Contemporary wireless communication systems rely on Multi-User Multiple-Input Multiple-Output (MU-MIMO) techniques. In such systems, each Access Point (AP) is equipped with multiple antenna elements and serves multiple devices simultaneously. Notably, traditional systems utilize fixed antennas, i.e., antennas without any movement capabilities, while the idea of movable antennas has recently gained traction among the research community. By moving in a confined region, movable antennas are able to exploit the wireless channel variation in the continuous domain. This additional degree of freedom may enhance the quality of the wireless links, and consequently the communication performance. However, movable antennas for MU-MIMO proposed in the literature are complex, bulky, expensive and present a high power consumption. In this paper, we propose an alternative to such systems that has lower complexity and lower cost. More specifically, we propose the incorporation of rotation capabilities to APs equipped with Uniform Linear Arrays (ULAs) of antennas. We consider the uplink of an indoor scenario where the AP serves multiple devices simultaneously. The optimal rotation of the ULA is computed based on estimates of the positions of the active devices and aiming at maximizing the per-user mean achievable Spectral Efficiency (SE). Adopting a spatially correlated Rician channel model, our numerical results show that the rotation capabilities of the AP can bring substantial improvements in the SE in scenarios where the line-of-sight component of the channel vectors is strong. Moreover, our proposed system is robust against imperfect positioning estimates.

翻译：当代无线通信系统依赖于多用户多输入多输出（MU-MIMO）技术。在此类系统中，每个接入点（AP）配备多个天线单元，并同时为多个设备提供服务。值得注意的是，传统系统采用固定天线，即不具备任何移动能力的天线，而可移动天线的概念近期在学术界引起了广泛关注。通过在有限区域内移动，可移动天线能够利用连续域中的无线信道变化。这一额外的自由度可提升无线链路质量，进而改善通信性能。然而，文献中提出的用于MU-MIMO的可移动天线存在结构复杂、体积庞大、成本高昂及功耗较高等问题。本文提出一种具有更低复杂度和成本的替代方案。具体而言，我们建议为配备均匀线性阵列（ULA）天线的AP增加旋转能力。我们考虑室内场景中的上行链路，其中AP同时为多个设备提供服务。基于对活跃设备位置的估计，以最大化每用户平均可实现频谱效率（SE）为目标，计算ULA的最优旋转角度。采用空间相关的莱斯信道模型后，数值结果表明：在信道向量视距分量较强的场景中，AP的旋转能力可显著提升SE。此外，所提出的系统对不完善的位置估计具有鲁棒性。