Energy efficient optimization for full-duplex assisted closed-loop MISO downlink transmission

This paper studies the energy efficient optimization for full duplex (FD) assisted closed-loop downlink transmission, where a FD base station (BS) serves multiple half duplex (HD) users in a time division multiple access manner. We optimize the durations of uplink training and downlink transmission, aimed at maximizing the energy efficiency (EE) of the system. We first show that the EE-optimal transmission scheme must use one of the two strategies: transmitting in HD mode or transmitting downlink data over all time slots so that the BS operates in FD mode during the whole uplink training phase. We then derive an approximate average net data rate of the system considering the bidirectional interference between uplink and downlink users in FD mode. Based on the result, a closed-form expression of the EE is obtained. We prove that the EE in FD mode is quasi-concave with respect to the duration of uplink training, with which the optimal durations of uplink training and downlink transmission are obtained. Simulation results show the evident gain of the proposed scheme over existing FD and HD schemes.