The Effects of Channel Model and Spacing on Slanted Subarrays in Single-User MIMO mmWave Systems

Slanting of subarrays in a hybrid MIMO configuration is known to mitigate loss from directional antenna elements typical of mmWave integrated circuit arrays, under the line-of-sight (LOS) plane wave model (PWM) of propagation. This paper considers optimal slanting of subarrays under the spherical wave model (SWM) of propagation, because the SWM is known to be more appropriate than PWM for short-range LOS MIMO channels. The capacity of MIMO under the LOS SWM is known to depend on subarray spacing for non-slanted subarrays, so this paper derives the optimal spacing for slanted subarrays, which is shown to be the same as for non-slanted subarrays. The paper goes on to show that slanting only degrades hybrid MIMO capacity under the SWM model. By comparing the capacities under the PWM and SWM, the authors explain why slanting is beneficial under one model and not under the other.