Energy-efficient joint source and relay precoding design for cooperative MIMO-AF systems

Abstract

This paper derives an optimal source and a close-to-optimal relay precoding structures for minimising the energy consumption of cooperative multiple-input-multiple-output (MIMO) amplify-and-forward (AF) systems, i.e. when relay and direct links are jointly considered. Even though the optimisation problem at hand is generally non-convex, we prove that the energy consumption optimisation function is unimodal when either the source or relay precoding matrix is known. Then, an iterative process is utilised to jointly optimise the source and relay precoding matrices. Simulation results confirm the benefit, in terms of energy consumption, of our novel approach for cooperative MIMO-AF systems in comparison with approaches optimising either the direct or relay link only, with a 20–30% improvement gain in favorable channel conditions.