PATENT DOCUMENT

Publication Number: US-8626187-B2
Application Number: US-201113152972-A
Country: US
Kind Code: B2

Title: Monitoring geofence exit

Abstract:
Methods, program products, and systems for monitoring geofence exits using wireless access points are disclosed. In general, in one aspect, a mobile device can detect one or more entry gateways that are wireless access points selected for monitoring a geofence. The mobile device can determine that the mobile device is located in the geofence based on the detection. The mobile device can monitor the entry gateways and one or more exit gateways, which can be wireless access points observable by the mobile device when the mobile device is in the geofence. When the mobile device determines, after a number of scans using a wireless processor, that the entry gateways and exit gateways are unobservable, the mobile device can use an application processor to determine whether the mobile device has exited from the geofence.

Claims:
What is claimed is: 
     
       1. A method performed by a mobile device, comprising:
 determining that the mobile device is inside of a first geofence defined by a plurality of first wireless access points and a second geofence defined by a plurality of second wireless access points, including determining that the mobile device has detected a signal from at least one of the first wireless access points and at least one of the second wireless access points; 
 creating a temporary geofence, including designating a current location of the mobile device as a fence location of the temporary geofence, the temporary geofence intersecting both the first geofence and the second geofence; 
 identifying one or more common gateways for monitoring the temporary geofence, the common gateways including one or more wireless access points observable by the mobile device when the mobile device is located in both of the first geofence and the second geofence; 
 designating at least one of the identified common gateways as an exit gateway for monitoring an exit from the temporary geofence; 
 detecting an exit of the mobile device from the temporary geofence, including determining that, for at least a threshold number of scans, the exit gateway is unobservable by the mobile device; and 
 upon detecting the exit from the temporary geofence, determining that the mobile device exited the first geofence or the second geofence. 
 
     
     
       2. The method of  claim 1 , wherein determining that the mobile device is inside of the first geofence and second geofence comprises:
 detecting the signal by a wireless processor of the mobile device. 
 
     
     
       3. The method of  claim 2 , wherein detecting the exit of the mobile device from the first geofence or the second geofence comprises:
 determining that the exit gateway is unobservable by the wireless processor; and then 
 determining that the mobile device exited the first geofence or second geofence using an application processor of the mobile device. 
 
     
     
       4. The method of  claim 1 , wherein the temporary geofence has a pre-specified radius. 
     
     
       5. The method of  claim 1 , wherein the second geofence intersects the first geofence. 
     
     
       6. The method of  claim 1 , wherein the exit gateway is a wireless access point not previously selected for monitoring a geofence but is observable by the mobile device when the mobile device is located at the fence location of the temporary geofence. 
     
     
       7. The method of  claim 6 , wherein determining that the mobile device exited the first geofence or the second geofence comprises:
 determining a new location of the mobile device; and 
 determining that the mobile device exited the first geofence or the second geofence based on a comparison between the new location and a location of the first geofence or a location of the second geofence. 
 
     
     
       8. The method of  claim 7 , wherein detecting that the mobile device exited the first geofence or the second geofence comprises:
 determining, based on the comparison, that the mobile device is still located in both the first geofence and the second geofence; 
 creating a second temporary geofence; and 
 determining that the mobile device exited the first geofence or the second geofence when the mobile device exits the second temporary geofence. 
 
     
     
       9. A non-transitory storage device storing computer program product configured to cause a mobile device to perform operations comprising:
 determining that the mobile device is inside of a first geofence defined by a plurality of first wireless access points and a second geofence defined by a plurality of second wireless access points, including determining that the mobile device has detected a signal from at least one of the first wireless access points and at least one of the second wireless access points; 
 creating a temporary geofence, including designating a current location of the mobile device as a fence location of the temporary geofence, the temporary geofence intersecting both the first geofence and the second geofence; 
 identifying one or more common gateways for monitoring the temporary geofence, the common gateways including one or more wireless access points observable by the mobile device when the mobile device is located in both of the first geofence and the second geofence; 
 designating at least one of the identified common gateways as an exit gateway for monitoring an exit from the temporary geofence; 
 detecting an exit of the mobile device from the temporary geofence, including
 determining that, for at least a threshold number of scans, the exit gateway is unobservable by the mobile device; and 
 
 upon detecting the exit from the temporary geofence, determining that the mobile device exited the first geofence or the second geofence. 
 
     
     
       10. The non-transitory storage device of  claim 9 , wherein determining that the mobile device is inside of the first geofence and second geofence comprises:
 detecting the signal by a wireless processor of the mobile device. 
 
     
     
       11. The non-transitory storage device of  claim 10 , wherein detecting the exit of the mobile device from the first geofence or the second geofence comprises:
 determining that the exit gateway is unobservable by the wireless processor; and then 
 determining that the mobile device exited the first geofence or second geofence using an application processor of the mobile device. 
 
     
     
       12. The non-transitory storage device of  claim 9 , wherein the temporary geofence has a pre-specified radius. 
     
     
       13. The non-transitory storage device of  claim 9 , wherein the second geofence intersects the first geofence. 
     
     
       14. The non-transitory storage device of  claim 9 , wherein the exit gateway is a wireless access point not previously selected for monitoring a geofence but is observable by the mobile device when the mobile device is located at the fence location of the temporary geofence. 
     
     
       15. The non-transitory storage device of  claim 14 , wherein determining that the mobile device exited the first geofence or the second geofence comprises:
 determining a new location of the mobile device; and 
 determining that the mobile device is in the first geofence or the second geofence based on a comparison between the new location and a location of the first geofence or a location of the second geofence. 
 
     
     
       16. The non-transitory storage device of  claim 15 , wherein detecting that the mobile device exited the first geofence or the second geofence comprises:
 determining, based on the comparison, that the mobile device is still located in both the first geofence and the second geofence; 
 creating a second temporary geofence; and 
 determining that the mobile device exited the first geofence or the second geofence when the mobile device exits the second temporary geofence. 
 
     
     
       17. A system, comprising:
 a mobile device; and 
 a non-transitory storage device storing computer program product configured to cause the mobile device to perform operations comprising:
 determining that the mobile device is inside of a geofence defined by a plurality of first wireless access points and a second geofence defined by a plurality of second wireless access points, including determining that the mobile device has detected a signal from at least one of the first wireless access points and at least one of the second wireless access points; 
 creating a temporary geofence, including designating a current location of the mobile device as a fence location of the temporary geofence, the temporary geofence intersecting both the first geofence and the second geofence; 
 identifying one or more common gateways for monitoring the temporary geofence, the common gateways including one or more wireless access points observable by the mobile device when the mobile device is located in both of the first geofence and the second geofence; 
 designating at least one of the identified common gateways as an exit gateway for monitoring an exit from the temporary geofence; and 
 detecting an exit of the mobile device from the temporary geofence, including: 
 determining that, for at least a threshold number of scans, the exit gateway is unobservable by the mobile device; and 
 upon detecting the exit from the temporary geofence, determining that the mobile device exited the first geofence or the second geofence. 
 
 
     
     
       18. The system of  claim 17 , wherein determining that the mobile device is inside of the first geofence and second geofence comprises:
 detecting the signal by a wireless processor of the mobile device. 
 
