  The array design problem of multiple-input multiple-output (MIMO) systems in
a line-of-sight (LoS) transmit environment is examined. As uniform array
configurations at the transmitter (Tx) and receiver (Rx) are optimal at
specific transmit distances only, they lead to reduced spectral efficiency over
a range of transmit distances. To that end, the joint design of nonuniform Tx
and Rx arrays towards maximizing the minimum capacity of a LoS MIMO system
across a range of transmit distances is investigated in this paper. By
introducing convex relaxation, the joint Tx and Rx array design is cast as a
convex optimization problem, which is solved in a iterative manner. In
addition, we also implement a local search to obtain a refined solution that
achieves an improved performance. It is shown that the non-uniform
configurations designed with our proposed approach outperform uniform and
non-uniform array designs of the literature in terms of capacity and/or
complexity.
