Abstract: A system and method is disclosed for transmitting TDMA packets between interactive terminals and a head station using a transmission medium. The system includes an iterative method for determining an optimal sampling instant by computing the average amplitudes only for a predetermined number of the input samples, determining a maximum of the average amplitudes of these samples, deriving an approximation of the optimal sample using the maximum, repeating the average amplitude computation for input samples between the approximation and a neighboring sample whose previously computed average amplitude is the largest, and comparing of the result of each average amplitude computation with a previously computed maximum corresponding to the previous approximation for deriving a new approximation of the optimal sample.

Abstract: The invention relates to a system for transmitting TDMA packets between interactive terminals and a head station via a transmission medium, in which the receiver effects a oversampling of the received signal so as to retrieve the optimal sample corresponding to the transmitted symbol. The invention proposes a method of recovering this optimal sampling instant very rapidly by performing a polynomial interpolation computation between the generated oversamples so as to derive the optimal sampling instant and by filtering the received signal by means of a low-pass filter centered at the optimal sampling instant.

Abstract: The invention relates to a simple method of forming a set of constellations of average power levels lower than a fixed threshold PMAX. The invention is applied to all the cases where the points of the constellations to be formed are not equiprobable, and thus the expression of the average power of the constellation set has a complex form. The invention comprises forming a first set of constellations by considering that the points of each constellation are equiprobable, which enables to form the constellations independently of each other. The exact value P of the average power of the set of constellations thus obtained is then calculated for verifying whether P>PMAX. In that case, the constellation set is modified by suppressing one or various points in one or various constellations so as to obtain an average power P<PMAX for said set.

Abstract: A method of estimating the frequency at the receiving end for a packet transmission system, for estimating a carrier frequency error between received symbols (rk) and transmitted symbols (ck). An error function (H(&Dgr;{circumflex over (f)})) defined for minimizing a magnitude which is representative of an average distance between the received symbols compensated in phase (r′k) and estimations of the received symbols affected by a frequency error estimation (ĉkej2&pgr;k&Dgr;{circumflex over (f)}) is computed. The estimations of the received symbols affected by the frequency error estimation are obtained by varying the frequency error (&Dgr;{circumflex over (f)}) in an acquisition interval ([−fmax, +fmax]) for estimations of the transmitted symbol (ĉk). The estimations of the transmitted, symbols (ĉk) are obtained based on a threshold relating to the phase of the received symbol which is compensated in phase (r′k), in the case of a modulation of the PSK type.

Abstract: An iterative decoder and decoding method for decoding a binary block code defined by a parity check matrix. The parity matrix is processed several times row-by-row so that each iteration of the decoding corresponds to the decoding of the code defined by a row of the matrix for received data. For decoding an extended code, each row defines two separate codes which are decoded with each iteration.

Abstract: The invention relates to a system for transmitting packets from interactive terminals to a head station. The terminals intended for consumers are provided with local oscillators which are not very accurate and use carriers having frequency errors which are relatively large with respect to the theoretical reference value (Fp). The invention provides an improvement of the reception of signals having such a frequency shift at the receiver end. To this end, the invention provides a method of estimating the frequency error &Dgr;{circumflex over (f)}, which consists of rapidly obtaining the maximum value of a discrete error function denoted Z(&Dgr;{circumflex over (f)}) for a given accuracy (Acc) by computing the function Z(&Dgr;{circumflex over (f)}) for a minimal number of points.

Abstract: The invention enables to estimate the frequency offset introduced by a transmission medium based on the transmission of a known sinusoidal-frequency signal. Two samples out of phase by Π/2+p.2Π where p is an integer are multiplied to obtain a trigonometric function of said frequency offset. The estimate thus obtained is advantageously applied for correcting test signals received during a learning period preceding a transmission period between a transmitter and receiver. The estimate is also applicable for initializing adaptive algorithms for recovering the timing or echo cancellation at the level of the receiver. Any transmission system that utilizes one or various carriers and enables to transmit a sinusoidal signal at a given instant, notably Recommendation V34 of the CCITT.

Abstract: The invention relates to any receiver for MPSK (M=2n) modulation, in which an error correction device is used for correcting Tretter type frequency errors and, upstream of this device, a phase estimation device based on decisions made on the received symbols.

Abstract: The invention relates to an interactive packet transmission system of the TDMA type with a return channel between terminals and a network head. The invention proposes a method of recovering the first packet transmitted by a terminal for connection to the system, in accordance with which the transmitted data are searched by performing successive correlations in variable computing windows along the received packet by using a known header. The correlation computations are solely performed on the optimal oversamples, while the estimation of the initial sampling instant is previously effected for each window considered.

