Importance

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Abstract

Method and apparatus for providing precise universal time coordination or synchronization for each of a plurality of N vehicles, numbered consecutively i=1, 2, . . ., N (N.gtoreq.2) that move within a selected geographic region and that communicate by radiowaves with one or more base stations located within or adjacent to the selected region. Each vehicle is provided with a sequence of Satellite Positioning System (SPS) signals, with a sequence of SPS timing signals, and with a SPS signal transceiver/processor that receives the SPS signals and SPS timing signals and determines the present location of the vehicle and the time the vehicle location determination is made. One or more base stations broadcast a sequence of base station timing signals that are received by each vehicle. A timing signal choice means on each vehicle receives the SPS timing signals sequence and the base station timing signals sequence and chooses the timing signal sequence that is both presently available and presently the most accurate. A sequence of nonoverlapping time slots is determined that includes substantially all times within a selected time interval. An ith group of these time slots is allocated to vehicle number i, with no two of these groups having one or more time slots in common. An on-board clock provides back-up time if SPS and base station timing signals are both unavailable; on-board clock time is continually corrected by SPS time or base station time, if available. The chosen sequence of timing signals for vehicle number i is then used to determine the times within the ith group of time slots during which that vehicle will transmit selected vehicle operating data, including present vehicle position, to one or more base stations. At any time, the chosen sequence of timing signals is accurate to within a range as low as 2-7 milliseconds. The Satellite Positioning System may be a Global Positioning System, a Global Orbiting Navigational System, or any other satellite-based system that provides accurate information on position and/or time of observation.

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First Claim