Differential GPS corrections using virtual stations

Abstract

Method and apparatus for providing GPS pseudorange correction and carrier phase correction information for navigation or surveying activities over a selected geographic region S of arbitrary size. In a navigation mode, a virtual reference station (VRS), positioned near a selected location L, receives differential GPS (DGPS) correction signals, translates these signals into a selected format, and broadcasts this DGPS information in this format for use by a local user. In a survey mode, the VRS receives corrected GPS information, translates this information into a selected format and broadcasts this translated and corrected GPS information and the VRS location, for use by a mobile station in forming a baseline vector from the GPS mobile station to the VRS location.

1 . (canceled)  
   
   
       2 . A method of processing SATPS signals, comprising: 
 a. Obtaining signal information derived from SATPS signals received from at least three satellites at three or more reference stations,    b. Obtaining ephemeris information for each of the satellites,    c. For each satellite, estimating from the signal information and from the ephemeris information a satellite location error vector,    d. For each satellite, determining a component of range error due to satellite location error at a selected location, and    e. Making available the component of range error for each satellite to compensate for satellite location error when computing a position estimate from SATPS signals received at a mobile station location.    
   
   
       3 . The method of  claim 2 , wherein determining a component of range error comprises, for each satellite: determining a calculated range from the selected location to the satellites; and combining the calculated range with the satellite location error vector.  
   
   
       4 . The method of  claim 2 , wherein estimating a satellite location error vector for each of the satellites comprises: determining from the SATPS signals a measured location of each satellite; determining from satellite ephemeris information a calculated location of each satellite; and, for each satellite, comparing the measured location with the calculated location to determine the satellite location vector.  
   
   
       5 . The method of  claim 3 , wherein estimating a satellite location error vector for each of the satellites comprises: determining from the SATPS signals a measured location of each satellite; determining from satellite ephemeris information a calculated location of each satellite; and, for each satellite, comparing the measured location with the calculated location to determine the satellite location vector.  
   
   
       6 . The method of  claim 4 , further comprising, at a mobile station location: receiving SATPS signals from the satellites; and applying the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of the mobile station location.  
   
   
       7 . The method of  claim 5 , further comprising, at a mobile station location: receiving SATPS signals from the satellites; and applying the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of the mobile station location.  
   
   
       8 . The method of  claim 6 , further comprising, at a mobile station location: receiving SATPS signals from the satellites; and applying the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of the mobile station location.  
   
   
       9 . The method of  claim 7 , further comprising, at a mobile station location: receiving SATPS signals from the satellites; and applying the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of the mobile station location.  
   
   
       10 . The method of  claim 8 , wherein the component of range error is determined for each satellite at a central station and transmitted to the mobile station location.  
   
   
       11 . The method of  claim 5 , wherein the component of range error is transmitted with an issue of data ephemeris label.  
   
   
       12 . The method of  claim 2 , further comprising calculating for the selected location an azimuth angle and an elevation angle for each satellite, and making the azimuth angle and the elevation angle for each satellite available to compensate at the mobile station location for at least one of ionospheric delay correction and tropospheric delay correction.  
   
   
       13 . The method of  claim 7 , further comprising determining for each satellite a pseudorange correction at the selected location by combining the component of range error for the satellite with an estimated clock error for the satellite and with a tropospheric delay correction and with an ionospheric delay correction.  
   
   
       14 . The method of  claim 2 , wherein the selected location corresponds approximately to the mobile station location.  
   
   
       15 . The method of  claim 2 , wherein determining a component of range error comprises running a Kalman filter having states for satellite clock error and for components of a satellite location error vector for each satellite.  
   
   
       16 . The method of  claim 2 , wherein making available the component of range error for each satellite comprises synthesizing a virtual-reference-station correction message which simulates a correction message that would be produced by a real reference station receiving SATPS signals at the selected location.  
   
   
       17 . The method of  claim 2 , wherein the signal information is derived from carrier phase measurements of SATPS signals received at the reference stations, and wherein the method further comprises: for each satellite, estimating from the signal information a satellite velocity error.  
   
   
       18 . The method of  claim 16 , wherein the signal information is derived from carrier phase measurements of SATPS signals received at the reference stations, and wherein the method further comprises: for each satellite, estimating from the signal information a satellite velocity error.  
   
