Method and system of determining user terminal position using a measured signal propagation delay and Doppler shift of a communications link

A method of determining a user terminal location on the surface of the earth by referencing a satellite rotating the earth, the method comprising the steps of:

• measuring a signal propagation delay and a Doppler shift of a carrier signal;
• determining an earth central angle α between the user terminal and a sub-satellite point, the earth central angle being a function of the signal propagation delay;
• determining an azimuth angle β between the user terminal and the direction of motion of the satellite measured at sub-satellite points, the azimuth angle being a function of the Doppler shift;
• determining an estimated user terminal location based on the earth central angle, the azimuth angle and a spherical approximation of the shape of the earth;
• and
• adjusting the estimated user terminal location using a refined approximation of the shape of the earth.

A system for determining a location of a user terminal on the surface of the earth, the system comprising:

• a ground station for tracking a position of a satellite;
• a receiver adapted to determine a signal propagation delay and a Doppler shift of a radio frequency (RF) signal transmitted between the user terminal and the satellite;
• a processor, in communication with the receiver, for determining the location of the user terminal, based on the signal propagation delay, the Doppler shift, and a spherical approximation of the shape of the earth in combination with an ellipsoid approximation of the shape of the earth;
• said processor having means for determining an earth central angle α between the user terminal and a sub-satellite point, the earth central angle being a function of the signal propagation delay;
• said processor having means for determining an azimuth angle β between the user terminal and the direction of the motion of the satellite, the azimuth angle being a function of the Doppler shift;
• said processor having means for determining the user terminal location based on the earth central angle and the azimuth angle.