Solution separation method and apparatus for ground-augmented global positioning system
First Claim
1. A method of determining accuracy of a position solution provided by a differential positioning system, wherein the system includes a plurality of ground receivers, each ground receiver tracking a plurality of satellite signals from a respective plurality of satellite transmitters, and wherein each ground receiver is located at a known position for deriving a receiver-specific differential correction for each of the plurality of satellite signals, the method comprising:
- determining correction data for each of the plurality of satellite signals, wherein the correction data for each of the plurality of satellite signals is based on an average value of the receiver-specific differential corrections derived from all of the plurality of ground receivers;
determining one or more subsets of the correction data for each of the plurality of satellite signals, wherein each of the one or more subsets of the correction data is based on an average value of a respective subset of the receiver-specific differential corrections, the respective subset of the receiver-specific differential corrections derived from a respective subset of the plurality of ground receivers;
forming the position solution using the plurality of satellite signals and the correction data for each of the plurality of satellite signals;
forming one or more position subsolutions using the plurality of satellite signals and the one or more subsets of the correction data, wherein each of the one or more position subsolutions is based on the plurality of satellite signals and a respective subset of the correction data for each of the plurality of satellite signals; and
calculating one or more separations as a function of a difference between the position solution and each of the one or more position subsolutions, the one or more separations providing an indication of the accuracy of the position solution.
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Abstract
Global positioning systems (GPSs) estimate positions of vehicles based on signals from earth-orbiting satellite transmitters. For accuracy and reliability reasons, these systems have traditionally not be used for critical phases of aircraft navigation and guidance, such as aircraft landings. However, recent years have seen the development of ground-augmented GPS systems for use in automatic landing systems. These augmented systems rely on broadcast correction data to correct positions estimates, or solutions, and thus provide more accurate position solutions. Unfortunately, the conventional methods of measuring accuracy in these augmented systems cannot adequately cope with loss of correction data or satellite signals and thus lead to more aborted landings than acceptable. Accordingly, the inventor devised a ground-augmented GPS system that incorporates a better method for determining the accuracy of its position solution. One exemplary embodiment determines a main position solution and one or more position subsolutions, with the main solution using all broadcast correction data and each subsolution using a respective subset of the correction data. Differences or separations between the main position solution and the subsolution are then used to determine accuracy, or protection, limits for the main position solution. Another embodiment uses Kalman filters to incorporate vehicle motion data into the calculation of the main solution and the subsolutions, enabling the determination of protection limits during periods lost GPS or correction data.
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Citations
16 Claims
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1. A method of determining accuracy of a position solution provided by a differential positioning system, wherein the system includes a plurality of ground receivers, each ground receiver tracking a plurality of satellite signals from a respective plurality of satellite transmitters, and wherein each ground receiver is located at a known position for deriving a receiver-specific differential correction for each of the plurality of satellite signals, the method comprising:
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determining correction data for each of the plurality of satellite signals, wherein the correction data for each of the plurality of satellite signals is based on an average value of the receiver-specific differential corrections derived from all of the plurality of ground receivers;
determining one or more subsets of the correction data for each of the plurality of satellite signals, wherein each of the one or more subsets of the correction data is based on an average value of a respective subset of the receiver-specific differential corrections, the respective subset of the receiver-specific differential corrections derived from a respective subset of the plurality of ground receivers;
forming the position solution using the plurality of satellite signals and the correction data for each of the plurality of satellite signals;
forming one or more position subsolutions using the plurality of satellite signals and the one or more subsets of the correction data, wherein each of the one or more position subsolutions is based on the plurality of satellite signals and a respective subset of the correction data for each of the plurality of satellite signals; and
calculating one or more separations as a function of a difference between the position solution and each of the one or more position subsolutions, the one or more separations providing an indication of the accuracy of the position solution. - View Dependent Claims (2, 3, 4, 5, 6)
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7. For use in a differential navigation system providing a position solution for a vehicle, wherein the system includes a plurality of ground receivers, each ground receiver tracking a plurality of satellite signals from a respective plurality of satellite transmitters, and wherein each ground receiver is located at a known position for deriving a receiver-specific differential correction for each of the plurality of satellite signals, a method of determining accuracy of the position solution, the method comprising:
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determining correction data for each of the plurality of satellite signals, wherein the correction data for each of the plurality of satellite signals is based on an average value of the receiver-specific differential corrections derived from all of the plurality of ground receivers;
determining a plurality of subsets of the correction data for each of the plurality of satellite signals, wherein each of the plurality of subsets of the correction data is based on an average value of a respective subset of the receiver-specific differential corrections, the respective subset of the receiver-specific differential corrections derived from a respective subset of the plurality of ground receivers, and wherein the respective subset of the plurality of ground receivers includes all but one distinct ground receiver;
forming the position solution using the plurality of satellite signals and the correction data for each of the plurality of satellite signals;
forming a plurality of position subsolutions using the plurality of satellite signals and the plurality of subsets of the correction data, wherein each of the plurality of position subsolutions is based on the plurality of satellite signals and a respective subset of the correction data for each of the plurality of satellite signals;
calculating a plurality of separations, wherein each of the plurality of separations is based on a difference between the position solution and a respective position subsolution; and
determining a protection limit of the position solution for the vehicle based on at least one of the plurality of separations. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16)
comparing the protection limit to an alarm limit; and
signaling an integrity failure if the protection limit exceeds the alarm limit.
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Specification