Maximum MIMO Capacity in Line-of-Sight

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