Systems and methods for fault detection and exclusion in navigational systems

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:

• 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.

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:

• 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.

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:

• 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.

A method for detecting and excluding a faulty ranging signal in a navigation system that relies upon more than one ranging signal, comprising:

• 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.