Kalman filter ionospheric delay estimator
AssigneeThe Aerospace Corporation
InventorRajendra Kumar
Life of this patent
Estimating the term…
Abstract
An estimator structure include a nonlinear modified Kalman filter for initial estimate and plurality of bias estimators and a parallel bank of Kalman filters for ambiguity resolution and providing final estimates. The estimator structure is useful for real-time computation of ionospheric propagation delay introduced in the navigation signals by dual frequency GPS receivers.
Claims16
A method of generating initial parameter estimates of parameters estimated from an input having a bias and being a series of inputs at a respective plurality of discrete times, the method comprising the steps of,
- bias estimating bias estimates from the inputs and from the initial parameter estimates, and
- initial parameter estimating the initial parameter estimates from the input and the bias estimates, the initial parameter estimates have an estimation error dependent upon the amount of the bias, the bias estimating step and the initial parameter estimating step recursively estimate in synchronism at each of the plurality of discrete times to suppress the bias from the input to reduce the estimation error, the initial parameter estimating step comprising the steps of:
- bias suppressing the input by removing the bias estimates from the inputs for providing a suppressed bias input;
- providing a prediction error from the suppressed bias input and from an input prediction, the prediction error indicating suppressed bias;
- providing a modified prediction error by modifying the prediction error with nonlinear bias rejection;
- providing the initial parameter estimates from the modified prediction error;
- and
- providing the input prediction error from the modified prediction error and the initial parameter estimates.
A method of generating final parameter estimates of parameters estimated from an input having a bias and being a series of signals at a respective plurality of discrete times, the parameters comprise integer ambiguity parameters and the final parameter estimates comprise final ambiguity parameter estimates, the method comprising the steps of,
- bias estimating bias estimates from the inputs and from initial parameter estimates,
- bias suppressing the input by removing the bias estimates from the inputs for providing a suppressed bias input,
- providing a prediction error from the suppressed bias input and from an input prediction,
- providing a modified prediction error by nonlinear bias rejection of the prediction error for suppressing the bias,
- providing the initial parameter estimates from the modified prediction error,
- providing the input prediction error from the modified prediction error, the initial parameter estimates have an estimation error dependant upon the amount of the bias, the bias estimating step and all of the providing steps function to recursively estimate in synchronism at each of the plurality of discrete times to suppress the bias from the input to reduce the estimation error,
- input delaying the inputs to provide delayed inputs delayed by one of the plurality of discrete times, and
- resolving in synchronism at the plurality of discrete times the integer ambiguity parameters to provide the final parameter estimates from the delayed inputs, the bias estimates and the initial parameter estimates.
A method of generating I.rho.N.sub.2 N.sub.1 final parameter estimates of parameters estimated from an input comprising four PR.sub.1 PR.sub.2 ADR.sub.1 and ADR.sub.2 pseudorange z (k+1) inputs each having a bias and each being a series of signals at a respective plurality of discrete times (k), thee parameters comprise range .rho. and ionospheric delay I parameters and N.sub.1 and N.sub.2 ambiguity parameters and the final parameter estimates comprise final range and ionospheric delay parameters estimates and N.sub.1 and N.sub.2 ambiguity parameter estimates, the method comprising the steps of,
- bias estimating b.sub.1 (k) b.sub.2 (k) b.sub.3 (k) and b.sub.4 (k) bias estimates in parallel from the respective four inputs PR.sub.1 PR.sub.2 ADR.sub.1 and ADR.sub.2 and from initial parameter estimates,
- bias suppressing the inputs by respectively removing the bias estimates from the inputs for providing respectively suppressed bias inputs, z.sub.mod (k+1),
- providing respective prediction error .epsilon. (k+1) the from suppressed bias inputs and from an input prediction,
- providing a modified prediction error .epsilon..sub.mod (k+1) f0r suppressing the bias,
- providing the initial parameter estimates z (k/k) from the modified prediction error,
- providing the input prediction error from the modified prediction error, the initial parameter estimates have an estimation error dependant upon the amount of the bias, the bias estimating step and all of the generating and providing steps function to recursively estimate in synchronism at each of the plurality of discrete times to suppress the bias from the input to reduce the estimation error,
- input delaying the four PR.sub.1, PR.sub.2, ADR.sub.1 and ADR.sub.2 pseudorange inputs to provide delayed inputs z (k) delayed by one of the plurality of discrete times, and
- resolving in synchronism at the plurality of discrete times the N.sub.1 and N.sub.2 ambiguity parameters to provide the final parameter estimates from the delayed inputs, the bias estimates and the initial parameter estimates.
Dependencies are inferred from the claim text.