Optimal power adaptive decode-and-forward cooperative device-to-device communication policies

Abstract

Cooperative device-to-device (D2D) wireless systems use relays such as amplify-and-forward (AaF) and decode-and-forward (DaF). The AaF relay is simple to implement but amplifies noise as well. Conventional DaF relay does decoding and acts as a regenerative relay, hence deliver better noise performance. In this study, the authors generalise the cooperative D2D model by designing power adaptive decode-and-forward relays. In it, the probabilistically selected relay subject to an average relay transmit power constraint does decoding and jointly adapt its gain and transmit power as a function of the channel gains to the destination link. For the proposed cooperative D2D system model, the authors derive the optimal relaying policies which set relay gains to (i) minimise the fading averaged symbol error rate; (ii) maximise fading averaged spectral efficiency and (iii) maximise fading averaged energy efficiency. Then they present a comprehensive performance analysis of the optimal policies. The mathematical analysis includes derivations of exact expressions and their upper bound expressions. To further extend the FAvSER analysis, they investigate diversity order in an insightful scaling regime. Then they present extensive numerical results to validate the derived analytical expressions and to show that the proposed optimal relaying policies outperform the benchmark policies.