A Novel Soft Forwarding Technique for Memoryless Relay Channels Based on Symbol-Wise Mutual Information

In this letter, we propose a mutual information based soft forwarding scheme for memoryless parallel relay networks. The relay forwarding function of the proposed scheme consists of the hard decisions of the symbol estimates and a reliability measure. The reliability measure is determined by the symbol-wise mutual information computed from the absolute value of the log-likelihood ratio at the relay. The superiority of the proposed scheme to the existing relay forwarding schemes is demonstrated through bit error rate performance and average mutual information at the destination. Simulation results show that for a parallel relay network with two relay nodes and BPSK modulation, the proposed mutual information based soft forwarding scheme yields signal-to-noise ratio gains of about 0.5-1 dB compared to various existing memoryless relay forwarding schemes.