Secrecy Energy Efficiency Optimization for IRS-Aided Multi-user Communication System

Energy efficiency and security are strongly required performance metrics for future wireless communication systems. As a high energy-efficiency technology, intelligent reflecting surface (IRS) can make wireless channel controllable, which is just desirable for physical layer security technology to extend the difference between the legal and eavesdropping channel. Up to now, most research on the secrecy energy efficiency (SEE) of IRS-aided communication systems are available for single legal user. In this paper, we investigate an IRS-aided multi-user wireless system and formulate a SEE maximization problem which is subject to the constraints of the transmit beamforming at base station and the reflecting beamforming at IRS. Generally, it is difficult to obtain an exact SEE under an imperfect eavesdropping channel state information. Thus, a lower bound of SEE is finally determined by an alternate optimization algorithm after a Dinkelbach transforming of the original problem. Simulation results show that IRS can effectively improve the SEE of the system, and the proposed algorithm is better than the benchmark algorithm in terms of SEE.