AmbShield: Enhancing Physical Layer Security with Ambient Backscatter Devices against Eavesdroppers

2026-01-14

AI Summary

This work addresses the critical challenge of passive eavesdropping in wireless networks, which severely compromises communication confidentiality. Conventional encryption and physical-layer security techniques often suffer from high power consumption, deployment complexity, or reliance on precise synchronization and channel state information—limitations that are particularly acute in resource-constrained scenarios. To overcome these bottlenecks, the paper proposes AmbShield, a novel framework that leverages distributed ambient backscatter devices (AmBDs) as cooperative passive jammers and relays. Without increasing transmit power or deployment overhead, AmbShield simultaneously enhances the legitimate link capacity and disrupts eavesdroppers. The authors develop a unified SINR statistical model, derive a closed-form expression for secrecy outage probability, and validate through Monte Carlo simulations and high-SNR asymptotic analysis that the system achieves significant secrecy gains and robust performance even under imperfect synchronization and channel estimation.

Technology Category

• Machine Learning: Privacy
• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Scheduling under Uncertainty

Application Category

• Security and Privacy: Privacy-enhancing technologies
• 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

Passive eavesdropping compromises confidentiality in wireless networks, especially in resource-constrained environments where heavyweight cryptography is impractical. Physical layer security (PLS) exploits channel randomness and spatial selectivity to confine information to an intended receiver with modest overhead. However, typical PLS techniques, such as using beamforming, artificial noise, and reconfigurable intelligent surfaces, often involve added active power or specialized deployment, and, in many designs, rely on precise time synchronization and perfect CSI estimation, which limits their practicality. To this end, we propose AmbShield, an AmBD-assisted PLS scheme that leverages naturally distributed AmBDs to simultaneously strengthen the legitimate channel and degrade eavesdroppers'without requiring extra transmit power and with minimal deployment overhead. In AmbShield, AmBDs are exploited as friendly jammers that randomly backscatter to create interference at eavesdroppers, and as passive relays that backscatter the desired signal to enhance the capacity of legitimate devices. We further develop a unified analytical framework that analyzes the exact probability density function (PDF) and cumulative distribution function (CDF) of legitimate and eavesdropper signal-to-interference-noise ratio (SINR), and a closed-form secrecy outage probability (SOP). The analysis provides clear design guidelines on various practical system parameters to minimize SOP. Extensive experiments that include Monte Carlo simulations, theoretical derivations, and high-SNR asymptotic analysis demonstrate the security gains of AmbShield across diverse system parameters under imperfect synchronization and CSI estimation.

Problem

• physical layer security
• eavesdropping
• wireless networks
• resource-constrained environments
• confidentiality

Innovation

• Ambient Backscatter
• Physical Layer Security
• Friendly Jamming
• Passive Relaying
• Secrecy Outage Probability