Optimum threshold-selection relaying for decode-and-forward cooperation protocol

This paper proposes a threshold-selection relaying scheme, in which each relay decides whether to forward the source information by comparing the received signal power with a decision threshold. The challenging problem is to design the threshold such that the relay is able to forward only correctly decoded information. In this work, bit-error-rate (BER) performance analysis is provided for the proposed scheme with BPSK signals. We develop a BER upper bound which is tight over the entire range of signal-to-noise ratio values. Based on the established BER formulation, we jointly determine optimum decision threshold and power allocation. An interesting result is that the effect of optimum threshold dominates that of optimum power allocation, especially when the relay is close to the destination. For example, in case of equal power allocation, the proposed scheme with optimum threshold yields 10 dB performance improvement over the fixed relaying scheme without threshold at a BER of 10^-2. If both the power allocation and the threshold are jointly optimized, then the performance of the proposed scheme can be further improved by 2 dB.