Ultratight navigation observation lock detector

• US 20070237269A1
• Filed: 04/07/2006
• Published: 10/11/2007
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Lukesh, John, Lillo, Walter, Raghavender, Manorama, Douglas, Randal
• Granted Patent: US 7,680,221 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 2201/70715 with application-specific features
• CPC Class Codes: H04L 2027/0057 quadrature phase

Abstract

An observation lock detector receives I and Q correlations and measurement residuals and transforms the I and Q quadrature correlation outputs based upon computed code phase and carrier phase into transformed I and Q quadrature signals communicated to conventional output lock detectors to provide validity and confidence indicator signals for indicating that the residual estimates are valid for dynamic propagation of the residuals in a navigation receiver for improved performance especially in low signal-to-noise environments such as for use in an ultratight GPS navigation system.

Claims

1. A detector for receiving quadrature correlations and residuals generated from the quadrature correlations, the detector for providing validity indicators indicating the validity of the residuals, the detector comprising,

a maximizer for receiving the quadrature correlations and the residuals and generating a code phase offset, the maximizer for combining the quadrature correlations into combined correlations using the code phase offset,

a rotation generator for receiving the residuals and generating a carrier phase angle offset,

a rotator for rotating the combined correlations by the carrier phase angle offset into transformed correlations, and

a lock detector for receiving the transformed correlations and for providing a validity indicator indicating validity of at least one of the residuals.

2. The detector of claim 1, wherein

the residuals are generated by a prefilter receiving the correlations,

the quadrature correlations are generated by a correlator receiving demodulated quadrature samples, and

the detector and prefilter and correlator are disposed in a navigation system.

3. The detector of claim 1 wherein,

the residuals are a measurement error vector comprising a carrier phase error and a carrier frequency error and a pseudorange error, and

the indicators comprise a carrier phase indicator and a carrier frequency indicator and a pseudorange error indicator.

12. The detector of claim 1 wherein,

the lock detectors comprise,

a carrier phase lock detector for providing a carrier phase validity indictor,

a carrier frequency lock detector for providing a carrier frequency lock validity indicator, and

a code lock detector for providing a code lock validity indicator.

13. The detector of claim 1 wherein the lock detectors comprise,

a carrier phase lock detector for providing a carrier phase validity indictor,

a carrier frequency lock detector for providing a carrier frequency lock validity indicator, and

a code phase lock detector for providing a code lock validity indicator,

the residuals comprise carrier phase and carrier frequency and pseudorange error, and

the transformed vector comprises an I_T inphase transformed vector and an IQ transformed vector,

when all of the residuals are valid, the I_T inphase transformed vector contains all of the signal power and the Q_T quadrature transformed vector contains no signal power, the carrier phase lock detector provides a valid carrier phase indicator and the carrier frequency lock detector provides a valid carrier frequency indicator and code phase lock detector provides a valid code phase indicator,

when the carrier phase is not accurate and the carrier frequency is accurate and when the I_T inphase transformed vector and the Q_T quadrature transformed vector both contain constant signal power having a sum greater than a first predetermined power value, the carrier phase lock detector provides an invalid indicator and the carrier frequency lock detector provides a valid indicator and the code phase lock detector provides a valid indicator,

when the carrier phase and carrier frequency are inaccurate and the pseudorange error is accurate, and when the sum of the power of the I_T inphase transformed vector and the Q_T transformed vector is above the predetermined power value, the carrier phase lock detector an invalid indicator and the carrier frequency lock detector provides an invalid indicator and the code phase lock detector provides a valid indicator, and

when the carrier phase and carrier frequency and pseudorange residuals are inaccurate, the carrier phase lock detector and the carrier frequency lock detector and the code phase lock detector all provide an invalid indicator.

15. The detector of claim 13 wherein,

the pseudorange error is a function of the code phase offset.

4. A detector for receiving quadrature correlations and residuals, the detector for providing indicators indicating validity of the residuals, the detector comprising,

a maximizer for receiving the quadrature correlations and the residuals, the maximizer for determining a code phase offset, the maximizer, the maximizer weighting by the weights the quadrature correlations into weighted correlations that are combined into maximized correlations,

a rotation matrices generator for receiving the residuals and determining a carrier phase offset angle for generating rotational matrices,

a rotator for rotating the maximized correlations into transformed correlations, and

lock detectors for receiving the transformed correlations and providing the indicators.

5. The detector of claim 4 further comprising,

a noise modifier for receiving noise signal estimates and generating modified noise estimates, the modified noise estimates communicated to the lock detectors for determining the indicators.

6. The detector of claim 4 further comprising,

a noise modifier for receiving noise signal estimates and generating modified noise estimates, the modified noise estimates communicated to the lock detectors for determining the indicators, the noise signal estimates are a noise amplitude signal and an noise SNR signal and the modified noise estimates are a modified noise amplitude and a modified noise SNR.

7. The detector of claim 4 wherein,

the maximizer comprises a table operator for determining weights as a function of the code phase offset, and

the maximized correlation are I and Q maximized correlations.

8. The detector of claim 4 wherein,

the quadrature correlations are I and Q correlations for each code replica used for correlating demodulating quadrature signals into the I and Q correlations.

9. The detector of claim 4 wherein,

the residual measurements are measurement errors from a prefilter that is selected from a group consisting of Kalman filters, batch filters, and particles filters.

10. The detector of claim 4 wherein,

the residual measurements are provided by a prefilter,

the quadrature correlations are provided by a correlator correlating demodulated quadrature signals into the quadrature correlations by despreading the demodulated quadrature signals by a code replica,

the indicators are communicated to an integration filter providing propagated signals for adjusting the code replica,

the detector and prefilter and correlator and integration filter are disposed in a navigation processor for coherently tracking a code phase error between a spread spectrum code of the demodulated quadrature signals and the replica code.

11. The detector of claim 4 wherein, the quadrature correlations comprise early and late and prompt I and Q correlations.

14. The detector of claim 11 further comprising

a noise modifier for receiving noise signal estimates and generating modified noise estimates, the modified noise estimates communicated to the carrier phase lock detector and the carrier frequency lock detector and the code phase lock detector for determining the indicators, the predetermined power value being dependent upon modified noise estimates.