Abstract: Echo canceler associated with a modem utilizing amplitude and phase modulation of a carrier, the echo canceler comprising adaptive filters (16-1) to (16-p) producing signals which are combined in an adder (15) for forming a synthetic echo signal .epsilon.(n). The coefficients of these filters are adjusted to minimize the mean square value of the residual echo signal e(n)=.epsilon.(n)-.epsilon.(n), where .epsilon.(n) is the echo received. The echo canceler comprises a code conversion circuit (17) which receives a signal D(n) characterizing in each modulation interval the amplitude and phase state of the carrier to be transmitted and which produces distinct configurations of several numbers of values +1, -1 or 0, said distinct configurations corresponding to the distinct possible states of the carrier to be transmitted such that elementary signals D.sub.1 (n) to D.sub.p (n) are formed which are mutually independent in the mean and which are applied to the filters (16-1) to (16-p).

Abstract: An arrangement for cancelling the composite echo signal formed by, for example, a linear component and a variable-phase component, comprises a linear echo canceller and a variable phase echo canceller, the difference circuits of these echo cancellers being arranged in cascade. The adjustable signal processing arrangements of each echo canceller are controlled for minimizing a predetermined function (mean square value or time average of this means square value), either of a residual echo signal appearing at the output of the difference circuit of this echo canceller itself or of a residual echo signal appearing at the output of the cascade arrangement of the difference circuits. In all cases the signal at the output of the linear echo canceller contains only a residual variable-phase signal which can be compensated for by the variable-phase echo canceller.

Abstract: Echo canceler associated with a modem utilizing amplitude and phase modulation of a carrier, the echo canceler comprising adaptive filters (16-1) to (16-p) producing signals which are combined in an adder (15) for forming a synthetic echo signal .epsilon. (n). The coefficients of these filters are adjusted to minimize the mean square value of the residual echo signal e(n)=.epsilon.(n)-.epsilon.(n), where .epsilon. (n) is the echo received. The echo canceler comprises a code conversion circuit (17) which receives a signal D(n) characterizing in each modulation interval the amplitude and phase state of the carrier to be transmitted and which produces distinct configurations of several veral numbers of values +1, -1 or 0, said distinct configurations corresponding to the distinct possible states of the carrier to be transmitted such that elementary signals D.sub.1 (n) to D.sub.p (n) are formed which are mutually independent in the mean and which are applied to the filters (16-1) to (16-p).

Abstract: The filter coefficients of an echo cancelling arrangement having a near echo canceller and a distant echo canceller are initialized in accordance with a method and apparatus wherein the following steps are performed:transmission of at least two training sequences each comprising a pair of complementary S and C sequences having autocorrelation functions such that, if added, their sidelobes cancel, each S and C sequence being followed by a variable time interval .DELTA., determined as a function of the measured distant echo delay .tau.

Abstract: A method of reducing the convergence time of an echo canceller including a transversal filter having N coefficients comprises at least the following steps:transmission of a training data signal D(n) constituted by data transmitted at instants nT, T being the data interval, and being periodically reproduced after a duration LT at least equal to NT and having the property: ##EQU1## where d and d.sup.x are the value of the data signal D(n) and its complex conjugate value, respectively;calculation of the coefficients of the transversal filter carried out after the instant of appearance of the echo signal produced in response to said training signal in accordance with the expression: ##EQU2## where C and C.sub.o are the vectors of the N coefficients of the transversal filter at the beginning and at the end of the period of calculating the coefficients, respectively,e(n) is the difference signal,D.sup.x (n) is the vector of the complex conjugate values of the N data stored in the transversal filter, and.sigma..sup.

Abstract: A self-adaptive equalizer for use in a data modem for correcting in the baseband a received data signal. The equalizer comprises a difference circuit for determining the difference between a received signal and a correction signal formed at a sampling frequency by a transversal filter having adjustable coefficients, and which produces a corrected signal which is applied to a decision circuit which recovers the data signal. The output of the decision circuit is applied to the transversal filter, the coefficients of which are adjusted so as to minimize the mean-square value of an error signal. The error signal at each actual sampling instant is formed by deriving the algebraic difference between the value of the corrected signal at that sampling instant and the value thereof at a previous sampling instant, the latter value being first multiplied by the ratio between the value of the recovered data signal at the actual sampling instant and the value thereof at the previous sampling instant.

Abstract: Method and apparatus for measuring the delay of the distant echo in an echo ancelling arrangement comprising a near echo canceller, a delay line and a distant echo canceller using the steps oftransmitting, by modulation of a carrier, a data sequence having a periodic autocorrelation function with sidelobes of negative or zero value, this sequence having a duration at least equal to the maximum value of the delay to be measured and a number of elements determined by the accuracy desired for measurement of the delay;calculating the correlation function between the data of a next transmitted sequence and the data formed by demodulating the received signal and storing calculated samples of the correlation function in a memory; and determining, among the samples stored, the sample corresponding to the maximum of the correlation function and the rank of that sample.

Abstract: An echo canceller used in a data transmission modem for cancelling in the baseband signal of the receive path an echo signal .epsilon.(t) produced by the data signal from the transmit path. The echo canceller comprises a difference circuit for forming the difference between the signal from the receive path s(t)+.epsilon.(t) and a synthetic echo copy signal .epsilon.(t). The echo copy signal is formed by at least one transversal filter which operates at a sampling frequency equal to the frequency of the data and whose coefficients are adjusted to minimize the mean-square value of an error signal. This error signal e(n) at an actual sampling instant n of the filter is determined by forming the difference between the value of the output signal of the difference circuit at the instant n and the value of this signal at the preceding sampling instant (n-1), which has been multiplied by the ratio between the value of the data recovered at the instant n and the value of the data recovered at the instant (n-1).

