Passive position determination using two low-earth orbit satellites
First Claim
1. A position determining system for a satellite communications system, comprising:
- a user terminal;
at least two satellites with known positions and known velocities;
a gateway for communicating with said user terminal through said satellites;
range difference parameter determining means for determining a range difference parameter that represents a difference between (1) the distance between one of said satellites and said user terminal and (2) the distance between another of said satellites and said user terminal;
range-rate difference parameter determining means for determining a range-rate difference parameter that represents a difference between (1) a relative radial velocity between one of said satellites and said user terminal and (2) a relative radial velocity between another of said satellites and said user terminal; and
position determining means for determining the position of said user terminal on the Earth'"'"'s surface based on said known positions and velocities of said satellites, said range difference parameter, and said range-rate difference parameter.
1 Assignment
0 Petitions
Accused Products
Abstract
A system and method for passively 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 difference parameter and a range-rate difference parameter. 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 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 difference parameter, and the range-rate difference parameter.
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Citations
19 Claims
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1. A position determining system for a satellite communications system, comprising:
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a user terminal; at least two satellites with known positions and known velocities; a gateway for communicating with said user terminal through said satellites; range difference parameter determining means for determining a range difference parameter that represents a difference between (1) the distance between one of said satellites and said user terminal and (2) the distance between another of said satellites and said user terminal; range-rate difference parameter determining means for determining a range-rate difference parameter that represents a difference between (1) a relative radial velocity between one of said satellites and said user terminal and (2) a relative radial velocity between another of said satellites and said user terminal; and position determining means for determining the position of said user terminal on the Earth'"'"'s surface based on said known positions and velocities of said satellites, said range difference parameter, and said range-rate difference parameter. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In a communications system comprising a user terminal, at least two satellites with known positions and known velocities, and a gateway for communicating with the user terminal through the satellites, a method for determining the position of the user terminal, comprising the steps of:
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(a) determining a range difference parameter that represents a difference between (1) the distance between one of the satellites and the user terminal and (2) the distance between another of the satellites and the user terminal; (b) determining a range-rate difference parameter that represents a difference between (1) a relative radial velocity between one of the satellites and the user terminal and (2) a relative radial velocity between another of the satellites and the user terminal; and (c) determining the position of the user terminal on the Earth'"'"'s surface based on the known positions and known velocities of the satellites, said range difference and said range-rate difference. - View Dependent Claims (9, 10, 11, 12)
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13. In a communications system comprising at least two satellites with known positions and known velocities and a gateway for communicating with user terminals through the satellites, a user terminal comprising:
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range difference parameter determining means for determining a range difference parameter that represents a difference between (1) the distance between one of the satellites and the user terminal and (2) the distance between another of the satellites and the user terminal; and range-rate difference parameter determining means for determining a range-rate difference parameter that represents a difference between (1) a relative radial velocity between one of the satellites and the user terminal and (2) a relative radial velocity between another of the satellites and the user terminal; wherein the position of the user terminal on the Earth'"'"'s surface can be determined based on the known positions and known velocities of the satellites, said range difference parameter, and said range-rate difference parameter.
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14. In a communications system comprising a user terminal, at least two satellites, and a gateway for communicating with the user terminal through the satellites, a method for maintaining, at the gateway, the position of the user terminal, comprising the steps of:
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(a) actively determining the position of the user terminal; (b) storing said actively-determined position at the user terminal; (c) after a predetermined interval, passively determining, at the user terminal, the position of the user terminal; (d) determining the expected error in said passively-determined position; (e) determining a difference between said actively-determined position and said passively-determined position when said expected error does not exceed a first predetermined threshold; and (f) informing the gateway when said difference exceeds a second predetermined threshold. - View Dependent Claims (15, 16, 17)
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18. In a communications system comprising a user terminal, at least two satellites, and a gateway for communicating with the user terminal through the satellites, a system for maintaining, at the gateway, the position of the user terminal, comprising:
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means for actively determining the position of the user terminal; means for storing said actively-determined position at the user terminal; means for passively determining the position of the user terminal after a predetermined interval; means for determining the expected error in said passively-determined position; means for determining a difference between said passively-determined position and said actively-determined position when said expected error does not exceed a first predetermined threshold; and means for informing the gateway when said difference exceeds a second predetermined threshold. - View Dependent Claims (19)
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Specification