The joint uplink/downlink (JUD) design of simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) is conceived in support of both uplink (UL) and downlink (DL) users. Furthermore, the dual STAR-RISs (D-STAR) concept is conceived as a promising architecture for 360-degree full-plane service coverage including users located between the base station (BS) and the D-STAR and beyond. The corresponding regions are termed as primary (P) and secondary (S) regions. The primary STAR-RIS (STAR-P) plays an important role in terms of tackling the P-region inter-user interference, the self-interference (SI) from the BS and from the reflective as well as refractive UL users imposed on the DL receiver. By contrast, the secondary STAR-RIS (STAR-S) aims for mitigating the S-region interferences. The non-linear and non-convex rate-maximization problem formulated is solved by alternating optimization amongst the decomposed convex sub-problems of the BS beamformer, and the D-STAR amplitude as well as phase shift configurations. We also propose a D-STAR based active beamforming and passive STAR-RIS amplitude/phase (DBAP) optimization scheme to solve the respective sub-problems by Lagrange dual with Dinkelbach transformation, alternating direction method of multipliers (ADMM) with successive convex approximation (SCA), and penalty convex-concave procedure (PCCP). Our simulation results reveal that the proposed D-STAR architecture outperforms the conventional single RIS, single STAR-RIS, and half-duplex networks. The proposed DBAP in D-STAR outperforms the state-of-the-art solutions in the open literature.

翻译：针对同时透射与反射可重构智能表面（STAR-RIS）提出了联合上下行（JUD）设计方案，以支持上行（UL）和下行（DL）用户。进一步提出了双STAR-RIS（D-STAR）概念，作为一种有前景的架构，能够实现360度全平面服务覆盖，包括位于基站（BS）与D-STAR之间及其后方的用户。相应区域分别称为主区域（P）和次区域（S）。主STAR-RIS（STAR-P）在解决P区域用户间干扰、来自BS的自干扰（SI）以及反射/折射型上行用户对下行接收机产生的干扰方面发挥关键作用。相比之下，次STAR-RIS（STAR-S）旨在减轻S区域干扰。针对所构建的非线性非凸速率最大化问题，采用交替优化方法求解，将问题分解为BS波束成形、D-STAR幅度及相位配置的凸子问题。我们还提出了基于D-STAR的有源波束成形与无源STAR-RIS幅度/相位（DBAP）联合优化方案，通过结合Dinkelbach变换的拉格朗日对偶法、基于逐次凸近似（SCA）的交替方向乘子法（ADMM）以及惩罚凸凹过程（PCCP）分别求解各子问题。仿真结果表明，所提出的D-STAR架构优于传统单RIS、单STAR-RIS及半双工网络。D-STAR中的DBAP方案亦优于现有文献中的先进解决方案。