Adaptive Turbo Trellis Coded Modulation Aided Distributed Space-Time Trellis Coding for Cooperative Communications

Abstract-In this contribution, we propose an adaptive Turbo Trellis Coded Modulation (TTCM) aided Distributed Space-Time Trellis Coding (STTC) scheme for cooperative communication over quasi-static Rayleigh fading channels. An adaptive TTCM (ATTCM) scheme is employed by the source node during the first transmission period for reliably conveying the source bits to N number of relay nodes by appropriately adjusting the code-rate and modulation mode according to the near-instantaneous channel condition. The TTCM switching thresholds are chosen to ensure that the Bit Error Ratio (BER) at each relay node becomes lower than 10^-6 in order to minimise the potential error propagation imposed by the relay nodes. During the second transmission period, an N-antenna assisted Distributed STTC (DSTTC) scheme is created with the aid of the aforementioned N single-antenna relay nodes. More specifically, the N relay nodes are utilised to form STTC codewords based on the re-encoded TTCM symbols of the relays for transmission to the destination node. At the destination node, iterative extrinsic information exchange is performed between the STTC and TTCM decoders for recovering the original source bits. It is shown that the proposed ATTCM-DSTTC scheme requires 12 dBs less transmission power in comparison to a standard TTCM scheme when aiming for a frame error ratio of 10^-3.