Precision Geolocation of Mobile WiMax Subscribers Using Timing Adjust Measurements

Timing adjusts, used for synchronization in control signaling in IEEE 802.16-2009 mobile WiMax systems, can be used to geolocate a mobile subscriber. From Time of Arrival (TOA) and Time Difference of Arrival (TDOA) calculations, two key observations are made. First, geolocation error occurs when calculating in a two-dimensional plane. Second, TDOA calculations can eliminate the initial bias of a measured timing adjust and thereby allow geolocation calculations with less knowledge of the system. Through simulation, the three-dimensional TOA and TDOA methods are shown to outperform the corresponding two-dimensional methods. Experimentation with an Alcatel-Lucent 802.16e-2005 OFDMA-based system validates the accuracy of the three-dimensional geolocation method with an average geolocation error of 23 meters compared to 87 meters for the two-dimensional approach.