     
     
       19. The system of  claim 18 , wherein detecting the exit of the mobile device from the first geofence or the second geofence comprises:
 determining that the exit gateway is unobservable by the wireless processor; and then 
 determining that the mobile device exited the first geofence or second geofence using an application processor of the mobile device. 
 
     
     
       20. The system of  claim 17 , wherein the temporary geofence has a pre-specified radius. 
     
     
       21. The system of  claim 17 , wherein the second geofence intersects the first geofence. 
     
     
       22. The system of  claim 17 , wherein the exit gateway is a wireless access point not previously selected for monitoring a geofence but is observable by the mobile device when the mobile device is located at the fence location of the temporary geofence. 
     
     
       23. The system of  claim 22 , wherein determining that the mobile device exited the first geofence or the second geofence comprises:
 determining a new location of the mobile device; and 
 determining that the mobile device exited the first geofence or the second geofence based on a comparison between the new location and a location of the first geofence or a location of the second geofence. 
 
     
     
       24. The system of  claim 23 , wherein detecting that the mobile device exited the first geofence or the second geofence comprises:
 determining, based on the comparison, that the mobile device is still located in both the first geofence and the second geofence; 
 creating a second temporary geofence; and 
 determining that the mobile device exited the first geofence or the second geofence when the mobile device exits the second temporary geofence.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to location-based processing on a mobile device. 
     BACKGROUND 
     A modern mobile device can incorporate functions of a computer, a cellular transceiver, and a wireless (e.g., WiFi™) transceiver. For example, the mobile device can perform traditional computer functions, such as executing application programs, storing various data, and displaying digital images. These functions can be performed in an application subsystem of the mobile device. The application subsystem can include an application processor, an application operating system, and various input/output devices. Using the cellular transceiver, the mobile device can function as a cellular phone. Using the wireless transceiver, the mobile device can access a communications network through one or more wireless access points (WAPs). 
     Some of the functions performed by a mobile device can be functions based on a geofence. A geofence can include a virtual boundary of a real-world geographic area. The mobile device can be programmed to perform a task when the mobile device is located inside of a geofence. The mobile device can determine whether the mobile device is located inside of a geofence by comparing a location of the mobile device with coordinates of the geographic area. A conventional mobile device can determine the current location using cell tower triangulation or global positioning system (GPS) functions. The application processor of the mobile device can perform the triangulation or GPS calculations. 
     SUMMARY 
     Methods, program products, and systems for monitoring a geofence using wireless access points are disclosed. In general, in one aspect, a mobile device receives data defining the geofence. The mobile device can select, from multiple wireless access points, one or more wireless access points for monitoring the geofence. The selected wireless access points can be monitored by a wireless processor of the mobile device. The wireless processor can detect a potential entry of the geofence when at least one of the selected one or more wireless access points is detected. Upon a detection of the potential entry of the geofence by the wireless processor, the mobile device can wake an application processor of the mobile device to determine whether the mobile device is inside of the geofence. 
     In another aspect, a mobile device can detect one or more entry gateways that are wireless access points selected for monitoring a geofence. The mobile device can determine that the mobile device is located in the geofence based on the detection. The mobile device can monitor the entry gateways and one or more exit gateways, which can be wireless access points observable by the mobile device when the mobile device is in the geofence. When the mobile device determines, after a number of scans using a wireless processor, that the entry gateways and exit gateways are unobservable, the mobile device can use an application processor to determine whether the mobile device has exited from the geofence. 
     In another aspect, a mobile device can monitor multiple geofences simultaneously. The mobile device can create a temporary geofence based on a current location of the mobile device. The mobile device can designate one or more wireless access points observable from each of the multiple geofences as common gateways for monitoring the temporary geofence. When the mobile device determines, after a number of scans using a wireless processor, that the common gateways are unobservable, the mobile device can wake an application processor to determine whether the mobile device has exited from each of the multiple geofences. 
     In another aspect, a mobile device can receive data defining a geofence. The mobile device can select, from multiple wireless access points, one or more wireless access points for monitoring the geofence. The selected wireless access points can be monitored by a wireless processor of the mobile device. The wireless processor can detect a potential exit of the geofence when none of the selected one or more wireless access points is detected by the wireless processor for a threshold number of consecutive scans. Upon a detection of the potential exit of the geofence by the wireless processor, the mobile device can wake an application processor of the mobile device to determine whether the mobile device exited the geofence. 
     In another aspect, the mobile device can select, from multiple wireless access points, one or more wireless access points for monitoring a geofence. Selecting the one or more wireless access points can include determining multiple geographic regions corresponding to the geofence. The mobile device can select the one or more wireless access points based on a maximum total number of wireless access points to be selected and an access point allowance for each of the geographic regions. The access point allowance can indicate a maximum number of wireless access points to be selected for the geographic region. The mobile device can detect a potential entry or exit of the geofence by monitoring the selected one or more wireless access points using a wireless processor. Upon a detection of the potential entry or exit of the geofence by the wireless processor, the mobile device can wake an application processor of the mobile device to determine whether the mobile device is inside or outside of the geofence. 
     The techniques described in this specification can be implemented to achieve the following advantages. Battery power can be conserved. Geofence monitoring can require constant or frequent location identification. The location identification is conventionally performed by an application processor. A mobile device implementing the described technology can monitor a geofence using a wireless processor (e.g., a WiFi™ chip), which often consumes less power than the application processor. The application processor can be put to an inactive mode, and be awakened when a location of the mobile device relative to the geofence has changed. Thus, the constant or frequent location identification operations can be performed by a less power-hungry component most of the time. 
     A relative position between a mobile device and a geofence can be detected by monitoring wireless access points using a wireless processor with limited scanning capacity without sacrificing accuracy. A geofence can be associated with more wireless access points than the wireless processor can monitor. A mobile device can select, using techniques described in this specification, a number of statistically more important wireless access points for scanning. Thus, the mobile device can monitor the geofence under constraints of the capacity of the wireless processor, or monitor multiple geofences at the same time. 
     The details of one or more implementations of the subject matter of this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are diagrams illustrating exemplary techniques of monitoring a geofence. 
         FIG. 2  is a block diagram illustrating exemplary components of a system implementing techniques of monitoring a geofence using wireless access points. 
         FIGS. 3A and 3B  are diagrams illustrating exemplary error prevention techniques in monitoring a geofence. 
         FIGS. 4A-4D  are flowcharts illustrating exemplary operations of monitoring a geofence. 
         FIG. 5  is a diagram illustrating an exemplary user interface of a mobile device using a geofence-based service. 
         FIG. 6  is a flowchart illustrating an exemplary process of selecting wireless access points for monitoring a geofence. 
         FIG. 7  is a diagram illustrating exemplary techniques for selecting wireless access points for monitoring using a geographic grid. 
         FIGS. 8A and 8B  are diagrams illustrating exemplary wireless access point allowances used in identifying candidate wireless access points for selection. 
         FIGS. 9A and 9B  are diagrams illustrating exemplary stages of assigning wireless access point allowances to a geographic grid. 
         FIG. 9C  is a flowchart illustrating an exemplary process of identifying candidate wireless access points based on geographic regions. 
