Gps receiver raim with slaved precision clock

Abstract

A method and a system for providing a substituted timing signal for a missing satellite ephemeris in execution of a RAIM algorithm includes deriving a plurality of position, velocity, and time solutions from a GPS navigation system. The position, velocity and time solutions are derived from a plurality of satellite ephemerides. An atomic clock provides an atomic clock signal. The atomic clock signal is compared to the derived time solutions to arrive at a correction factor. The atomic clock signal is adjusted according to the correction factor to develop an adjusted atomic clock signal. The adjusted atomic clock signal is substituted for a missing satellite ephemeris to execute the RAIM algorithm.

1 . A method for providing a timing signal to the execution of a GPS RAIM algorithm to eliminate the time unknown of the GPS solution and thus reducing the number of required satellite measurement sets by one, the method comprising:
 deriving position, velocity, and time solutions from a GPS navigation system derived from a plurality of satellite ephemerides and measurements;   receiving an atomic clock signal from one or more atomic clocks located in the navigation system;   comparing the atomic clock signal to the derived time solutions to derive a correction factor;   adjusting the atomic clock signal according to the correction factor to develop an adjusted atomic clock signal; and   using the adjusted atomic clock signal to remove the clock unknown of the GPS RAIM solution and thus reducing the number of required satellite measurement sets by one.   
     
     
         2 . The method of  claim 1 , wherein the navigation system is an inertial GPS system. 
     
     
         3 . The method of  claim 1 , wherein the atomic clock is a chip scale atomic clock. 
     
     
         4 . A GPS navigation system including a RAIM processor, the GPS navigation system comprising:
 a GPS receiver for receiving satellite ephemerides from a plurality of GPS satellites, the receiver configured to derive position, velocity, and time solutions along with range measurements from all tracked satellites;   an atomic clock producing a clock signal;   a clock follower to compare time solutions from the GPS receiver to the clock signals of the navigation system and deriving a correction factor to synthesize a corrected clock signal; and   a RAIM algorithm processor to receive the satellite measurements and the time solutions from the GPS receiver and the corrected clock signal to test the integrity of each of the satellite ephemeris in the satellite ephemerides.   
     
     
         5 . The system of  claim 4 , wherein the navigation system includes an inertial measurement unit. 
     
     
         6 . The system of  claim 4 , wherein the ephemerides include at least one military GPS satellite ephemeris. 
     
     
         7 . The system of  claim 4 , wherein the atomic clock is a chip scale atomic clock. 
     
     
         8 . An apparatus for providing a timing signal to reduce the number of required satellite measurements by one in execution of a RAIM algorithm, the method comprising:
 a GPS receiver for deriving position, velocity, and time solutions from a GPS navigation system along with range measurements from each satellite tracked;   an atomic clock for generating an atomic clock signal;   a clock follower for:
 receiving an atomic clock signal; 
 comparing the atomic clock signal to the time signal of the navigation system to derive a correction factor; 
 adjusting the atomic clock signal according to the correction factor to develop an adjusted atomic clock signal; and 
 a processor for executing the RAIM algorithm based upon the adjusted atomic clock signal to eliminate the time unknown of the GPS solution and this reduce the number of required satellites by one. 
   
     
     
         9 . The system of  claim 8 , wherein the navigation system is an inertial GPS system. 
     
     
         10 . The system of  claim 8 , wherein the atomic clock is a chip scale atomic clock.