Performance Analysis of RIS Assisted Power Domain NOMA System with Discrete Phase Shifter

Abstract

Reconfigurable Intelligent Surface (RIS/IRS) technology has the potential of improving coverage, capacity, and energy efficiency in wireless communication. RIS has control over the scattering and propagation of the transmitted signal to the receiver and it improves the Signal to Noise Ratio (SNR). The new encoding Non-Orthogonal Multiple Access (NOMA) system provide immense connectivity to the users from the base station at low latency. In an ideal scenario, the RIS completely compensate the phase of the signal, but this is not possible in a practical environment. The RIS using discrete phase shifters are analyzed with power variation for the near and far users. The probability error of the RIS-assisted NOMA system is analyzed for the various quantized bits of phase shifter which are one-bit shifter $(0,\ \pi)$, two-bit shifter $(0,\ \pi/2,\ \pi,\ 3\pi/2)$ and three-bit shifter $(0, \pi/4,\pi/2,3\pi/4, \pi, 5\pi/4,3\pi/2,7\pi/4)$. The quantized phase shifters at the RIS degrade the Bit Error Rate (BER) performance and are compared with the ideal continuous phase shifter. This research shows that, while using a one-bit phase shifter the presence of residue reduces the system's performance. Further, increasing the levels of the phase shifter to two-bit and three-bit improves the system performance compared to the one-bit phase shifter.