Reliability is becoming increasingly important for many applications envisioned for future wireless systems. A technology that could improve reliability in these systems is massive MIMO (Multiple-Input Multiple-Output). One reason for this is a phenomenon called channel hardening, which means that as the number of antennas in the system increases, the variations of channel gain decrease in both the time- and frequency domain. Our analysis of channel hardening is based on a joint comparison of theory, measurements and simulations. Data from measurement campaigns including both indoor and outdoor scenarios, as well as cylindrical and planar base station arrays, are analyzed. The simulation analysis includes a comparison with the COST 2100 channel model with its massive MIMO extension. The conclusion is that the COST 2100 model is well suited to represent real scenarios, and provides a reasonable match to actual measurements up to the uncertainty of antenna patterns and user interaction. Also, the channel hardening effect in practical massive MIMO channels is less pronounced than in complex independent and identically distributed (i.i.d.) Gaussian channels, which are often considered in theoretical work.

中文翻译：

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大规模MIMO中的信道硬化：模型参数和实验评估

对于未来无线系统中预期的许多应用，可靠性变得越来越重要。可以提高这些系统可靠性的技术是大规模MIMO（多输入多输出）。造成这种情况的一个原因是一种称为信道硬化的现象，这意味着随着系统中天线数量的增加，信道增益的变化在时域和频域均减小。我们对通道硬化的分析基于理论，测量和模拟的联合比较。分析了包括室内和室外场景以及圆柱和平面基站阵列在内的测量活动的数据。仿真分析包括与具有大规模MIMO扩展功能的COST 2100信道模型的比较。结论是，COST 2100模型非常适合表示真实情况，并提供与实际测量值的合理匹配，直到天线方向图和用户交互的不确定性为止。而且，在实际的大规模MIMO信道中，信道硬化效果不如在理论上经常考虑的复杂独立且均匀分布的（iid）高斯信道中强。