[Paper Review] Performance Analysis of an Interference-Limited RIS-Aided Network

Liang Yang, Yin Yang+2 more|arXiv (Cornell University)|Nov 15, 2020

Advanced Wireless Communication Technologies14 references9 citations

TL;DR

This paper analyzes the performance of reconfigurable intelligent surface (RIS)-assisted systems under co-channel interference (CCI), deriving exact expressions for outage probability (OP), average bit error rate (BER), and ergodic capacity under Rayleigh fading. It shows that the number of RIS elements and interferers critically impact system performance, with diversity order determined by the Rician fading parameters and interference level significantly degrading performance.

ABSTRACT

In this work, the performance of reconfigurable intelligent surface (RIS)-aided communication systems corrupted by the co-channel interference (CCI) at the destination is investigated. Assuming Rayleigh fading and equal-power CCI, we present the analysis for the outage probability (OP), average bit error rate (BER), and ergodic capacity. In addition, an asymptotic outage analysis is carried in order to obtain further insights. Our analysis shows that the number of reflecting elements as well as the number of interferers have a great impact on the overall system performance.

Motivation & Objective

• To analyze the impact of co-channel interference (CCI) on RIS-aided wireless systems, a scenario often overlooked in prior work.
• To derive exact performance metrics—outage probability (OP), average BER, and ergodic capacity—under Rayleigh fading and equal-power CCI.
• To provide asymptotic outage analysis to reveal the diversity order and system behavior at high SNR.
• To validate analytical results through Monte Carlo simulations and assess the impact of practical phase shifts.

Proposed method

• The system model assumes a single-antenna source communicating with a single-antenna destination via an RIS with N reflecting elements, under interference from L equal-power interferers.
• The effective signal-to-interference ratio (SIR) is derived assuming perfect channel state information (CSI) at the RIS, enabling optimal phase shifts to maximize SIR.
• The PDF of the SIR is modeled using a squared K_G distribution for the desired link and a chi-squared distribution for the interference, enabling exact performance analysis.
• Exact expressions for OP, average BER, and ergodic capacity are derived using generalized Meijer G-functions and special functions.
• An asymptotic outage expression is derived to reveal the diversity order and high-SNR behavior.
• Numerical results validate analytical expressions via Monte Carlo simulations, including practical phase shift models with amplitude loss.

Experimental results

Research questions

• RQ1 How does co-channel interference (CCI) affect the outage probability in RIS-aided systems with perfect CSI?
• RQ2 What is the exact expression for the average bit error rate (BER) under CCI and Rayleigh fading in RIS-assisted systems?
• RQ3 How does the number of RIS reflecting elements (N) and interferers (L) influence the ergodic capacity and diversity gain?
• RQ4 What is the asymptotic outage behavior, and what is the achievable diversity order in the presence of CCI?
• RQ5 How does practical phase shift imperfection (e.g., amplitude loss) affect system performance compared to ideal phase shifts?

Key findings

• The derived analytical expressions for outage probability, average BER, and ergodic capacity match Monte Carlo simulation results perfectly across all scenarios.
• The diversity order of the system is found to be (k + m)/2, where k and m are shaping parameters of the Rician fading model for the RIS links.
• Increasing the number of RIS elements (N) significantly improves system performance, reducing outage probability and BER.
• Higher interference power (P_I) and more interferers (L) degrade system performance, with OP increasing as P_I or L increases.
• The asymptotic outage expression confirms that the diversity order is independent of the number of interferers, but the diversity gain is limited by the Rician fading parameters.
• Practical phase shifts with amplitude loss (e.g., ω_min = 0.8) introduce a measurable performance gap compared to ideal phase shifts, especially at high SNR.