Distributed Turbo Trellis Coded Modulation for Cooperative Communications

In this contribution, we propose a Distributed Turbo Trellis Coded Modulation (DTTCM) scheme for cooperative communications. The DTTCM scheme is designed based on its decoding convergence with the aid of non-binary Extrinsic Information Transfer (EXIT) charts. The source node transmits TTCM symbols to both the relay and the destination nodes during the first transmission period. The relay performs TTCM decoding and re-encodes the information bits using a Recursive Systematic Convolutional (RSC) code regardless whether the relay can decode correctly or not. Only the parity bits are transmitted from the relay node to the destination node during the second transmission period. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated TTCM scheme. At the destination node, a novel three-component TTCM decoding is performed. It is shown that the performance of the DTTCM matches exactly the EXIT chart analysis. It also performs very closely to its idealised counterpart that assumes perfect decoding at the relay.