Systems and methods for fault detection and exclusion in navigational systems
First Claim
1. An apparatus for use in a navigation system to determine when to initiate a process to isolate one or more faulty ranging signals from a navigation calculation, comprising at least one processing element, wherein said processing element:
- receives a test value and estimated position error associated with at least two ranging signals from a measurement device;
compares the test value to a first threshold value and initiates a signal if the test value is at least as great as the first threshold value;
compares the estimated position error to a second threshold value based upon the initiated signal; and
initiates a procedure to eliminate one or more faulty ranging signals from use in the navigation calculation if the estimated position error is at least as great as the second threshold value.
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Accused Products
Abstract
The Fault Detection and Exclusion (FDE) system for use in navigational systems that rely upon multiple ranging signals, such as GPS satellites, uses an FDE algorithm to detect, as soon as possible, whether a fault exists in a signal associated with one or more of the GPS satellites. The system makes this determination by comparing a computed residual error with a first fault detection threshold. After determining that the computed residual error has exceeded the first, relatively low, fault detection threshold, the system transmits a signal to one or more external systems indicating that one or more signals associated with the various GPS satellites may be faulty. The system then monitors horizontal estimated position error (HUL) until this value has met or exceeded a relatively high fault isolation threshold value. The system then attempts to isolate and exclude the faulty satellite from the current navigational solution.
65 Citations
31 Claims
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1. An apparatus for use in a navigation system to determine when to initiate a process to isolate one or more faulty ranging signals from a navigation calculation, comprising at least one processing element, wherein said processing element:
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receives a test value and estimated position error associated with at least two ranging signals from a measurement device;
compares the test value to a first threshold value and initiates a signal if the test value is at least as great as the first threshold value;
compares the estimated position error to a second threshold value based upon the initiated signal; and
initiates a procedure to eliminate one or more faulty ranging signals from use in the navigation calculation if the estimated position error is at least as great as the second threshold value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for use in a navigation system to determine when to initiate a process to isolate one or more faulty ranging signals from a navigation calculation, comprising:
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determining a test value associated with at least two of the ranging signals and an estimated position error value;
comparing the test value to a first threshold value and indicating if the test value is at least as great as the first threshold value thereby representing a potential faulty ranging signal;
comparing the estimated position error value to the second threshold value if the test value is at least as great as the first threshold value; and
if the estimated position error value is at least as great as the second threshold value initiating a fault detection and isolation procedure to eliminate the one or more faulty ranging signals from use in the navigation calculation. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. A method for initiating a process of excluding at least one faulty ranging signal from a navigation calculation used in a navigation system that relies on more than one ranging signal, comprising:
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selecting a first threshold and a second threshold;
monitoring a test value associated with at least two ranging signals;
monitoring a estimated position error value; and
initiating the process of detecting and isolating at least one faulty ranging signal, if the test value is at least as great as the first threshold and the estimated position error is at least as great as the second threshold. - View Dependent Claims (21, 22, 23)
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24. An apparatus for detecting and excluding a faulty ranging signal in a navigation system that relies upon more than one ranging signal, comprising at least one processing element that:
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receives a residual error and a horizontal estimated position error associated with at least two ranging signals;
determines whether the residual error is at least as great as a fault detection threshold, whereby a residual error that is at least as great as the fault detection threshold indicates that at least one ranging signal is potentially faulty;
determines whether the horizontal estimated position error is at least as great as a fault isolation threshold, wherein the horizontal estimated position error that is at least as great as the fault isolation threshold indicates that isolation and exclusion of at least one ranging signal from a navigation solution can be attempted with a sufficient degree of confidence of successfully identifying the faulty ranging signal or signals; and
initiates a detection and isolation procedure to detect and isolate the at least one faulty ranging signal when the horizontal estimated position error is at least as great as the fault isolation threshold. - View Dependent Claims (25, 26, 27)
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28. A method for detecting and excluding a faulty ranging signal in a navigation system that relies upon more than one ranging signal, comprising:
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receiving a residual error and a horizontal estimated position error associated with at least two ranging signals;
determining whether the residual error is at least as great as a fault detection threshold, whereby a residual error that is at least as great as the fault detection threshold indicates that at least one ranging signal is potentially faulty;
determines whether the horizontal estimated position error is at least as great as a fault isolation threshold, wherein the horizontal estimated position error that is at least as great as the fault isolation threshold indicates that at least one ranging signal from which the signal is transmitted is faulty; and
initiating a detection and isolation procedure to detect and isolate the at least one faulty ranging signal when the horizontal estimated position error is at least as great as the fault isolation threshold. - View Dependent Claims (29, 30, 31)
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Specification