Spectrally-Efficient Wireless Relaying Based on Superposition Coding

The wireless relay systems represent an important segment in the wireless communication systems. In a simple wireless relay scenario, a source node A_S needs to communicate to a destination A_D, with the help of a relay A_R. In this paper we introduce a new two-step relaying scheme based on superposition coding, SC-relaying. In step 1, A_S broadcasts a message, created by superposition coding, to A_R and A_D. After decoding the information from A_S, A_R relays a part of this message in step 2, by adapting the transmission rate with respect to the link quality towards A_D. The unique point of the proposed scheme is that the signal format in the two steps is chosen in a way that enables a simple combining at A_D. The numerical results show that the proposed scheme can bring a notable gain in spectral efficiency over the conventional multi-hop transmission with adaptive modulation, even in the case when the instantaneous SNR about all the links is not fully known at the source. In addition, the proposed scheme performs very closely to the scheme that is optimal in an information-theoretic sense.