In this paper, we propose a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) empowered transmission scheme for symbiotic radio (SR) systems to make more flexibility for network deployment and enhance system performance. The STAR-RIS is utilized to not only beam the primary signals from the base station (BS) towards multiple primary users on the same side of the STAR-RIS, but also achieve the secondary transmission to the secondary users on another side. We consider both the broadcasting signal model and unicasting signal model at the BS. For each model, we aim for minimizing the transmit power of the BS by designing the active beamforming and simultaneous reflection and transmission coefficients under the practical phase correlation constraint. To address the challenge of solving the formulated problem, we propose a block coordinate descent based algorithm with the semidefinite relaxation, penalty dual decomposition and successive convex approximation methods, which decomposes the original problem into one sub-problem about active beamforming and the other sub-problem about simultaneous reflection and transmission coefficients, and iteratively solve them until the convergence is achieved. Numerical results indicate that the proposed scheme can reduce up to 150.6% transmit power compared to the backscattering device enabled scheme.

翻译：本文针对共生无线电系统提出了一种基于同时透射与反射可重构智能表面（STAR-RIS）的传输方案，旨在增强网络部署灵活性并提升系统性能。STAR-RIS不仅可将基站主信号波束成形至同一侧的多主用户，还可实现向另一侧次用户的辅助传输。我们同时考虑了基站侧广播信号模型与单播信号模型。针对每种模型，通过设计有源波束成形以及满足实际相位相关性约束下的同时反射与透射系数，以最小化基站发射功率为目标。为解决所构建问题的求解挑战，我们提出了一种基于块坐标下降的算法，融合半定松弛、罚对偶分解与逐次凸近似方法，将原始问题分解为有源波束成形子问题和同时反射与透射系数子问题，并迭代求解至收敛。数值结果表明，与基于背散射设备的方案相比，所提方案可降低高达150.6%的发射功率。