RIS-Assisted Coverage Enhancement in Millimeter-Wave Cellular Networks

TL;DR

This paper analyzes how reconfigurable intelligent surfaces (RISs) can significantly improve coverage in millimeter-wave 5G networks by passively reflecting signals, with analytical and simulation results demonstrating their effectiveness.

Contribution

It provides the first analytical framework using stochastic geometry to evaluate RIS-assisted mmWave coverage, deriving closed-form expressions for reflection power and SIR coverage.

Findings

RIS deployment enhances mmWave coverage effectively.

Passive RISs are as beneficial as adding more antennas to base stations.

Analytical results are validated by simulations.

Abstract

The use of millimeter-wave (mmWave) bandwidth is one key enabler to achieve the high data rates in the fifth-generation (5G) cellular systems. However, mmWave signals suffer from significant path loss due to high directivity and sensitivity to blockages, limiting its adoption within small-scale deployments. To enhance the coverage of mmWave communication in 5G and beyond, it is promising to deploy a large number of reconfigurable intelligent surfaces (RISs) that passively reflect mmWave signals towards desired directions. With this motivation, in this work we study the coverage of an RIS-assisted large-scale mmWave cellular network using stochastic geometry, and derive the peak reflection power expression of an RIS and the downlink signal-to-interference ratio (SIR) coverage expression in closed forms. These analytic results clarify the effectiveness of deploying RISs in the mmWave SIR coverage enhancement, while unveiling the major role of the density ratio between active base stations (BSs) and passive RISs. Furthermore, the results show that deploying passive reflectors is as effective as equipping BSs with more active antennas in the mmWave coverage enhancement. Simulation results confirm the tightness of the closed form expressions, corroborating our major findings based on the derived expressions.