Abstract: A method for soft demapping of complex-valued symbols y(k) (k=1, 2, . . . , K) by calculation of a Logarithm of Likelihood Ratio (LogLR) such that: Log ? ? LR ? ( b I , q ) = ln ? ? ? ? ? S l , q ( 1 ) ? exp ( - 1 2 ? ? ? ? y ~ ? ( k ) - ? ? 2 ) ? ? ? ? S q , l ( 0 ) ? exp ( - 1 2 ? ? ? ? y ~ ? ( k ) - ? ? 2 ) wherein bI,q is the qth coded bit of an in-phase part of a transmitted signal, ? is an asymptotic Signal-to-Interference-plus-Noise Ratio, {tilde over (y)}(k) is a standardized symbol associated with y(k), ? is a reference symbol of QAM constellation associated with a M-QAM modulation, S(1)I,q and S(0)I,q are complex plane partitions that bring together, respectively, all reference symbols ? having a “1” at the position (I, q) and all reference symbols ? having a “0” at the position (I, q), a formula similar to LogLR being given for the bit bQ,p, pth coded bit of a quadrature part of the transmitted signal.

Abstract: This invention relates to a method of estimating the SINR ratio of an OFDM-CDMA type transmission using spread codes (ck), in which this ratio is estimated independently of the value of these codes.

Abstract: To select the frequency (SF) and/or time (ST) spreading parameters for a communication system using a quadrature amplitude modulation and implementing a CDMA technique and an OFDM multiplexing the attenuation coefficients of the propagation channel are estimated For all the F sub-bands of SF subcarriers and the T blocks of ST OFDM symbols, at least one asymptotic signal-to-interference+noise ratio (SINR) is determined, based on the attenuation coefficients of the propagation channel and the type of equalizer used by the receiver. From this, for each coded information block obtained from the modulation, the compressed asymptotic SINR is deduced, expressed by an analytical formula dependent on the frequency (SF) and time (ST) spreading parameters and the frequency (SF) and time (ST) spreading parameters which maximize the value of the compressed asymptotic SINR are selected.