Method and apparatus for precision attitude determination
First Claim
1. A method for determining the angular position of a secondary receiving antenna with respect to a reference receiving antenna in a satellite-based positioning system, the secondary antenna being held at a fixed distance from the reference antenna, the method comprising the steps of:
- making carrier phase measurements based on the reception of a carrier signal from each of a plurality N of satellites, where N is the number of satellites needed to compute the relative position of the secondary antenna and is at least two;
deriving from the carrier phase measurements an initial set of potential solutions for the relative position, wherein the initial set of potential solutions all fall within a region of uncertainty defined by the surface of a sphere having a radius equal to the distance between the two antennas, and wherein multiple potential solutions arise because of whole-cycle ambiguity of the carrier signal;
making redundant carrier phase measurements based on the reception of a carrier signal from an additional (N+1)th satellite;
eliminating false solutions from the initial set of potential solutions, based on a comparison of the redundant carrier phase measurements with the initial set of potential solutions, to reduce the number of potential solutions to close to one, whereby the number of potential solutions is not increased by use of the redundant carrier phase measurements; and
determining from the relative position of the secondary antenna the angular attitude of a line between the two antennas, with respect to a selected set of coordinate axes.
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Abstract
A technique for resolving whole-cycle ambiguity that is inherent in phase-angle measurements of signals received from multiple satellite-based transmitters in a global positioning system. The relative position of a secondary receiving antenna with respect to a reference antenna is approximately known or approximately initially determined and then measurements from a minimum number of satellites are used to determine an initial set of potential solutions to the relative position of the secondary antenna that fall within a region of uncertainty surrounding the approximate position. Redundant measurements are taken from one or more additional satellites and used to progressively reduce the number of potential solutions to close to one. Even if the number of potential solutions is not reduced to one true solution, the number can be further reduced by using additional measurements taken at different time intervals, at which different satellite geometries prevail. The disclosed technique produces rapid elimination of false solutions and permits realtime computation of angular orientation in attitude determination applications.
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Citations
26 Claims
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1. A method for determining the angular position of a secondary receiving antenna with respect to a reference receiving antenna in a satellite-based positioning system, the secondary antenna being held at a fixed distance from the reference antenna, the method comprising the steps of:
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making carrier phase measurements based on the reception of a carrier signal from each of a plurality N of satellites, where N is the number of satellites needed to compute the relative position of the secondary antenna and is at least two; deriving from the carrier phase measurements an initial set of potential solutions for the relative position, wherein the initial set of potential solutions all fall within a region of uncertainty defined by the surface of a sphere having a radius equal to the distance between the two antennas, and wherein multiple potential solutions arise because of whole-cycle ambiguity of the carrier signal; making redundant carrier phase measurements based on the reception of a carrier signal from an additional (N+1)th satellite; eliminating false solutions from the initial set of potential solutions, based on a comparison of the redundant carrier phase measurements with the initial set of potential solutions, to reduce the number of potential solutions to close to one, whereby the number of potential solutions is not increased by use of the redundant carrier phase measurements; and determining from the relative position of the secondary antenna the angular attitude of a line between the two antennas, with respect to a selected set of coordinate axes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for determining the angular attitude of a line of fixed length between a reference receiving antenna and a secondary receiving antenna, from the relative position of the secondary receiving antenna with respect to the reference receiving antenna as determined in a satellite-based positioning system, the method comprising the steps of:
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making carrier phase measurements based on the reception of a carrier signal from each of two satellites, where two is the minimum number of satellites needed to compute the relative position of the secondary antenna; deriving from the carrier phase measurements an initial set of potential solutions for the relative position, wherein the initial set of potential solutions all fall within a region of uncertainty defined by the surface of a sphere having a radius equal to the fixed distance between the two antennas, and wherein multiple potential solutions arise because of whole-cycle ambiguity of the carrier signal; making redundant carrier phase measurements based on the reception of a carrier signal from a third satellite; and eliminating false solutions from the initial set of potential solutions, based on a comparison of the redundant carrier phase measurements with the initial set of potential solutions, to reduce the number of potential solutions to close to one, whereby the number of potential solutions is not increased by use of the redundant carrier phase measurements. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. Apparatus for determining the angular position of a secondary receiving antenna with respect to a reference receiving antenna in a satellite-based positioning system, the secondary antenna being held at a fixed distance from the reference antenna, the apparatus comprising:
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means for making carrier phase measurements based on the reception of a carrier signal from each of a plurality N of satellites, where N is the number of satellites needed to compute the relative position of the secondary antenna, and is at least two; means for deriving from the carrier phase measurements an initial set of potential solutions for the relative position, wherein the initial set of potential solutions all fall within a region of uncertainty defined by the surface of a sphere having a radius equal to the distance between the two antennas, and wherein multiple potential solutions arise because of whole-cycle ambiguity of the carrier signal; means for making redundant carrier phase measurements based on the reception of a carrier signal from an additional (N+1)th satellite; means for eliminating false solutions from the initial set of potential solutions, based on a comparison of the redundant carrier phase measurements with the initial set of potential solutions, to reduce the number of potential solutions to close to one, whereby the number of potential solutions is not increased by use of the redundant carrier phase measurements; and the apparatus further comprises means for determining from the relative position of the secondary antenna the angular attitude of a line between the two antennas, with respect to a selected set of coordinate axes. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25)
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26. Apparatus for determining the angular attitude of a line of fixed length between a reference receiving antenna and a secondary receiving antenna, from the relative position of the secondary receiving antenna with respect to the reference receiving antenna as determined in a satellite-based positioning system, the apparatus comprising:
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means for making carrier phase measurements based on the reception of a carrier signal from each of two satellites, where two is the minimum number of satellites needed to compute the relative position of the secondary antenna; means for deriving from the carrier phase measurements an initial set of potential solutions for the relative position, wherein the initial set of potential solutions all fall within a region of uncertainty defined by the surface of a sphere having a radius equal to the fixed distance between the two antennas, and wherein multiple potential solutions arise because of whole-cycle ambiguity of the carrier signal; means for making redundant carrier phase measurements based on the reception of a carrier signal from a third satellite; and means for eliminating false solutions from the initial set of potential solutions, based on a comparison of the redundant carrier phase measurements with the initial set of potential solutions, to reduce the number of potential solutions to close to one, whereby the number of potential solutions is not increased by use of the redundant carrier phase measurements.
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Specification