Method for Locating Mobile Units Based on Received Signal Strength Ratio
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Abstract
Location of mobile units in a wireless local area network is based on use of signal strength ratios and other criteria. In one embodiment absolute value of signal strength is used to derive a second value of location. The second value may be used as the location if the system is not calibrated and may also be used to calibrate the system. Alternatively time difference of arrival may be used in combination with signal strength ratio.
16 Citations
28 Claims
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1-8. -8. (canceled)
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9. A method for locating mobile units arranged for radio communication with fixed devices, comprising:
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detecting received signal strength for transmissions from one of said mobile units to a first selected plurality of fixed devices having known locations;
detecting time of arrival for said transmissions at a second selected plurality of said fixed devices;
computing ratio of said received signal strength for at least one pair of said fixed devices in said first plurality;
computing time difference of arrival for at least one pair of said fixed devices in said second plurality; and
calculating the maximum likelihood location for said mobile unit using said computed ratio and said time difference of arrival. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A system for locating mobile units arranged for radio communication with fixed devices, comprising:
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means for detecting received signal strength for transmissions from one of said mobile units to a first selected plurality of fixed devices having known locations;
means for detecting time of arrival for said transmissions at a second selected plurality of said fixed devices;
means for computing ratio of said received signal strength for at least one pair of said fixed devices in said first plurality;
means for computing time difference of arrival for at least one pair of said fixed devices in said second plurality; and
means for calculating the maximum likelihood location for said mobile unit using said computed ratio and said time difference of arrival. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
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28. A device for storing computer instructions that when executed results in a performance of the following:
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computing a ratio of a detected received signal strength for at least one pair of fixed devices in a first plurality of fixed devices;
computing a time difference of arrival for at least one pair of fixed devices in a second plurality of fixed devices; and
calculating the maximum likelihood location for a mobile unit using said computed ratio and said time difference of arrival.
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Specification