Improved receiver for cooperative wireless communication systems using QAM and Galois Field network coding

In this paper, we study a network coding in high order Galois Field (GF) compatible with Quadrature Amplitude Modulation (QAM) applied to the multiple-access relay channel (MARC). Our proposal is described in the context of orthogonal Rayleigh fading plus Gaussian noise channels. The proposed decoder takes into account possible decoding errors at the relay, which are expressed as cross-transition probability of network-coded symbols in the constellation. It is shown by simulation that the proposed decoder significantly outperforms the mismatched decoder, which does not take care of decoding error at the relay, for both coding gain and diversity order. In addition, compared with a recently cooperative maximum ratio combining (C-MRC) decoder, the proposed decoder improves the performance by 1.5dB for 16-QAM and 2dB for 64-QAM at bit error rate (BER) of 10^-4.