First Commercial Hybrid Massive MIMO System for Sub-6Hz Bands

Abstract

Massive multiple-input and multiple-output (MIMO) has been the subject of interest in both industry and academia for the past few years. Massive MIMO refers to the use of a large number of antennas typically at the base station (BS) to serve multiple user equipment (UE) simultaneously to deliver reliable and high data throughput. Two basic architectures have been considered in the literature. First is a full digital massive MIMO where all the beamforming and precoding is performed digitally in baseband and a radio frequency (RF) chain is required for every antenna element. In the second architecture referred to as hybrid massive MIMO, beamforming and precoding are done in two stages, digital precoding over fewer digital ports followed by analog beamforming across large number of antenna elements. In this paper, we provide a comparison of implementation challenges for each approach. We introduce the High Definition Active Antenna System (HDAAS), a novel scalable architecture to implement a hybrid Massive MIMO system. This design philosophy is used to build BeamCraft500, which we believe is a first commercial hybrid 3D beamforming system operating at 2 GHz. We also present results from one of the field trials in a live LTE network that validate the stability and performance of the system under real world conditions.