Robust and Secure Near-Field Communication via Curved Caustic Beams

TL;DR

This paper introduces a physics-informed beamforming method using electromagnetic caustic effects to enhance near-field communication security, significantly reducing eavesdropping risk despite localization errors.

Contribution

It proposes a novel robust beamforming strategy that partitions the array and leverages EM caustic effects for improved security and robustness against eavesdropper localization errors.

Findings

Achieves up to 80% reduction in worst-case eavesdropping rate

Demonstrates robustness against 0.25 m localization error

Enhances physical layer security with phase-only beamforming

Abstract

Near-field beamfocusing with extremely large aperture arrays can effectively enhance physical layer security. Nevertheless, even small estimation errors of the eavesdropper's location may cause a pronounced focal shift, resulting in a severe degradation of the secrecy rate. In this letter, we propose a physics-informed robust beamforming strategy that leverages the electromagnetic (EM) caustic effect for near-field physical layer security provisioning, which can be implemented via phase shifts only. Specifically, we partition the transmit array into caustic and focusing subarrays to simultaneously bypass the potential eavesdropping region and illuminate the legitimate user, thereby significantly improving the robustness against the localization error of eavesdroppers. Moreover, by leveraging the connection between the phase gradient and the EM wave departing angle, we derive the corresponding piece-wise closed-form array phase profile for the subarrays. Simulation results demonstrate that the proposed scheme achieves up to an 80% reduction of the worst-case eavesdropping rate for a localization error of 0.25 m, highlighting its superiority for providing robust and secure communication.