Asymmetric subarray structure design for mmWave LoS MIMO communication systems

Abstract

In this paper, a millimeter wave (mmWave) multiple input multiple output (MIMO) channel with asymmetric subarray structures in the line of sight (LoS) scenario is considered. The concept of effective degrees of freedom (EDoF) is introduced to measure the maximum spatial multiplexing gain available for the MIMO system. A criterion based on the maximized EDoF is given out for the design of antenna deployments. A specific analytic relation between the parameters of antenna configuration and transmission distance is further obtained for codebook based phase shifters. Compared to previous structures, the asymmetric subarray structure can provide both array gains and spatial multiplexing gains and is beneficial for making a tradeoff between multiplexing gains and diversity gains. At the same time, the upper and lower bounds of the EDoF are also estimated under extreme cases. Based on the Ricean fading channel model, the sensitivity of our system is studied by taking more realistic deployments and propagation conditions into consideration. The simulation results indicate that the optimally designed structure is robust to the geometrical change and misplacement and thus it is a feasible solution for mmWave LoS MIMO applications.