Terminal device, positioning method, and recording medium

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.

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.