Ray-based Predictions of the Outdoor-to-Indoor Massive MIMO Channel

Massive MIMO systems serve multiple users in the same time-frequency resource by utilizing large antenna arrays. A uniform linear array (ULA) containing 128 antenna elements is considered in an urban North American city environment with multiple user channels. The simulations are conducted with a ray-based tool with the latest enhancements of outdoor-to-indoor (O2I) channel prediction capabilities. Most massive MIMO research often uses theoretical models which are based on various assumptions which cannot accurately predict the channel performance. In this paper, simulations are conducted to characterize and evaluate massive MIMO channels in O2I scenarios. A comparison is drawn with regard to line-of-sight (LoS) channels using the singular value spread (SVS) analysis for users located in a same building. It is concluded that the channel dispersion caused by the various multi-paths created at the O2I interface contributes to better channel performance in smaller antenna arrays which is only limited by the path-loss. For larger arrays, there is a saturation of the O2I SVS contribution.