摘要
A reconfigurable intelligent surface (RIS) is a passive beamforming technology that uses densely packed elements with tunable phase shifts to control the reflection of incident signals. While a large-scale RIS provides a significant beamforming gain to offset the severe double pathloss inherent in reflected links, maintaining precise phase control across thousands of elements presents substantial practical challenges. Moreover, RIS operation in interference-limited environments has received relatively little attention, with most prior works focusing on interference-free scenarios. In this paper, we analyze the performance of a RIS-aided link with imperfect phase control under co-channel interference (CCI) and address two key limitations of existing analyses. First, previous fading power models do not account for asymmetric fading conditions between the source-RIS and RIS-destination channels. Second, existing models often lack tractable forms for analyzing CCI impact. To overcome these issues, we develop a Gaussian approximation for the fading power distribution under imperfect phase control using the central limit theorem and moment matching, more accurately capturing both phase errors and asymmetric fading statistics. Building on this result, we propose a novel Fourier-transform-based method to derive the signal-to-interference ratio (SIR) distribution, avoiding the need for high-order derivatives of the interference power's Laplace transform required by classical approaches. Our analysis reveals that the performance gain from a large RIS with imperfect phase control strongly depends on the interference level.