Analysis of RIS-Assisted Links: Toward Reliable and Low-Latency Communications

Reconfigurable intelligent surface (RIS) has recently emerged as a promising technology to enhance the performance of wireless communication networks. While outage probability has been widely analyzed in RIS-assisted systems, the impact of packet delay remains largely unexplored, despite its critical role in ensuring Quality of Service (QoS) for delay-sensitive applications. This paper presents a comprehensive analysis of packet delay in single and double RIS-assisted communication systems. The analysis derives the signal-to-noise ratio (SNR) distribution under Nakagami-m fading conditions, explicitly incorporating small-scale fading, inter-RIS channel correlations, and RIS phase errors–factors often ignored in previous studies. The RIS phase error, arising from imperfect channel estimation or limited phase control precision, is modeled by a von Mises distribution. Using these distributions, we establish closed-form expressions for average packet delay, providing a novel characterization of RIS-assisted communication performance. Additionally, an outage probability analysis is conducted for the double RIS scenario, capturing the effects of inter-RIS fading and cascaded channel interactions to offer a more complete performance characterization. Performance evaluations, comprising numerical and simulation-based tests, examine the impact of key system parameters, including the number of RIS reflecting elements, fading severity, transmit SNR, and user-RIS distance on outage and delay. Results demonstrate that increasing the number of reflecting elements improves both delay and outage performance, with double RIS configurations outperforming single setups in supporting higher target rates, extending communication coverage, and reducing latency. These results provide insights for optimizing RIS deployment in next-generation wireless networks, particularly for ultra-reliable low-latency communications (URLLC) and real-time applications.