   
       19 . The method of  claim 2 , wherein the signal information is derived from SATPS signals obtained at an observation time during which at least one satellite is visible from at least three reference stations.  
   
   
       20 . Apparatus for processing SATPS signals, comprising a VRS computer operative to: 
 receive signal information derived from SATPS signals received from at least three satellites at three or more reference stations;    receive ephemeris information for each of the satellites;    for each satellite, estimate from the signal information and from the ephemeris information a satellite location error vector;    for each satellite, determine a component of range error due to satellite location error at a selected location; and    make available the component of range error for each satellite to compensate for satellite location error when computing location of a mobile station from SATPS signals received at the mobile station.    
   
   
       21 . The apparatus of  claim 20 , further comprising a network central processor to collect the signal information from the reference stations and to provide the signal information to the VRS computer in a network format.  
   
   
       22 . The apparatus of  claim 20 , further comprising a transmitter responsive to the VRS computer to transmit the component of range error for each satellite for use by a mobile station.  
   
   
       23 . The apparatus of  claim 20 , wherein the VRS computer is operative to determine a component of range error for each satellite by: determining a calculated range from the selected location to the satellites; and combining the calculated range with the satellite location error vector.  
   
   
       24 . The apparatus of  claim 20 , wherein the VRS computer is operative to estimate a satellite location error vector for each of the satellites by: determining from the SATPS signals a measured location of each satellite; determining from satellite ephemeris information a calculated location of each satellite; and, for each satellite, comparing the measured location with the calculated location to determine the satellite location vector.  
   
   
       25 . The apparatus of  claim 23 , wherein the VRS computer is operative to estimate a satellite location error vector for each satellites by: determining from the SATPS signals a measured location of each satellite; determining from satellite ephemeris information a calculated location of each satellite; and, for each satellite, comparing the measured location with the calculated location to determine the satellite location vector.  
   
   
       26 . The apparatus of  claim 22 , further comprising a mobile station operative to receive SATPS signals from the satellites, to receive the component of range error for each satellite, and to apply the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of location of the mobile station.  
   
   
       27 . The apparatus of  claim 24 , further comprising a mobile station operative to receive SATPS signals from the satellites, to receive the component of range error for each satellite, and to apply the component of range error for each satellite to compute from the SATPS signals received at the mobile station location a compensated estimate of location of the mobile station.  
   
   
       28 . The apparatus of  claim 20 , wherein the VRS computer makes the component of range error available with an issue of data ephemeris label.  
   
   
       29 . The apparatus of  claim 20 , wherein the VRS computer is further operative to calculate for the selected location an azimuth angle and an elevation angle for each satellite, and to make the azimuth angle and the elevation angle for each satellite available to compensate at the mobile station location for at least one of ionospheric delay correction and tropospheric delay correction.  
   
   
       30 . The apparatus of  claim 20 , wherein the VRS computer is operative to determine for each satellite the pseudorange correction at the selected location by combining the component of range error for the satellite with an estimated clock error for the satellite and with a tropospheric delay correction and with an ionospheric delay correction.  
   
   
       31 . The apparatus of  claim 26 , wherein the selected location corresponds approximately to the mobile station location.  
   
   
       32 . The apparatus of  claim 20 , wherein the VRS computer comprises a Kalman filter operative to determine for each satellite a component of range error at the selected location, the Kalman filter having states for satellite clock error and for components of a satellite location error vector for each satellite.  
   
   
       33 . The apparatus of  claim 20 , wherein the VRS computer is operative to make available the component of range error for each satellite by synthesizing a virtual-reference-station correction message which simulates a correction message that would be produced by a real reference station receiving SATPS signals at the selected location.  
   
   
       34 . The apparatus of  claim 20 , wherein the signal information is derived from carrier phase measurements of SATPS signals received at the reference stations, and wherein the VRS computer is further operative to estimate from the signal information a satellite velocity error for each satellite.  
   
   
       35 . The apparatus of  claim 33 , wherein the signal information is derived from carrier phase measurements of SATPS signals received at the reference stations, and wherein the VRS computer is further operative to estimate from the signal information a satellite velocity error for each satellite.  
   
   
       36 . The apparatus of  claim 20 , wherein the signal information is derived from SATPS signals obtained at an observation time during which at least one satellite is visible from at least three reference stations.