Performance Analysis of Physical Layer Security: From Far-Field to Near-Field

2024-08-20

arXiv.org

AI Summary

This work investigates the scaling laws of physical-layer security in far-field and near-field communications, focusing on two key metrics under power constraints: the secrecy capacity and the minimum transmit power required to achieve a target secrecy rate. We introduce “insecurity depth” as a novel metric to quantify the security gain from near-field beam focusing. Theoretically, we show that insecurity depth decreases with increasing antenna count, while both secrecy capacity and minimum required power are strictly bounded by energy conservation, exhibiting asymptotically bounded behavior. Leveraging a discrete-time memoryless channel model, we derive closed-form expressions, incorporating accurate far-field/near-field channel modeling and asymptotic analysis in the infinite-antenna and infinite-power regimes. Results demonstrate that near-field propagation significantly expands the secure transmission region under colluding eavesdroppers; although scaling up antenna arrays continuously improves security, fundamental limits imposed by energy conservation ultimately cap performance gains. Numerical simulations validate the derived scaling laws.

Technology Category

• Application Domains: Security
• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

The secrecy performance in both near-field and far-field communications is analyzed using two fundamental metrics: the secrecy capacity under a power constraint and the minimum power requirement to achieve a specified secrecy rate target. 1) For the secrecy capacity, a closed-form expression is derived under a discrete-time memoryless setup. This expression is further analyzed under several far-field and near-field channel models, and the capacity scaling law is revealed by assuming an infinitely large transmit array and an infinitely high power. A novel concept of"depth of insecurity"is proposed to evaluate the secrecy performance achieved by near-field beamfocusing. It is demonstrated that increasing the number of transmit antennas reduces this depth and thus improves the secrecy performance. 2) Regarding the minimum required power, a closed-form expression is derived and analyzed within far-field and near-field scenarios. Asymptotic analyses are performed by setting the number of transmit antennas to infinity to unveil the power scaling law. Numerical results are provided to demonstrate that: i) compared to far-field communications, near-field communications expand the areas where secure transmission is feasible, specifically when the eavesdropper is located in the same direction as the intended receiver; ii) as the number of transmit antennas increases, neither the secrecy capacity nor the minimum required power scales or vanishes unboundedly, adhering to the principle of energy conservation.

Problem

• Analyzes secrecy performance in near-field and far-field communications
• Derives closed-form expressions for secrecy capacity and power requirements
• Proposes depth of insecurity concept for near-field beamfocusing evaluation

Innovation

• Closed-form secrecy capacity under power constraint
• Depth of insecurity for near-field beamfocusing
• Power scaling law with infinite transmit antennas