Fine-grained network time synchronization using reference broadcasts
ACM SIGOPS Operating Systems Review - OSDI '02: Proceedings of the 5th symposium on Operating systems design and implementation
The Horus WLAN location determination system
Proceedings of the 3rd international conference on Mobile systems, applications, and services
PinPoint: An Asynchronous Time-Based Location Determination System
Proceedings of the 4th international conference on Mobile systems, applications and services
Mobile phone location determination and its impact on intelligent transportation systems
IEEE Transactions on Intelligent Transportation Systems
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The ability to measure location using time of flight in 802.11 networks is impeded by the standard one microsecond clock resolution, imprecise synchronization of the 802.11 protocol, and the inaccuracy of available clock oscillators. We demonstrate a technique for off-the-shelf 802.11 hardware that enables accurate determination of location of transmitting 802.11 devices using time difference of arrival (TDOA). The technique refines the PinPoint clock model for 802.11 wireless cards, enabling accurate translation of times from one frame of reference to another for free-running clocks and producing accurate location of transmitting nodes to within 3m. This technique can locate nodes regardless of their participation in the location system and may be applied to other wireless communication protocols where send and receive timestamps are available.