On the energy-efficiency optimisation of OSTBC-MIMO two-way cooperative systems

Abstract

This paper addresses the optimisation of energy consumption of a two-way Amplify-and-Forward (AF) cooperative Multiple-Input, Multiple-Output (MIMO) system based on Orthogonal Space Time Block Code (OSTBC) under data rate constraint. The energy minimisation problem is written as a geometric problem and then solved employing a useful optimisation tool denoted as geometric programs in posynomial form (gpposy). The effects of the number of antennas, the relay's location and the predefined data rate transmission on the total transmit energy consumption are investigated. A comparison between the energy consumption of one- and two-way relaying is done. Evaluating the total energy consumption including both the transmission energy and the circuit energy consumption is also a contribution of this work. Simulation results show the significant transmit energy saving achieved by the proposed optimisation scheme. Thus, the OSTBC-MIMO cooperative system decreases the total transmit energy consumption compared to a SISO cooperative one. Generally, the cooperative MIMO systems are more energy efficient than the cooperative SISO systems even when circuit energy consumption is considered. Furthermore, our results indicate that the two-way MIMO systems are more energy efficient than one-way MIMO systems for high rates.