Retransmission Strategies for Symmetric Relaying Using Superposition Modulation

In this paper, we study retransmission strategies for the symmetric relaying scenario when the number of retransmissions for a data packet is limited. We propose a retransmission scheme based on superposition modulation and give the exact packet drop probability expression for it when only one retransmission is allowed. We compare the performance of the proposed retransmission scheme with retransmission schemes based on classical decode-and-forward (DF) relaying and non-cooperative transmission. When only two retransmissions are allowed, the proposed scheme has a performance gain of 3 dB in SNR over the retransmission scheme based on classical DF relaying. Through simulations, we also study the effect of varying the superposition ratio for the retransmissions.