[Paper Review] Impact of Interference on the Performance of RIS-Assisted Source DF Relaying Networks

Doaa Salim, Monjed H. Samuh+1 more|arXiv (Cornell University)|Nov 10, 2020

Advanced Wireless Communication Technologies4 citations

TL;DR

This paper investigates co-channel interference (CCI) in a reconfigurable intelligent surface (RIS)-assisted decode-and-forward (DF) relaying network, deriving closed-form approximations for outage probability over Rayleigh fading channels. Results show that the number of relays $K$ significantly improves diversity order and system performance, while the number of RIS elements $N$ has minimal impact on coding gain but no effect on diversity order.

ABSTRACT

This letter investigates the impact of co-channel interference (CCI) on the performance of a decode-and-forward (DF) relaying network with a reconfigurable intelligent surface (RIS)-assisted source. We consider one source, multiple DF relays, and one destination with CCI at both the relays and destination. We derive closed-form accurate approximations for the system outage probability assuming Rayleigh fading channels. In addition, we study the system performance at the high signal-to-noise ratio (SNR) regime, where closed-form expressions are derived for the asymptotic outage probability, diversity order, and the coding gain. The results show that the number of reflecting elements N at the source has a small effect on the coding gain of the system and not on the diversity order. Furthermore, findings illustrate that the number of relays K is affecting the diversity order and is more impactful on the performance than N. Finally, results show that utilizing RIS at the source node mitigates the interference effect at the relay nodes.

Motivation & Objective

• To analyze the performance degradation caused by co-channel interference (CCI) in RIS-assisted DF relaying networks.
• To derive accurate closed-form approximations for system outage probability under Rayleigh fading conditions.
• To investigate the high-SNR regime to extract diversity order and coding gain for performance analysis.
• To evaluate the impact of RIS at the source on mitigating interference at relay nodes.
• To compare the performance gains of RIS reflecting elements $N$ versus number of relays $K$.

Proposed method

• Models a dual-hop DF relaying system with one RIS-aided source, $K$ relays, one destination, and co-channel interferers at both relays and destination.
• Uses opportunistic relay selection to select the best relay based on channel quality.
• Derives the end-to-end SINR as a ratio of the desired signal power to interference-plus-noise power at the destination.
• Applies the central limit theorem approximation for interference power and uses order statistics for the best relay selection.
• Employs the binomial rule and integral identities (e.g., [19, Eq. (8.351.2)]) to derive closed-form expressions for CDFs and outage probability.
• Performs high-SNR asymptotic analysis using Taylor series expansion of exponential CDFs to extract diversity order and coding gain.

Experimental results

Research questions

• RQ1 How does co-channel interference (CCI) affect the outage performance of RIS-assisted DF relaying networks?
• RQ2 What is the impact of the number of RIS reflecting elements $N$ on the system's diversity order and coding gain?
• RQ3 How does the number of relays $K$ influence the system's diversity order and overall performance?
• RQ4 To what extent does deploying RIS at the source mitigate interference at relay nodes?
• RQ5 What are the asymptotic outage behavior, diversity order, and coding gain in the high-SNR regime?

Key findings

• The number of relays $K$ directly affects the system's diversity order, while the number of RIS elements $N$ does not influence the diversity order.
• The coding gain $G_c$ is minimally affected by $N$, indicating that increasing the number of reflecting elements provides limited performance improvement in terms of coding gain.
• The number of relays $K$ has a more significant impact on system performance than $N$, making $K$ a more effective design parameter for performance enhancement.
• Utilizing RIS at the source effectively mitigates the interference effect at relay nodes, improving the reliability of signal decoding.
• Closed-form expressions for asymptotic outage probability, diversity order, and coding gain are derived and validated for high-SNR regimes.
• The derived outage probability approximations are accurate for arbitrary $N$, including low numbers of reflecting elements, avoiding reliance on the central limit theorem.