Construction and capacity analysis of high-rank line-of-sight MIMO channels

This paper describes a technique for realizing a high rank channel matrix in a line-of-sight (LOS) multiple-input-multiple-output (MIMO) transmission scenario. This is beneficial for systems which can not make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading channels. Typical applications are fixed wireless access and radio relay systems. The technique is based on optimization of antenna placement in a uniform linear array. By introducing a new and more general geometrical model than that applied in earlier works, additional insight into the optimal design parameters is gained. A novel analysis of the sensitivity of the optimal design parameters is performed. The LOS transmission matrix is used in a Rician fading channel model, and performance is evaluated with respect to ergodic capacity, outage capacity, and effective degrees of freedom. The results show that even with some deviation from optimal design, the LOS MIMO case outperforms the i.i.d. Rayleigh case in terms of Shannon capacity.

I. Introduction

Fixed wireless access (FWA) is a flexible and cost-efficient way to bring network applications such as Internet and telephony to offices and homes. This technology requires no expensive and time consuming digging of cables, and is easily scalable with regard to the applications' demand. Some predictions on the role of FWA in the future communication environment are given in [1] and [2], while a presentation of emerging technologies for upcoming FWA systems can be found in [3].