A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted simultaneous wireless information and power transfer (SWIPT) system is proposed. More particularly, an STAR-RIS is deployed to assist in the information/power transfer from a multi-antenna access point (AP) to multiple single-antenna information users (IUs) and energy users (EUs), where two practical STAR-RIS operating protocols, namely energy splitting (ES) and time switching (TS), are employed. Under the imperfect channel state information (CSI) condition, a multi-objective optimization problem (MOOP) framework, that simultaneously maximizes the minimum data rate and minimum harvested power, is employed to investigate the fundamental rate-energy trade-off between IUs and EUs. To obtain the optimal robust resource allocation strategy, the MOOP is first transformed into a single-objective optimization problem (SOOP) via the {\epsilon}-constraint method, which is then reformulated by approximating semi-infinite inequality constraints with the S-procedure. For ES, an alternating optimization (AO)-based algorithm is proposed to jointly design AP active beamforming and STAR-RIS passive beamforming, where a penalty method is leveraged in STAR-RIS beamforming design. Furthermore, the developed algorithm is extended to optimize the time allocation policy and beamforming vectors in a two-layer iterative manner for TS. Numerical results reveal that: 1) deploying STAR-RISs achieves a significant performance gain over conventional RISs, especially in terms of harvested power for EUs; 2) the ES protocol obtains a better user fairness performance when focusing only on IUs or EUs, while the TS protocol yields a better balance between IUs and EUs; 3) the imperfect CSI affects IUs more significantly than EUs, whereas TS can confer a more robust design to attenuate these effects.

翻译：提出了一种同时发射和反射可重构智能表面（STAR-RIS）辅助的同步无线信息与功率传输（SWIPT）系统。具体而言，部署STAR-RIS以辅助从多天线接入点（AP）到多个单天线信息用户（IU）和能量用户（EU）的信息/功率传输，其中采用了两种实用的STAR-RIS运行协议，即能量分裂（ES）和时间切换（TS）。在不完美信道状态信息（CSI）条件下，采用多目标优化问题（MOOP）框架，同时最大化最小数据速率和最小采集功率，以研究IU与EU之间的基本速率-能量权衡。为获得最优鲁棒资源分配策略，首先通过ε约束法将MOOP转化为单目标优化问题（SOOP），进而利用S过程近似半无限不等式约束进行重新表述。针对ES方案，提出了一种基于交替优化（AO）的算法联合设计AP主动波束成形和STAR-RIS被动波束成形，其中在STAR-RIS波束成形设计中采用了惩罚方法。此外，将所提算法扩展至TS方案，以两层迭代方式优化时间分配策略与波束成形向量。数值结果表明：1）相较于传统RIS，部署STAR-RIS可显著提升性能增益，尤其是在EU的采集功率方面；2）当仅关注IU或EU时，ES协议可获得更优的用户公平性，而TS协议则能在IU与EU之间实现更好的平衡；3）不完美CSI对IU的影响大于EU，而TS能够提供更鲁棒的设计以减弱这些影响。