-02-13 |
| EP0107246A1 (en) | 1984-05-02 |
| US4531220A (en) | 1985-07-23 |
| AU558758B2 (en) | 1987-02-05 |
| DE3375871D1 (en) | 1988-04-07 |
| EP0107246B1 (en) | 1988-03-02 |
| JPS5994928A (en) | 1984-05-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |