Energy-Efficient Joint Source and Relay Precoding for Two-Hop MIMO-AF Two-Relay Networks

Abstract

This paper focuses on improving the energy efficiency of two-hop multiple-input-multiple-output (MIMO) amplify-and-forward (AF) systems having two relays (in parallel) by relying on optimisation theory. Although the joint optimisation of the source and relays precoding structures is non-convex by nature, we first formulate the energy consumption of the system as an optimisation function and prove that the latter is unimodal when the source and/or relay precoding matrices are known. In turn, we derive an optimal source and robust relays precoding structures; joint optimisation of the source and relays precoding matrices is then performed via an iterative process. Simulation results show that our novel approach can reduce the energy consumption of two-hop MIMO-AF systems by up to 30% when compared to the most relevant existing approaches.