Exploration of User Separation Capabilities by Distributed Large Antenna Arrays

In this paper, we present a novel exploration of spatial separation of closely-located users by a massive MIMO system in line-of-sight (LoS) for both an anechoic chamber and an indoor corridor propagation environments. A distributed massive multiple-input multiple-output (DM-MIMO) system powered by software defined radios (SDRs) has been used for the measurement campaign. For the user separation study, we first conduct an analysis with a spherical wave channel model for physically-large rectangular arrays. Preliminary simulation results show that a single antenna array achieves better user separation for users distributed on a line parallel to the array plane rather than when users are distributed on a line normal to the array. An intuitive idea is that, by splitting a collocated antenna array into two subarrays, additional diversity is created if the second sub-array is on a plane orthogonal to the first sub-array. Figures of merit such as the correlation coefficients, condition numbers and sum-rates of both centralized and distributed antenna arrays have been chosen to determine the impact of array split and positioning on user separation. Extensive measurements, performed on two 32-element antenna arrays of a massive MIMO testbed at 2.6GHz, show that an improvement of around 140% can be achieved in a poor scattered environment if distributed arrays are used instead of centralized ones.