A Trellis Coded Modulation Scheme for the Fading Relay Channel

TL;DR

This paper introduces a Trellis Coded Modulation scheme for the fading relay channel that achieves high spectral efficiency and near-optimal performance at high SNR, with design criteria for maximizing diversity and coding gains.

Contribution

It proposes a novel TCM scheme with a near-ML decoder for the relay channel, providing design criteria and demonstrating significant SNR gains through simulations.

Findings

Large SNR gain over uncoded and direct transmission schemes

Performance of the near-ML decoder approaches optimal ML at high SNR

Labelling scheme significantly impacts BER performance

Abstract

A decode and forward protocol based Trellis Coded Modulation (TCM) scheme for the half-duplex relay channel, in a Rayleigh fading environment, is presented. The proposed scheme can achieve any spectral efficiency greater than or equal to one bit per channel use (bpcu). A near-ML decoder for the suggested TCM scheme is proposed. It is shown that the high SNR performance of this near-ML decoder approaches the performance of the optimal ML decoder. The high SNR performance of this near-ML decoder is independent of the strength of the Source-Relay link and approaches the performance of the optimal ML decoder with an ideal Source-Relay link. Based on the derived Pair-wise Error Probability (PEP) bounds, design criteria to maximize the diversity and coding gains are obtained. Simulation results show a large gain in SNR for the proposed TCM scheme over uncoded communication as well as the direct transmission without the relay. Also, it is shown that even for the uncoded transmission scheme, the choice of the labelling scheme (mapping from bits to complex symbols) used at the source and the relay significantly impacts the BER vs SNR performance. We provide a good labelling scheme for $2^l$-PSK signal set, where $l\geq 2$ is an integer.