Method and system for synchronizing location finding measurements in a wireless local area network
First Claim
1. A method for synchronizing location finding measurements in a wireless network, comprising:
- receiving transmissions from at least one transmitter at multiple receivers, wherein said multiple receivers are located at predetermined locations with respect to said at least one transmitter;
determining actual times-of-arrival of said received transmissions in response to said receiving;
first computing differences between said actual times-of-arrival for said multiple receivers to determine actual time-differences-of-arrival for pairs of said multiple receivers;
second computing differences between said actual time-differences-of-arrival and theoretical time-differences-of-arrival determined in conformity with said predetermined locations;
estimating error in timebases of said multiple receivers in conformity with said second computed differences; and
correcting measurements of other time-differences-of-arrival of other transmissions in conformity with said estimated error.
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Accused Products
Abstract
A method and system for synchronizing location finding measurements in a wireless local area network (WLAN) provides a low cost mechanism for correcting location measurements within a WLAN location finding system. Multiple location receivers compute the time-of-arrival (TOA) of a reference transmitter signal, which is generally a beacon signal. The TOAs are collected and reported to a master unit that contains stored predetermined position information for the location receivers. The master unit computes the time-differences-of-arrival (TDOA) between multiple receivers and computes differences between the measured TDOAs and theoretical TDOAs computed in conformity with the predetermined position of each location receiver. The deviations between theoretical and measured TDOAs are collected in a statistical sample set and Kalman filters are used to produce a model of location receiver timebase offset and drift over multiple received beacon signals. The filter outputs are used to then either correct subsequent TDOA measurements for each location receiver, improving the accuracy of subsequent and/or prior TDOA measurements, or commands are sent to the location receivers to calibrate the timebases within the location receivers in order to improve the accuracy of subsequent TOA measurements.
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Citations
41 Claims
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1. A method for synchronizing location finding measurements in a wireless network, comprising:
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receiving transmissions from at least one transmitter at multiple receivers, wherein said multiple receivers are located at predetermined locations with respect to said at least one transmitter;
determining actual times-of-arrival of said received transmissions in response to said receiving;
first computing differences between said actual times-of-arrival for said multiple receivers to determine actual time-differences-of-arrival for pairs of said multiple receivers;
second computing differences between said actual time-differences-of-arrival and theoretical time-differences-of-arrival determined in conformity with said predetermined locations;
estimating error in timebases of said multiple receivers in conformity with said second computed differences; and
correcting measurements of other time-differences-of-arrival of other transmissions in conformity with said estimated error. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A wireless network comprising:
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at least one transmitter for providing reference beacon transmissions;
multiple receivers, each including a timebase for detecting actual times-of-arrival of said periodic reference beacon transmissions, wherein said multiple receivers are located at predetermined locations with respect to said at least one transmitter; and
a processor coupled to a memory, said memory containing program instructions for execution by said processor, wherein said program instructions comprise program instructions for;
first computing differences between said actual times-of-arrival for said multiple receivers to determine actual time-differences-of-arrival for pairs of said multiple receivers;
second computing differences between said actual time-differences-of-arrival and theoretical time-differences-of-arrival determined in conformity with said predetermined locations, estimating error in said timebases of said receivers in conformity with said second computed differences, and correcting measurements of other time-differences-of-arrival of other transmissions in conformity with said estimated error. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A computer program product comprising signal-bearing media encoding program instructions for execution by a processor within a device coupled to a wireless network, wherein said wireless network includes multiple receivers each including a timebase for detecting actual times-of-arrival of periodic reference beacon transmissions originating from a transmitter, wherein said multiple receivers are located at predetermined locations with respect to said at least one transmitter, and wherein said program instructions comprise program instructions for:
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first computing differences between said actual times-of-arrival for said multiple receivers to determine actual time-differences of arrival for pairs of said multiple receivers;
second computing differences between said actual time-differences-of-arrival and theoretical time-differences-of-arrival determined in conformity with said predetermined locations, estimating error in said timebases of said multiple receivers in conformity with said computed differences, and correcting measurements of other time-differences-of-arrival of other transmissions in conformity with said estimated error. - View Dependent Claims (36, 37, 38, 39, 40, 41)
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Specification