Decode-and-forward differential modulation scheme with threshold-based decision combining

This paper proposes a threshold-based differential decode-and-forward cooperative scheme that efficiently exploits the cooperative relay channels via the use of a pre-determined decision threshold. In the proposed scheme, the source information is forwarded by the relay only if it is correctly decoded. The properly-designed threshold enables the destination to decide whether the received signal from the relay contains information such that the received signals from the source and the relay can be efficiently combined and jointly decoded. The bit error rate (BER) analysis of the proposed scheme is analyzed in case of differential M-ary phase shift keying signals. A tight BER approximation is established, and BER upper bound and lower bound are determined. Based on the tight BER approximation, joint optimum decision threshold and power allocation is numerically evaluated. Both analytical and simulation results reveal that the decision threshold and the power allocation depend on channel link qualities. Interestingly, when the link quality between the relay and the destination is very good, the effect of the threshold dominates the effect of the power allocation at high signal-to-noise ratio. Extensive simulation results are provided to validate the merit of the proposed scheme and confirm the theoretical analysis