Relay-Assisted Joint Coded Modulation

Abstract

In this letter, we propose a joint coded modulation scheme for a 3-node relay system. In the relay system, the source node broadcasts modulation symbols to relay and destination node simultaneously. With the directly received modulation symbols as side information at destination node, the relay node can send coset coded modulation symbols at the second slot to destination node. Since the coset coding takes place at modulation symbol level instead of bit level, its decoding algorithm is quite different from the traditional bit-level coset decoding. We derive the probability distribution and design a coset decoding algorithm to resolve the ambiguity at the receiver of destination node. Coset coding can reduce the peak to average power ratio in relay node effectively and thus improve the system capacity. The simulation shows that the proposed scheme can lead to gain of 3–4 dB at a BER of $10^{ {-5}}$ compared to the original single link random projection code.