Non-uniform linear antenna array design for millimeter wave MIMO channels

In this paper, we study the achievable multiplexing gain of millimeter wave (MMW) line-of-sight (LoS) multiple-input multiple-output (MIMO) channels with non-uniform linear antenna arrays (NULAs) at both the transmitter and receiver. We first present an analytical characterization for the asymptotic channel eigenvalues with arbitrarily deployed NULAs. Then, aiming at achieving an effective multiplexing gain of two at practical signal-to-noise ratios, we mathematically formulate the array optimization problem. We show that the optimal NULA deployment at both link ends should follow a bi-ULA arrangement, consisting of two separate uniform linear antenna arrays (ULAs) with the minimum allowable antenna spacing within each ULA and the maximum feasible separation between the two ULAs. Numerical results demonstrate that significant capacity gain can be achieved by our optimized NULAs over the conventional ULAs.