Energy efficient relay antenna selection for AF MIMO two-way relay channels

In this paper, we investigate the energy efficiency (EE) maximization in amplify-and-forward (AF) MIMO two-way relay channel (TWRC) combined with relay antenna selection (AS). An iterative energy efficient AS algorithm is proposed to jointly select the active receive and transmit antennas at the relay, as well as optimize the transmission power of the sources and relay. Specifically, the AS at each iteration is based on a derived closed-form iterative equation of EE, which guides us to select a pair of receive and transmit relay antennas that achieves the largest increment of EE under an initial transmission power. After the AS of each iteration, a power adaptation is immediately adopted where we calculate the optimal transmission power using fractional programming and set it as the initial one for the AS of the next iteration. Simulation results show that our proposed scheme achieves nearly the same performance of exhaustive search while with significantly reduced complexity. Moreover, it is capable of simultaneously improving EE and reducing the transmission power.