Abstract: Method and apparatus for reducing the convergence time of an echo canceller including a transversal filter having N adjustable complex coefficients comprises the following steps:transmitting a complex training signal constituted by data d(n) transmitted at instants nT, where T is the data interval, having a period LT at least equal to NT and having the following two properties: ##EQU1## for every integer i such that 1.ltoreq.i.ltoreq.N-1, and ##EQU2## for every integer i such that 0.ltoreq.i.ltoreq.N-1; after the transmission of N data, calculating the coefficients C of the transversal filter from the sequence formed by the next L data transmitted, in accordance with the expression: ##EQU3## where C.sub.o represents the N initial coefficients,e.sub.R (n) is the difference signal between the received signal and the real output signal of the transversal filter,D.sup.* (n) represents the complex conjugate value of the last N data entering the transversal filter, and.sigma..sup.

Abstract: The test arrangement is intended to test, for example, a modem whose transmitter and receiver are coupled to the transmission line by means of a hybrid junction and comprises an echo canceller. The test consists of comparing a test signal applied to the transmitter with the signal restituted by the receiver when the modem is fedback from the line side. The test arrangement comprises an adder one input of which receives the error signal coming from the echo canceller, the other input receiving, during the test the feedback signal, its output being connected to the receiver. Means have been provided to make the signal restituted by the receiver different from the test sequence, when the error signal of the echo canceller exceeds a threshold.

Abstract: A receiver used in a data transmission modem having a receive path containing a baseband signal and clock signal, and a transmit path. An echo canceller is employed having a transversal filter connected to the transmit path for generating a synthetic echo signal. A self-adaptive equalizer includes a transversal filter connected to receive a data signal from the receive path. Subtracting means subtract the signals from the echo canceller and equalizer from the baseband signal in the receive path. The subtracting means output is sampled at a sampling rate which satisfies the Shannon criteria with respect to a transmit signal in the transmit path. The filter coefficients are controlled in response to the sampled signal. The second and third clocking signals for the echo canceller and transversal filter and self-adaptive equalizer transversal filter are derived from recovered clock signals.

Abstract: A carrier detector in a modem provided with an echo canceler comprises a first detection circuit which processes the level of the echo canceler output signal. In addition, the detector comprises a second detection circuit which processes the level of the output signal of an amplitude regulator connected to the output of the echo canceler. This second detection circuit produces an indication of the carrier interruption in the range of the high carrier levels, in which the first circuit is not operative for detecting a carrier interruption.

Abstract: A circuit for the synchronization of the operating cycles of a digital arrangement with an external clock signal which arrangement includes a calculating unit and a circulating store which must produce a sequence of coefficients in a predetermined order at each cycle. The circuit has switching means for circulating the coefficients in the store either in series or word-by-word, means for producing a word clock, means for forming operating cycles synchronous with the word clock and for starting each operating cycle at each characteristic transition of the external clock signal appearing after the end of each cycle. The switching means are controlled to have the sequence of coefficients circulate in series once in each cycle and for having the coefficients circulate word-by-word for the remaining period of time.

Abstract: A resynchronization arrangement for a data receiver having an auto-adaptive equalizer and a demodulator which utilizes a local carrier phaselocked on the received carrier by means of a control loop comprising an integrating circuit. Starting from a signal indicating a synchronization loss the arrangement generates three command pulses: a first pulse makes the adjustable coefficients of the equalizer and the signal in the memory of the integrating circuit equal to zero; a second pulse is used for making a reduced number of coefficients of the equalizer operative immediately after the first pulse and for reducing the time constant of the integrating circuit; a third pulse is used to make the synchronization loss indication signal equal to zero a given period of time after the end of the second pulse. Resynchronization is obtained without the necessity of a return connection to the transmitter.

Abstract: Phase discriminator in a receiver of a system for data transmission by means of phase modulation of a carrier. The phase discriminator comprises a calculating unit arranged for receiving digital signals, whose associated signal samples occur at a rate equal to the data modulation rate, the digital signals being representative of the inphase and quadrature components of the received passband signals at each sampling instant and of the inphase and quadrature components of a reference carrier at a preceding sampling instant. This calculating unit calculates the signal samples of digital signals which are representative of the in-phase and quadrature components of a signal which is derived from the received passband signal by a phase shift over an angle which is equal and opposite to the phase of the reference carrier at the preceding sampling instant.

Abstract: A receiver of a system for data transmission by means of p-phase modulation comprises a digital phase discriminator with a calculating unit which calculates in a first interval of each sampling period the in-phase and quadrature components of a signal derived from a passband signal at sampling instant jT by a phase rotation over an angle equal and opposite to the phase of a reference carrier at instant (j-1)T.A simple derangement detector is obtained by means of a sign detector for a component supplied by the calculating unit during a second interval of each sampling period, the phase of the reference carrier then having been subjected to a phase rotation equal to the phase variation of the transmitted carrier, and by means of a calculated circuit which calculates the quantity .vertline.x.sub.3 .vertline.-kx.sub.3, where k<tan (.pi./p) and x.sub.3, x.sub.