In a data receiver (40) for a quadrature-amplitude-modulated signal s (t) having symbol interval T, which is at least equal to the Nyquist frequency. With the sampling being performed at this rate, the functions conventionally provided by individual bandpass filter (12), phase splitter (14) and equalizer (22) circuits are performed by a single transversal filter equalizer (122). Tap coefficents for the transversal filter equalizer are derived in a decision-directed manner. The tendency of the tap coefficient values to drift is suppressed by adding energy to the received signal at frequencies within the band (0-n/2T) Hz at which the received signal has negligible energy.

Equalizer for complex data signals

A digital telecommunication line circuit implementable on one or more large scale integrated circuit (LSI) chips is described. A simplified integrated hardware structure is provided so as to achieve the combination on an LSI chip of an electronic two-to-four wire hybrid, line impedance matching by automatic digital impedance synthesizing of an output impedance and all digital filtering functions for an all LSI telephone line circuit including automatic equalizing.

All digital LSI line circuit for analog lines

PURPOSE: To lower the level of an error signal by inserting a variable attenuator between an input terminal and an output terminal, comparing the level of an input signal and that of an output signal of a filter whose characteristic is unknown so as to operate a variable attenuator at the lower signal level thereby attenuating the signal. CONSTITUTION: The adaptive digital filter 1 is added with variable attenuators 10, 11 and a signal level comparison circuit 9. When a level of an input signal ak continues to be larger than the level of an output signal of, e.g., a filter 2 whose characteristic is unknown, since +Δ1 is incremented to a storage memory 16, the content is positive, the variable attenuator 11 of the output terminal 5 is operated, an error signal ek is outputted while being attenuated. Since -Δ2 is added to a storage memory 15, the content is negative and since the variable attenuator 10 at the input terminal 4 is not operated, the input signal ak is inputted as it is. The constant +Δ1, -Δ2 are stored to control the attenuators, because the attenuators are not operated against a momentary level change and the time until the attenuators are turned on and the time until they are turned off are set separately. COPYRIGHT: (C)1987,JPO&Japio

Adaptive digital filter

An adaptive analog processor incorporating a analog shift register having a plurality of taps, multipliers at each tap for multiplying the tap value times a weight value, a first adder for summing the output of the multipliers, a second adder for subtracting the output of the adder from a second analog signal, means for incrementing the weights in response to the magnitude and polarity of the error signal and the polarity of the data signal. The invention overcomes the problem of building monolithic multitap adaptive filters utilizing the clipped-data least mean square error algorithm.

Adaptive analog processor

Echo cancellation is carried out on a received demodulated analog signal. The apparatus comprises an analog transversal filter, a computing circuit for generating the direct coefficients a1 to ar and, eventually, feedback coefficients b2 to bm of an analog transversal filter. The input of a computing circuit is connected to the input of an analog transversal filter. The computing circuit is comprised of an analog-to-digital converter, whose output is connected to a self-adaptive digital transversal filter. The values of the digital transversal filter multiplication coefficients are applied, as coefficients, to the multipliers of the analog transversal filter. The optimization criterion is that of the mean quadratic error. The convergence algorithm is that of the gradient. The iterative correction may be carried out at each step on the digital transversal filter's group of coefficients. Or, it can be carried out cyclically of each of the digital transversal filter's coefficients. Variations of the self-adaptive digital transversal filter are described.

Echo correction especially for television broadcast systems

The invention consists in an equalization system with two sections, one at each end of a transmission channel. The section at the transmission end adds control signals to information signals to be transmitted over the line. The section at the reception end generates control signals identical to those added at the transmission end and in phase with the control signals received over the transmission channel, which are separated from the received information signals by means of a first transversal filter with controllable weighting coefficients, the reciprocal transfer function of the transmission channel being synthesized from the locally generated and the received control signals by means of a second transversal filter with controllable weighting coefficients, equalization being achieved by means of a third transversal filter with the same design and same weighting coefficients as the second transversal filter. The invention is applicable to the transmission of data over telephone lines.

Self-correcting equalization system

Selbstadaptives entzerrungssystem fuer einen signaluebertragungskanal

L'invention est du domaine des transmissions. Elle a pour but d'ameliorer les caracteristiques en amplitude et en phase d'une voie de transmission. Elle a pour objet un ensemble d'egalisation compose de deux parties placees aux extremites d'une voie de transmission. La partie placee a l'emission permet d'ajouter des signaux d'asservissement au signal de transmission proprement dit. La partie placee a la reception permet de regenerer des signaux d'asservissement identiques a ceux emis, en phase avec ceux recus par la voie de transmission, de separer dans le signal recu les signaux d'asservissement du signal de transmission au moyen d'un premier filtre transversal a coefficients de ponderation asservis, de synthetiser la transmittance inverse de la voie de transmission a partir des signaux d'asservissement regeneres et de ceux recus, au moyen d'un deuxieme filtre transversal a coefficients de ponderation asservis et de realiser l'egalisation proprement dite au moyen d'un troisieme filtre transversal ayant meme structure et memes coefficients de ponderation que le deuxieme. Elle s'applique avantageusement a la transmission de donnee sur voie telephonique.

Claude Le Dily

Papers

Self-correcting equalization system

Selbstadaptives entzerrungssystem fuer einen signaluebertragungskanal

Ensemble d'egalisation autoadaptatif