Calibration and correction system for satellite position location systems
First Claim
1. A method of correcting a GPS receiver comprising:
- producing a first frequency locked to a cellular network signal;
generating a second frequency in a GPS oscillator during a first time period;
computing a first error based upon comparisons of said first and second frequencies during said first time period;
computing a second error base upon comparisons of said first and second frequencies during a second time period;
providing an error function from said first and second errors;
predicting a GPS oscillator error using said error function for a next time period; and
correcting said GPS oscillator in said next time period responsive to said predicted GPS oscillator error.
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Accused Products
Abstract
To provide accurate and quick position measurements in a practical mobile position location system, the GPS receiver is calibrated, a frequency error in the next time period is predicted using a first frequency locked to an externally transmitted signal, and a second frequency is generated by a GPS oscillator. To predict the error in the next time period, several measurements are made over time, error estimations are made, an error function is approximated responsive to the set of error estimations. This predicted error is then used to correct the GPS receiver in the next time period. In one implementation, a multiple function portable device is disclosed for providing cellular communication using a network of cellular stations that operate at predefined ideal cellular frequencies, and also for providing position location using GPS satellites that transmit GPS signals at a predefined GPS frequency.
203 Citations
24 Claims
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1. A method of correcting a GPS receiver comprising:
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producing a first frequency locked to a cellular network signal;
generating a second frequency in a GPS oscillator during a first time period;
computing a first error based upon comparisons of said first and second frequencies during said first time period;
computing a second error base upon comparisons of said first and second frequencies during a second time period;
providing an error function from said first and second errors;
predicting a GPS oscillator error using said error function for a next time period; and
correcting said GPS oscillator in said next time period responsive to said predicted GPS oscillator error. - View Dependent Claims (2, 3, 4, 5)
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6. A method of correcting a GPS receiver in a mobile device using a cellular network signal having a predefined precision carrier frequency, to receive a GPS signal transmitted at a predefined GPS frequency, comprising:
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generating a first frequency signal responsive to said precision carrier frequency;
generating a second frequency signal in said GPS receiver, to process said GPS signal;
computing an error between said first and second frequencies in a first time period;
repeating said error computing at least once during at least a second respective time period to provide a set of error estimations;
providing an error function of said second frequency directly from said set of error computations;
predicting an error in a next time period following said repeating utilizing said error function; and
correcting said second frequency to process said GPS signal in said next time. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
averaging said set of error estimations; and
performing a mathematical regression method utilizing said set of error computations to produce a least-mean-square fit to said set of error estimations.
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10. The method of claim 6 wherein said cellular network signal is provided by a cellular base station, said mobile device comprises a cellular transceiver, and further comprising:
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frequency-locking said precision carrier frequency to provide said first frequency; and
communicating between said mobile device and said cellular base station.
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11. The method of claim 6 further comprising extracting a precision carrier frequency from said cellular network signal to provide said first frequency.
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12. The method of claim 6 wherein said correcting comprises correcting a GPS local oscillator that supplies said second frequency to convert said GPS signal at said GPS frequency into a predetermined intermediate frequency.
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13. The method of claim 6 wherein said GPS receiver comprises a digital local oscillator, and said correcting comprises correcting said digital local oscillator.
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14. A method of correcting a GPS receiver in a mobile device to receive a GPS signal transmitted at a predefined GPS frequency using a communication signal transmitted from a cellular base station, said communication signal including a predefined precision carrier frequency, comprising:
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synchronizing a first local oscillator to the precision carrier frequency to generate a first frequency;
generating a second frequency signal in said GPS receiver having a nominal value close to a predetermined value, said second frequency signal applied to process said GPS signal;
monitoring said first and second frequencies over a plurality of time periods to provide a frequency measurement for each of said plurality of time periods;
computing an error in said first and second frequencies for each monitored time period to provide a set of error estimations;
providing a frequency error vs. time function for said second frequency by fitting a mathematical function responsive to said set of error estimations;
predicting an error in a next time period utilizing said function;
developing a correction signal for said next time period responsive to said predicted error; and
processing said GPS signal responsive to said correction signal. - View Dependent Claims (15, 16, 17, 18)
averaging said error computations in said set;
performing a mathematical regression method utilizing the error computations in said set in order to calculate a least-mean-square curve to said error estimations computations.
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17. The method of claim 14 further comprising correcting a frequency of a GPS local oscillator that supplies said second frequency to convert said GPS signal at said GPS frequency into a predetermined intermediate frequency, responsive to said correction signal.
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18. The method of claim 14 wherein said GPS receiver comprises a digital local oscillator, and further comprising correcting a frequency output from said digital local oscillator responsive to said correction signal.
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19. A multiple function portable device for providing cellular communication using a network of cellular stations that operate at predefined ideal cellular frequencies, and also for providing position location using GPS satellites that transmit GPS signals at a predefined GPS frequency, comprising:
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a cellular communication system including a first local oscillator that generates a first frequency for demodulating communications with said network of cellular stations;
a GPS system including a second local oscillator that generates a second frequency coupled to process said GPS signals;
an error prediction and correction system that predicts an error in a next time period according to an error function representing measurements of said first and second frequencies over a plurality of previous time periods, said system also generating a correction signal for said next time period responsive to said predicted error; and
said second local oscillator receiving said correction signal and responsive thereto processes said GPS signal during said next time period. - View Dependent Claims (20, 21, 22, 23, 24)
a frequency comparison circuit;
an error monitor and prediction circuit; and
a frequency correction generation circuit.
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21. The multiple function portable device of claim 20 wherein said frequency comparison circuit includes:
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means for monitoring said first and second frequencies and periodically providing measurements indicative of difference between said first and second frequencies during an observation period, and said error monitor and prediction circuit periodically compares each said measurement with a predetermined number to provide an error estimation for each time period.
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22. The multiple function portable device of claim 20 wherein said error function is a mathematical function and said monitor and prediction circuit comprises a system for approximating said mathematical function according to said plurality of error estimations.
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23. The multiple function portable device of claim 22 wherein said approximating system comprises one of:
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means for averaging said error estimations over a predefined number of periods;
means for performing a mathematical regression method utilizing said error estimations over a predefined number of periods of time to calculate a least-mean-square of said error estimations over said plurality of periods of time.
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24. The multiple function portable device of claim 19 wherein said second local oscillator comprises a digital local oscillator that is utilized in the digit frequency translation of a GPS signal.
Specification