Finite Large Antenna Arrays for Massive MIMO: Characterization and System Impact

TL;DR

This paper examines how mutual coupling and edge effects in finite large antenna arrays influence gain pattern variation in massive MIMO systems, revealing significant impacts on system performance and user fairness.

Contribution

It provides a comparative analysis of patch antennas versus dipoles, highlighting the effects of finite array size on gain patterns and system capacity in massive MIMO.

Findings

Patch arrays have lower gain pattern variation than dipoles.

Gain pattern variation reduces the effective number of antennas per user.

System capacity decreases by up to 20% with patch arrays and 35% with dipoles.

Abstract

Massive MIMO is considered a key technology for 5G. Various studies analyze the impact of the number of antennas, relying on channel properties only and assuming uniform antenna gains in very large arrays. In this paper, we investigate the impact of mutual coupling and edge effects on the gain pattern variation in the array. Our analysis focuses on the comparison of patch antennas versus dipoles, representative for the antennas typically used in massive MIMO experiments today. Through simulations and measurements, we show that the finite patch array has a lower gain pattern variation compared with a dipole array. The impact of a large gain pattern variation on the massive MIMO system is that not all antennas contribute equally for all users, and the effective number of antennas seen for a single user is reduced. We show that the effect of this at system level is a decreased rate for all users for the zero-forcing MIMO detector, up to 20% for the patch array and 35% for the dipole array. The maximum ratio combining on the other hand, introduces user unfairness.