Method and system for calibrating wireless location systems
First Claim
1. A system for calibrating receivers used for locating a transmitter comprising:
- a transmitter at an unknown location that transmits a signal;
a proxy receiver that reflects and/or refracts the signal;
a plurality of spatially oriented receivers that receive the signal from the proxy receiver, each receiver having a clock for determining Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals, wherein the clocks are calibrated based on the clock offset.
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Accused Products
Abstract
This invention relates to a method for calibrating a wireless location system (WLS) to enable the system to make highly accurate differential measurements such as time difference of arrival (TDOA) and frequency difference of arrival (FDOA). Calibration is accomplished by transmitting a signal from an unknown location and measuring at each of two receivers the parameter to be calibrated from that part of the received signal reflected or refracted from an object at a known location in the area. A differential measurement error is determined by comparing the expected difference in the parameter measurements with the actual difference in the parameter measurements. The expected difference is known, a priori, based on the locations of the receivers and the location of the object.
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Citations
42 Claims
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1. A system for calibrating receivers used for locating a transmitter comprising:
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a transmitter at an unknown location that transmits a signal;
a proxy receiver that reflects and/or refracts the signal;
a plurality of spatially oriented receivers that receive the signal from the proxy receiver, each receiver having a clock for determining Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals, wherein the clocks are calibrated based on the clock offset. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A system for calibrating receivers used for locating a transmitter determination comprising:
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a transmitter at an unknown location that transmits a signal;
a proxy receiver that reflects and/or refracts the signal;
a plurality of spatially oriented receivers each having an antenna directed at the proxy receiver for receiving the signal from the proxy receiver, each receiver having a clock for determining Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals, wherein the clocks are calibrated based on the clock offset. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method of calibrating spatially oriented receivers used in a location determination system comprising the steps of:
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transmitting a signal from an unknown location;
receiving within each spatially oriented receiver the signal after having reflected and/or refracted from a proxy receiver having a known location, each receiver having a clock for determining at least Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals;
calculating the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival for the signal at each receiver;
determining the clock offset between the plurality of receivers based on the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of the signal within each receiver; and
calibrating the clocks based on the clock offset. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30)
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31. A method of calibrating spatially oriented receivers used in a location determination system comprising the steps of:
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transmitting a signal from an unknown location;
reflecting and/or refracting the signal from a proxy receiver having a known location;
directing an antenna of each receiver at the proxy receiver for receiving the signal within each spatially oriented receiver;
calculating the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival for the signal at each receiver;
determining the clock offset between the plurality of receivers; and
calibrating the clocks based on the clock offset. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40)
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41. A method for calibrating a wireless location system comprises the steps of:
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transmitting a signal from the unknown location;
receiving the signal and measuring at each of first and second receivers a parameter of that portion of the signal reflected or refracted to each of the two receivers by a proxy reference transmitter comprising one of a natural or man-made object;
determining an error value based on the difference between the expected difference between parameter values and the actual difference between measured parameter values; and
using the error value to apply corrections to any wireless location system equipment to minimize the errors in subsequent measurements and/or apply corrections to any prior, concurrent or subsequent measurements of the parameter. - View Dependent Claims (42)
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Specification