Method for setting search widthsband of a GPS receiver

摘要

A GPS receiver searches for a satellite radio wave over a predetermined search band width to allow for frequency shift of the received signal (the Doppler effect) and fluctuations in the oscillating frequency of the oscillator. When a high accuracy oscillator is used, the search band width can always be set relatively narrow. The invention provides a system in which the search band width can be set relatively narrow when using lower accuracy oscillators. A search centre frequency f_s is used as a start point, and an offset value A f_osc of an oscillator is calculated when the receiver is turned off on completion of the position measurement, and the offset value is stored as a backup value into a memory. When the power source of the receiver is turned on at the next position measurement, the back- up offset value A f_osc is read out and an initial search band width W_o at the start of the position measurement is set in accordance with the magnitude of the offset value. According to another feature, when the offset value of the oscillator which was calculated during the position measurement exceeds a predetermined reference value, the time of the calculation is backed up into a memory. If a predetermined reference time has not elapsed from the next measurement, the initial search band width at the start of the position measurement is set to a wide band.