System and method for satellite positioning

Abstract

A method and system for determining a receiver position comprising receiving satellite observations from a set of satellites, determining differenced observations based on the satellite observations, determining an all-in-view position of the receiver based on the differenced observations, determining a set of fault modes each associated with a subset of the differenced observations, for a fault mode of the set of fault modes, determining a fault-tolerant position of the receiver using the subset of differenced observations associated with the fault mode, when the all-in-view position and the fault tolerant position of the receiver for each fault mode are within a solution separation threshold, calculating a protection level associated with the all-in-view position of the receiver.

We claim: 
     
         1 . A method for determining a receiver position comprising:
 receiving a set of satellite carrier phase observations from a set of satellites;   receiving a set of reference observations from a set of reference stations;   determining double-differenced observations based on the set of satellite carrier phase observations and the set of reference observations;   determining an all-in-view position of the receiver based on the double-differenced observations;   determining a fault-tolerant position of the receiver by processing a subset of the double-differenced observations, wherein the subset of the double-differenced excludes at least one double-differenced observation from the double-differenced observations; and   comparing the all-in-view position and the fault-tolerant position of the receiver;   when the all-in-position and the fault tolerant position of the receiver for each fault mode are within a solution separation threshold, determining a protection level associated with the all-in-view position of the receiver.   
     
     
         2 . The method of  claim 1 , wherein the set of satellites comprises at least one satellite associated with a first satellite constellation and at least one satellite associated with a second satellite constellation. 
     
     
         3 . The method of  claim 1 , wherein each fault mode of the set of fault modes is associated with at least one potentially faulty satellite from the set of satellites, wherein each fault mode is associated with a subset of the differenced observations with the potentially faulty satellites excluded. 
     
     
         4 . The method of  claim 1 , wherein the solution separation threshold depends on a covariance of the all-in-view receiver position. 
     
     
         5 . The method of  claim 4 , further comprising, for each fault mode, determining an integrity risk based on the covariance. 
     
     
         6 . The method of  claim 1 , wherein when the all-in-view position and the fault tolerant position of the receiver for a fault mode of the set of fault modes differ by more than the solution separation threshold, determining a second set of differenced satellite observations that excludes observations associated with the fault mode. 
     
     
         7 . The method of  claim 6 , further comprising: when the potentially faulty satellites associated with the fault comprises a reference satellite, determining the second set of differenced observations using a second reference satellite. 
     
     
         8 . A method comprising:
 at a GNSS receiver, receiving satellite observations from a set of satellites;   determining differenced observations based on the satellite observations;   determining an all-in-view position of the receiver based on the differenced observations;   for each fault mode of a set of fault modes, determining a fault-tolerant position of the receiver using a subset of differenced observations associated with the respective fault mode; and   when the all-in-view position and a fault tolerant position of the receiver for a fault mode of the set of fault modes differ by more than a solution separation threshold, detecting that a fault has occurred with a probability greater than a threshold probability.   
     
     
         9 . The method of  claim 8 , wherein each fault mode is associated with a distinct subset of the differenced observations. 
     
     
         10 . The method of  claim 9 , wherein each fault mode is associated with one or more test satellites, wherein the distinct subset of the differenced observations associated with a respective fault mode excludes differenced observations associated with the one or more test satellites. 
     
     
         11 . method of  claim 8 , further comprising when the all-in-view position and the fault tolerant positions of the receiver for each fault mode differ by at most the solution separation threshold, calculating a protection level associated with the all-in-view position of the receiver. 
     
     
         12 . The method of  claim 11 , wherein the protection level is determined based on off-diagonal covariance terms of the all-in-view position. 
     
     
         13 . The method of  Claim 11 , further comprising performing a chi-squared test on the all-in-view position and the fault tolerant positions, wherein when the chi-squared test fails, the protection level is invalid. 
     
     
         14 . The method of  claim 8 , further comprising receiving a set of reference station observations, wherein the differenced observations comprise double-differenced observations. 
     
     
         15 . The method of  claim 8 , further comprising:
 determining a second set of differenced satellite observations that excludes observations associated with the potentially faulty satellites associated with the fault mode,   determining a second all-in-view receiver position using the second set of differenced satellite observations;   for each fault mode of a second set of fault modes, determining a second fault-tolerant position of the receiver using a subset of the second set of differenced observations associated with the respective fault mode; and   determining whether a fault is probable within the second set of differenced satellite observations.   
     
     
         16 . The method of  claim 15 , wherein the second set of fault modes is independent of the set of fault modes. 
     
     
         17 . The method of  claim 8 , wherein each fault mode is associated with at most a maximum number of potentially faulty satellites based on a probability that the maximum number of potentially faulty satellites have contemporaneous faults. 
     
     
         18 . The method of  claim 8 , wherein determining the all-in-view receiver position comprises resolving carrier phase ambiguities of the satellite observations. 
     
     
         19 . The method of  claim 18 , wherein resolving carrier phase ambiguities comprises:
 determining a set of float phase ambiguities associated with the differenced observations;   determining a set of integer phase ambiguity hypotheses using an integer search algorithm; and   selecting an integer phase ambiguity of the set of integer phase ambiguity hypotheses based on results of a hypothesis test comparing integer phase ambiguities of the set of integer phase ambiguity hypotheses.   
     
     
         20 . The method of  claim 8 , wherein the all-in-view receiver position is determined using a snapshot least-squares calculation.