         FIG. 9D  is an exemplary histogram illustrating techniques of identifying candidate wireless access points based on channel optimization. 
         FIG. 10  is a diagram illustrating exemplary techniques for evaluating a set of candidate wireless access points. 
         FIG. 11  is a diagram illustrating exemplary techniques of selecting wireless access points for monitoring a geofence from sets of candidate wireless access points. 
         FIG. 12  is a diagram illustrating exemplary techniques of selecting wireless access points for multiple geofences from sets of candidate wireless access points. 
         FIG. 13A  is a flowchart illustrating exemplary operations for selecting wireless access points for monitoring multiple geofences. 
         FIG. 13B  illustrates an exemplary application of the operations of  FIG. 13A . 
         FIG. 14  is a block diagram illustrating exemplary components of a system implementing techniques of selecting wireless access points for monitoring a geofence. 
         FIG. 15  is a flowchart illustrating exemplary operations of wireless access point selection. 
         FIG. 16  is a block diagram illustrating an exemplary device architecture of a mobile device implementing the features and operations described in reference to  FIGS. 1-15 . 
         FIG. 17  is a block diagram of an exemplary network operating environment for the mobile devices of  FIGS. 1-16 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Exemplary Detection of a Geofence 
       FIGS. 1A and 1B  are diagrams illustrating exemplary techniques of detecting a geofence. Detecting a geofence can include detecting whether a mobile device is located inside or outside of a geofence.  FIG. 1A  is a diagram illustrating exemplary techniques of detecting an entry into a geofence by mobile device  100 . 
     Mobile device  100  can be an exemplary mobile device that implements the techniques of detecting a geofence. Mobile device  100  can include application subsystem  102  that includes an application processor, wireless communications subsystem  104  that includes a wireless processor, and a baseband subsystem that includes a baseband processor. 
     Mobile device  100  can be configured to detect a potential entry into geofence  110  using wireless communication subsystem  104 . Geofence  110  can include a fence location (e.g., a center of the fence) and a fence dimension (e.g., a radius when the fence is a circle). The fence location can include latitude and longitude coordinates. Geofence  110  can be associated with an entity (e.g., a company, school, or home). 
     To detect the potential entry into geofence  110 , mobile device  100  can select one or more wireless access points for monitoring. The one or more wireless access points can be selected from wireless access points determined to be detectable from a mobile device when a mobile device is located in geofence  110 . The selected one or more wireless access points are represented in  FIG. 1A  and other figures as black triangles. The selected one or more wireless access points can include wireless access point  112 . Not all wireless access points that are detectable from a mobile device when a mobile device is located in geofence  110  need to be selected for monitoring geofence  110 . For example, wireless access point  114  can be such a wireless access point not selected by mobile device  100 . In  FIG. 1A  and other figures, the wireless access points that are (a) detectable from mobile device  100  when mobile device  100  is located in geofence  110  and (b) not selected by mobile device  100  for monitoring are represented as white triangles. The selection is facilitated by virtual geographic grid  116 . Virtual geographic grid  116  is a geographic area corresponding to geofence  110  that is created by mobile device  100  for determining which wireless access point to select. Further details of selecting wireless access points are described below in reference to  FIGS. 6-15 . 
     Mobile device  100  can monitor an entry into geofence  110  by scanning signals from the selected one or more wireless access points using wireless communications subsystem  104 . Wireless communications subsystem  104  can include a wireless processor and fence detection instructions  108 . Execution of fence detection instructions  108  can cause the wireless processor to scan one or more communication channels to detect signals from wireless access points and device identifiers of the wireless access points. The device identifier of a wireless access point can include, for example, a media access control (MAC) address of the wireless access point. If the scan detects a device identifier and the device identifier matches a device identifier of one of the selected wireless access points, a potential fence entry can be detected. Mobile device  100  can scan signals continuously or frequently without draining a battery, when wireless communications subsystem  104  consumes a small amount of power during each scan. 
     In this example, wireless communications subsystem  104  of mobile device  100  detects ( 111 ) a signal associated with a device identifier matching that of wireless access point  112 . Accordingly, wireless communications subsystem  104  detects a potential entry into geofence  110 . Upon the detection of the potential entry, wireless communications subsystem  104  can activate application subsystem  102 . Activating application subsystem  102  can include, for example, waking application subsystem  102  from a “sleep” state. Inactive application subsystem  102  is represented as an unshaded block in  FIG. 1A  and other figures. Activated application subsystem  102  is represented as a shaded block in  FIG. 1A  and other figures. 
     Application subsystem  102  can include an application processor and geofence instructions  106 . Application subsystem  102  can be configured to, upon being activated by wireless communications subsystem  104 , execute geofence instructions  106  to determine whether mobile device  100  entered into geofence  110 . Geofence instructions  106  can include location determination instructions and location comparison instructions. The location determination instructions can, upon execution, cause application subsystem  102  to determine a current location of mobile device  100  using various location-determining devices or programs. Determining a current location of mobile device  100  may or may not include operations by wireless communications subsystem  104 . The location comparison instructions can, upon execution, cause application subsystem  102  to compare ( 117 ) the current location with geofence  110 . 
     If application subsystem  102  determines that the current location is inside of geofence  110  (e.g., at location  118 ), application subsystem  102  can determine that mobile device  100  entered geofence  110 , and perform a task associated with the entry of geofence  110 . The task can include, for example, displaying or sounding an alarm, displaying an advertisement, or activating a security measure. 
     If application subsystem  102  determines that the current location is not in geofence  110 , application subsystem  102  can determine that mobile device  100  did not enter geofence  110 , and that the potential entry detected by wireless communications subsystem  104  may be an error. Application subsystem  102  can perform error prevention operations regarding wireless access point  112  (e.g., “blacklisting” wireless access point  112 ). Further details of the error correction operations are described below in reference to  FIGS. 3A and 3B . 
     After determining the current location of mobile device  100  and determining that an entry into geofence  110  did or did not occur, application subsystem  102  can stop monitoring the current location and allows the wireless communications subsystem to continue the scanning for determining a potential entry to another geofence, or for determining a potential exit from geofence  110 . Thus, application subsystem  102  can be deactivated (e.g., put to “sleep” mode) while the wireless subsystem continues monitoring geofence  110 . 
       FIG. 1B  is a diagram illustrating exemplary techniques of detecting an exit from a geofence. Mobile device  100  can be a device that has determined to be located in geofence  110  using the techniques described in reference to  FIG. 1A . Application subsystem  102  of mobile device  100  can be in a deactivated mode (e.g., a “sleep” mode). 
     Upon detecting that mobile device  100  entered geofence  110 , fence detection instructions  108  can cause a wireless processor of wireless communications subsystem  104  to scan wireless access points to detect a potential exit. The wireless processor can scan communication channels for signals from (a) the wireless access points selected based on grid  116 , and (b) wireless access points not selected but are detectable by mobile device  100  when mobile device  100  is in geofence  110  (e.g., wireless access point  114 ). When the wireless processor does not detect ( 113 ) a signal from any of wireless access points of (a) and (b) in N consecutive scans, wireless communications subsystem  104  can determine that a potential exit of geofence  110  has occurred. The number N can be a scan threshold. 
     Upon detecting the potential exit, wireless communications subsystem  104  can activate application subsystem  102 . Application subsystem  102  can then determine a current location of mobile device  100  (e.g., location  120 ) and compare ( 117 ) the current location with geofence  110 . If, based on the comparison, application subsystem  102  determines that the current location is outside of geofence  110 , application subsystem  102  can determine that mobile device  100  exited geofence  110 . Wireless communications subsystem  104  can then scan the wireless access points selected based on grid  116  and determine whether there is another potential entry into geofence  110 . In some implementations, mobile device  100  can monitor multiple wireless access points to monitor multiple geofences. 
