Design and performance assessment of high-capacity MIMO architectures in the presence of a line-of-sight component

In this paper, the capacity of multiple-input multiple- output (MIMO) communication systems is investigated in the presence of a line-of-sight (LoS) component. Under this scenario, the channel-response matrix is usually rank deficient due to the high correlation between the LoS responses. Previous studies have shown that this problem can be overcome by the use of specifically designed antenna arrays. The antenna elements are positioned to preserve orthogonality and, hence, maximize the LoS-channel rank. To help in the design of such architectures, we derive a 3-D criterion for maximizing the LoS MIMO capacity as a function of the distance, the orientation, and the spacing of the arrays. The sensitivity of these systems to imperfect positioning and orientation is examined using a geometric MIMO model. The spectral efficiency is also investigated in the presence of scattered signals in the environment using a stochastic channel model and a Monte Carlo simulator. To demonstrate the validity of our predictions, we present the results of two MIMO measurement campaigns in an anechoic and an indoor environment where the measured capacities are compared with the capacities obtained from our models. All experimental results validate our predictions and, hence, confirm the potential for superior MIMO performance (when the developed criterion is applied) in strong LoS channels.