Passive Three-Dimensional User Equipment Tracking Using Long-Term Evolution Uplink Signals

This study introduces a three-dimensional passive LTE user equipment tracker (3D-PLUT) system, which precisely locates multiple user equipments (UEs) in three dimensions by passively monitoring their uplink signals within LTE networks. Unlike conventional methods that are restricted to two-dimensional tracking or require active UE participation, this system employs a novel algorithm that utilizes unencrypted LTE uplink signals for three-dimensional location tracking. The system features a mechanically rotating antenna array for azimuth angle determination and a digital monopulse method for elevation measurement. The distance is calculated based on the timing advances and differences in the time of arrival. Furthermore, the system includes a calibration process with a designated UE, which significantly enhances its capability to differentiate between line-of-sight and multipath signals, thereby substantially improving localization accuracy in complex environments. Experimental results indicate an azimuth accuracy within 5°, an elevation accuracy within 6°, and an average distance error of 12 m. Notably, calibration reduced the variance in positional estimates over time from 22 m to 10 m. Therefore, the 3D-PLUT system offers a robust and effective solution for passive three-dimensional tracking of UEs, making it suitable for applications such as emergency response and urban navigation.