Movable-Element STARS-Aided Secure Communications

TL;DR

This paper introduces a movable-element enabled STARS system that enhances physical layer security against eavesdropping by jointly optimizing beamforming and element positions, demonstrating significant secrecy improvements.

Contribution

It proposes a novel movable-element STARS system with an optimization framework for joint passive and active beamforming and element positioning, advancing physical layer security techniques.

Findings

ME-STARS significantly outperforms fixed-element STARS in secrecy performance.

Secrecy rate saturates within a limited movable region.

The proposed iterative algorithm effectively optimizes beamforming and element positions.

Abstract

A novel movable-element (ME) enabled simultaneously transmitting and reflecting surface (ME-STARS)-aided secure communication system is investigated. Against the full-space eavesdropping, MEs are deployed at the STARS for enhancing the physical layer security by exploiting higher spatial degrees of freedom. Specifically, a sum secrecy rate maximization problem is formulated, which jointly optimizes the passive beamforming and the MEs positions at the ME-STARS, as well as the active beamforming at the base station. To solve the resultant non-convex optimization problem involving highly-coupled variables, an alternating optimization-based iterative algorithm is developed, decomposing the original problem into three subproblems. In particular, for the MEs position optimization subproblem, a gradient ascent algorithm is employed to iteratively refine the MEs' locations within the confined region. Moreover, the the active and passive beamforming subproblems are solved by employing successive convex approximation. Numerical results unveil that: 1) ME-STARS significantly improves the secrecy performance compared to the conventional STARS with fixed-position elements; and 2) The secrecy rate achieved by the ME-STARS gets saturated within limited movable region size.