A Line-of-Sight Optimised MIMO Architecture for Outdoor Environments

The authors present an investigation on the capacity of Line-of-Sight (LoS) optimised and conventional (narrow-spaced) Multiple-Input Multiple-Output (MIMO) communication systems in outdoor environments. Under a LoS scenario, the channel is normally 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 to preserve the orthogonality of the LoS signal at the receiver; hence maximising the channel rank. A previously derived maximum capacity criterion is employed in the design of the proposed LoS-optimised MIMO system. The performance of this system is then assessed by means of a raytracing simulation and compared with that of a conventional MIMO system. It is shown that the proposed system exhibits a significant capacity enhancement (453 %) in the deployment area. Moreover, the capacity was found to be higher than that predicted by the i.i.d. Rayleigh fading model due to non-fading nature of the LoS signals.