Coverage Analysis for Reconfigurable Intelligent Surface-Assisted Cellular Networks Over Nakagami-m Fading Channels

Abstract

Unlike prior research works that focus on cell-level coverage analysis and optimization, this letter develops a system-level analysis framework based on stochastic geometry for RIS-assisted cellular networks experiencing Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> fading. First, we reveal that the passive beamforming gain of RISs for the signal approachs a deterministic value due to the channel hardening effect, while it is approximated as a Gamma distribution for the interference. Then, the tractable closed-form expressions for the signal-to-interference ratio (SIR) coverage probability of each tier and the entire network are derived. The simulation results verify the correctness of the theoretical analysis. Finally, it is shown that given RIS element density, for scenarios with the path loss exponent greater than 4, densely deploying small-size RISs achieves better coverage performance, while for scenarios with the path loss exponent less than 4, sparse deployment of large-size RISs is a better option.