Near-Field Secure Beamfocusing With Receiver-Centered Protected Zone

2025-05-26

AI Summary

This work addresses secure near-field communication against eavesdroppers located arbitrarily outside a designated region. To safeguard legitimate reception, we propose a beamfocusing mechanism that constructs either a physical or a full-duplex virtual protected zone centered at the legitimate receiver—introducing the novel concept of a “receiver-centered protection zone” to explicitly distinguish physical isolation from virtual construction enabled by aggressive self-interference suppression. To tackle the NP-hard robust max-min secrecy rate optimization problem, we develop a synchronized gradient ascent–descent framework and a low-complexity near-optimal algorithm. Integrating near-field electromagnetic modeling, artificial noise injection, and strong self-interference cancellation, the proposed scheme significantly enhances secrecy rate across broad SNR regimes and antenna array scales. Notably, the virtual protection variant achieves secrecy gains close to the ideal secure performance even when physical isolation is infeasible.

Technology Category

• Search and Optimization: Distributed Search
• Machine Learning: Privacy
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: User privacy protection in personalized systems
• Systems and Infrastructure for Web, Mobile and WoT: Virtualization and resource management in Web systems and infrastructures

Abstract

This work studies near-field secure communications through transmit beamfocusing. We examine the benefit of having a protected eavesdropper-free zone around the legitimate receiver, and we determine the worst-case secrecy performance against a potential eavesdropper located anywhere outside the protected zone. A max-min optimization problem is formulated for the beamfocusing design with and without artificial noise transmission. Despite the NP-hardness of the problem, we develop a synchronous gradient descent-ascent framework that approximates the global maximin solution. A low-complexity solution is also derived that delivers excellent performance over a wide range of operating conditions. We further extend this study to a scenario where it is not possible to physically enforce a protected zone. To this end, we consider secure communications through the creation of a virtual protected zone using a full-duplex legitimate receiver. Numerical results demonstrate that exploiting either the physical or virtual receiver-centered protected zone with appropriately designed beamfocusing is an effective strategy for achieving secure near-field communications.

Problem

• Secure near-field communications via transmit beamfocusing
• Optimizing secrecy performance against eavesdroppers outside protected zone
• Creating virtual protected zones for secure full-duplex receiver scenarios

Innovation

• Transmit beamfocusing for secure near-field communications
• Synchronous gradient descent-ascent for maximin solution
• Virtual protected zone using full-duplex receiver