Patent ID: 6614393
Filing Date: 2003-09-02
Classification: G01S,H04L,H04W,Y02D

Abstract:
A method of disseminating location information to devices equipped with short-range transceivers, the method comprising automatically carrying out the steps of:disseminating reference time data for establishing a common timing reference across multiple items of equipment; transmitting location information from location beacons by short-range communication at known times relative to said common timing reference, this location information comprising, for each location beacon, the location of that beacon; receiving said reference time data at said devices and using it to synchronise an internal clock of each device with said common timing reference; and for each said device, powering up its short-range transceiver for successive limited periods starting at said known times relative to the common timing reference as represented by the internal clock of the device, and during an initial portion of each said limited period, using the transceiver to receive location information transmitted by any said location beacon within range, and after said initial portion of each said limited period using the transceiver to exchange location information with nearby devices.