Evaluating the Spatial Resolution of 2D Antenna Arrays for Massive MIMO Transmissions

Massive MIMO has been identified as one of the key technologies for the 5th generation of mobile cellular networks. By utilizing 2D antenna arrays with a large number of antenna elements, it enables to form orthogonal beams towards spatially separated User Equipments (UEs). In this paper we evaluate the channel energy and the average throughput of typical indoor-and outdoor UEs at various heights and distances to the macro site. Our goal is to demonstrate the achievable spatial resolution of the beamforming in vertical direction with large antenna arrays. Existing work on directional beamforming strategies is commonly based on simplistic signal propagation assumptions under LOS conditions. This paper considers a realistic 3D channel model that also accounts for multi-path propagation under NLOS conditions. Our results exhibit the dependency of the achievable spatial resolution on both, the size of the antenna array as well as the channel conditions. They show that depending on whether the UE is located indoors or outdoors, the channel has an opposing impact on the achievable spatial resolution.