On Energy Efficiency Maximization of AF MIMO Relay Systems with Antenna Selection

In this paper, we investigate the maximization of energy efficiency (EE) in amplify-and-forward (AF) MIMO relay systems combined with relay antenna selection. An iterative algorithm is proposed to jointly select the active receive and transmit antennas at the relay, as well as optimize the transmission power of the source and relay. Specifically, the antenna selection process is based on a derived iterative property 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 at each step. Then a power adaptation is adopted where we calculate the optimal transmission power using fractional programming and set it as the initial one for the next antenna selection. Simulation results show that the proposed algorithm achieves near-optimal performance at all the transmission distances. Moreover, it is capable of simultaneously improving EE and reducing the transmission power.