Optimized Frequency-Diverse Movable Antenna Arrays for Directional Secrecy in Wireless Systems

TL;DR

This paper introduces an optimized frequency-diverse movable antenna array design that enhances directional secrecy in wireless systems, especially when eavesdroppers align with legitimate users, by jointly optimizing antenna positions and frequency shifts.

Contribution

It proposes a joint design of MA and FDA arrays with closed-form solutions for optimal parameters, improving secrecy performance against aligned eavesdroppers.

Findings

Significant secrecy performance improvement demonstrated through simulations.

Closed-form expressions for optimal antenna positions and frequency shifts derived.

Enhanced security in line-of-sight dominated mmWave/THz bands achieved.

Abstract

Movable-antenna (MA) arrays are envisioned as a promising technique for enhancing secrecy performance in wireless communications by leveraging additional spatial degrees of freedom. However, when the eavesdropper is located in the same direction as the legitimate user, particularly in mmWave/THz bands where line-of-sight (LOS) propagation dominates, the secrecy performance of MA arrays becomes significantly limited, thus directionally insecure. To address this challenge, we employ a joint design that combines an MA array with a frequency-diverse array (FDA) at the transmitter to secure the transmission across both range and direction. Specifically, we derive closed-form expressions for the optimal antenna positions and frequency shifts, assuming small perturbations in both parameters from a linear frequency-diverse MA configuration. Furthermore, we compare the worst-case secrecy rate under this minor perturbation assumption with that obtained under a general constraint, where simulated annealing is employed to numerically determine the optimal parameters. Simulation results confirm that the proposed optimized frequency diverse MA approach significantly enhances secrecy performance in the presence of an eavesdropper aligned with the direction of the legitimate receiver.