Coverage Analysis of RIS-Assisted mmWave Cellular Networks With 3D Beamforming

Millimeter-wave (mmWave) is highly susceptible to obstacles and requires significant directivity of beams. To address these challenges, a promising solution is to deploy antenna arrays at base stations (BSs) and reconfigurable intelligent surfaces (RISs). Antenna arrays enable 3D beamforming and provide highly directional beams, while RISs create favorable transmission environments. In this paper, we propose an analytical framework to quantify the coverage performance of the RIS-assisted mmWave cellular network with 3D beamforming. Modeling obstacles and RISs with a line Boolean model and BSs with a Poisson point process (PPP), we provide the distance distribution between a UE and its associated RIS by evaluating the impact of the RIS orientation. Moreover, we adopt a 3D sectorized flat-top antenna model to characterize the interference introduced by dynamic directional beams (i.e., mainlobe/sidelobe). Furthermore, we derive the signal-to-interference ratio (SIR) coverage probability, where an equivalent PPP is proposed to enhance the computation efficiency. Numerical results validate the accuracy of our analysis and show that the proposed network achieves significant coverage improvement. We also investigate the impacts of the key parameters on the coverage probability, providing useful insights for deploying RISs and antenna arrays in mmWave cellular networks.