Method of detecting OTFS SCMA signals and receiver implementing the method

A method for detecting superimposed sparse code multiple access (SCMA) signals from multiple user equipment (UE) received by radio from a receiver of an orthogonal time frequency space communication system, comprising:

• receiving an orthogonal time frequency space (OTFS) demodulated signal representing the received signals of all UEs,
• receiving a corresponding channel matrix,
• initialising and executing an iteration loop, wherein the iteration loop comprises:
• a) determining an a posteriori estimate of the transmitted signal using the demodulated signal, the channel matrix and the respective mean vectors and associated variances that were determined for each UE in a respective immediately preceding iteration or were determined in the first iteration for each UE in the initialisation as input signals,
• b) generating an extrinsic mean value of the current iteration from all a posteriori estimates determined so far and corresponding extrinsic variances of the current iteration,
• c) Determining a posteriori probabilities for each UE and for each of the non-zero elements of the SCMA codebook of the respective UE, based on the extrinsic mean value of the current iteration and the corresponding extrinsic variances of the current iteration,
• d) Calculating an a posteriori Gaussian distribution of the a posteriori probabilities of the current iteration and the corresponding variance for each UE and over all non-zero elements of the SCMA codebook of the respective UE,
• e) updating the elements of the respective mean vector and the corresponding extrinsic variances for each UE based on the a posteriori Gaussian distribution,
• and
• repeating steps a) to e) until a termination criterion is met.