Method and system for calibrating group delay errors in a combined gps and glonass receiver

Abstract

A combined GPS and GLONASS receiver receives GPS signals and GLONASS signals. A calibration signal is generated utilizing the received GPS signals and/or the received GLONASS signals to offset group delay errors in the received GLONASS signals. The generated calibration signal is filtered through Kalman filters to estimate group delay variations in the received GLONASS signals. The estimated group error delay variations are combined with the received GLONASS signals to calibrate the received GLONASS signals by offsetting the estimated group error delay variations. When GPS signals are not available for use, the combined GPS and GLONASS receiver obtains group delay errors stored or in the received GLONASS signals to estimate calibration coefficients. The estimate calibration coefficients are updated utilizing received GPS and/or GLONASS signals. The updated estimated calibration coefficients are stored before turning off the combined GPS and GLONASS receiver to expedite calibrating of GLONASS signals received upon turning on.

What is claimed is: 
     
         1 . A method for processing signals in a global navigation receiver, comprising:
 receiving a first signal corresponding to a first satellite navigation system;   generating a calibration signal using the first signal; and   reducing group delay errors in the first signal using the calibration signal.   
     
     
         2 . The method of  claim 1 , further comprising:
 filtering the calibration signal to generate a filtered calibration signal, wherein reducing the group delay errors in the first signal comprises combining the filtered calibration signal with the first signal.   
     
     
         3 . The method of  claim 2 , wherein the filtered calibration signal includes group delay variations associated with the first signal. 
     
     
         4 . The method of  claim 3 , wherein reducing the group delay errors in the first signal further comprises offsetting the group delay errors in the first signal using the group delay variations associated with the first signal. 
     
     
         5 . The method of  claim 1 , wherein the calibration signal includes calibration coefficients for offsetting the group delay errors. 
     
     
         6 . The method of  claim 1 , further comprising:
 retrieving stored group delay variations associated with the first signal from memory;   wherein reducing the group delay errors in the first signal further comprises offsetting the group delay errors in the first signal using the stored group delay variations.   
     
     
         7 . The method of  claim 6 , further comprising:
 receiving a second signal corresponding to a second satellite navigation system; and   updating the stored group delay variations using the second signal.   
     
     
         8 . The method of  claim 1 , further comprising:
 estimating group delay variations associated with the first signal using the first signal;   wherein reducing the group delay errors in the first signal further comprises offsetting the group delay errors in the first signal using the estimated group delay variations.   
     
     
         9 . The method of  claim 1 , further comprising:
 receiving a second signal corresponding to a second satellite navigation system;   generating second navigation information corresponding to the second satellite navigation system using the second signal;   converting the second navigation information to first navigation information corresponding to the first satellite navigation system;   calculating an estimate of the first signal using the first navigation information; and   comparing the first signal and the estimate of the first signal to generate the calibration signal.   
     
     
         10 . The method of  claim 9 , wherein the first satellite navigation system corresponds to a Global Orbiting Navigation Satellite System (GLONASS) and the second satellite navigation system corresponds to a Global Positioning System (GPS). 
     
     
         11 . A global navigation receiver, comprising:
 a receiver front end configured to receive a first signal corresponding to a first satellite navigation system;   a calibration signal generator configured to generate a calibration signal using the first signal; and   a signal calibrator configured to reduce group delay errors in the first signal using the calibration signal.   
     
     
         12 . The global navigation receiver of  claim 11 , wherein the signal calibrator comprises:
 a filter configured to filter the calibration signal to generate a filtered calibration signal; and   a signal coupler configured to combine the filtered calibration signal with the first signal to reduce the group delay errors in the first signal.   
     
     
         13 . The global navigation receiver of  claim 12 , wherein the filtered calibration signal includes group delay variations associated with the first signal. 
     
     
         14 . The global navigation receiver of  claim 13 , wherein the signal coupler is further configured to offset the group delay errors in the first signal using the group delay variations associated with the first signal. 
     
     
         15 . The global navigation receiver of  claim 11 , wherein the calibration signal further includes calibration coefficients for offsetting the group delay errors. 
     
     
         16 . The global navigation receiver of  claim 11 , wherein the global navigation receiver is configured to retrieve stored group delay variations associated with the first signal from memory;
 wherein the signal calibrator is further configured to reduce the group delay errors in the first signal by offsetting the group delay errors in the first signal using the stored group delay variations.   
     
     
         17 . The global navigation receiver of  claim 16 , wherein the receiver front end is further configured to receive a second signal corresponding to a second satellite navigation system and update the stored group delay variations using the second signal. 
     
     
         18 . The global navigation receiver of  claim 11 , wherein the global navigation receiver is configured to estimate group delay variations associated with the first signal using the first signal;
 wherein the signal calibrator is further configured to reduce the group delay errors in the first signal by offsetting the group delay errors in the first signal using the estimated group delay variations.   
     
     
         19 . The receiver front end of  claim 11 , further configured to receive a second signal corresponding to a second satellite navigation system,
 wherein the global navigation receiver further comprises:   a navigation processor configured to generate second navigation information corresponding to the second satellite navigation system using the second signal,   wherein the calibration signal generator comprises:
 a time transfer module configured to convert the second navigation information to first navigation information corresponding to the first satellite navigation system; 
 a signal estimator configured to calculate an estimate of the first signal using the first navigation information; and 
 a signal comparator configured to compare the first signal and the estimate of the first signal to generate the calibration signal. 
   
     
     
         20 . The global navigation receiver of  claim 19 , wherein the first satellite navigation system corresponds to a Global Orbiting Navigation Satellite System (GLONASS) and the second satellite navigation system corresponds to a Global Positioning System (GPS).