The effect of delay spread (DS), the specular multipath components (SMCs), and the impact of dense multipath components (DMCs) on multiple-input/multiple-output (MIMO) system performance in a tunnel environment are studied by considering a Richter’s maximum-likelihood (RiMAX)-based estimator. The path loss (PL), angular spread, interuser spatial correlation, and capacity of a massive MIMO framework are analyzed at the 3.5-GHz frequency band through a measurement campaign inside a subway tunnel to implement the latest 5G standards. The radio channel consists of a uniform rectangular array of 32 transmitting elements and a uniform cylindrical array of 64 receiving elements with horizontal and vertical polarizations. The power ratio of the DMCs is found to be distance dependent, as the DMCs and SMCs behave differently in tunnels. Moreover, the study shows that the channel capacity, angular spread, and DS are reduced as the distance between the transmitting and receiving antenna arrays increases, whereas the PL exponent increases with the distance. This research highlights the importance of considering spatial characteristics in 5G massive MIMO system models and provides guidelines to enhance the networks’ accuracy in underground mobile communications.

中文翻译：

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隧道环境中大规模多输入/多输出系统的信道传播特性 [测量角]

通过考虑 Richter's基于最大似然 (RiMAX) 的估计器。通过地铁隧道内的测量活动，在 3.5 GHz 频段分析大规模 MIMO 框架的路径损耗 (PL)、角度扩展、用户间空间相关性和容量，以实施最新的 5G 标准。无线电信道由 32 个发射元件的均匀矩形阵列和 64 个具有水平和垂直极化的接收元件的均匀圆柱阵列组成。DMC 的功率比与距离有关，因为 DMC 和 SMC 在隧道中的行为不同。而且，研究表明，随着发射和接收天线阵列之间距离的增加，信道容量、角度扩展和 DS 会降低，而 PL 指数会随着距离的增加而增加。本研究强调了在 5G 大规模 MIMO 系统模型中考虑空间特性的重要性，并为提高地下移动通信网络的准确性提供了指导。