Wireless time reference system and method
First Claim
1. A system that provides normalization of time of local clock circuits of plural spatially-located monitoring stations, said system comprising:
- a reference transmitter to transmit at least two RF pulses that define a time reference interval,said local clock circuits having respective detection circuits that detect and measure time durations of said time reference interval at receivers of said monitoring stations, anda processing device that determines a relationship between time durations measured at receivers of at least two monitoring stations and that effects normalization of time of said local clock circuits according to said relationship.
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Accused Products
Abstract
Instead of normalizing time reference of independent spatially-located clocks using a reference tag transmission from known location, the present invention uses an interarrival time interval between a pulse pair of UWB pulses as a timing metric. Thus, a method of synchronizing spatially-located clocks or normalizing time indications thereof comprises transmitting a UWB pulse pair, determining at first and second monitoring stations a respective count value indicative of a locally measured time interval between received pulse pairs, determining a ratio between clock counts of first and second monitoring stations, and utilizing the ratio to determine clock skew, e.g., a timing correction to be applied to respective local clocks of the monitoring stations. A corresponding system comprises a reference tag transmitter that transmits a pulse pair of UWB pulses to define a time reference interval, a first independent receiver that receives, the pulse pair to generate a first count value indicative an interarrival interval between the pulse pair, a second independent receiver that receives the pulse pair to similarly generate a second count value, and a processor hub responsive to the count values to determine a ratio corresponding to the ratio of respective clock frequencies of the first and second receiver clocks. Once the correction is applied, time-of-arrival information from object tag transmissions may be used to determine object location with sub-foot position accuracies.
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Citations
17 Claims
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1. A system that provides normalization of time of local clock circuits of plural spatially-located monitoring stations, said system comprising:
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a reference transmitter to transmit at least two RF pulses that define a time reference interval, said local clock circuits having respective detection circuits that detect and measure time durations of said time reference interval at receivers of said monitoring stations, and a processing device that determines a relationship between time durations measured at receivers of at least two monitoring stations and that effects normalization of time of said local clock circuits according to said relationship. - View Dependent Claims (2, 3, 4, 12, 13)
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5. A time reference system for independent clocks of spatially-located wireless receivers of an object locating system that determines the position of an object, said time reference system comprising:
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a reference tag transmitter to transmit a pair of short-pulse signals that define a time reference interval therebetween, a first wireless receiver that receives said short-pulse signals to generate a first count value according to a first local clock indicative of a time interval between pulses of said pair of short-pulse signals, a second wireless receiver that receives said short-pulse signals to generate a second count value according to a second local clock indicative of a time interval between pulses of said short-pulse signals and a processor hub responsive to the first and second count values of said first and second receivers to determine an offset between said first and second local clocks whereby to enable determination of object location according to said offset. - View Dependent Claims (6, 7, 8, 14, 15)
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9. A time reference system for independent clocks of spatially-located wireless receivers of an object locating system that determines the position of an object, said time reference system comprising:
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a reference tag transmitter to transmit a pair of short-pulse signals that define a time reference interval therebetween, a first wireless receiver to receive said short-pulse signals to generate a first count value according to a first local clock in order to measure a time interval between pulses of said pair of short-pulse signals, a second wireless receiver to receive said short-pulse signals to generate a second count value according to a second local clock in order to measure a time interval between pulses of said short-pulse signals, and a processor responsive to the first and second count values of the first and second receivers to determine an offset and to use said offset to effect adjustment of the frequency of at least one of said first and second local clocks to maintain relative synchronization thereof. - View Dependent Claims (10, 16, 17)
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11. A method of normalizing timing references of spatially-located receivers in a geoposition system comprising:
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receiving an indication of a first count value determined for a first wireless receiver based on a first time difference determined based on a UWB pulse pair transmission received at the first wireless receiver; receiving an indication of a second count value determined for a second wireless receiver based on a second time difference determined based on receipt of the UWB pulse pair transmission at the second wireless receiver; determining a ratio between the first and second count values to determine offsets between clocks of said first and second wireless receivers; and normalizing timing references of the first and second wireless receivers by wirelessly adjusting respective frequencies of the clocks of the first and second wireless receivers based on the determined offsets.
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Specification