Qualcomm Incorporated

Edward B Victor

Jon James Anderson

Francis M Ngai

Jin Dai

Nadav Levanon

Sridhar Vembu

A system and method for determining timing offset errors in a low earth orbit satellite system based upon Doppler and Doppler rate of change is provided. A user terminal determines first and second timing offsets respectively associated with first and second satellite beams from respective first and second satellites. Next, the user terminal determines the Doppler and Doppler rate of change associated with the first and second satellite beams. A timing offset is estimated from the measured Doppler and Doppler rate of change and is then compared with the user terminal's own determined timing offset. If the comparison does not produce a value within a predetermined threshold, a beam identification error is declared.

Aiding beam identification in a satellite system

A system and method for unambiguously determining the position of a user terminal (for example, a mobile wireless telephone) in a low-Earth orbit satellite communications system. The system includes a user terminal, at least two satellites with known positions and known velocities, and a gateway (that is, a terrestrial base station) for communicating with the user terminal through the satellites. The method includes the steps of determining a range parameter, a range difference parameter, and either or both of a range-rate parameter and a range-rate difference parameter. A range parameter represents a distance between one of the satellites and the user terminal. A range difference parameter represents the difference between (1) the distance between a first one of the satellites and the user terminal and (2) the distance between a second one of the satellites and the user terminal. A range-rate parameter represents a relative radial velocity between one of the satellites and the user terminal. A range-rate difference parameter represents the difference between (a) a relative radial velocity between a first one of the satellites and the user terminal and (b) a relative radial velocity between a second one of the satellites and the user terminal. The position of the user terminal on the Earth's surface is then determined based on the known positions and known velocities of the satellites, the range parameter, the range difference parameter, and either or both of the range-rate parameter and the range-rate difference parameter.

Unambiguous position determination using two low-earth orbit satellites

A system and method for resolving ambiguity in an ambiguous position solution for a user terminal position in a satellite communications system which includes a user terminal, at least one satellite, and a gateway communicating with the user terminal through the satellite. Each satellite has a plurality of satellite beams which each illuminate a region on the Earth in a known pattern relative to a satellite sub-track. A satellite beam illuminating the user terminal is identified along with its corresponding position relative to the sub-track. The orientations of possible user terminal positions and the identified beam relative to the satellite sub-track are compared to each other. Possible user terminal positions falling on an incorrect side of the sub-track from the detected beam illuminating the user terminal, are considered as incorrect solutions for that user terminal. The ambiguity solution can be determined using satellite identification and comparison elements in the user terminal, or at the gateway, in which case certain beam information is reported to the gateway. In further aspects of the invention, the beam being identified can be either a forward link or reverse link beam, or both, and each link has a different beam pattern.

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Louisville, CO, United States of America

Edward B Victor