Angular domain processing for MIMO wireless systems with non-uniform antenna arrays

Many works have proposed spatial channel models for MIMO applications in the 1 to 10 GHz band. However, attention has shifted to the 60 GHz regime where the opening up of the spectrum has created new opportunities for multi-antenna communications. With a broad focus on the 60 GHz regime, we revisit MIMO channel modeling in the classical setting and propose an angular domain decomposition of the channel in this work. In the special case of non-uniform linear arrays, this proposal corresponds to non-uniformly partitioning the angular domain commensurate with the non-uniformity structure of the arrays and estimating the channel gains in each partition with a multi-window spectral estimator. We show that the optimal choice of basis functions that minimize the worst-case bias of the spectral estimator are solutions to certain generalized eigenvalue problems. Based on this structure, we develop a spatial model that generalizes existing MIMO channel modeling paradigms.