Terminal device, positioning method, and recording medium

• US 7,679,558 B2
• Filed: 06/12/2007
• Issued: 03/16/2010
• Est. Priority Date: 06/15/2006
• Status: Expired due to Fees

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Hayashi, Akifumi, Nagahara, Mikio, Imafuku, Shigeru, Kurata, Tomoyuki, Mizuochi, Shunichi
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Nguyen; Nga X
• Application Number:
  US11/808,687
• Publication Number:
  US 20080030402A1
• Time in Patent Office: 1,008 Days
• Field of Search: 34235701-35717
• US Class Current: 342/357.69
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

A terminal device includes a plurality of search channel sections which search for a positioning satellite, a candidate reception frequency calculation section which calculates a candidate reception frequency of a first acquisition target satellite by causing the search channel sections to perform the correlation accumulation process for a first accumulation time, a candidate frequency confirmation section which confirms reliability of the candidate reception frequency by causing the search channel sections to perform the correlation accumulation process for a second accumulation time longer than the first accumulation time, a final frequency calculation section which calculates a final frequency by causing the search channel sections to perform the correlation accumulation process for a third accumulation time longer than the second accumulation time, and a first difference calculation section which calculates a difference between an estimated synchronization frequency corresponding to each first acquisition target satellite and the final frequency.

Claims

1. A terminal device that locates a present position based on signals from a plurality of positioning satellites, the terminal device comprising:

a plurality of search channel sections that search for the positioning satellite while changing an accumulation time of a correlation accumulation process for the signal from the positioning satellite;

a first acquisition target satellite determination section that determines a first acquisition target satellite;

a candidate reception frequency calculation section that calculates a frequency with a signal strength that is equal to or greater than a first threshold value as a candidate reception frequency of the first acquisition target satellite by causing the search channel sections to perform the correlation accumulation process using a first accumulation time within a first frequency search range;

a determination section that determines whether or not the signal strength is equal to or greater than a second threshold value that is larger than the first threshold value by causing the search channel sections sot perform the correlation accumulation process corresponding to the candidate reception frequency using a second accumulation time being longer than the first accumulation time;

a final frequency calculation section that calculates a frequency with the maximum signal strength as a final frequency when the determination section has determined that the signal strength is equal to or greater than the second threshold value by causing the search channel sections to perform the correlation accumulation process using a third accumulation time that is longer than the second accumulation time within a second frequency search range that includes the candidate reception frequency and is narrower than the first frequency search range;

a drift error calculation section that calculates a drift error from a difference between an estimated synchronization frequency of the first acquisition target satellite and the final frequency; and

a necessary-for-positioning satellite acquisition section that corrects a search frequency of each of the plurality of positioning satellites using the drift error, and acquires the positioning satellite in a number necessary for positioning.

2. The terminal device as defined in claim 1, further comprising

a candidate reception frequency recalculation section that recalculates a frequency with a signal strength that is equal to or greater than the first threshold value as the candidate reception frequency of the first acquisition target satellite when the determination section has determined that the signal strength is not equal to or greater than the second threshold value by causing the search channel sections to perform the correlation accumulation process using a fourth accumulation time that is longer than the first accumulation time within the first frequency search range.

3. The terminal device as defined in claim 1, wherein

the first acquisition target satellite determination section determines a plurality of the first acquisition target satellites.

4. The terminal device as defined in claim 1, wherein

the first acquisition target satellite determination section determines a plurality of the first acquisition target satellites;

the drift error calculation section calculates the drift error for each of the plurality of first acquisition target satellites,

the terminal device includes an average calculation section that calculates an average value of the drift errors calculated for the plurality of the first acquisition target satellites, and

the necessary-for-positioning satellite acquisition section acquires the positioning satellite using the average value of the drift errors calculated by the average calculation section.

5. A positioning method of locating a present position based on signals from a plurality of positioning satellites by searching for the positioning satellites using a plurality of search channel sections that search for the positioning satellite while changing an accumulation time of a correlation accumulation process for the signal from the positioning satellite, the method comprising:

a first acquisition target satellite determination step of determining a first acquisition target satellite;

a candidate reception frequency calculation step of calculating a frequency with a signal strength that is equal to or greater than a first threshold value as a candidate reception frequency of the first acquisition target satellite by causing the search channel sections to perform the correlation accumulation process using a first accumulation time within a first frequency search range;

a determination step of whether or not the signal strength is equal to or greater than a second threshold value that is longer than the first threshold value by causing the search channel sections to perform the correlation accumulation process corresponding to the candidate reception frequency using a second accumulation time that is longer than the first accumulation time;

a final frequency calculation step of calculating a frequency with the maximum signal strength as a final frequency when it has been determined that the signal strength is equal to or greater than the second threshold value by causing the search channel sections to perform the correlation accumulation process using a third accumulation time that is longer than the second accumulation time within a second frequency search range that includes the candidate reception frequency and is narrower than the first frequency search range;

a drift error calculation step of calculating a drift error from a difference between an estimated synchronization frequency of the first acquisition target satellite and the final frequency; and

a necessary-for-positioning satellite acquisition step of correcting a search frequency of each of the plurality of positioning satellites using the drift error, and acquiring positioning satellites in a number necessary for positioning.

6. A computer-readable recording medium having recoded thereon a program for causing a computer to locate a present position based on signals from a plurality of positioning satellites by causing a plurality of search channel sections to search for the positioning satellites while changing an accumulation time of a correlation accumulation process for the signal from the positioning satellite, the program causing the computer to execute:

a first acquisition target satellite determination step of determining a first acquisition target satellite;

a candidate reception frequency calculation step of calculating a frequency with a signal strength that is equal to or greater than a first threshold value as a candidate reception frequency of the first acquisition target satellite by causing the search channel sections to perform the correlation accumulation process using a first accumulation time within a first frequency search range;

a determination step of determining whether or not the signal strength is equal to or greater than a second threshold value that is larger than the first threshold value by causing the search channel sections to perform the correlation accumulation process corresponding to the candidate reception frequency using a second accumulation time that is longer than the first accumulation time;

a final frequency calculation step of calculating a frequency with the maximum signal strength as a final frequency when it has been determined that the signal strength is equal to or greater than the second threshold value by causing the search channel sections to perform the correlation accumulation process using a third accumulation time that is longer than the second accumulation time within a second frequency search range that includes the candidate reception frequency and is narrower than the first frequency search range;

a drift error calculation step of calculating a drift error from a difference between an estimated synchronization frequency of the first acquisition target satellite and the final frequency; and

a necessary-for-positioning satellite acquisition step of correcting a search frequency of each of the plurality of positioning satellites using the drift error, and acquiring the positioning satellites in a number necessary for positioning.