Intelligent reflecting surface (IRS) is an emerging technology to enhance spatial multiplexing in wireless networks. This letter considers the discrete passive beamforming design for IRS in order to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among multiple users in an IRS-assisted downlink network. The main design difficulty lies in the discrete phase-shift constraint. Differing from most existing works, this letter advocates a convex-hull relaxation of the discrete constraints which leads to a continuous reformulated problem equivalent to the original discrete problem. This letter further proposes an efficient alternating projection/proximal gradient descent and ascent algorithm for solving the reformulated problem. Simulation results show that the proposed algorithm outperforms the state-of-the-art methods significantly.

翻译：智能反射表面(IRS)是一种增强无线网络空间复用的新兴技术。本文针对IRS辅助下行链路网络，研究以最大化多用户最小信干噪比(SINR)为目标的IRS离散无源波束成形设计。主要设计难点在于离散相移约束。与现有大多数研究不同，本文提出对离散约束进行凸包松弛，从而得到与原离散问题等效的连续重构问题。本文进一步提出一种高效的交替投影/邻近梯度下降上升算法来求解重构问题。仿真结果表明，所提算法性能显著优于现有最优方法。