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Robust and Secure Near-Field Communication via Curved Caustic Beams

Shicong Liu, Xianghao Yu, Robert Schober

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.

Robust and Secure Near-Field Communication via Curved Caustic Beams

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.
Paper Structure (16 sections, 29 equations, 5 figures, 1 table)

This paper contains 16 sections, 29 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Problem Statement
  3. System Model
  4. Problem Formulation
  5. Proposed Beam Trajectory Design
  6. Phase Gradients
  7. Caustic Trajectory Design
  8. Proposed Secure Beam Trajectory
  9. Caustic Subarray
  10. Focusing Subarray
  11. Main Results
  12. Simulation Setup
  13. Caustic Beam Visualization
  14. Secrecy Rate
  15. Computational Complexity
  16. ...and 1 more sections

Figures (5)

  • Figure 1: (a) Illustration of near-field secure communication and (b) table with notations.
  • Figure 2: Illustration of (a) steering beam, (b) focusing beam, and (c) caustic beam, as well as the corresponding phase profiles (d), (e), and (f).
  • Figure 3: The proposed piece-wise trajectory design.
  • Figure 4: The visualization of spatial beams of different phase profiles, with corresponding radiation details in the region $\Omega_{\varepsilon}$ zoomed in.
  • Figure 5: Mean and worst-case rate performance versus transmit power $P_{\rm T}$.

Theorems & Definitions (1)

  • Remark 1