There is described a location determining system comprising multiple mobile devices and multiple sensors at a facility as well as a sensor hub communicating directly or indirectly with the sensors. The sensors receive from the mobile devices broadcast beacons and identify measured times associated with receipt of the broadcast beacons from the mobile devices. The sensor hub stores the locations of sensors receives the measured times from the sensors. The sensor hub also determines sensor time errors based on the measured times, the locations of the sensors, and a transmission velocity associated with the broadcast beacons. The location determining system determines locations of the mobile devices based at least in part on the sensor time errors.