Method for determining position of mobile earth station in satellite communication system

A method for determining a position of one mobile earth station of a plurality of mobile earth stations in a satellite communication system composed of non-geostationary satellites for communicating with a terrestrial communication network, said mobile earth stations each for communication with at least one of said non-geostationary satellites and land earth stations each connected to said terrestrial communication network for communication with said mobile earth stations via said non-geostationary satellites,

• said method comprising the steps of:
• assuming an XYZ three-dimensional orthogonal coordinate system wherein a given point of a preknown position on the earth surface is positioned as a reference point and defined as a center coordinate of a reference three-dimensional coordinate system, a straight line which extends from the central point of the earth toward said center coordinate is defined as a Z-axis of said three-dimensional coordinate system, a straight line in contact with the earth surface and orthogonal to the equator of the earth and passed through said center coordinate is defined as a Y-axis of said three-dimensional coordinate system, and a straight line in contact with the earth surface and parallel to the equator of the earth and passed through said center coordinate is defined as an X-axis of said three-dimensional coordinate axis;
• making a first-order estimation of a position of said one mobile earth station with respect to the reference coordinate system by the use of the information on a measured distance and a Doppler shift amount between said one mobile earth station of unknown position and any one of said non-geostationary satellites;
• making a second-order estimation of the position of said one mobile earth station by using measured distance and Doppler shift amount, in a newly updated three-dimensional coordinate system using, as a center coordinate, the estimated position of said one mobile earth station obtained by said first-order estimation;
• making a plurality of higher-order estimation operations of the position of said one mobile earth station by using measured distances and Doppler shift amounts, in a finally updated three-dimensional coordinate system using, as a center coordinate, the estimated position of said one mobile earth station obtained by a just preceding-order estimation, until a distance error between the center coordinate of said finally updated three-dimensional coordinate system and a newly obtained higher-order estimated position of said one mobile earth station comes to be less than a predetermined, extremely small threshold value;
• and
• determining said higher-order presumed position at the completion of an estimated position of said one mobile earth station, thereby determining the position of said one mobile earth station with high accuracy.