Bandwidth synthesis for wireless location system
First Claim
1. A wireless location system for estimating the geographic location of a mobile transmitter, wherein said mobile transmitter is operative to transmit narrowband signals at frequencies spanning a predefined wide band of frequencies, and wherein said predefined wide band of frequencies is wider than the bandwidth of the individual narrowband signals transmitted by said mobile transmitter, comprising:
- (a) at least three geographically separated receivers for receiving the narrowband signals transmitted by said mobile transmitter;
(b) bandwidth synthesis means for effecting the transmission by said mobile transmitter of narrowband signals at a plurality of frequencies spanning said predefined wide band of frequencies;
(c) means for resolving integer cycle ambiguity in phase relationships between the plurality of transmitted narrowband signals; and
(d) time difference of arrival means for determining the location of said mobile transmitter using the plurality of narrowband signals.
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Accused Products
Abstract
A wireless location system receives signals transmitted by wireless telephones at a plurality of signal collection sites. To improve the accuracy of the location information, the system synthesizes greater bandwidth, and thus greater time resolution, than would otherwise be available. The location system commands an MTSO to make the wireless transmitter to be located change frequency channels, and a doubly-differenced carrier phase of the transmitted signal, or the time difference of arrival, is observed at each of many frequencies spanning the widest possible bandwidth. The phase-measurement data from these many frequencies are combined to resolve the inherent integer-wavelength ambiguity. To begin the process of ambiguity resolution, single-frequency channel, doubly-differenced, group delay measurements are used to resolve the ambiguity in the doubly-differenced phase difference between the most closely spaced frequency channels. The invention may be utilized to obtain a bandwidth greater than the typical 20 KHz bandwidth of the signals to be cross-correlated (in either the time or frequency domains) in a cellular telephone location application, With such bandwidth synthesis, up to the 12.5 MHz bandwidth allocated by the FCC to each cellular system operator may be exploited for location purposes.
277 Citations
27 Claims
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1. A wireless location system for estimating the geographic location of a mobile transmitter, wherein said mobile transmitter is operative to transmit narrowband signals at frequencies spanning a predefined wide band of frequencies, and wherein said predefined wide band of frequencies is wider than the bandwidth of the individual narrowband signals transmitted by said mobile transmitter, comprising:
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(a) at least three geographically separated receivers for receiving the narrowband signals transmitted by said mobile transmitter; (b) bandwidth synthesis means for effecting the transmission by said mobile transmitter of narrowband signals at a plurality of frequencies spanning said predefined wide band of frequencies; (c) means for resolving integer cycle ambiguity in phase relationships between the plurality of transmitted narrowband signals; and (d) time difference of arrival means for determining the location of said mobile transmitter using the plurality of narrowband signals. - View Dependent Claims (2, 3, 4, 5, 6, 19, 20, 21)
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7. A method for estimating the geographic location of a mobile transmitter, wherein said mobile transmitter is operative to transmit narrowband signals at frequencies spanning a predefined wide band of frequencies, and wherein said predefined wide band of frequencies is wider than the bandwidth of the individual narrowband signals transmitted by said mobile transmitter, comprising the steps of:
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(a) receiving the narrowband signals transmitted by said mobile transmitter at three geographically separated receiver sites; (b) effecting the transmission by said mobile transmitter of narrowband signals at a plurality of frequencies spanning said predefined wide band of frequencies; (c) resolving integer cycle ambiguity in phase relationships between the plurality of transmitted narrowband signals; and (d) determining the location of said mobile transmitter using the plurality of narrowband signals. - View Dependent Claims (8, 9, 10, 11, 12, 22, 23, 24)
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11. A method as recited in claim 7, further comprising the step of employing a calibration transmitter to obtain a doubly differenced time difference of arrival measurement.
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12. A method as recited in claim 7, further comprising determining a wideband phase versus frequency characteristic of the transmissions from said mobile transmitter.
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22. A method as recited in claim 7, wherein the bandwidth of the individual narrowband signals is approximately 20 kHz.
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23. A method as recited in claim 22, wherein the bandwidth of the wide band of frequencies is approximately 12.5 MHz.
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24. A method as recited in claim 7, wherein the mobile transmitter uses an air interface protocol selected from the group consisting of AMPS, NAMPS, TDMA, and GSM.
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13. A wireless location system (WLS) for locating a mobile transmitter that transmits narrowband signals spanning a predefined wideband of frequencies, wherein the wideband is greater than the narrowband, comprising:
- three geographically separated receivers for receiving narrowband signals;
bandwidth synthesis means to make the mobile transmitter transmit at a plurality of narrowbands within the wideband;
means for resolving integer cycle ambiguity in phase relationships; and
TDOA means for determining the location of the mobile transmitter. - View Dependent Claims (14, 15, 16, 17, 18, 25, 26, 27)
- three geographically separated receivers for receiving narrowband signals;
Specification