Thales

Airbus Defence and Space Sas

Centre National De La Recherche Scientifique

Institut National Polytechnique De Toulouse

Centre National Detudes Spatiales

Benjamin Gadat

Lyonel Barthe

Nicolas Van Wambeke

Catherine Lamy-Bergot

Marie-Laure Boucheret

Charly Poulliat

Thibault Maisonnat

Marc Ratiney

Lionel Ries

Mathieu Gineste

Christian Peyrotte

Cyril Bergeron

Hanaa Al Bitar

Erwann Renan

Mehdi Anteur

Vincent Deslandes

Mathieu Raimondi

Sébastien Marcille

Gomez Cécile

Poulliat Charly

Nicholas Van Wambeke

Tarik Benaddi

Nathalie Thomas

Bilel Raddadi

Arnaud Collin

Jean-Frédéric Chouteau

Christophe Charbonnieras

Hugo Bourgoin

Cécile Gomez

The disclosure relates to an LDPC decoding method which involves performing iterations until a stop criterion is satisfied. Each iteration involves calculating variable messages (α), calculating parity check messages (β), and calculating a posteriori estimation variables. The parity check messages (β) and the posteriori estimation variables (γn) being saturated at a predetermined maximum value. At the end of an iteration, when the number of saturations reaches a specified threshold, the method involves at least a first scaling of the parity check messages (β) and the a posteriori estimation variables (γ). Scaling corresponds to assigning, to a value, an integer which has the same sign and whose absolute value is the nearest integer greater than the absolute value of the value divided by two.

Adaptive scaling of parity check messages for LDPC decoding

An LDPC decoding method is disclosed in which the LDPC code is defined by a parity matrix having a layered structure, and the method involves performing iterations until a stop criterion is satisfied. Each iteration involves the successive processing of the different layers. Processing a layer involves calculating variable messages (a), calculating parity check messages, calculating a posteriori estimation variables (γ), and calculating a partial syndrome. The evaluation of the stop criterion involves checking if, for a plurality of successive iterations, the number of iterations for which all the partial syndromes are zero, from which the number of iterations for which at least one of the partial syndromes is non-zero is subtracted, is greater than or equal to a predetermined stop threshold.

Stop criterion for decoding an LDPC code

The disclosure relates to an LDPC decoding method which involves performing iterations until a stop criterion is satisfied. Each iteration involves computing variable messages (α), computing parity check messages (β), and computing a posteriori estimation variables. Computing a parity check message (β) for a parity check node (CN) involves determining the two smallest values (Mini1, Min2) among the absolute values of the variable messages associated with the parity check node (CN), comparing a difference between said values with a threshold, determining a correction value according to the result of the comparison, and computing the parity check message according to the correction value.

Optimization of the computation of parity check messages in a min-sum LDPC decoding method

A data encoding device suitable for encoding a plurality of LDPC codes is disclosed including an input interface and an output interface, and a first circuit for encoding quasi-cyclic LDPC code, connected at an input to the input interface and at an output to the input of a first multiplexer circuit, a second circuit for encoding quasi-cyclic LDPC code, connected at an input to the input interface and at an output to the input of the first multiplexer circuit, a third circuit for encoding quasi-cyclic LDPC code, connected at an input to the output of the first multiplexer circuit and at an output to the input of a second multiplexer circuit.

Device and method for efficiently encoding quasi-cyclic LDPC codes

A method and a receiver device for detecting the start of a frame of a satellite communication signal. A shaping filtering is applied directly after sampling of the signal, before a frequency correction is applied. During a first phase, an approximate frequency error and a candidate first sample for the start of the frame are estimated by performing several correlations respectively associated with different frequency hypotheses. The samples obtained after sampling or after shaping filtering are buffered during the execution of the first phase. Then, during a second phase, a final candidate sample for the start of the frame is determined from the memorised samples, using the approximate frequency error and the candidate first sample estimated during the first phase.

Method and receiver device for detecting the start of a frame of a satellite communications signal

A method for receiving an ADS-B message is disclosed including a synchronisation phase for detecting the start of the message and a decoding phase for recovering a bit stream corresponding to a block of data in the message. The synchronisation phase is based on determining a sequence of log-likelihood ratios having the greatest likelihood of corresponding to a sequence of symbols expected from a preamble of the message. Each log-likelihood ratio corresponds to a ratio between the respective probabilities that a symbol of the signal received corresponds to one of two possible values for a symbol. The decoding phase applies a belief propagation algorithm to a sequence of log-likelihood ratios respectively associated with the symbols in the block of data in the message, with an optimised parity matrix of the cyclic redundancy code of the message.

Method and device for receiving an ADS-B message via a satellite

A method for transmitting, by a terminal, a message destined for a receiver station of a wireless communication system. The message being transmitted on a shared channel on which the transmission of messages is performed at the start of predetermined time intervals, termed slots. Data to be included in the message to be transmitted is encoded. The encoded data is distributed between Nb sub-messages of the message to be transmitted, Nb being an integer number greater than or equal to two. A slot is selected for transmitting the message. Nb transmission frequencies are selected, each respectively associated with the Nb sub-messages of the message. The message is transmitted at the start of the selected slot, by successively transmitting the sub-messages on their respective associated transmission frequencies.

