GPS carrier phase measurement representation and method of use

• US 20070024496A1
• Filed: 01/19/2006
• Published: 02/01/2007
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: Ansys Government Initiatives Incorporated (Ansys Incorporated)
• Original Assignee: Analytical Graphics
• Inventors: Wright, James, Chuba, William, Hujsak, Richard
• Granted Patent: US 7,423,583 B2
• Time in Patent Office: Days
• US Class Current: 342/357.680
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

Sequential GPS Doppler carrier phase count measurements are used for precision sequential determination of position and velocity of a GPS receiver, such as for orbit determination and geolocation, with minimum throughput time. Real-time orbit determination and geolocation performance is enabled with an optimal sequential filter, and near-real-time performance is enabled with an optimal fixed-lag smoother. Many problems associated with prior art orbit determination are eliminated by addressing the “cycle slip” problem, the unknown initial range problem with RANGE^CP measurement representations, the problem of serial correlation in the measurements due to reprocessing of overlapping thermal noise. Also, the present invention significantly attenuates the carrier signal phase variation due to rotation of receiver antenna relative to transmitter antenna because the sequential phase count time intervals are sufficiently short.

Claims

1. A method of refining state estimates of a Global Positioning System (GPS) receiver based upon sequential GPS carrier phase measurements, comprising:

the GPS receiver receives sequential GPS Doppler carrier phase signals from Navigation System with Timing And Ranging (NAVSTAR) transmitter at a defined phase count interval;

the GPS receiver internal clock generates nominal frequencies and derives received frequencies from phase count measurements;

determining a frequency differences to define instantaneous Doppler frequencies in units of cycles per second (Hz);

counting positive zero crossings of the instantaneous Doppler frequencies to measure rational Doppler carrier phase count number in cycles;

calculating an estimated representation of Doppler carrier phase count number;

differencing measured and estimated representations of Doppler carrier phase count number to obtain measurement residuals

mapping the measurement residuals to state estimate corrections sequentially; and

applying the state estimate corrections to propagated state estimates.

2. A method of using a sequential Global Positioning System (GPS) carrier phase measurement at time K to correct a propagated a priori state estimate at time K to calculate an improved state estimate at time K, comprising:

propagating a state estimate and its realistic error covariance matrix to time K+1

using the propagated state estimate at time K+1 to calculate an expected phase count measurement for time K+1;

acquiring a measurement of sequential phase count at time K+1;

calculating a measurement residual between measured and expected phase count;

comparing an absolute value of the measurement residual to a threshold determined by a measurement residual variance matrix;

skipping the measurement if over the threshold;

keeping the measurement if at or under the threshold;

mapping the measurement residual to a state estimate correction; and

applying the state estimate correction to the propagated a priori state estimate at time K to obtain the improved state estimate at time K.