Power Control in Energy-Efficient Secure Transmission under QoS and Transmitter's Imperfect CSI

Under the constraints of quality of service and average transmission power, this paper studies the power control to maximize the energy efficiency of secure transmission. Assuming that the transmitter has imperfect channel state information, the derivation of the optimum power control rule and comparison of its resulting energy efficiency with various power control strategies are presented. Then, the impact of estimation error and number of antennas on the average secrecy energy efficiency (SEE) as well as the trade-off between the average SEE and quality of service will be characterized. The results show that the average SEE with the optimum power control increases significantly for small number of antennas or low transmit power. The results also show that the loss of average SEE is remarkably at high estimation error or extremely-high quality of service.