Energy efficiency of relaying systems with ARQ and inter-relay listening

Various advantages including higher order of diversity gain and transmission power saving can be obtained in wireless communications through relay-aided transmissions. In this paper, the energy efficiency of a wireless relaying system based on an automatic repeat request (ARQ) protocol is investigated. A system with multiple relays between a source node (SN) and a destination node (DN) is considered. The signal transmission consists of two phases and in each phase the ARQ protocol is used. Some of the relay nodes are selected for forwarding the message and overhearing between them in the second phase is allowed. As a result, the number of relay nodes that can decode source message increases as the ARQ round goes on. The energy efficiency of two relaying schemes, namely the selection relay (SR) scheme and the distributed space-time block coding (D-STBC) scheme, are investigated. It is shown that the energy efficiency of the system can be improved through inter-relay listening and the SR-ARQ scheme has better energy efficiency as compared with the D-STBC scheme.