Energy-Efficient Beamforming for IRS Aided Integrated Sensing and Communication

This paper studies the energy-efficient beamforming design in a time division multiple access (TDMA) based integrated sensing and communication (ISAC) system consisting of an intelligent reflecting surface (IRS) with a uniform linear array (ULA) and a dual-functional radar-communication base station (BS). The IRS is used to assist the BS to sense multiple targets and communicate with single antenna users. For this system setup, we jointly optimize the transmit beamforming at the BS and the reflection coefficients at the IRS, to maximize the energy efficiency (EE) of the system, subject to the sensing beampattern gain at desired angles, the signal-to-noise ratio (SNR) requirement at communication user (CU) and the maximum transmit power constraint at the BS. Although the formulated problem is non-convex and difficult to solve due to non-convex constraints and the coupled variables, we propose an effective algorithm based on alternating optimization (AO), fractional programming (FP), semi-definite relaxation (SDR) and Riemannian optimization. Furthermore, simulation results show that our proposed algorithm design achieves higher EE performance than the benchmark schemes.