Calibration for wireless location system
First Claim
1. An external calibration method for a TDOA wireless location system (WLS), comprising the steps of:
- transmitting a reference signal, receiving the reference signal at first and second receivers, determining an error value, and using the error value to correct subsequent TDOA measurements.
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Abstract
Methods and apparatus for calibrating a Wireless Location System to enable the system to make highly accurate TDOA and FDOA measurements are disclosed. An external calibration method in accordance with the present invention comprises the steps of transmitting a first reference signal from a reference transmitter; receiving the first reference signal at first and second receiver systems; determining a first error value by comparing a measured TDOA (or FDOA) value with a theoretical TDOA (or FDOA) value associated with the known locations of the receiver systems and the known location of the reference transmitter; and utilizing the first error value to correct subsequent TDOA measurements associated with a mobile transmitter to be located. An internal calibration method in accordance with the present invention comprises the steps of injecting a comb signal into the first receiver system; utilizing the comb signal to obtain an estimate of the manner in which the transfer function varies across the bandwidth of the first receiver system; and utilizing the estimate to mitigate the effects of the variation of the first transfer function on the time measurements made by the first receiver system.
408 Citations
63 Claims
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1. An external calibration method for a TDOA wireless location system (WLS), comprising the steps of:
- transmitting a reference signal, receiving the reference signal at first and second receivers, determining an error value, and using the error value to correct subsequent TDOA measurements.
- View Dependent Claims (2, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21)
- 3. A method as recited in claim 3, wherein the first and second error values are combined in a weighted average.
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13. An internal calibration method for a receiver system characterized by a time- and frequency-varying transfer function, wherein the receiver system is used in a wireless location system, comprising the steps of:
- injecting a stable, known wideband signal into the receiver system;
using the wideband signal to estimate the transfer function across a prescribed bandwidth of the receiver system; and
using the estimate to mitigate the variation of the transfer function on subsequent time measurements.
- injecting a stable, known wideband signal into the receiver system;
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22. An external calibration method for use with a wireless location system having first and second receivers, wherein the location system estimates velocity using frequency difference of arrival (FDOA), comprising:
- transmitting a first reference signal, receiving the reference at the first and second receivers, determining an error value, and utilizing the error value to correct subsequent FDOA measurements.
- View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32)
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23. An external calibration method for use with a wireless location system including a receiver system characterized by a time- and frequency-varying transfer function, comprising the steps of:
- transmitting a stable, known wideband calibration signal from an external transmitter;
using the wideband calibration signal to estimate the transfer function across a prescribed bandwidth; and
using the estimate to mitigate effects of variation of the transfer function on subsequent time measurements.
- transmitting a stable, known wideband calibration signal from an external transmitter;
- 33. An external synchronization system for a receiver system used in a wireless location system (WLS), comprising a GPS receiver, an oven controlled crystal oscillator, and a phase-locked loop that generates various signals required for use within the receiver system, each signal being synchronized in time and frequency to a signal output by the GPS receiver, and each generated signal having a low phase noise.
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37. A method for calibrating and correcting for station biases in a receiver system employed in a wireless location system (WLS), the receiver system comprising an antennae array, cabling, a filter, preamplifier, and a wideband receiver, and a station bias defined as the finite delay between when an RF signal from a mobile transmitter reaches the antennae and when that same signal reaches the wideband receiver, comprising the steps of:
- measuring the length of cable from the antennae to the filter and determining the corresponding delay associated with the cable length;
injecting a known signal into the filter and measuring the delay from the filter input to the wideband receiver;
combining the delays and using the combined delays to correct subsequent location measurements.
- measuring the length of cable from the antennae to the filter and determining the corresponding delay associated with the cable length;
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41. An external calibration method for calibrating a location system having a first receiver system and a second receiver system, wherein the location system is operative to estimate the location of a mobile transmitter by, in part, determining a difference in time of arrival of a signal transmitted by said mobile transmitter and received by said first and second receiver systems, and wherein the accuracy of the location estimate is dependent, in part, upon the accuracy of time difference of arrival (TDOA) measurements made by the location system, the method comprising the steps of:
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(A) transmitting a first reference signal from a reference transmitter;
(B) receiving said first reference signal at said first and second receiver systems;
(C) determining a first error value by comparing a measured TDOA value with a theoretical TDOA value associated with the known locations of the receiver systems and the known location of the reference transmitter; and
(D) utilizing said first error value to correct subsequent TDOA measurements associated with a mobile transmitter to be located. - View Dependent Claims (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54)
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55. An internal calibration method for calibrating a first receiver system, wherein said first receiver system is characterized by a time- and frequency-varying transfer function, said transfer function defining how the amplitude and phase of a received signal will be altered by said first receiver system, and wherein the first receiver system is utilized in a location system that is operative to determine the location of a mobile transmitter by, in part, determining a difference in time of arrival of a signal transmitted by a mobile transmitter and received by said first receiver system and another receiver system, and wherein the accuracy of the location determination is dependent, in part, upon the accuracy of time measurements made by said receiver systems, the method comprising the steps of:
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(A) injecting an internally generated stable, known wideband signal into said first receiver system;
(B) utilizing the generated wideband signal to obtain an estimate of the manner in which said transfer function varies across the bandwidth of said first receiver system; and
(C) utilizing said estimate to mitigate the effects of said variation of the first transfer function on the time measurements made by the first receiver system. - View Dependent Claims (56, 57, 58, 59, 60, 61, 62)
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63. An external calibration method for calibrating a location system having a first receiver system and a second receiver system, wherein the location system is operative to estimate the location and velocity of a mobile transmitter by, in part, determining a difference in frequency of arrival of a signal transmitted by said mobile transmitter and received by said first and second receiver systems, and wherein the accuracy of the location and velocity estimate is dependent, in part, upon the accuracy of frequency difference of arrival (FDOA) measurements made by the location system, the method comprising the steps of:
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(A) transmitting a first reference signal from a reference transmitter;
(B) receiving said first reference signal at said first and second receiver systems;
(C) determining a first error value by comparing a measured FDOA value with a theoretical FDOA value associated with the known locations of the receiver systems and the known location of the reference transmitter; and
(D) utilizing said first error value to correct subsequent FDOA measurements associated with a mobile transmitter to be located.
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Specification