Robust Security Energy Efficiency Optimization for RIS-Aided Cell-Free Networks with Multiple Eavesdroppers

TL;DR

This paper proposes a robust energy efficiency optimization framework for RIS-assisted secure cell-free networks with multiple eavesdroppers, employing iterative algorithms and convex optimization techniques to enhance security and efficiency.

Contribution

It introduces a joint beamforming design for secure energy efficiency in RIS-aided cell-free networks, including robust optimization under imperfect channel information.

Findings

The proposed algorithms effectively improve energy efficiency and security.

Robust optimization under channel uncertainty enhances system resilience.

Simulation results confirm the effectiveness of the proposed schemes.

Abstract

In this paper, we investigate the energy efficiency (EE) problem under reconfigurable intelligent surface (RIS)-aided secure cell-free networks, where multiple legitimate users and eavesdroppers (Eves) exist. We formulate a max-min secure EE optimization problem by jointly designing the distributed active beamforming and artificial noise at base stations as well as the passive beamforming at RISs under practical constraints. To deal with it, we first divide the original optimization problem into two sub-ones, and then propose an iterative optimization algorithm to solve each sub-problem based on the fractional programming, constrained convex-convex procedure (CCCP) and semi-definite programming (SDP) techniques. After that, these two sub-problems are alternatively solved until convergence, and the final solutions are obtained. Next, we extend to the imperfect channel state information of the Eves' links, and investigate the robust SEE beamforming optimization problem by bringing the outage probability constraints. Based on this, we first transform the uncertain outage probability constraints into the certain ones by the bernstein-type inequality and sphere boundary techniques, and then propose an alternatively iterative algorithm to obtain the solutions of the original problem based on the S-procedure, successive convex approximation, CCCP and SDP techniques. Finally, the simulation results are conducted to show the effectiveness of the proposed schemes.