Source Energy-Saving Performance in Amplify-and-Forward Relay-Assisted Wireless Systems

Nowadays, the increasing demand for higher data rate and ubiquitous connectivity of a smart phone significantly conflicts with its limited battery lifetime. In order to prolong the battery lifetime, we desire to save the uplink transmit power of a mobile terminal with the aid of a cooperative relay with higher transmit power level (e.g., powered by electrical networks), since the battery power is much more limited. In this paper, we consider a relay-aided two-hop system consisting one source (e.g., a mobile terminal in uplink), one Amplify-and-Forward (AF) relay and one destination (e.g., a base station). For this scenario, the source transmit power is reduced on the expense of the relay power. More precisely, we jointly optimize the transceiver strategies to minimize the source transmit power subject to a rate requirement. The closed-form optimal transceiver strategies are obtained when the perfect instantaneous channel statement information (CSI) is known. Furthermore, for the Rayleigh fading channel, an exact form of source energy-saving probability of this AF relay-aided transmission compared with direct transmission (DT) is derived. Monte Carlo simulations are provided to verify the analytical results, from which we additionally find the source energy-saving region for a source when the relay location is fixed and that for a relay when the source location is fixed.