Selection of Parity Check Equations for the Iterative Message-Passing Detection of M-Sequences

Mathieu Des Noes (1) , Valentin Savin (1) , Laurent Ros (2) , Jean-Marc Brossier (2)

1 CEA-LETI - Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information
2 GIPSA-CICS - GIPSA - Communication Information and Complex Systems

We consider the joint detection and decoding of m-sequences. The receiver has to decide whether an m-sequence is received and possibly to decode its initial state. To do so, it implements an iterative message-passing decoding algorithm that operates on a parity check matrix, built upon a number of reference parity-check equations satisfied by the m-sequence. This matrix concatenates several elementary parity check matrices which are derived from reference equations. Unlike the conventional decoding case, the detection problem imposes to consider false alarms that may occur when the decoder is only fed with noise. While absorbing sets are known to be responsible for the error floor phenomenon of iterative message-passing decoders, we show that they may have a beneficial effect on the detection performance, in that they may prevent the decoder to produce false alarms. We further compute the number of hybrid cycles of length 6 and 8 in the Tanner graph of the decoder and use the minimization of this number as criterion to derive an algorithm for selecting the reference parity check equations. This algorithm was found to be efficient for minimizing the probability of false alarm and decreases also the probability of wrong detection in the very small SNR region. This has been achieved at the cost of a reduction of the probability of correct detection.

Mots clés: spread spectrum communication; probability; signal detection; graph theory; iterative decoding; matrix algebra; message passing; m-sequences; parity check codes; binary M-sequences; bipartite graph

Domaines: Traitement du signal et de l'image [eess.SP]

Mathieu Des Noes, Valentin Savin, Laurent Ros, Jean-Marc Brossier. Selection of Parity Check Equations for the Iterative Message-Passing Detection of M-Sequences. IEEE Transactions on Communications, 2017, IEEE Transactions on Communications, 65 (8), pp.3214-3225 ⟨10.1109/TCOMM.2017.2706724⟩. ⟨hal-01583254⟩