Design and performance assessment of maximum capacity MIMO architectures in line-of-sight

The authors investigate the capacity of multiple-input, multiple-output (MIMO) communication systems in line-of-sight (LoS). Under this scenario, the channel is normally rank deficient owing 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 such a way as to preserve orthogonality; hence maximising the channel rank. To help in the design of such systems we derive the criterion for achieving maximum MIMO capacity in a LoS environment as a function of the transmit–receive separation distance, the array orientation and the inter-element spacings. We investigate the performance and the capacity sensitivity for a number of MIMO architectures using a Monte-Carlo simulation and a stochastic channel model. We then present a number of MIMO measurements performed inside an anechoic chamber and in an indoor office environment. Finally, our theoretic predictions are compared against the LoS measurements