PA-Assisted Symbiotic Radio: Joint PA Positioning and Resource Allocation for Sum Rate Maximization

Abstract

We propose a pinching-antenna (PA)-assisted downlink symbiotic radio system to alleviate the double-fading effect in backscatter communications. By dynamically activating predefined PA positions along multiple parallel waveguides, the transmitter can select radiating points close to multiple backscatter devices (BDs) simultaneously, enabling spatial multiplexing while preserving the constructive multipath gain inherent to symbiotic radio. Under the primary user’s quality-of-service constraint, a BD sum rate maximization problem is formulated by jointly optimizing PA positions, beamforming vectors, and BD reflection coefficients. A joint matching and alternating optimization (JMAO) algorithm is developed, where the outer layer optimizes PA positions through discrete matching, while the inner layer alternately updates beamforming vectors and reflection coefficients. Simulation results demonstrate that the proposed scheme achieves a higher BD sum rate than benchmark methods and scales effectively with the number of BDs.