Performance Analysis of RIS-Assisted Communication With Direct Link: A New Copula Application

Reconfigurable intelligent surface (RIS) has received remarkable attention as a promising solution to enhance the capacity and coverage of wireless cellular networks. In this paper, we evaluate the performance of RIS-assisted communication systems in the presence of phase noise by exploring different copulas. In particular, we first analyze the cumulative distribution function and the probability density function of the signal-to-noise-ratio under phase noise in the presence of both direct and cascaded channel links. Then, we propose a copula-based solution to effectively model the non-linear dependencies among signal components induced by phase noise, and derive several exact closed-form expressions for outage probability in reconfigurable intelligent surfaces-assisted networks. In our method of analysis, we consider various copula families, including Archimedean copulas such as Farlie-Gumbel-Morgenstern, Frank, and Clayton, along with Elliptical copulas such as Gaussian and Student-T. Finally, numerical results are shown to confirm the validity of the closed-form expressions.