Abstract

Signals representing navigation messages from four GPS artificial satellites are received by a GPS receiver and supplied to receiving processors of respective channels, which spectrally reverse-spread and demodulate the signals by way of PSK to produce the navigation messages. The navigation messages are then supplied to a CPU that determines the position of the GPS receiver using satellite time and orbit data contained in the navigation messages. The CPU determines whether each channel is synchronized or not based on the level of a spectrally reverse-spread output (correlated output) signal. If a channel is out of synchronism, the CPU effects a synchronization process. After the synchronization process, the CPU obtains time base data equal to or higher than a bit number. To obtain such time base data in a channel after the synchronization process, the CPU uses time base data equal to or higher than a bit number of another channel that has already been synchronized. Since a preamble is not detected to produce time base data equal to or higher than a bit number, the synchronization process can be effected in a short period of time.