An improved complex field network coding scheme for wireless relay system in asymmetric link environment

In this paper, a complex field network coding (CFNC) scheme is presented, which focuses on improving transmission efficiency by reducing time slots that are needed to exchange data frames. Conventional CFNC scheme has the advantage of minimizing the number of time slots required for information exchanges. However, there exists serious performance deterioration because the transmit signals are interfered with each other. Also, considering a typical asymmetric link whose data traffic is biased in downlink such as orthogonal frequency division multiple access (OFDMA) system, conventional CFNC scheme cannot obtain sufficient coding gain due to frequency selective fading. In order to overcome these problems, we propose a repetition-based CFNC scheme as well as the corresponding maximum likelihood (ML) decision rule. The proposed repetition scheme is considered for obtaining frequency diversity gain, which is used to improve the decision accuracy in the proposed ML decision process. Simulation results verify that the proposed scheme has superior coded bit error rate (BER) performance compared with the conventional scheme.