Method of acquiring error correction value of reference frequency, terminal device, and recording medium

• US 7,741,995 B2
• Filed: 08/29/2007
• Issued: 06/22/2010
• Est. Priority Date: 09/14/2006
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Maezawa, Hidekazu, Yano, Koichiro
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Nguyen; Nga X
• Application Number:
  US11/847,087
• Publication Number:
  US 20080068258A1
• Time in Patent Office: 1,028 Days
• Field of Search: 34235701-35717
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A terminal device receives satellite signals from a plurality of satellite positioning system (SPS) satellites and locates a position. The terminal device periodically calculates a first drift df1 of a local oscillator using a reference frequency Hr, calculates a search range of the satellite signal using the first drift df1, calculates a second drift df2 of the local oscillator using a reception frequency of the satellite signal, calculates a reference frequency error β which is an error of the reference frequency by calculating a difference between the first drift df1 and the second drift df2, and calculates an error correction value βav of the reference frequency by subjecting a plurality of the reference frequency errors β to a statistical process.

Claims

1. A method implemented by a terminal device that receives satellite signals from a plurality of satellite positioning system (SPS) satellites and locates a position, the method comprising:

outputting a reference frequency from an oscillator of the terminal device;

periodically calculating a drift of an output frequency of a local oscillator of the terminal device, the local oscillator being different from the oscillator, the drift of the output frequency of the local oscillator being calculated as a first drift using the reference frequency that is output from the oscillator and the output frequency of the local oscillator, an oscillation frequency of the oscillator being continually corrected;

calculating a search range of a reception frequency of the satellite signal using a transmission frequency of the satellite signal, a Doppler shift, and the first drift;

calculating a drift of the output frequency of the local oscillator as a second drift using an estimated reception frequency that is estimated based on the transmission frequency of the satellite signal and the Doppler shift and a reception frequency when the satellite signal has been received;

calculating a difference between the first drift and the second drift as a reference frequency error that is an error of the reference frequency;

calculating an error correction value of the reference frequency based on a plurality of the reference frequency errors;

selecting a search range update method using an amount of change in the first drift and the error correction value;

updating the search range using the search range update method that has been selected;

searching the satellite signal within the search range, and receiving the satellite signal;

calculating a position of the terminal device based on the satellite signal; and

recording the position in the terminal device.

2. The method as defined in claim 1, further comprising

correcting the first drift based on a tendency of a change in the first drift with respect to elapsed time.

3. The method as defined in claim 2, wherein correcting the first drift includes generating a regression line based on a plurality of the first drifts, and calculating the first drift on the regression line corresponding to a present time.

4. The method as defined in claim 1, wherein

selecting the search range update method includes

determining whether or not to perform a basic update operation that updates the search range using the second drift and an error of the second drift set in advance based on a relationship between the amount of change in the first drift and the error of the second drift, and

determining whether to perform a first update operation that updates the search range using the first drift and an error of the first drift set in advance or a second update operation that updates the search range using the first drift, the error of the first drift, and the error correction value, based on a relationship between the error correction value and the error of the first drift.

6. The terminal device as defined in claim 4, further comprising

a first drift correction section that corrects the first drift based on a tendency of a change in the first drift with respect to elapsed time.

7. The terminal device as defined in claim 6, wherein the first drift correction section corrects the first drift by generating a regression line based on a plurality of the first drifts, and calculates the first drift on the regression line corresponding to a present time.

5. A terminal device that receives satellite signals from a plurality of satellite positioning system (SPS) satellites and locates a position, the terminal device comprising:

an oscillator that outputs a reference frequency, an oscillation frequency of the oscillator being continually corrected;

a local oscillator that outputs a frequency signal used to receive the satellite signal, the local oscillator being different from the oscillator;

a first drift calculation section that periodically calculates a drift of an output frequency of the local oscillator as a first drift using the reference frequency and the output frequency of the local oscillator;

a search range calculation section that calculates a search range of a reception frequency of the satellite signal using a transmission frequency of the satellite signal, a Doppler shift, and the first drift;

a second drift calculation section that calculates a drift of the output frequency of the local oscillator as a second drift using an estimated reception frequency that is estimated based on the transmission frequency of the satellite signal and the Doppler shift and a reception frequency when the satellite signal has been received;

a reference frequency error calculation section that calculates a difference between the first drift and the second drift as a reference frequency error that is an error of the reference frequency;

an error correction value calculation section that calculates an error correction value of the reference frequency based on a plurality of the reference frequency errors;

an update method selection section that selects a search range update method using an amount of change in the first drift and the error correction value;

a search range update section that updates the search range using the search range update method that has been selected by the update method selection section;

a reception section that searches the satellite signal within the search range, and receives the satellite signal; and

a positioning section that calculates a position of the terminal device based on the satellite signal.

8. The terminal device as defined in claim 5, wherein

the update method selection section determining whether or not to perform a basic update operation that updates the search range using the second drift and an error of the second drift set in advance based on a relationship between the amount of change in the first drift and the error of the second drift, and determining whether to perform a first update operation that updates the search range using the first drift and an error of the first drift set in advance or a second update operation that updates the search range using the first drift, the error of the first drift, and the error correction value, based on a relationship between the error correction value and the error of the first drift.

9. A computer-readable recording medium storing a program that is executed by a computer included in a terminal device that receives satellite signals from a plurality of satellite positioning system (SPS) satellites and locates a position, the program causing the computer to:

periodically calculate a drift of an output frequency of a local oscillator as a first drift using a reference frequency that is output from a given oscillator different from the local oscillator and the output frequency of a local oscillator, an oscillation frequency of the oscillator being continually corrected;

calculate a search range of a reception frequency of the satellite signal using a transmission frequency of the satellite signal, a Doppler shift, and the first drift;

calculate a drift of the output frequency of the local oscillator as a second drift using an estimated reception frequency that is estimated based on the transmission frequency of the satellite signal and the Doppler shift and a reception frequency when the satellite signal has been received;

calculate a difference between the first drift and the second drift as a reference frequency error that is an error of the reference frequency;

calculate an error correction value of the reference frequency based on a plurality of the reference frequency errors;

select a search range update method using an amount of change in the first drift and the error correction value;

update the search range using the search range update method that has been selected;

search the satellite signal within the search range, and receive the satellite signal; and

calculate a position based on the satellite signal.

10. The recording medium as defined in claim 9, wherein the program causes the computer to correct the first drift based on a tendency of a change in the first drift with respect to elapsed time.

11. The recording medium as defined in claim 10, wherein the first drift is corrected by generating a regression line based on a plurality of the first drifts, and calculates the first drift on the regression line corresponding to a present time.

12. The recording medium as defined in claim 9, wherein

selecting the search range update method includes

determining whether or not to perform a basic update operation that updates the search range using the second drift and an error of the second drift set in advance based on a relationship between the amount of change in the first drift and the error of the second drift, and

determining whether to perform a first update operation that updates the search range using the first drift and an error of the first drift set in advance or a second update operation that updates the search range using the first drift, the error of the first drift, and the error correction value, based on a relationship between the error correction value and the error of the first drift.