       FIG. 1C  is a diagram illustrating exemplary techniques of detecting an exit from a geofence when multiple geofences are monitored. Mobile device  100  can be a device that has determined to be located in geofence  110  using the techniques described in reference to  FIGS. 1A and 1B . Application subsystem  102  of mobile device  100  can be in a deactivated mode (e.g., a “sleep” mode). 
     In addition to geofence  110 , mobile device  100  can be located in geofences  144  and  146 . Geofences  144  and  146  can be geofences that intersect geofence  110 . Each of geofences  110 ,  144 , and  146  can correspond to a set of wireless access points for monitoring the respective geofence. Mobile device  100  can move in such a way that mobile device enters and exits a geofence (e.g., geofence  110 ) while remaining in the other geofences (e.g., geofences  144  and  146 ). For example, mobile device  100  can move from location  148  (which is inside each of geofences  110 ,  144 , and  146 ) to location  150  (which is inside of geofences  144  and  146 , but outside of geofence  110 ). 
     Mobile device  100  can monitor geofences  110 ,  144 , and  146  by creating temporary geofence  152 . Mobile device  100  can create temporary geofence  152  based on a current location of mobile device  100  when mobile device  100  is located in multiple geofences. For example, when an application processor of mobile device  100  determines that mobile device  100  in geofence  110  and geofence  144 , mobile device  100  can create a first temporary geofence. When the application processor determines that mobile device  100  subsequently entered geofence  146  while still in geofences  110  and  144 , mobile device  100  can create temporary geofence  152 . Mobile device  100  can designate the current location (e.g., location  148 ) as a location of temporary geofence  152 . Mobile device  100  can designate a specified dimension (e.g., 100 meters) as a dimension (e.g., a radius) of temporary geofence  152 . 
     Mobile device  100  can designate one or more exit gateways for monitoring temporary geofence  152 . The exit gateways can be selected from wireless access points located within temporary geofence  152  or otherwise related to temporary geofence  152 . The exit gateways can be wireless access points observable from geofences  110 ,  142 , and  146  in which mobile device  100  is located. The exit gateways can include wireless access point  154 , which was previously selected by mobile device  100  to monitor at least one of geofences  110 ,  142 , or  146 . The exit gateways can include wireless access point  156 , which was not previously selected for monitoring a geofence but is observable by mobile device  100  when mobile device  100  is located at location  148 . 
     Upon creating temporary geofence  152  and designating the exit gateways (e.g., wireless access points  154  and  156 ), fence detection instructions  108  can cause a wireless processor of wireless communications subsystem  104  to scan the exit gateways to detect a potential exit. The wireless processor can scan ( 158  and  160 ) communication channels for signals from the exit gateways. When the wireless processor does not detect a signal from any of the exit gateways in N consecutive scans, wireless communications subsystem  104  can determine that a potential exit of temporary geofence  152  has occurred. The number N can be a scan threshold. 
     Upon detecting the potential exit from temporary geofence  152 , wireless communications subsystem  104  can activate application subsystem  102 . Application subsystem  102  can then determine new location  150  of mobile device  100  and compare new location  150  with each of the geofences  110 ,  144 , and  146 . If, based on the comparison, application subsystem  102  determines that new location  150  is outside of geofence  110 , but still in geofence  144  and  146 , application subsystem  102  can determine that mobile device  100  exited geofence  110 . Mobile device  100  can then create a new temporary geofence and associate a new set of exit gateways for monitoring the new temporary geofence, and thus monitoring exit of geofence  144  and  146 . Mobile device  100  can monitor wireless access gateways associated with geofence  110  for re-entry into geofence  110 . 
     Exemplary Fence Detection System 
       FIG. 2  is a block diagram illustrating exemplary components of a system implementing techniques of monitoring a geofence using wireless access points. The system can be implemented on mobile device  100  as described above in reference to  FIGS. 1A and 1B . 
     Mobile device  100  can include application subsystem  102 . Application subsystem  102  can include software and hardware components configured to perform operations of geofence detection. Application subsystem  102  can include geofence definition unit  202 . Geofence definition unit  202  is a component of application subsystem  102  configured to receive data defining a geofence. Geofence definition unit  202  can receive the data defining the geofence from a user interface (e.g., a touch-sensitive display screen), from a remote server, or from an application program executing on mobile device  100 . 
     The data received by geofence definition unit  202  can be processed by geofence processing unit  204 . Geofence processing unit  204  can be a component of application subsystem configured to perform operations relating to geofence detection. Geofence processing unit  204  can include geofence instructions  106  and geofence interface  206 . Geofence interface  206  can be a component of geofence processing unit  204  configured to interface between a system component (e.g., geofence definition unit  202 ) and geofence instructions  106 . 
     Geofence instructions  106  can include instructions that, upon execution, cause application processor  208  to perform various operations. The operations can include access point selection operations and location determination operations. When performing the access point selection operations, application processor  208  can select, based on the data defining the geofence received from geofence definition unit  202 , one or more wireless access points from data store  230 . Data store  230  is a component of application subsystem  102  configured to store a list of identifiers of wireless access points and related information. The data stored in data store  230  can be received from a remote server. 
     Geofence processing unit  204  can send the selected wireless access points to wireless communications subsystem  104  for monitoring. Wireless communications subsystem  104  can include interface  212  configured to send information to application subsystem  102  or receive information from application subsystem  102 . Wireless communications subsystem  104  can include data store  216 . Data store  216  is a component of wireless communications subsystem  104  configured to store a list of wireless access points received from application subsystem  102 . Wireless communications subsystem  104  can include wireless transceiver  220 . Fence detection instructions  108 , when executed, can cause wireless transceiver  220  to scan for wireless signals. 
     In addition to a list of the selected wireless access points, geofence processing unit  204  can send operation modes instructions to wireless communications subsystem  104 . The operation modes can include entry detection mode and exit detection mode. When wireless communications subsystem  104  operates under entry detection mode, if wireless transceiver  220  detects a signal from a wireless access point matching one of the wireless access points stored in data store  216 , wireless communications subsystem  104  can send an activation signal to application subsystem  102  for detecting an entry. When wireless communications subsystem  104  operates under exit detection mode, wireless communications subsystem  104  can count a number of consecutive scans in which wireless transceiver  220  does not detect any wireless access points that can match the wireless access points stored in data store  216 . Then, wireless communications subsystem  104  can send an activation signal to application subsystem  102  for detecting an exit. 
     Wireless communications subsystem  104  can monitor multiple geofences concurrently, including monitoring the wireless access points for each of the geofences. Wireless communications subsystem  104  can operate in an entry detection mode for one geofence, and in an exit detection mode for another geofence. Some or all components of wireless communications subsystem  104  can be implemented on a wireless processor (e.g., a WiFi™ chip). 
     Exemplary Error Prevention 
       FIGS. 3A and 3B  are diagrams illustrating error prevention in monitoring a geofence. False positives of potential geofence entry or exit can occur. A false positive occurs when a wireless processor detects a potential entry of a geofence, but the entry did not actually occur. Error prevention techniques can be utilized to prevent a future false positive based on a known false positive. 
       FIG. 3A  illustrates exemplary geofence  110  and an error tolerance zone  302 . Some of the potential entries of mobile device  100  into geofence  110  (as described above in reference to  FIGS. 1A-1C , and  2 ) can be detected when mobile device  100  did not enter into geofence  110 . To reduce the false positives, error tolerance zone  302  can be created. 
