Interference-Free RIS-Aided Cell-Free Massive MIMO with Physical Layer Security

TL;DR

This paper proposes a RIS-assisted cell-free massive MIMO framework that enhances physical layer security and eliminates multi-user interference through joint optimization of beamforming, power allocation, and RIS phase shifts.

Contribution

It introduces a novel joint optimization approach using Riemannian manifold optimization to improve secrecy and interference mitigation in CFmMIMO networks.

Findings

Significant increase in secrecy sum rate.

Effective interference elimination.

Enhanced security in dense wireless environments.

Abstract

In this paper, a reconfigurable intelligent surface (RIS) assisted cell free massive MIMO (CFmMIMO) framework is designed to enhance physical layer security (PLS) and mitigate multi user (MU) interference in next generation wireless networks. A channel state information (CSI) based precoder is designed at the access point (AP) to suppress MU interference, enabling interference free reception for the legitimate users. To further enhance secrecy performance, we formulate a joint optimization problem that maximizes the secrecy sum rate using an alternating optimization (AO) framework, which iteratively updates the active beamforming at the AP, user power allocation, and the RIS phase shift matrix. The highly nonconvex problem is addressed under the Riemannian manifold optimization (RMO) framework and solved using a Riemannian Conjugate Gradient (RCG) algorithm for RIS phase shift design. Simulation results verify that the proposed framework effectively enhances the secrecy sum rate and eliminates interference, demonstrating its potential for secure and scalable CFmMIMO networks in dense wireless environments.