Maximum MIMO Capacity in Line-of-Sight

Abstract

In this paper, we investigate the capacity limits of Multiple-Input, Multiple-Output (MIMO) communication systems in Line-of-Sight (LoS) environments. Under this scenario, the channel is usually rank deficient due to the linear dependence of the LoS rays' phases on the receive elements. To overcome this problem, specifically designed antenna arrays can be employed, where the antenna elements are positioned in a way that orthogonality is preserved; hence maximizing the channel rank. To help in the design of such systems we derive the criteria for the maximum MIMO capacity in LoS environments as a function of the distance and the spacing of the arrays. The performance of these architectures is investigated in a number of optimal and suboptimal locations using a geometrical channel model. Finally, the performance is also studied in various degrees of scatter using a stochastic Monte-Carlo simulator.