Method of transmission, by a terminal of a slot-based access communication system, of a message with intra-message frequency hops

A method () for estimating a frequency shift and a frequency drift affecting a useful signal including a code word formed by a channel encoder, including an analysis phase () including: for two analysis frequency drifts: a compensation () of the analysis frequency drift on the useful signal, an estimation () of the frequency shift on each useful signal obtained after compensation, a selection () of frequency hypotheses, and an estimation phase () including: for each frequency hypothesis: a frequency recalibration () of the useful signal depending on the frequency hypothesis, in order to obtain sample sequences, an evaluation () of the probability of each sample sequence to be a code word of said channel encoder, an estimation () of the frequency shift and of the frequency drift depending on the most probable frequency hypothesis.

Method and receiver device for estimating a frequency offset and a frequency drift of a useful signal

A method for detecting useful signals in an overall signal. Each useful signal may be affected with a frequency drift. In the detection phase, frequency spectra for detecting the overall signal for multiple detection time windows are calculated and useful signals according to the detection frequency spectra are detected. In the estimation phase, for each useful signal detected: the frequency of the overall signal for multiple frequency drift values is reset. In the estimation phase, for each useful signal detected, a frequency spectrum is calculated for the estimation of the overall signal for each frequency drift value over an estimation time window having the useful signal detected and of a duration higher than the detection time window. In the estimation phase, for each useful signal detected, the frequency drift is estimated affecting the useful signal detected according to the estimation frequency spectra.

Method and system for detecting useful signals with significant respective frequency drifts in an overall signal

A method for transmitting data in a telecommunication network having a satellite component and a terrestrial component, the data being organized into a set of packets having an identifier, the telecommunication network comprising at least one bearer, at least one satellite and at least one terrestrial station, the method comprises the steps of: transmission of a data packet having an identifier from said satellite, reception of the data packet by the bearer, transmission of a data packet having an identifier in response to a transmitted negative acknowledgement message by the terrestrial station. A method for receiving data to be implemented on a bearer, a method for transmitting data to be implemented on a terrestrial station, and an associated data transmission system are also provided.

Method and system for communication in a hybrid satellite/terrestrial network

A coding method with differentiated protection to protect, with a different protection efficiency, a number of groups of data in a frame to be transmitted. The invention is based for that on the use of a correcting code of the LDPC type concatenated with an algebraic correcting code. The invention also proposes a decoding method compatible with the coding method with differentiated protection.

Coding and decoding methods with differentiated protection

A data communication method between a mobile radio communications equipment and a gateway connected to a network, the data being organized in the form of packets comprising at least one first internal header and a second external header, comprises: an initial information exchange phase comprising: transmission by the radio communications equipment to the gateway of at least one predictable field out of the fields of the external and internal headers, reception by the radio communications equipment from the gateway of at least one predictable field of the external header, a phase of transmission of at least one data packet comprising: the deletion of the external and internal headers of at least one data packet, the generation, in at least one data packet, of a header of level lower than a network layer comprising at least one non-predictable field of the internal header, the transmission of at least one data packet.

Data communication method between a roaming radio equipment item and a network access gateway

A method for synchronizing the transmission of messages in a communication system comprises a user terminal, a main communication network comprising a first station, and a secondary communication network comprising a second station, the method consisting of an exchange of synchronization signals to calculate an offset to be applied to the instant of emission of the messages transmitted by the second station so that the messages transmitted by the first station and the second station are received by the user terminal in a synchronous manner. A communication system implementing the invention is provided.

Method for synchronizing signals in a terrestrial and satellite link and associated architecture

A method for equalizing a signal comprising modulated symbols comprising a block of N received symbols comprises: demultiplexing the N received symbols by factor L to generate a predetermined number L of sub-blocks of symbols, each comprising a version of the N received symbols sub-sampled by factor L, the independent equalization of each sub-block using an identical equalization algorithm, multiplexing the equalized symbols of each sub-block to obtain a block of N equalized symbols, removing instances of interference linked to paths other than two paths of higher power comprising generating an interference term resulting from the influence, on the equalized symbols, of all paths of the channel having the impulse response of the transmission channel except two paths of higher power, subtracting the interference term from the symbols of the block of N received symbols, and, a second equalization step equal to a second iteration of the first equalization step.

Equalization method for a parsimonious communication channel and device implementing the method

A method for iteratively decoding a word of a correcting code by an iterative decoding algorithm in the course of which, for each bit of said code word, at least one extrinsic information item is generated at each iteration, includes the following steps: an initial step of decoding by means of said iterative decoding algorithm; simultaneously, for each bit of said code word, a step of developing a criterion representing the number of oscillations of at least one extrinsic information item or of one extrinsic information item with regard to another extrinsic information item; if the decoding does not converge; a step of modifying the value of the bit of said code word for which said number of oscillations is highest; and, an additional step of decoding said at least one modified code word by means of said iterative decoding algorithm.

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Toulouse, France

Benjamin Gadat