Abstract: According to one example embodiment, a communication system includes a transmitter and a receiver for receiving symbols from a phase-shift shift keying modulation. The system also includes estimation means for estimating a frequency error relating to a symbol based on a sequence of symbol phases. The receiver includes calculation means for calculating a phase sequence, called an initial sequence, based on decisions made on symbols. The receiver also includes means for detecting and correcting phase jumps in this initial sequence in order to supply a phase sequence, called a final sequence, to the frequency error estimation means.

Abstract: The invention relates to digital transmission. It particularly relates to a method of transmitting data using multi-carrier Code-division Multiple Access (CDMA) for accessing a transmission system. The method comprises a step of modulating the data to be transmitted using Orthogonal Frequency-division Multiplexing (OFDM) for producing OFDM modulated data symbols and a step of spreading the OFDM modulated data symbols with spreading codes including a set of predefined sequences, wherein the sequences are predefined so that they satisfy predetermined auto-correlation and/or cross-correlation criteria within a region around the zero-time offset of the correlation function, defined as an interference Free Window (IFW).

Abstract: A digital transmission system utilizing data coding at the transmitter and data decoding at the receiver, the decoding being iterative, reliability data about soft decisions being calculated for each iteration. The last iteration results in a hard decision. Soft decisions are transformed so as to normalize the mean value of the reliability data, using evolutive weighting of the soft decisions with the received data. The coding is preferably a product code concatenated with a block code such as, for example, a Reed Solomon code. Such coding is well suited to upstream transmission in an interactive satellite communication system.

Abstract: An antenna system (1) transmits return signals, for example, in the band Ka, based on signals received from a distribution network in the band from 2.5-3 GHz. The return signals are transmitted through the network from a user receiver (PC) with a frequency lying below 65 MHz, they are processed in a frequency converter (up-C) between the network and the antenna system so as to be delivered to the antenna system with a frequency lying in the 2.5-3 GHz band, and frequency management data received in the downstream channel are used in the frequency converter (up-C) for selecting the frequency in the 2.5-3 GHz band.

Abstract: Disclosed is a communication system comprising a main station, a transmission medium, and terminals. The terminals transmit requests to the main station have reservations granted to them on the transmission medium. Each request indicates a number of reservations. Upon receiving a request, the main station adds the number of reservations indicated to an allocation counter associated with the requesting terminal. The invention enables the requesting method to be less vulnerable to data losses. It consists in a resetting of the request counter and allocation counter, for example when an anomaly is detected in the transmission of the data.

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: 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: 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 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: A communication protocol for use by stations in multiple access telecommunication network wherein communication between stations is via a master station. An upstream channel to the master station is shared by the other stations and has successive frames each consisting of K message slots, each message slot including a data part (DM) for the transmission of a message and M minislots for transmission of slot reservation signals. According to the invention, in case of unsuccessful message transmission and collision between transmission requests, reservation signals for retransmission of a message can be transmitted in any of the K.times.M minislots of each entire frame. The large number of minislots thereby made available reduces the danger of collision between retransmission requests.

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 communication protocol is disclosed where unsuccessful transmissions between stations are reduced. Each station includes a first queue for receiving newly generated messages and a second queue for receiving recycled messages which were not successfully transmitted. A detector in a reception sub-assembly of each station detects that the number of unsuccessful transmissions or collisions exceeds a predetermined threshold. Until the collisions are solved, a recycling circuit recycles the collided messages by providing them to the second queue and increasing their transmission priority over any newly generated messages contained in the first queue.

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 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.