RIS-assisted cellular networks with multiple D2D pairs: Outage and ergodic achievable rate

Reconfigurable Intelligent Surface (RIS) is envisioned as a promising technology to improve the system capacity of 6G network, by controlling the electromagnetic wave propagation. Most existing works use the Central Limit Theorem (CLT) to analyze the performance of RIS-assisted systems for large number of reflective elements. However, the assumption of extremely large number of elements may not be practical in the actual situation. In addition, the CLT-based approximation yields an inaccurate scaling law of the outage probability when the transmit Signal-to-Noise Ratio (SNR) tends to infinity. Motivated by these limitations, in this paper, we investigate the performance of RIS-assisted cellular networks with multiple Device-to-Device (D2D) users under the general fading channels, i.e., Nakagami- m fading channels. We propose a tractable solution to evaluate the outage probability and the ergodic achievable rate, which is accurate for any number of reflective elements, any network topology, as well as any SNR. In addition, the accurate approximations for the high SNR case and the large number of reflective elements case are further derived in simpler closed form. Numerical results verify the accuracy of our analytical results and analyze the performance between CLT and the proposed method.