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

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.

Binary phase-controlled multi-beam-switching antenna array for reconfigurable 5G applications

“…The operational frequency is of the same order. The paper in [6] states that in the case of the directional patch array, there is a lower gain variation between elements at angles closer to the direction normal to the array; similar observations have been made and verified experimentally in the proposed 4 × 4 antenna array. The gain along the boresight is similar with no much variation, although for oblique directions to the normal, there is a slight drop in gain.…”

“…The gain along the boresight is similar with no much variation, although for oblique directions to the normal, there is a slight drop in gain. The paper in [6] also concludes that more directive patch elements are a better choice for massive MIMO. In comparison to the paper in [7], the proposed 4 × 4 antenna array provides multi-beams using a two-vector state beamswitching scheme and operates at 14 GHz.…”

“…Up to nine beams can be obtained with a gain around 10 dBi. The paper in [6] investigates the impact of mutual coupling and edge effects on the gain variation along large arrays. Two arrays made of dipoles and patch elements are compared.…”

User Scheduling and Antenna Topology in Dense Massive MIMO Networks: An Experimental Study

“…From Eq. 5and [19] and [23], we observe that a high channel gain variance in the selected UE set has a negative impact on user fairness. The average channel gain per UE is an important information and can be represented as…”

“…However, the extension and some parameters are obtained from a virtual linear array. The mutual coupling, which causes gain variation [19] among the finite antennas, is not considered in a virtual antenna array. Moreover, it is not realistically captured in the virtual array, where it impacts the cluster visibility region derived from the angular transform algorithms [20].…”