Passive Beamforming Design for IRS Communication System with Few-Bit ADCs

Utilizing intelligent reflecting surface (IRS) was proven to be efficient in improving the energy efficiency for wireless networks. In this paper, we investigate the passive beamforming design in an IRS assisted single-input multiuser-output (SIMO) system. Prior works on IRS mainly assume receiver with infinite or high precision quantization. In contrast, proceed from reality, the receiver is equipped with finite precision quantization analog-to-digital converters (ADCs) in the IRS assisted system, which is a novel exploration. Our objective is to optimize the passive beamforming to minimize the bit error rate (BER) and maximize the achievable rate, respectively. First, we give the expression of BER and apply the branch-and-bound algorithm to find a high quality optimal solution. Also, we derive the approximate achievable rate according to the Bussgang theorem. Based on the derived analytical achievable rate expression, we propose a gradient-based method in the passive beamforming design to maximize the achievable rate. To improve the quality of the suboptimal solution obtained by gradient-based method, we apply the branch-and-bound algorithm in low signal-to-noise ratio (SNR) regime. Numerical results show that with few-bit quantization, the proposed beamforming design can significantly improve the performance.