Method for refining state estimates of a global positioning system (GPS) receiver based upon sequential GPS carrier phase measurements
View Patent ↗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.
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. The method of claim 1 , wherein the state estimates comprise a state estimate structure that contains GPS receiver position, GPS receiver velocity, and GPS receiver clock parameters.
3. The method of claim 1 , further comprising eliminating cycle slip by autonomous identification and rejection of any sequential carrier phase measurement that suffers loss of phase lock.
4. The method of claim 3 , further comprising continuing processing with a next acceptable sequential carrier phase measurement.
5. The method of claim 1 , further comprising processing the state estimates in a sequential filter or a sequential smoother.