Topology Optimized Design of Non-uniform Planar Array for Massive MIMO Systems.

Compared to uniform arrays, non-uniform arrays can substantially increase the rank of the channel matrix and achieve considerable performance gains. However, theoretically optimizing the deployment of non-uniform arrays remains a challenging open problem in millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems. In this paper, we investigate the optimization design of non-uniform planar array (NUPA) topology in line-of-sight (LOS) scenarios. Specifically, the geometry model of the transceiver arrays is first established in a general scenario where the transceiver arrays have rotation along different axes, and the asymptotic analysis of the eigenvalues is utilized to construct mathematical relations between the array element positions and the eigenvalues that can be used to evaluate the quality of the channel transmission. The effective degree of freedom (EDoF) is taken as the maximization objective, which can reflect the number of large eigenvalues and measure the contribution of subchannels to the system capacity. We present a design criterion of antenna deployment for EDoF maximization via adaptive gradient descent method, and discuss the impact of the rotation angles. Simulation results confirm the correctness of the theoretical analysis and demonstrate that the designed NUPA can further improve the EDoF.