Calibration and correction system for satellite position location systems

• US 20040130484A1
• Filed: 01/03/2003
• Published: 07/08/2004
• Est. Priority Date: 12/13/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Krasner, Norman
• Granted Patent: US 6,816,111 B2
• Time in Patent Office: Days
• US Class Current: 342/357.02
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H03J 2200/11 Cellular receiver, e.g. GSM, combined with a GPS receiver

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.

Claims

1. A method of calibrating and correcting a GPS receiver to receive a GPS signal in a mobile device using an externally transmitted signal, comprising:

producing a first frequency locked to said externally transmitted signal;

generating a second frequency in a GPS oscillator that is applied to process said GPS signal;

predicting a GPS oscillator error for the next time period; and

correcting the GPS receiver in the next time period responsive to said predicted GPS frequency error.

2. The method of claim 1 wherein said step of predicting a GPS oscillator error further comprising repeatedly measuring said first and second frequencies over a plurality of time periods to provide a plurality of measurements.

3. The method of claim 2 wherein said step of predicting a GPS oscillator error in the next time period includes:

calculating a set of error estimations responsive to said plurality of measurements; and

fitting a mathematical function responsive to said set of error estimations.

4. The method of claim 1 wherein said correcting step 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.

5. The method of claim 1 wherein said GPS receiver comprises a digital processing system that includes a digital local oscillator, and said correcting step comprises correcting said digital local oscillator.

6. A method of calibrating and correcting a GPS receiver in a mobile device using an externally transmitted signal other than a GPS signal, said externally transmitted signal having a predefined precision carrier frequency, to receive a GPS signal transmitted at a predefined GPS frequency, comprising the steps of:

generating a first frequency signal responsive to said precision carrier frequency;

generating a second frequency signal in said GPS receiver, said second frequency signal applied to process said GPS signal;

estimating an error in said first and second frequencies in a first time period, and

repeating said error estimating step for at least one additional time period to provide a set of error estimations;

approximating an error function of said second frequency responsive to said set of error estimations;

predicting an error in a next time period utilizing said approximated function; and

correcting said second frequency of said GPS receiver to process said GPS signal in said next time period responsive to said predicted error.

7. The method of claim 6 further comprising repeatedly measuring a ratio of said second and said first frequencies over a plurality of time periods, and for each time period comparing this ratio to a predetermined number to estimate said error respectively for each time period.

8. The method of claim 6 wherein said error prediction step includes determining a frequency error vs. time of said second frequency by fitting a mathematical function responsive to said set of error estimations.

9. The method of claim 8 wherein said error prediction step comprises one of:

averaging said set of error estimations; and

performing a mathematical regression method utilizing said set of error estimationsto produce a least-mean-square fit to said set of error estimations.

10. The method of claim 6 wherein said externally-transmitted signal is provided by a cellular base station, said mobile device comprises a cellular transceiver, and further comprising:

frequency-locking said precision carrier frequency to provide said first frequency; and

communicating between said mobile device and said cellular base station.

11. The method of claim 6 further comprising extracting a precision carrier frequency from said externally-transmitted signal to provide said first frequency.

12. The method of claim 6 wherein said correcting step 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.

13. The method of claim 6 wherein said GPS receiver comprises a digital processing system that includes a digital local oscillator, and said correcting step comprises correcting said digital local oscillator.

14. A method of calibrating and 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 staion, said communication signal including a predefined precision carrier frequency, comprising the steps of:

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;

estimating an error in said first and second frequencies for each monitored time period to provide a set of error estimations;

approximating 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 approximated 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.

15. The method of claim 14 wherein said monitoring step comprises repeatedly measuring a ratio of said second and said first frequencies over a plurality of time periods, and for each time period comparing this ratio to a predetermined number to estimate said error respectively for each time period.

16. The method of claim 14 wherein said error prediction step comprises one of:

averaging said error estimations in said set;

performing a mathematical regression method utilizing the error estimations in said set in order to

calculate a least-mean-square curve to said error estimations.

17. The method of claim 14 further comprising the step of correcting the 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.

18. The method of claim 14 wherein said GPS receiver comprises a digital processing system that includes a digital local oscillator, and further comprising the step of correcting a frequency output from said digital local oscillator, responsive to said correction signal.

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:

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 responsive to 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

a local oscillator in said GPS system that receives said correction signal and responsive thereto processes said GPS signal during said next time period.

20. The multiple function portable device of claim 19 wherein said error prediction and correction system comprises:

a frequency comparison circuit;

an error monitor and prediction circuit; and

a frequency correction generation circuit.

21. The multiple function portable device of claim 19 wherein said frequency comparision circuit includes means for monitoring said first and second frequencies and periodically providing measurements indicative of said the 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.

22. The multiple function portable device of claim 19 wherein said error monitor and prediction circuit comprises a system for approximating a mathematical function responsive to said plurality of error estimations.

23. The multiple function portable device of claim 22 wherein said approximating system comprises one of:

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.

24. The multiple function portable device of claim 19 wherein said local oscillator comprises a GPS local oscillator that provides said second frequency.

25. The multiple function portable device of claim 19 wherein said local oscillator comprises a digital local oscillator that is utilized in the digital frequency translation of a GPS signal.