AI 中文总结
本文针对可旋转天线增强的半双工放大转发中继系统，联合优化基站与中继预编码及可旋转天线指向，提出MFW等算法，在单用户及多用户场景下提升用户最小信干噪比，仿真验证其性能优于对比方案。
AI 中文摘要
本文研究一种可旋转天线（RA）增强型半双工放大转发中继系统，其中多天线基站（BS）通过多天线中继为多个单天线用户提供服务。基站和用户采用各向同性天线，而中继采用定向可旋转天线，其指向矩阵由两跳共享，以避免跳间重新定向延迟和控制开销。我们旨在通过联合优化基站预编码、中继预编码和可旋转天线指向矩阵，最大化所有用户中的最小信干噪比（SINR）。为解决这一非凸问题，我们首先研究单用户场景，利用闭式形式的最优中继预编码矩阵将联合设计简化为可旋转天线指向优化，随后采用流形感知弗兰克-沃尔夫（MFW）方法获取次优指向解。在对称远场视距几何下，我们进一步刻画全局最优指向结构，推导区分普通指向与天线分裂的方向性阈值。基于该MFW流程，我们接着处理一般多用户场景：首先应用二次变换得到等效辅助变量公式，随后通过交替优化（AO）次优求解；具体而言，我们采用基于对数求和指数平滑的MFW方法的带保护扩展，在每次AO迭代中更新可旋转天线指向矩阵。仿真结果表明，所提算法在所有对比方案中始终实现最佳信噪比（SNR）和信干噪比性能；进一步分析显示，优化后的可旋转天线指向适配两跳几何，优选方向性因子取决于用户负载，且两跳传播条件相对均衡的中继部署通常更优。
英文摘要
This paper investigates a rotatable antenna (RA)-enhanced half-duplex amplify-and-forward relaying system, where a multi-antenna base station (BS) serves multiple single-antenna users via a multi-antenna relay. The BS and users employ isotropic antennas, whereas the relay employs directional RAs whose pointing matrix is shared by both hops to avoid inter-hop reorientation delay and control overhead. We aim to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among all users by jointly optimizing the BS precoding, relay precoding, and RA pointing matrices. To tackle this non-convex problem, we first investigate the single-user scenario and reduce the joint design to RA pointing optimization using the optimal relay precoding matrix available in closed form. A manifold-aware Frank--Wolfe (MFW) method is then employed to obtain a suboptimal pointing solution. Under a symmetric far-field line-of-sight geometry, we further characterize the globally optimal pointing structure and derive a directivity threshold separating common pointing from antenna splitting. Building on this MFW procedure, we next address the general multiuser scenario. Specifically, the quadratic transform is first applied to obtain an equivalent auxiliary-variable formulation, which is subsequently solved suboptimally via alternating optimization (AO). In particular, we employ a safeguarded extension of the MFW method based on log-sum-exp smoothing to update the RA pointing matrix in each AO iteration. Simulation results demonstrate that the proposed algorithms consistently achieve the best signal-to-noise ratio (SNR) and SINR performance among all considered schemes. It is further shown that the optimized RA pointing adapts to the two-hop geometry, the preferred directivity factor depends on user load, and relay placement with relatively balanced two-hop propagation conditions is generally preferable.
Comments13 pages,8 figures,submitted to an IEEE journal for possible publication
