UNAMBIGUOUS POSITION DETERMINATION METHOD USING TWO LOW-EARTH ORBIT SATELLITES AND SYSTEM USING THIS METHOD

摘要

A system and method for unambiguously determining the position ofa user terminal (for example, a mobile wireless telephone) in a low-Earthorbit satellite communications system (100). The system includes a userterminal (106), at least two satellites (104A, 1104B) with known positionsand known velocities, and a gateway (102) (that is, a terrestrial basestation)for communicating with the user terminal (106) through the satellites (104A,104B). The method includes the steps of determining a range parameter (1002,1102, 1202), a range difference parameter (1004, 1104, 1204), and eitheror both of a range-rate parameter (1106, 1206) and a range-rate differenceparameter (1008 1208). A range parameter represents a distance between oneof the satellites (104B, 104B) and the user terminal (106). A range differenceparameter represents the difference between (1) the distance between a firstoneof the satellites (104B, 104B) and the user terminal (106) and (2) thedistancebetween a second one of the satellites (104A, 104B) and the user terminal(106). A range-rate parameter represents a relative radial velocity betweenone of the satellites (104A, 104B) and the user terminal (106). A range-ratedifference parameter represents the difference between (a) a relative radialvelocity between a first one of the satellites (104A, 104B) and the userterminal(106) and (b) a relative radial velocity between a second one of thesatellites(104A, 104B) and the user terminal (106). The position of the user terminal(106) on the Earth's surface is then determined based on the known positionsand known velocities of the satellites (104A, 104B), the range parameter, therange difference parameter, and either or both of the range-rate parameter andthe range-rate difference parameter.