Terahertz (THz) communications has emerged as a promising technology for future wireless systems due to its potential to support extremely high data rates. However, severe path loss, blockage effects, and sensitivity to beam misalignment pose major challenges to reliable indoor THz communications. In this paper, we investigate the coverage probability of downlink transmission in a three-dimensional (3D) indoor THz communication system under structured access point (AP) deployments, with a focus on square and hexagonal grid topologies. A tractable analytical framework is developed to jointly account for human blockages, correlated wall blockages across APs, beam training, and residual pointing error. Numerical results demonstrate that wall blockage correlation significantly reduces the association and coverage probabilities, and its impact cannot be neglected in system performance analysis. Compared with square grid AP deployments, hexagonal grids consistently achieve higher coverage by mitigating correlated wall blockage effects and reducing the distances between user equipments (UEs) and their associated APs. Furthermore, coverage performance is shown to strongly depend on the UE location, with noticeable degradation as the UE moves away from its nearest AP. Residual pointing error is found to introduce substantial coverage loss, especially for longer links. In addition, beam training analysis reveals a non-monotonic relationship between antenna array size and training overhead, highlighting an inherent tradeoff among antenna configuration, beamwidth selection, and beam training efficiency. These findings provide useful insights into the design and deployment of practical indoor THz communication systems.

翻译：太赫兹（THz）通信因其支持极高数据速率的潜力，已成为未来无线系统中一项前景广阔的技术。然而，严重的路径损耗、遮挡效应以及对波束失准的敏感性，对可靠的室内太赫兹通信构成了重大挑战。本文研究了在结构化接入点（AP）部署（重点关注正方形和六边形网格拓扑）下，三维（3D）室内太赫兹通信系统中下行链路传输的覆盖概率。我们建立了一个易于处理的分析框架，以综合考虑人体遮挡、跨AP的相关墙体遮挡、波束训练以及残余指向误差。数值结果表明，墙体遮挡相关性显著降低了关联概率和覆盖概率，其影响在系统性能分析中不可忽视。与正方形网格AP部署相比，六边形网格通过减轻相关墙体遮挡效应并缩短用户设备（UE）与其关联AP之间的距离，始终能获得更高的覆盖率。此外，覆盖性能被证明强烈依赖于UE的位置，随着UE远离其最近的AP，性能会出现明显下降。研究发现，残余指向误差会引入显著的覆盖损失，尤其对于较长链路。此外，波束训练分析揭示了天线阵列尺寸与训练开销之间的非单调关系，突显了天线配置、波束宽度选择和波束训练效率之间固有的权衡。这些发现为实用室内太赫兹通信系统的设计与部署提供了有益的见解。