     Example geofence  110  is a circular geofence having a center and a radius. Wireless communications subsystem  104  of mobile device  100  can detect a signal from wireless access point  304  designated for monitoring geofence  110 . Then, application subsystem can determine that mobile device  100  is located at location  314 . If location  314  is outside error tolerance zone  302 , mobile device  100  can determine that wireless access point  304  is unreliable for monitoring geofence  110 . Accordingly, mobile device  100  can blacklist wireless access point  304 . In some implementations, blacklisting wireless access point  304  can include excluding wireless access point  304  from future monitoring. In some implementations, blacklisting wireless access point  304  can include reducing a probability that wireless access point  304  is selected for monitoring geofence  110 . For example, mobile device  100  can assign a score to wireless access point  304  that reduces a weight of wireless access point  304  in device selection operations. 
     Error tolerance zone  302  can be defined using an error tolerance value. The error tolerance value can include a threshold distance from an edge of geofence  110 . Thus, if the distance between location  314  and center of geofence  110  is greater than a sum of the radius of geofence  110  and the threshold distance, mobile device  100  can determine that wireless access point  304  is unreliable for monitoring geofence  110 . 
       FIG. 3B  illustrates exemplary geofence  318  and an error tolerance zone  320 . A geofence can have any shape and size. For example, geofence  318  can be an ellipse defined using a center and a width and a height, or a polygon defined using vertices of the polygon. Error tolerance zone  320  can be defined using a threshold distance from each edge of the ellipse or polygon. 
     Exemplary Fence Detection Processes 
       FIGS. 4A and 4B  are flowcharts illustrating exemplary operations of monitoring a geofence.  FIG. 4A  is a flowchart illustrating exemplary operations  400  of monitoring a geofence. The operations can be performed by mobile device  100  as described above in reference to the previous figures. 
     Mobile device  100  can receive ( 402 ) data defining a geofence. The data defining the geofence can include a fence location and a fence dimension. The fence location can include latitude, longitude, and altitude coordinates. The fence location can be a center point of the geofence. The fence dimension can be a radius. The data can be received from a user. 
     Mobile device  100  can identify ( 404 ) one or more wireless access points for monitoring the geofence. Identifying the one or more wireless access points can include selecting the one or more wireless access points from multiple geofences. The selection operations will be described in further details below in reference to  FIGS. 6-15 . 
     Mobile device  100  can determine ( 406 ) a tentative location of mobile device  100  relative to the geofence. A location of mobile device  100  relative to the geofence can include a location inside of the geofence or a location outside of the geofence. Mobile device  100  can use a wireless processor of the mobile device to determine the tentative location of the mobile device relative to the geofence. To determine the tentative location, mobile device  100  can monitor the one or more identified access points. Monitoring the access points can include scanning, on one or more channels, a signal from the one or more identified wireless access points. Detecting at least one of the one or more identified wireless access points can include receiving a signal associated with a media access control (MAC) address of a wireless access point, the MAC address of the wireless access point matching one of a list of MAC addresses associated with the one or more identified wireless access points. The wireless processor can include a wireless chip that consumes less power than the application processor. 
     Determining the tentative location of the mobile device relative to the geofence can include detecting a potential entry into the geofence, or detecting a potential exit from a geofence. In a potential entry case, determining the tentative location of the mobile device relative to the geofence can include detecting a potential entry of the geofence when at least one of the one or more identified wireless access points is detected by the wireless processor. In a potential exit case, determining the tentative location of the mobile device relative to the geofence can include detecting a potential exit from the geofence when, in a threshold number of consecutive scans, none of the one or more identified wireless access points and none of the wireless access points detectable in the geofence is detected. 
     Upon determining the tentative location of the mobile device relative to the geofence by the wireless processor, mobile device  100  can wake an application processor of mobile device  100 . Waking the application processor of mobile device  100  can include changing the application processor of mobile device  100  from an inactive state (e.g., power conserving state) to an active state. Mobile device  100  can use the application processor to determine ( 408 ) whether mobile device  100  is inside of the geofence. Determining whether mobile device  100  is inside of the geofence can include enabling the application processor of mobile device  100  to determine a current location of mobile device  100 , and determine whether the current location is located inside of the geofence. If the application processor of mobile device  100  determines, based on the current location, that an entry has occurred, mobile device  100  can proceed to determine a potential exit using the wireless processor. 
     If the application processor of mobile device  100  determines that mobile device  100  is located inside of the geofence, the application processor can perform a task related to the geofence. The application processor can set the operation mode of the wireless processor to an exit detection mode. If the wireless processor tentatively determined that mobile device  100  is located inside of the geofence, but the application processor of mobile device  100  determines that mobile device  100  is located outside of and at least a threshold away from the geofence, the application processor can perform error prevention operations. For example, after the wireless processor tentatively determined that mobile device  100  is located inside of the geofence, mobile device  100  can determine, using the application processor, that mobile device  100  is located at a distance away from the geofence. The application processor can determine that the distance exceeds an error threshold. Then, mobile device  100  can designate a detected wireless access point as an unreliable wireless access point, including excluding the wireless access point from future monitoring or decreasing an access point score associated with the wireless access point. 
     Upon an exit from a geofence, mobile device  100  can set the wireless processor to an entry detection mode. 
       FIG. 4B  is a flowchart illustrating exemplary operations  420  of monitoring a geofence exit. The operations can be performed by mobile device  100  as described above in reference to the previous figures. Mobile device  100  can determine ( 422 ), using an application processor of mobile device  100 , that mobile device  100  is inside of a geofence. 
     Mobile device  100  can monitor ( 424 ), using the wireless processor, a combined collection of wireless access points. The combined collection of wireless access points can include (a) one or more wireless access points identified in stage  404  as described in reference to  FIG. 4A , and (b) one or more currently visible wireless access points. Monitoring the combined collection of wireless access points can include scanning for signals from the combined collection of wireless access points using the wireless processor. 
     Mobile device  100  can determine ( 426 ), that for at least a threshold number of scans, none of the combined collection of wireless access points is observable. Then, mobile device  100  can wake the application processor of mobile device  100 . Mobile device  100  can determine ( 428 ) whether mobile device  100  exited from the geofence using the application processor. When the application processor of mobile device  100  that mobile device  100  exited from the geofence, mobile device  100  can perform a task associated with the exit from the geofence (e.g., displaying or sounding an alarm). 
       FIG. 4C  is a flowchart illustrating exemplary operations  440  of monitoring a geofence exit. The operations can be performed by mobile device  100  as described above in reference to the previous figures. Mobile device  100  can determine ( 442 ), using an application processor of mobile device  100 , that mobile device  100  is inside of a geofence. Determining that mobile device  100  is inside of the geofence can include monitoring, using a wireless processor of mobile device  100 , one or more entry gateways. The one or more entry gateways can be one or more wireless access points selected for monitoring an entry into the geofence. Determining that mobile device  100  is inside of the geofence can include waking the application processor and using the application processor to determine that the mobile device entered the geofence upon detecting, by the wireless processor, at least one of the one or more entry gateways. The application processor can determine a location of mobile device  100  using various location-determination devices or programs. 
     Mobile device  100  can designate ( 444 ) one or more exit gateways. The exit gateways can include one or more wireless access points observable when mobile device  100  is in the geofence. Mobile device  100  can use the exit gateways to monitor an exit from the geofence. 
