MIMO Performance Evaluation of Isotropic, Directional and Highly-Directional Antenna Systems for mm-Wave Communications

In this paper, we investigate how directional and highly-directional antenna systems using fixed beams can be beneficial in terms of aggregated channel and antenna gains, channel correlation and the massive multiple-input multiple-output (MIMO) capacity in both line-of-sight (LOS) and non-LOS (NLOS) scenarios for single user MIMO (SU-MIMO). It is shown that narrower beams have stronger aggregated channel and antenna gain. However, narrow beamwidth triggers a higher channel correlation as fewer scatterers are seen. A possible solution to reduce the correlation among the beams is to properly decorrelate the beams in advance. To this end, we partition the area of interest and devote one specific partition to each beam to minimize the possible overlaps among the beams. Simulation results show that fixed beam SU-MIMO systems using such highly-directional beams can provide higher MIMO capacity in comparison to isotropic and directional antenna systems.