Method for GPS positioning in a weak signal environment

A method for synchronizing a GPS receiver with a satellite, comprising the steps of:

• obtaining assistance data for a GPS signal received from the satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data;
• estimating a predicted receiving time for the GPS signal reaching the GPS receiver;
• capturing the GPS signal through channels of the GPS receiver;
• acquiring the GPS signal at each channel by using the assistance data to obtain a local receiving time for the GPS signal, wherein the GPS signal at each channel has a starting point and a predetermined search period;
• and
• correcting a real-time clock of the GPS receiver based on the local receiving time and the predicted receiving time.

A method for positioning of a GPS receiver in a weak signal environment, comprising the steps of:

• a) obtaining assistance data for a GPS signal from a satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data;
• b) estimating a predicted receiving time for the GPS signal reaching the GPS receiver;
• c) capturing the GPS signal;
• d) converting the GPS signal to an intermediate frequency signal;
• e) acquiring a code phase of the pseudorandom code from the intermediate frequency signal by using the assistance data and the predicted receiving time;
• and
• f) obtaining a position for the GPS receiver based on the predicted navigation data and the code phase of the pseudorandom code.

A method for controlling a GPS receiver, comprising the steps of:

• initiating the GPS receiver to a stand-alone mode;
• determining whether the GPS receiver succeeded to acquire GPS signals from at least four satellites;
• shifting the GPS receiver to a self-assisted mode if the GPS receiver failed to acquire the GPS signals from the at least four satellites;
• determining whether valid assistance data are stored in memory of the GPS receiver;
• and
• shifting the GPS receiver to an assisted-GPS mode if no valid assistance data are stored in the memory of the GPS receiver.