     Mobile device  100  can detect ( 446 ) an exit from the geofence based at least in part on monitoring the exit gateways. Detecting the exit can include monitoring, using the wireless processor, a combined collection of wireless access points including the one or more entry gateways and the one or more exit gateways. Mobile device  100  can determine that, for at least a threshold number of scans by the wireless processor, none of the combined collection of wireless access points is observable by the wireless processor. Then, mobile device  100  can wake the application processor of the mobile device to determine whether the mobile device exited the geofence. 
       FIG. 4D  is a flowchart illustrating exemplary operations  450  of monitoring a geofence exit when a mobile device is in multiple geofences. The operations can be performed by mobile device  100  as described above in reference to the previous figures. 
     Mobile device  100  can determine that mobile device  100  is located in multiple geofences, for example, a first geofence and a second geofence. The first geofence can intersect the second geofence. Upon determining that mobile device  100  is located in both geofences, mobile device  100  can create ( 452 ) a temporary geofence around a current location of mobile device  100 . Creating the temporary geofence can include defining the temporary geofence using a fence location and a fence dimension. The fence location can be a current location of mobile device  100 . The current location can be determined by an application processor of mobile device  100 . The fence dimension can be a specified value (e.g., 100 meters). In some implementations, the fence dimension can be determined based on the sizes of the first geofence and second geofence. 
     Mobile device  100  can identify one or more common gateways for monitoring the temporary geofence. The common gateways can include one or more wireless access points that are observable by mobile device  100  when mobile device  100  is in the first geofence and the second geofence. 
     Mobile device  100  can monitor ( 454 ) an exit of the temporary geofence. Monitoring the exit of the temporary geofence can include scanning signals from the identified common gateways using a wireless processor. 
     Mobile device  100  can detect ( 456 ) whether the mobile device is inside of the first geofence and whether the mobile device is inside of the second geofence upon detecting the exit from the temporary geofence. Upon detecting the exit from the temporary geofence, mobile device  100  can wake an application processor of mobile device  100  to determine whether mobile device  100  exited from the first geofence or whether mobile device  100  exited from the second geofence. Detecting the exit from the temporary geofence can include determining, using the wireless processor of mobile device  100 , that the common gateways are unobservable in a threshold number of consecutive scans. 
     Exemplary User Interface of a Geofence Detection System 
       FIG. 5  is a diagram illustrating an exemplary user interface of a mobile device using a geofence-based service. The mobile device can be mobile device  100  as described above. Mobile device  100  can allow a user to create geofence  110  using the user interface. Mobile device  100  can be, for example, a handheld computer, a personal digital assistant, a cellular telephone, an electronic tablet, a network appliance, a camera, a smart phone, an enhanced general packet radio service (EGPRS) mobile phone, a network base station, a media player, a navigation device, an email device, a game console, or a combination of any two or more of these data processing devices or other data processing devices. 
     In some implementations, mobile device  100  can include touch sensitive screen  502 . Mobile device  100  can provide map  504  for display on touch sensitive screen  502 . Mobile device  100  can receive a touch input on map  504 . Based on a location of the touch input on map  504 , mobile device  100  can create geofence  110  when mobile device  100  receives an input (e.g., a tap on “Create Fence” button  508 ). Geofence  110  can have a location (e.g., a center) that corresponds to the location of the touch input on map  504 . Upon creation of the geofence, mobile device  100  can select, from multiple wireless access points, one or more wireless access points for monitoring geofence  110 . 
     Mobile device  100  can associate a task with geofence  110 . For example, mobile device  100  can receive a user input to associate an application program with geofence  110 . In the example shown, geofence  110  can correspond to a beach area. The application program can be an application that retrieves information related to surf condition at the beach area. 
     Mobile device  100  can invoke the application program when mobile device  100  enters geofence  110 . If mobile device  100  detects at least one of the selected wireless access points, mobile device  100  can use various location determination operations to determine that mobile device  100  entered geofence  110 . Upon determination that mobile device  100  entered geofence  110 , mobile device  100  can provide for display interface  510  of the application program. Interface  510  can include, for example, text information relating to surf condition associated with the geofence, and controls  512  and  514  for navigating through pages of the text information. 
     A search bar  524  and a bookmarks list object  526  can be displayed at the top of interface  510 . Below the bottom of interface  510  one or more display objects can be displayed, for example a search object  528 , a directions object  530 , a map view object  532 , and a current location object  534 . 
     Search bar  524  can be used to find an address or other location on the map. For example, a user can enter a home address in search bar  524 . Bookmarks list object  526  can, for example, display a Bookmarks list that contains addresses that are frequently visited, such as the user&#39;s home address. The Bookmarks list can also, for example, contain special bookmarks such as bookmarked locations of mobile device  100 . 
     Search object  528  can be used to display search bar  524  and other map related search menus. Directions object  530  can, for example, display a menu interface that allows the user to enter a start and end location. The interface can then display information (e.g., directions and travel time for a route from the start location to the end location). Map view object  532  can display a menu that can allow the user to select display options for a crowdware application program. Current location object  534  can allow the user to see a geographic region on map  504  indicating where mobile device  100  is currently located. 
     Exemplary Access Point Selection Techniques 
       FIG. 6  is a flowchart illustrating exemplary process  600  for selecting wireless access points for monitoring a geofence. Process  600  can be performed by mobile device  100  (as described above). 
     Upon receiving geofence  110  (as described above in reference to  FIGS. 1 and 5 ), mobile device  100  can designate ( 602 ) multiple geographic regions to correspond to geofence  110 . Mobile device  100  can select wireless access points for monitoring geofence  110  based on the geographic regions. Further details of designating the geographic regions will be described below in reference to  FIG. 7 . 
     Mobile device  100  can identify ( 604 ) candidate wireless access points for monitoring in each of the geographic regions. Further details of identifying candidate wireless access points for monitoring in each of the geographic regions will be described below in reference to  FIGS. 8A-8B  and  9 A- 9 B. 
     Mobile device  100  can iterate through the geographic regions and evaluate ( 606 ) a detection probability for each region. The detection probability of a region can indicate a probability that a mobile device  100 , if located in the region, can detect a wireless access point selected for monitoring, and thus detecting a potential entry into geofence  110 . The detection probability of a region can be measured using a probing point detection probability. Further details of evaluating the probing point detection probability will be described below in reference to  FIG. 10 . 
     Based on the detection probability of the regions, mobile device  100  can calculate ( 608 ) a detection probability for the regions as a whole. The detection probability for the regions as a whole can indicate a likelihood that mobile device  100  can determine a potential entry into geofence  110  using the set of the candidate wireless access points. This probability can be measured using a value designated as a grid detection probability. Further details of calculating and applying the grid detection probability will be described below in reference to  FIG. 10 . Based on the grid detection probability, mobile device  100  can select ( 610 ) one or more wireless access points for monitoring geofence  110  or other geofences or both. 
       FIG. 7  is a diagram illustrating exemplary techniques for selecting wireless access points for monitoring using a geographic grid. Mobile device  100  (as described above) can perform the operations of selecting the wireless access points. 
     Mobile device  100  can receive geofence  110  from a user (e.g., as described in reference to  FIG. 5 ). Upon receiving geofence  110 , mobile device  100  can designate multiple geographic regions to correspond to geofence  110 . For example, mobile device  100  can create virtual geographic grid  116  that corresponds to geofence  110 . Mobile device  100  can select wireless access points based on virtual geographic grid  116 . 
     Geographic grid  116  can include N×N equally distributed tiles. Each tile can be a substantially rectangular area. Each tile can have a same size. For example, geographic grid  116  can include 25 square tiles. Mobile device  100  can determine the total number of tiles (N 2 ) in grid  116  based on a scanning capacity of a wireless processor of mobile device  100 . Specifically, the number of tiles can be determined using the following formula:
 
