Frequency Diverse RIS (FD-RIS) Enhanced Wireless Communications via Joint Distance-Angle Beamforming

TL;DR

This paper introduces a frequency diverse RIS (FD-RIS) that enables joint distance-angle beamforming, significantly enhancing wireless communication performance by leveraging time modulation technology and an innovative optimization algorithm.

Contribution

It proposes a novel FD-RIS design for joint distance-angle beamforming and develops a cross-entropy based algorithm to optimize the system, surpassing traditional RIS performance.

Findings

FD-RIS achieves higher achievable rates than traditional RIS.

The CEO algorithm effectively solves the non-convex optimization problem.

Numerical results confirm performance improvements with FD-RIS.

Abstract

The conventional reconfigurable intelligent surface (RIS) assisted far-field communication systems can only implement angle beamforming, which actually limits the capability for reconfiguring the wireless propagation environment. To overcome this limitation, this paper proposes a newly designed frequency diverse RIS (FD-RIS), which can achieve joint distance-angle beamforming with the assistance of the time modulation technology. The signal processing model for FD-RIS-aided wireless communications is first derived. Then, an optimization problem aimed at maximizing the achievable rate is formulated where the frequency-time modulations are jointly optimized to achieve distance-angle beamforming. Furthermore, a novel iterative algorithm based on the cross-entropy optimization (CEO) framework is proposed to effectively handle the non-convex optimization problem. The numerical results validate that the proposed FD-RIS assisted communication scheme can achieve a notable performance improvement compared with the baseline scheme utilizing traditional RIS. In addition, the effectiveness of the proposed CEO algorithm is further verified by comparing with the benchmark using the genetic algorithm (GA).