Simulation-based Investigation on Massive Multi-Antenna System as to Spatial Channel Hardening for Mobile Single User in a Controlled Multipath Environment

This paper brings up the concept of spatial hardening of massive MIMO radio channel in a controlled multipath cavity. The motivation is that, for a mobile user being active in certain area, the massive multi-antenna system shall guarantee the channel hardening in that area. This paper simulates the radio channel confined in a controllable indoor cavity using ray tracing, where the propagation environment contains reflecting and absorbing walls. The multipath channels composing of direct paths and specularly reflected paths up to a second order are analyzed as function of the large scale array topology and configuration in the cavity. We analyze the area focusing performance using a novel spatial channel hardening metric. This study is instructive for massive MIMO system design targeting at steadily hardened channel in an area for user with mobility. Different from the existing work on 'separability of close users' and 'serving dense users', this paper is to understand the spatial focusing and spatial hardening, as well as how different antenna topologies impact both under different multipath conditions.