Method and system for selecting optimal satellites for a-gps location of handsets in wireless networks

Abstract

A system and method for determining a set of satellites for which assistance data may be provided to a wireless device. A boundary for an approximate area in which the wireless device is located may be determined and one or more sets of satellites may be determined as a function of the boundary. An optimum set of satellites from the one or more sets of satellites may then be determined using a satellite selection function on the one or more sets of satellites at predetermined points substantially on the boundary.

What is claimed is: 
     
         1 . A method comprising:
 determining a first number of satellites that are searchable by the wireless device;   determining a second number of satellites visible from a boundary of an approximate area containing the wireless device;   determining a third number of satellites to be removed from a set of satellites searched for by the wireless device;   determining a plurality of sets of satellites as a function of the first, second and third numbers; and   selecting an optimum set of satellites of the plurality of sets of satellites as a function of the visibility of each of the plurality of sets of satellites at predetermined points substantially on the boundary.   
     
     
         2 . The method of  claim 1 , wherein the optimum set of satellites has a maximum number of satellites in view from each of the one or more predetermined points. 
     
     
         3 . The method of  claim 1 , wherein the optimum set of satellites is selected as a function of the relationship:
     f   satsViewBased =Σ i=1   noPo int s noSatsInView i   ≧Z ×noSatsInView i : 0);
   wherein noSatsIn View i  represents a fourth number of satellites visible for each point selected substantially on the boundary of the approximate area; and   Z represents a minimum number of satellites visible from the approximate area.   
     
     
         4 . The method of  claim 1 , wherein the boundary defines an area selected one of a city, municipality, county, state, country, continent, a serving area of a base station serving the wireless device and an approximate area of a communications network. 
     
     
         5 . The method of  claim 1 , wherein the satellites are part of a Global Navigation Satellite System (“GNSS”). 
     
     
         6 . The method of  claim 1 , wherein the wireless device is a cellular phone. 
     
     
         7 . The method of  claim 1 , further comprising determining the location of the wireless device based on a signal received from each satellite in the optimum set of satellites. 
     
     
         8 . A wireless device comprising a computing device, the wireless device being configured to:
 determine a boundary for an approximate area in which a wireless device is located;   determine an optimum set of satellites from a plurality of sets of satellites based on a satellite selection function at predetermined points substantially on the boundary; and   determine the location of the wireless device based on signals received from the optimum set of satellites.   
     
     
         9 . The wireless devices of  claim 8 , wherein the wireless device is further configured to:
 determine a first number of satellites searchable by the wireless device;   determine a second number of satellites visible from the approximate area;   determine a third number of satellites to be removed from the plurality of sets of satellites; and   determine the plurality of sets of satellites as a function of the first, second and third numbers.   
     
     
         10 . The wireless device of  claim 9 , wherein the optimum set of satellites has a maximum number of satellites in view from each of the one or more predetermined points. 
     
     
         11 . The wireless device of  claim 10 , wherein the optimum set of satellites is determined as a function of the relationship:
     f   satsViewBased =Σ i=1   noPo int s noSatsInView i   ≧Z ×noSatsInView i : 0);
   wherein:   noSatsInView i  represents a fourth number of satellites visible for each point (i) selected substantially on the boundary of the approximate area; and   Z represents a minimum number of satellites visible from the approximate area.   
     
     
         12 . The wireless device of  claim 9 , wherein the optimum set of satellites has a minimum dilution of precision (DOP) for satellites in view from each of the one or more predetermined points. 
     
     
         13 . The wireless device of  claim 12 , wherein the optimum set of satellites is determined as a function of the relationship:
     f   DOPBased =Σ i=1   noPo int s DOP i   o;  
   wherein DOP i  is the DOP for satellites in view at each point (i) selected substantially on the boundary of the approximate area.   
     
     
         14 . A non-transitory machine readable medium comprising a location information system, the location information system being configured to:
 determine a boundary for an approximate area in which a wireless device is located;   determine an optimum set of satellites from one or more sets of satellites visible within the boundary based on a satellite selection function at predetermined points substantially on the boundary; and   transmit assistance data that includes the optimum set of satellites to a global positioning system (GPS) receiver operating on the wireless device.   
     
     
         15 . The medium of  claim 14 , wherein the satellite selection function is defined as:
     f   satsViewBased =Σ i=1   noPo int s noSatsInView i   ≧Z ×noSatsInView i : 0);
   wherein:   noSatsInView i  represents a number of satellites visible from each point (i) selected substantially on the boundary of the approximate area; and   Z represents a minimum number of satellites visible from the approximate area.   
     
     
         16 . The medium of  claim 14 , wherein the boundary defines an area selected from one of a city, municipality, county, state, country, continent, a serving area of a base station serving the wireless device and an approximate area of a communications network. 
     
     
         17 . The medium of  claim 14 , wherein the satellites are part of a Global Navigation Satellite System (“GNSS”). 
     
     
         18 . The medium of  claim 14 , wherein the wireless device is a cellular phone. 
     
     
         19 . The medium of  claim 14 , wherein the optimum set of satellites has a minimum dilution of precision (DOP) for satellites in view from each of the one or more predetermined points. 
     
     
         20 . The medium of  claim 19 , the wherein the satellite selection function is defined as:
     f   DOPBased =Σ i=1   noPo int s DOP i   o;  
   wherein DOP i  is the DOP for satellites in view at each point (i) selected substantially on the boundary of the approximate area.