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RIS-Enhanced Information-Decoupled Symbiotic Radio Over Broadcasting Signals

Shu Cai, Ya-Feng Liu, Jun Zhan, Qi Zhang

TL;DR

This work addresses power-efficient broadcasting in a RIS-enhanced ID-SR system where a multi-antenna PTx sends a common primary stream to multiple PRs and a RIS-BDx backscatters a secondary stream to a BRx that uses energy detection. A rate-balanced reformulation together with a BER-ratio characterization enables a penalty-based block coordinate descent (PBCD) algorithm with closed-form updates, scalable to large RIS sizes due to near-linear complexity in the number of RIS elements $N_r$. Numerical results demonstrate fast convergence (about 10 iterations) and clear transmit-power reductions compared to conventional SR baselines, highlighting the benefits of information decoupling and RIS-assisted design for green, confidential IoT broadcasting. The proposed framework effectively trades off a common rate requirement $R_k \ge r_p$ and a BRx BER constraint $P_b(\cdot) \le \Lambda_s$, offering a practical approach for RIS-enabled, energy-efficient wireless systems with controlled information exposure.

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.

RIS-Enhanced Information-Decoupled Symbiotic Radio Over Broadcasting Signals

TL;DR

This work addresses power-efficient broadcasting in a RIS-enhanced ID-SR system where a multi-antenna PTx sends a common primary stream to multiple PRs and a RIS-BDx backscatters a secondary stream to a BRx that uses energy detection. A rate-balanced reformulation together with a BER-ratio characterization enables a penalty-based block coordinate descent (PBCD) algorithm with closed-form updates, scalable to large RIS sizes due to near-linear complexity in the number of RIS elements . Numerical results demonstrate fast convergence (about 10 iterations) and clear transmit-power reductions compared to conventional SR baselines, highlighting the benefits of information decoupling and RIS-assisted design for green, confidential IoT broadcasting. The proposed framework effectively trades off a common rate requirement and a BRx BER constraint , offering a practical approach for RIS-enabled, energy-efficient wireless systems with controlled information exposure.

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.
Paper Structure (15 sections, 1 theorem, 20 equations, 4 figures, 1 algorithm)

This paper contains 15 sections, 1 theorem, 20 equations, 4 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Network and Channel Model
  4. Signal Model
  5. Primary Rates and BRx Energy Detection
  6. Transmit Power Minimization
  7. The Proposed PBCD Method
  8. Penalty Reformulation
  9. The q_k,i-subprobelms with k>=1
  10. The q_0,i-subproblem
  11. The w-subproblem
  12. The RIS Phase Update
  13. Algorithm and Complexity
  14. Simulation Results
  15. Conclusion

Key Result

Lemma 1

The optimal solutions of eq:q00q01 satisfy

Figures (4)

  • Figure 1: The RIS-Enhanced ID-SR (RIS-ID-SR) over broadcasting signals.
  • Figure 2: Symbols in the RIS-ID-SR system, where one secondary symbol period comprises $T$ primary symbols. Due to the weak power of the backscattered signal, the achievable rate at the BRx is lower than that at the PRx.
  • Figure 3: Convergence behavior of Algorithm \ref{['alg:BCD']}. Left: equality constraint violation versus iterations; right: transmit power versus iterations.
  • Figure 4: Average transmit power versus spatial deployment and number of PRs.

Theorems & Definitions (1)

  • Lemma 1