User Localization Using Random Access Channel Signals in LTE Networks with Massive MIMO

Recent studies show that real-time precise user localization enables to deliver accurate beamforming in MIMO systems without the need for channel estimation. This paper presents new solutions for accurate user localization in massive MIMO LTE systems. A key novelty of the developed schemes is the ability to locate users during LTE's random access channel synchronization procedure before they are connected to the network, by which the obtained location information can be immediately used to optimize the allocation of radio resource and perform accurate beamforming. To achieve this, the developed solutions leverage the advantages of spherical wave propagation since it allows simultaneously estimating the angle of arrival and the propagation distance from the user equipment to each antenna element in the base station. We design solutions for both single-path line-of-sight communication and multi-path propagation environments. The developed schemes were evaluated through both simulations and proof-of-concept experiments. Simulation results show that both algorithms can achieve decimeter-level localization accuracy using 64 and more antenna elements for the distances up to 300 meters. The proof-of-concept experiment justifies the feasibility of user localization based on the estimation of the shape of the incoming wavefront.