 N   2 =(floor(√{square root over (MAX_EL)})) 2 ,  (1)
 
where N 2  is the total number of tiles, MAX_EL is a maximum number of elements, which can correspond to the total number of wireless access points a wireless processor can monitor (e.g.,  150 ).
 
     When geofence  110  is a units wide and a units long, each tile can have a size of (a/N) 2 . Geofence  110  can be served by MAX_AP number of wireless access points. In this example, geofence  110  is a substantially circular area having center  702 . Center  702  can be associated with a latitude and a longitude. Geofence  110  can have a radius a/2. In various implementations, the geographic regions can have other shapes and varying sizes. Mobile device  100  can select wireless access points for monitoring geofence  110  based on a total number of wireless access points to scan, and a maximum number of wireless access points to scan in each of the geographic regions. This maximum number will be referred to as a wireless access point allowance, as described in further details below in reference to  FIGS. 8A and 8B . 
     Per-Region Limitations in Selecting Wireless Access Points 
       FIGS. 8A and 8B  are diagrams illustrating exemplary wireless access point allowances used in selecting wireless access points. A wireless access point allowance can be a value associated with a tile in geographic grid  116 . The value can indicate a maximum number of wireless access points located in the tile that can be selected.  FIG. 8A  illustrates an allowance setting where wireless access point allowance is set to “1” for each tile. The allowances are shown as numbers in the tiles. In this setting, at most one wireless access point can be selected in each tile. If, for example, wireless access points  802  and  804  are both located in tile  806  of geographic grid  116 , at most one of wireless access points  802  and  804  can be selected for monitoring a geofence. A selected wireless access point is represented using a black triangle; an unselected one, a white triangle. 
       FIG. 8B  illustrates an allowance setting where different wireless access point allowances are associated with different tiles. In some implementations, the wireless access point allowance for tile  806  is set to three. Accordingly, both wireless access points  802  and  804  can be selected. Not all tiles are equal. Some tiles may have greater wireless access point allowance than others. For example, tiles located at or near a center of geographic grid  116  can have higher wireless access point allowances than tiles located at the edge do. 
       FIGS. 9A and 9B  are diagrams illustrating exemplary stages of assigning wireless access point allowances to a geographic grid. Selecting wireless access points can include identifying sets of candidate wireless access points in multiple iterations. In each iteration, a set of candidate wireless access points can be identified. In each iteration, one or more wireless access point allowances can be increased.  FIG. 9A  shows exemplary wireless access point allowances assigned in an iteration (e.g., an initial iteration). A wireless access point allowance associated with center tile  902  can have a higher value than a wireless access point allowance associated with edge tile  904 .  FIG. 9B  shows exemplary wireless access point allowances assigned in a subsequent iteration. The wireless access point allowances assigned in previous iterations can be increased. 
       FIG. 9C  is a flowchart illustrating exemplary process  920  of identifying candidate wireless access points based on geographic regions. Process  920  can be performed by a mobile device such as mobile device  100  as described above. The geographic regions can be tiles in a geographic grid corresponding to a geofence. Mobile device  100  can add wireless access points to geographic regions in multiple iterations, and designate the wireless access points added in an iteration and its prior iterations as a set of candidate wireless access points. 
     Mobile device  100  can initialize ( 922 ) the geographic regions. Initializing the geographic regions can include assigning a wireless access point allowance to each of the geographic regions in a setting as described above in reference to  FIG. 9A . 
     Mobile device  100  can order ( 924 ) the not-yet-added wireless access points by an access point score (AP score) associated with each wireless access point. The AP score of a wireless access point is a value that can indicate an importance of the wireless access point. The AP score of the wireless access point can be determined by (a) a number of observations of the wireless access point, which can be a number of times various mobile devices detected or communicated with the wireless access point in the past; or (b) a time of observation, where an observation closer to present time can correspond to a higher score; or (c) a combination of (a) and (b). 
     Mobile device  100  can add ( 926 ) the not-yet-added wireless access points to the geographic regions based on AP scores and the wireless access point allowance of each geographic region. For example, if (a) a wireless access point having a high AP score is associated with a region (based on a location of the wireless access point), and (b) a number of selected access points in the region has not reached the wireless access point allowance, then, mobile device  100  can add the wireless access point to the region. In some implementations, adding the not-yet-added wireless access points to the geographic regions can include selecting the wireless access points to be added based on channel optimization in addition to the AP scores. Channel optimization will be described in further details below in reference to  FIG. 9D . 
     Mobile device  100  can calculate ( 928 ) a grid detection probability for wireless access points already added. Each set of candidate wireless access points can be associated with a grid detection probability. The grid detection probability can indicate the probability of detecting the geofence by monitoring the candidate wireless access points in the set (e.g., the already added wireless access points). The grid detection probability can be used to balance accuracy (the more wireless access points to monitor, the likelier the detection) and efficiency (the more wireless access points to monitor, the higher the power consumption), and to balance whether to use limited scan capacity of a wireless processor (e.g., 150 access points at one time) to monitor this or another geofence. Further details on calculating the grid detection probability will be described below in reference to  FIG. 10 . 
     Mobile device  100  can determine ( 930 ) whether all wireless access points geographically corresponding to the grid are added. Determining whether all wireless access points geographically corresponding to the grid are added can include performing a search in a wireless access point list using the location of the grid as an index. If all are added, process  920  can terminate. 
     If there are more wireless access points, mobile device  100  can increment ( 932 ) wireless access point allowances for the geographic regions. For example, mobile device  100  can increment the wireless access point allowances according to  FIG. 9B . After the incrementing operations, mobile device  100  can iterate the operations by returning to stage  924 . 
     Channel Optimization 
       FIG. 9D  is exemplary histogram  960  illustrating techniques of identifying candidate wireless access points based on channel optimization. Channel optimization can be performed by a mobile device such as mobile device  100  as described above. 
     Mobile device  100  can use a wireless processor to monitor the selected wireless access points for a geofence. The wireless processor can scan multiple channels for signals from the wireless access points. The wireless processor often consumes more power when more channels are scanned. Mobile device  100  can reduce the number of channels scanned by selecting as many wireless access points that operate in the same channels as possible, when other conditions are equal. 
     Mobile device  100  can store a list of wireless access points. Each of the wireless access points can be associated with a channel in which the wireless access point operates. Mobile device  100  can generated histogram  960  on all wireless channels (e.g., channel  1  through channel  11 ) using a probability density function. Each channel can be assigned a channel score based on the probability density function for a given geofence or for a given group of geofences. The probability density function can indicate a likelihood that a wireless access point operates in a particular channel. In some implementations, the channel score of a channel can be determined based on a number of wireless access points using this channel. 
     In some implementations, mobile device  100  can use the probability density function to identify the most common access points for a given group of fences. Mobile device  100  can select these access points for monitoring the group of geofences. The selection can improve a likelihood of observing a wireless access point by mobile device  100 . In some implementations, mobile device  100  can identify one or more popular channels. For example, mobile device  100  can select top X (e.g., three or four) most populate channels. In some implementations, mobile device  100  can specify selection threshold  962 . Mobile device  100  can designate the wireless channels whose channel scores satisfy the selection threshold  962  as the popular channels. 
     Mobile device  100  can make wireless access points operating in the popular channels more likely to be selected. In some implementations, mobile device  100  can increase the AP score of a wireless access point operating in a popular channel. In some implementations, mobile device  100  can select the wireless access points from wireless access points operating the popular channels. Accordingly, when monitoring a geofence, a wireless processor of mobile device  100  may, for example, scan three or four channels rather than all channels. 
     Evaluating Selected Wireless Access Points 
       FIG. 10  is a diagram illustrating exemplary techniques for evaluating a set of candidate wireless access points. The techniques can be implemented on a mobile device such as mobile device  100  as described above. 
     Mobile device  100  can evaluate multiple sets of candidate wireless access points, and determine which set of candidate wireless access points is finally selected for monitoring geofence  110 . Each set of candidate wireless access points be a set of wireless access points added in an iteration (I) and the iteration&#39;s prior iterations (1, . . . I−1) of process  920  as described above in reference to  FIG. 9C . To evaluate each set of candidate wireless access points, mobile device  100  can determine a grid detection probability for each set. 
     Mobile device  100  can determine the grid detection probability using multiple probing points. Mobile device  100  can designate at least one probing point (e.g., probing point  1002 ) for each geographic region. A probing point (PP) is a virtual point from which a probability of detecting at least one of the already-added wireless access points can be calculated. The probability will be referred to as a probing point detection probability. Mobile device  100  can determine the grid detection probability based on the probing point detection probability of each probing point. 
     To calculate a probing point detection probability for probing point  1002 , mobile device  100  can model signal propagation of a wireless access point using path loss calculation below.
 
