On Ergodic Rates and Optimal Array Geometry in Line-of-Sight Massive MIMO

Abstract

We investigate the achievable ergodic rate of Massive multi-input-multi-output (MIMO) system in environments with high mobility and line-of-sight (LoS). A 3-dimensional geo- metric model with uniform rectangular array at the base station (BS) is used for the investigation. We derive the closed form expression for lower bound of uplink ergodic rate take into account imperfection on the channel state information, number of BS antennas, antenna spacing, and spatial distribution of user terminals. The results show that, in LoS Massive MIMO, when the terminals are uniformly distributed around the BS, the ergodic rate is maximized for antenna spacing equal to integer multiples of one-half wavelength.