STAR-RIS Assisted Wireless Communications With Discrete Phase Shifter

Reconfigurable Intelligent Surface (RIS) presents a promising solution for achieving a balance between communication quality and power consumption. However, traditional reflecting RIS designs are limited to covering signals within a 180-degree range. Fortunately, the development of Simultaneous Transmitting and Reflecting RIS (STAR-RIS) technology enables the simultaneous transmission and reflection of signals, allowing for 360-degree coverage. In this paper, we investigate the STAR-RIS assisted wireless communications under Nakagami-m fading channels, and the channel state information (CSI) is assumed perfectly obtained. Considering the hardware design complexity, the RIS phase shifts are discretely configured with quantization errors. We derive the closed-form expressions of the outage probability and the ergodic achievable rate under the discrete phase. In addition, the approximations for the special cases including the random phase case, the continuous phase case, the Rayleigh fading case, as well as the high signal-noise ratio (SNR) case are further deduced. Numerical results verify the correctness of the analytical results.