RIS-Assisted Quasi-Static Broad Coverage for Wideband mmWave Massive MIMO Systems

TL;DR

This paper proposes a RIS-assisted quasi-static broad coverage design for wideband mmWave MIMO systems that reduces overhead and improves performance by leveraging statistical CSI and a power pattern synthesis framework.

Contribution

It introduces a novel quasi-static broad coverage design for RIS that minimizes overhead and enhances multiuser mmWave MIMO communication performance.

Findings

Quasi-static broad coverage outperforms instantaneous CSI-based methods.

Analytical downlink rate increases logarithmically with RIS power gain.

Numerical simulations confirm the effectiveness of the proposed design.

Abstract

Reconfigurable intelligent surfaces (RISs) can establish favorable wireless environments to combat the severe attenuation and blockages in millimeter-wave (mmWave) bands. However, to achieve the optimal enhancement of performance, the instantaneous channel state information (CSI) needs to be estimated at the cost of a large overhead that scales with the number of RIS elements and the number of users. In this paper, we design a quasi-static broad coverage at the RIS with the reduced overhead based on the statistical CSI. We propose a design framework to synthesize the power pattern reflected by the RIS that meets the customized requirements of broad coverage. For the communication of broadcast channels, we generalize the broad coverage of the single transmit stream to the scenario of multiple streams. Moreover, we employ the quasi-static broad coverage for a multiuser orthogonal frequency division multiplexing access (OFDMA) system, and derive the analytical expression of the downlink rate, which is proved to increase logarithmically with the power gain reflected by the RIS. By taking into account the overhead of channel estimation, the proposed quasi-static broad coverage even outperforms the design method that optimizes the RIS phases using the instantaneous CSI. Numerical simulations are conducted to verify these observations.