Abstract: The invention relates to a method of estimating the frequency at the receiving end for a packet transmission system, for estimating a carrier frequency error between received symbols (rk) and transmitted symbols (ck). The method according to the invention comprises the computation of an error function (H(&Dgr;{circumflex over (f)})) defined for minimizing a magnitude which is representative of an average distance between the received symbols which are compensated in phase (r′k) and estimations of the received symbols affected by a frequency error estimation (ĉkej2&pgr;k&Dgr;{circumflex over (f)}). These are obtained by varying the frequency error (&Dgr;{circumflex over (f)}) in the acquisition interval ([−fmax, +fmax]) for estimations of the transmitted symbol (ĉk).

Abstract: The invention relates to a transmission system via a channel subjected to fading.

Abstract: A digital transmission system provides selective protection by combining a convolutional coding, a punctured coding and a digital quadrature amplitude modulation. The rate of the convolutional coding in N/2N and the modulation uses a 2.sup.2N -point constellation, with N>1.

Abstract: A digital transmission system includes a receiver which is synchronized with a transmitter wherein a correlation is established between a reference sequence and an initialization sequence transmitted by the transmitter. The system further includes an equalizer for operating with a first part of the initialization sequence, and a correlator for operating with a second part of the initialization sequence. This makes it possible to enhance the established correlation with the reference frequency and realize the synchronization, with great precision.

Abstract: A digital transmission system which provides transmission error protection for transmitted data. The input data is encoded using a punctured systematic convolutional trellis code. Row and column components of a matrix formed by the encoded input data are then used to generate a product code in blocks, with trellis closure by addition of redundant data. The data thus encoded is then allocated to quadrature amplitude modulation symbols. At the receiver end the transmitted modulation symbols are decoded by iterative decoding, the reliability of hard decisions being computed so as to provide generation of soft decision output symbols.

Abstract: A digital communication system having a transmitter and a receiver. The receiver transmits a radio-frequency (RF) signal that is continuous phase modulated by digital data. The receiver having a converter, a differential detector, and a sequential decoder. The receiver receives the RF signal. The RF signal is converted into a baseband signal by the converter. The baseband signal is received by the differential detector wherein the continuous phase modulation of the baseband signal is detected. The detected signal is received and the digital data is decoded by the sequential decoder. The sequential decoder has a Viterbi decoder to compensate for intersymbol interference caused by the differential detector. The Viterbi decoder performs reduced Viterbi decoding utilizing a feedback loop (FB) for reducing computing inaccuracies due to the reduction of the number of trellis states.

Abstract: A communication system having a transmitter that supplies test sequences formed from several test frequencies and a receiver having test means for testing the quality of a channel. The test means calculates for the plurality of frequencies both the transfer function of the channel and the channel noise variance. By taking the noise caused by the receiver into account, the test means determine the most suitable frequency band and bit rate for the transmission. This information is supplied to the transmitter to establish the transmission.

Abstract: A digital transmission system comprising a receiver with cascaded equalizers. The transmission system may also include multicarrier modulation means and multicarrier demodulation means comprising a semi-fixed equalizer cascaded with an adaptive equalizer. The semi-fixed equalizer equalizes the relatively stable or slowly and/or slightly changing imperfections which are due to the channel and the adaptive equalizer equalizes the imperfections which are due to transmission noise. The invention likewise relates to a process for determining the characteristics of the semi-fixed equalizer.

Abstract: Digital signal transmission system operating with constellation coding, the system comprising an orthogonal frequency-division multiplexing modulation unit which generates multicarrier signals, and an amplifier which causes signal distortion. The system comprises a predistortion circuit inserted between the multicarrier modulation unit and the amplifier, the circuit predistorting the multicarrier signals received on an input, in opposite sense to distortions created by the amplifier, and generating predistorted multicarrier signals so that, after the predistorted multicarrier signals passing through the amplifier, the amplifier delivers undistorted multicarrier signals. The system may operate in the fixed mode or in the adaptive mode.

Abstract: A multicarrier frequency hopping spread spectrum communications system wherein a transmitting station assigns encoded data symbols to particular ones of a predetermined series of fixed carrier frequencies, the frequency assignments being periodically mixed according to a frequency hopping code, and the encoded data symbols are combined with their assigned carrier frequencies in accordance with an inverse Fourier transform so as to multiplex the encoded data symbols by orthogonal frequency division modulation. A receiving station performs demultiplexing and de-mixing of such multiplexed signals in accordance with the inverse of the multiplexing and mixing performed at the transmitter. The system thereby provides frequency hopping operation without requiring a rapidly tunable and accurately phase controlled oscillator at each of the transmit/receive stations.

Abstract: Multi-user communication system which combines means that implement the spread spectrum coding technique SSC with means that implement the modulation technique of orthogonal frequency-division multiplexing OFDM. This makes it possible to inhance the performance of the SSC system by simplifying certain data processing and data acquisition mechanisms.A preferred use is the use in telephone communication systems between mobile stations and base stations.