We consider reconfigurable intelligent surface (RIS) aided sixth-generation (6G) terahertz (THz) communications for indoor environment in which a base station (BS) wishes to send independent messages to its serving users with the help of multiple RISs. For indoor environment, various obstacles such as pillars, walls, and other objects can result in no line-of-sight signal path between the BS and a user, which can significantly degrade performance. To overcome such limitation of indoor THz communication, we firstly optimize the placement of RISs to maximize the coverage area. Under the optimized RIS placement, we propose 3D hybrid beamforming at the BS and phase adjustment at RISs, which are jointly performed at the BS and RISs via codebook-based 3D beam scanning with low complexity. Numerical simulations demonstrate that the proposed scheme significantly improves the average sum rate compared to the cases of no RIS and randomly deployed RISs. It is further shown that the proposed codebook-based 3D beam scanning efficiently aligns analog beams between BS--user links or BS--RIS--user links and, as a consequence, achieves the average sum rate close to that of coherent beam alignment requiring global channel state information.
翻译:我们考虑使用可重构智能表面(RIS)辅助第六代(6G)太赫兹(THz)通信的室内环境,其中基站(BS)希望在多个RISs的帮助下向其服务用户发送独立消息。针对室内环境,各种障碍物(例如柱子、墙壁和其他物体)可能导致BS和用户之间没有直线视野信号路径,从而可能极大地降低性能。为了克服室内THz通信的此种限制,我们首先优化RISs的部署以最大化覆盖面积。在优化RIS部署的情况下,我们提出了在BS和RISs通过基于码本的三维波束扫描低复杂度联合执行的3D混合波束成形和相位调整。数值模拟表明,与没有RIS和随机部署RIS的情况相比,所提出的方案显着提高了平均总速率。进一步表明,所提出的基于码本的三维波束扫描有效地使BS-用户链路或BS-RIS-用户链路之间的模拟波束对准,并因此实现了与需要全局信道状态信息的相干波束对准相近的平均总速率。