RIS-Enhanced Information-Decoupled Symbiotic Radio Over Broadcasting Signals

TL;DR

This paper introduces a RIS-enhanced, energy-detection-based symbiotic radio system that reduces power consumption and improves security by decoupling primary and secondary data transmissions, with an efficient optimization algorithm.

Contribution

It proposes a novel RIS-assisted decoupled symbiotic radio system with a new optimization framework and low-complexity algorithm for power minimization under rate and BER constraints.

Findings

Fast convergence of the proposed algorithm.

Reduced power consumption compared to conventional systems.

Enhanced security by decoupling primary and secondary data.

Abstract

This paper studies a reconfigurable intelligent surface (RIS)-enhanced decoupled symbiotic radio (SR) system in which a primary transmitter delivers common data to multiple primary receivers (PRs), while a RIS-based backscatter device sends secondary data to a backscatter receiver (BRx). Unlike conventional SR, the BRx performs energy detection and never decodes the primary signal, thereby removing ambiguity and preventing exposure of the primary payload to unintended receivers. In this paper, we formulate the problem as the minimization of the transmit power subject to a common broadcast rate constraint across all PRs and a bit error rate (BER) constraint at the BRx. The problem is nonconvex due to the unit-modulus RIS constraint and coupled quadratic forms. Leveraging a rate-balanced reformulation and a monotonic BER ratio characterization, we develop a low-complexity penalty-based block coordinate descent algorithm with closed-form updates. Numerical results show fast convergence of the proposed algorithm and reduced power consumption of the considered RIS-enhanced information-decoupled SR system over conventional SR baselines.