Energy Efficiency Optimization in IRS-Aided Multiuser MISO Communication Systems

In this article, the energy efficiency (EE) of an intelligent reflecting surface (IRS)-aided downlink multiuser multiple-input single-output (MISO) system is investigated. In order to maximize the system EE, the transmit beams at the access point (AP), and the phase shifts at the IRS are jointly optimized, while satisfying power and phase constraints. Since these two variables are coupled together and the problem is nonconvex, an alternating optimization framework is used as the algorithmic framework in order to decouple them, and for optimizing the phase shift, we use the successive convex approximation (SCA) approach to convert the original nonconvex objective function into a series of convex sub-problems and solve them with the CVX toolbox. In order to reduce the complexity of the design, minimum mean square error (mmse) beamforming is used at the AP, so that only the power allocation needs to be optimized. The numerical results show that the proposed SCA-mmse method exhibits the superiority in terms of system EE, compared with a few benchmark schemes.