Compagnie Industrielle Des Telecommunications Cit-alcatel

Alcatel

Agence Nationale De Valorisation De La Recherche (anvar)

Michel Levy

Christian Poinas

Jean Lassaux

Serge Surie

Odile Macchi Nee Danjon

Cesar Macchi

Jean-Philippe Haag

Jean Le Bourlot

A subscriber card includes a controller for concentrating Internet frames so as not to occupy a telephone circuit for each call to an Internet service provider. The subscriber card is connected to a switching matrix that facilitates transmission of the concentrated Internet frames to a data transmission network. The subscriber card handles multiple subscriber inputs and statistically multiplexes data from the multiple subscriber inputs in order to increase throughput.

Subscriber card, a subscriber unit, and an exchange for concentrating internet frames

Subscriber card, subscriber connecting unit and relay centre for concentrating internet frames

In a QPSK system using one cycle of a squared-off sinusoid per Baud period to represent the data dibits, the following are disclosed:

QPSK system with one cycle per Baud period

Echoes occur in telephone systems whenever signals in one channel of a two way conversation spill over into the other channel. The present echo canceller is particulary intended for use with a hands free telephone where the spill over is in the form of an acoustic echo from the loud speaker (2) to the microphone (1). The signals are sampled at a rate 1/T and are made available as digital samples. A synthetic copy of the echo signal is generated by means of an adaptive digital non-recursive time domain transversal filter. Instead of tapping the filter at unit time intervals equal to the sampling period T in the conventional manner, the filter is tapped at unit intervals equal to twice the sampling interval. For a given amount of calculation in the filter, this has the effect of doubling the length of the filter's impulse response.

Digital echo canceller

A phase noise correction circuit for a synchronous data transmission system using symbols and including a decision circuit (33) at its receiving end for supplying an estimate of the transmitted symbols on the basis of the received symbols, wherein said correction circuit comprises a phase shifter circuit (36) located at the receiving end ahead of the decision circuit (33) and provided with a third-order phase-controlling feedback circuit (37) comprising:

Phase noise correction circuit for a data transmission system

An echo canceller for a full-duplex carrier modulation transmission system terminal. The echo canceller includes a digital time-domain complex transversal filter with controlled weighting coefficients and an offset equal to a submultiple l of a Baud period .DELTA. related to a rate at which a stream of complex symbols is received at the input of the filter. These complex symbols include complex symbols outputted by a coder of a transmitter of the terminal at the rate l/.DELTA. interleaved with l-1 null symbols. The transversal filter output is connected to a digital modulator operated at the transmitter carrier frequency with instantaneous values updated at intervals equal to the Baud period to generate a passband echo copy signal. The invention is of particular benefit in transmission systems in which the product of the transmission carrier frequency and the Baud period is an integral multiple of l/4, as digital implementation of the modulator is then extremely simple.

Adaptive echo canceller for full-duplex transmission of data

Data in the form of multi-value symbols is transmitted at a symbol rate 1/.DELTA.T. At the receiver a decision circuit supplies estimates of the transmitted symbols on the basis of the received symbols. The present invention concerns compensating phase noise after equalization if any of the received symbols and before application of the received symbols to the decision circuit (38, 39). The received symbols are in complex form with in-phase and quadrature components y.sub.k ' and y.sub.k ' respectively. Phase noise is compensated by complex multiplication in a multiplier (36) of the received symbols by a complex coefficient. The invention is particularly applicable to quadrature modulation systems, but if only one channel is transmitted the quadrature channel can be simulated using the Hilbert transform of the one channel.

Method of compensating phase noise at the receiver end of a data

Data in the form of multi-value symbols is transmitted at a symbol rate 1/.DELTA.T. At the receiver a decision circuit supplies estimates of the transmitted symbols on the basis of the received symbols. The present invention concerns compensating phase noise after equalization, if any, of the received symbols and before application of the received symbols to the decision circuit (38, 39). The received symbols are in complex form with in-phase and quadrature components y.sub.k ' and y.sub.k ' respectively. Phase noise is compensated by complex multiplication in a multiplier (36) of the received symbols by a complex coefficient m.sub.k

Method of reducing phase noise at the receiver end of a data

A system for transmitting data between distant locations comprises a modem at each location and a communication channel, typically a telephone line, whose transfer function has a principal component whose variation is slow and a second component whose variation is faster, but whose action is lesser. A correction device is located in the modem at the output of the channel and comprises an equalization filter constructed to compensate for the principal component and a digital adaptive network having a few coefficients and a low time constant, compatible with the frequency of the second component. The coefficients of the digital network may be adapted independently of those of the equalization filter.

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Massy, France

Michel Levy