AI 中文总结
该研究针对CSI不完善场景，提出ME-STARS辅助RSMA系统，通过联合优化发射波束成形等变量及可移动单元位置，采用迭代MM框架求解，性能优于基准方案且对CSI不确定性鲁棒。
AI 中文摘要
本文研究了信道状态信息（CSI）不完善情况下，可移动单元同时发射与反射可重构智能表面（ME-STARS）辅助的速率分割多址（RSMA）系统。与单元位置固定的传统STARS不同，ME-STARS的单元可在预定义区域内重新定位，为改善级联的发射机-STARS-用户信道提供额外空间自由度。为利用该灵活性并考虑CSI不确定性，我们构建了一个稳健的和速率最大化问题，联合优化发射波束成形、公共速率分配、反射与传输系数，以及ME-STARS单元位置，约束条件包括发射功率、用户速率、最小单元间距和移动区域约束。由于设计变量与位置相关信道间的强耦合，该问题具有高度非凸性。为应对这一挑战，我们开发了一种迭代优化框架，通过可处理的凸重构依次优化发射波束成形、STARS系数和单元位置。具体而言，单元位置利用 majorization-minimization（MM）框架顺序更新，其中基于位置相关信道的一阶和二阶导数构造二次代理函数，同时保留最小单元间距约束。仿真结果表明，所提出的ME-STARS设计始终优于所考虑的基准方案；此外，随着CSI不确定性增加，性能增益仍显著，凸显了单元重新定位对稳健RSMA传输的有效性。
英文摘要
This paper investigates a movable-element simultaneously transmitting and reflecting reconfigurable intelligent surface (ME-STARS) assisted rate-splitting multiple access (RSMA) system under imperfect channel state information (CSI). Unlike conventional STARS with fixed element positions, the elements of ME-STARS can be repositioned within a predefined region, providing additional spatial degrees of freedom for improving the cascaded transmitter--STARS--user channels. To exploit this flexibility while accounting for CSI uncertainty, we formulate a robust sum-rate maximization problem that jointly optimizes the transmit beamforming, common-rate allocation, reflection and transmission coefficients, and ME-STARS element positions, subject to transmit-power, user-rate, minimum inter-element spacing, and movement-region constraints. The resulting problem is highly non-convex due to the strong coupling among the design variables and the position-dependent channels. To address this challenge, an iterative optimization framework is developed in which the transmit beamforming, STARS coefficients, and element positions are successively optimized through tractable convex reformulations. In particular, the element positions are updated sequentially using a majorization--minimization (MM) framework, where quadratic surrogate functions are constructed from the first- and second-order derivatives of the position-dependent channels while preserving the minimum inter-element spacing constraint. Simulation results demonstrate that the proposed ME-STARS design consistently outperforms the considered benchmark schemes. Moreover, the performance gains remain significant under increasing CSI uncertainty, highlighting the effectiveness of element repositioning for robust RSMA transmission.
Comments13 pages, 10 figures
