LLR-based symbol selective transmission with a near-optimal threshold to minimize BEP for demodulation-forward relay systems

Error propagation in the source-relay link limits the performance of demodulation-forward (MF) relay systems. In order to solve this problem and efficiently exploit the relay, we propose log likelihood ratio (LLR)-based symbol selective transmission with a near-optimum threshold to minimize the bit error probability (BEP). In the proposed scheme, the source information is forwarded by the relay only if it is likely to be detected correctly, as determined by a comparison of the LLR with the near-optimum threshold. To derive the near-optimum threshold, the BEP of the proposed scheme is analyzed in the case of binary phase shift keying (BPSK) signals. Simulation results confirm the accuracy of the analysis and prove that the proposed scheme efficiently mitigates error propagation.