Patent ID: 7741995
Filing Date: 2010-06-22
Classification: G01S

Abstract:
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.