ISAC-Enhanced Secure Symbiotic Radio With Passive Localization and Joint Beamforming Design
TL;DR
The proposed framework effectively translates the sensing gains into PLS advantages, significantly outperforming existing benchmarks and developing an algorithm based on Riemannian manifold optimization and alternating method to solve the resulting non-convex problem.
Abstract
Symbiotic radio (SR) is a promising technology for next-generation wireless networks, yet its broadcast nature exposes it to critical security risks, particularly from passive eavesdroppers. To overcome the reliance of conventional physical-layer security (PLS) schemes on impractical prior information about the eavesdropper’s location, this paper proposes an integrated sensing and communication (ISAC)-enhanced secure SR framework. By exploiting the backscattering characteristics of secondary transmitters, we endow the SR system with passive sensing capabilities to localize passive eavesdroppers. Specifically, we design a hybrid time division multiple access (TDMA) and code-domain superposition strategy for multi-backscatter device (BD) scenarios. This protocol coordinates assistive BDs to passively modulate orthogonal variable spreading factor (OVSF) sequences, which act as structured artificial noise (AN) to jam the eavesdropper while simultaneously establishing separable observation paths for localization. Furthermore, we formulate a joint transmit and receive beamforming optimization problem to maximize the secondary secrecy throughput, subject to the constraints on the primary system’s throughput and sensing Cramér-Rao lower bound (CRLB). To solve the resulting non-convex problem, we develop an algorithm based on Riemannian manifold optimization and alternating method. The simulation results demonstrate that the proposed framework effectively translates the sensing gains into PLS advantages, significantly outperforming existing benchmarks.