Recovery from position and time outliers in positioning

Abstract

A mobile device may use one or more outlier detectors to detect likelihoods that an outlier condition exists for a satellite positioning system (SPS) position fix. In some implementations, a method may comprise checking a position fix of a SPS receiver for consistency with assistance data used to generate a position fix. The method may further comprise determining whether to generate a new position fix using less than all of the assistance data based, at least in part, on results of the checking of the position fix.

What is claimed is: 
     
         1 . A machine implemented method comprising:
 checking a position fix of a satellite positioning system (SPS) receiver for consistency with assistance data used to generate said position fix; and   determining whether to generate a new position fix using less than all of said assistance data based, at least in part, on results of said checking said position fix.   
     
     
         2 . The method of  claim 1 , further comprising:
 computing a reliability of said position fix,   wherein said determining whether to generate said new position fix is based, at least in part, on said reliability of said position fix and said results of said checking said position fix.   
     
     
         3 . The method of  claim 1 , wherein said checking said position fix comprises:
 comparing said position fix to a first element of said assistance data to generate a first outlier likelihood; and   comparing said position fix to a second element of said assistance data to generate a second outlier likelihood,   wherein said determining whether to generate said new position fix is based, at least in part, on said first and second outlier likelihoods.   
     
     
         4 . The method of  claim 1 , further comprising:
 instructing an SPS receiver to re-acquire satellites using less than all of said assistance data if a determination is made to generate said new position fix.   
     
     
         5 . The method of  claim 1 , wherein:
 said less than all of said assistance data includes a predefined subgroup of elements of said assistance data.   
     
     
         6 . The method of  claim 1 , wherein:
 said less than all of said assistance data includes no assistance data.   
     
     
         7 . The method of  claim 1 , wherein:
 said less than all of said assistance data is selected based, at least in part, on said results of said checking said position fix.   
     
     
         8 . The method of  claim 1 , wherein:
 said assistance data includes one or more of the following: an estimate of current location, an estimate of SPS time, almanac data, and ephemeris data.   
     
     
         9 . An apparatus comprising:
 a satellite positioning system (SPS) receiver to: acquire positioning satellites using assistance data, compute a position fix using SPS signals received from acquired satellites, and calculate a reliability of said position fix;   a plurality of outlier detectors to compare said position fix to elements of said assistance data to generate outlier likelihood information; and   a recovery manager to determine whether to instruct said SPS receiver to compute a new position fix using less than all of said assistance data based, at least in part, on said reliability of said position fix and said outlier likelihood information.   
     
     
         10 . The apparatus of  claim 9 , wherein:
 said plurality of outlier detectors includes a first outlier detector to compare said position fix to a rough position estimate of said assistance data to generate a first outlier likelihood indication.   
     
     
         11 . The apparatus of  claim 9 , wherein:
 said plurality of outlier detectors includes a second outlier detector to compare said position fix to an estimated SPS time of said assistance data to generate a second outlier likelihood indication.   
     
     
         12 . The apparatus of  claim 9 , wherein:
 said plurality of outlier detectors includes a first outlier detector having a variable threshold that is capable of being adjusted over time to improve performance of said apparatus.   
     
     
         13 . The apparatus of  claim 9 , wherein:
 said less than all of said assistance data includes a predefined subgroup of elements of said assistance data.   
     
     
         14 . The apparatus of  claim 9 , wherein:
 said less than all of said assistance data includes no assistance data.   
     
     
         15 . The apparatus of  claim 9 , wherein:
 said less than all of said assistance data is selected based, at least in part, on said outlier likelihood information.   
     
     
         16 . An apparatus comprising:
 a digital storage medium having instructions stored thereon executable by a computing system to:   check a position fix of a satellite positioning system (SPS) receiver for consistency with assistance data used to generate said position fix; and   determine whether to generate a new position fix using less than all of said assistance data based, at least in part, on results of said check of said position fix.   
     
     
         17 . The apparatus of  claim 16 , wherein said digital storage medium further includes instructions to:
 compute a reliability of said position fix, wherein said determination of whether to generate said new position fix is based, at least in part, on said reliability of said position fix and said results of said check of said position fix.   
     
     
         18 . The apparatus of  claim 16 , wherein said instructions to check said position fix include instructions to:
 compare said position fix to a first element of said assistance data to generate a first outlier likelihood; and   compare said position fix to a second element of said assistance data to generate a second outlier likelihood,   wherein said determination of whether to generate a new position fix is based, at least in part, on said first and second outlier likelihoods.   
     
     
         19 . An apparatus comprising:
 means for acquiring satellites of a satellite positioning system (SPS) using assistance data;   means for computing a position fix using signals received from satellites acquired by said means for acquiring satellites;   means for generating a reliability of said position fix;   means for generating outlier likelihoods by comparing said position fix to elements of said assistance data; and   means for determining whether to initiate a recovery procedure to compute a new position fix based, at least in part, on said outlier likelihoods.   
     
     
         20 . The apparatus of  claim 19 , wherein:
 said means for determining includes means for determining whether to initiate said recovery procedure based, at least in part, on said reliability and said outlier likelihoods.   
     
     
         21 . The apparatus of  claim 19 , wherein:
 said means for determining whether to initiate a recovery procedure instructs said means for acquiring satellites to re-acquire satellites using less than all of said assistance data if a determination is made to initiate a recovery procedure.   
     
     
         22 . The apparatus of  claim 21 , wherein:
 said less than all of said assistance data includes a specific subset of said assistance data.   
     
     
         23 . The apparatus of  claim 21 , wherein:
 said means for determining includes means for selecting said less than all of said assistance data based, at least in part, on said outlier likelihoods.   
     
     
         24 . The apparatus of  claim 21 , wherein:
 said less than all of said assistance data includes no assistance data.   
     
     
         25 . The apparatus of  claim 21 , wherein:
 said means for generating outlier likelihoods includes means for modifying thresholds used to compare said position fix to elements of said assistance data over time.