 P   k =−10β log 10 ( d )+ P   0 +η,  (2)
 
where P k  is a signal strength at a point that is at distance d away from the wireless access point (e.g., wireless access point  1004 ), P 0  is a signal strength at the wireless access point, η is a constant which accounts for system losses, and β is path loss exponent. The path loss exponent can reflect an environment of the signal propagation. For example, outdoors, in free space, β can have a value of two; in shadowed urban area, β can have a value between 2.7 and 5. In buildings, in line-of-sight, β can have a value between 1.6 and 1.8; when obstructions exist, β can have a value between 4 and 6. A potential detection range of a wireless access point can be determined when a signal strength ratio P k /P 0  is in the range from −30 dB to −113 dB.
 
     According to formula (2), detectability of a wireless access point can be subject to variations such as indoor/outdoor propagation, wireless transmission power, among others. Mobile device  100  can base the calculation of a probing point detection probability on a lower bound detection distance, which can be defined using the following calculation: 
                     Z   =              θ   u     -     θ   0              σ     θ   ⁢           ⁢   u           ,           (   3   )               
where Z is the lower bound detection distance, θu is a potential user location, θ 0  is an estimated location of the wireless access point (which can be determined using an independent process by a server), and σ θu  is an estimated lower bound signal propagation.
 
     Mobile device  100  can then determine a probability of probing point PP detecting a wireless access point by integrating over the lower bound detection distance using the following calculation: 
                       P     DPP   →     SAP   n         =       2   π     ⁢       ∫   Z   ∞     ⁢       ⅇ     -     t   2         ⁢           ⁢     ⅆ   t             ,           (   4   )               
where
 
             P     D     PP   →     SAP   n               
is a probability of probing point PP detecting an nth selected wireless access point SAPn (e.g., wireless access point  1004 ); Z is the lower bound detection distance, and t is a distance over which the probing point detection probability is integrated.
 
     Mobile device  100  can determine a probing point detection probability based on the probabilities that a probing point detects, or does not detect, wireless access points already added, using the following calculations: 
                         P   D     ⁡     (     PP   k     )       =     1   -       (     1   -     P       D     PP   k       -&gt;     SAP   1           )     ⁢     (     1   -     P       D     PP   k       -&gt;     SAP   2           )     ⁢           ⁢   …   ⁢           ⁢     (     1   -     P       D     PP   k       -&gt;     SAP   n           )           ,           (   5   )               
where P D (PP k ) is a probing point detection probability for the kth probing point PPk (e.g., probing point  1002 ).
 
     Mobile device  100  can determine the grid detection probability for a set of candidate wireless access points based on the probing point detection probability for each probing point. The grid detection probability can be an average of the probing point detection probabilities for all probing points, or a minimum probing point detection probability among all probing points. 
     Selecting Access Points from Candidates 
       FIG. 11  is a diagram illustrating exemplary techniques of selecting wireless access points for a monitoring geofence from sets of candidate wireless access points. The techniques can be implemented on a mobile device, such as mobile device  100  as described above. Mobile device  100  can store identifiers of a set of wireless access points  1102  that are located sufficiently close to a geofence such that the wireless access points  1102  can potentially be used to monitor the geofence. 
     Using the operations described above (e.g., in reference to  FIGS. 8A-10 ), mobile device  100  can identify sets of candidate wireless access points  1104 ,  1106 , and  1108 . Each set of candidate wireless access points  1104 ,  1106 , or  1108  can include one or more wireless access points from the set of wireless access points  1102 . Each set of candidate wireless access points  1104 ,  1106 , or  1108  can correspond to a detection probability (e.g., a grid detection probability as described above in reference to  FIG. 10 ). For example, set  1104 , including wireless access points AP 1  and AP 2 , can be associated with a grid detection probability 0.1; set  1106 , including wireless access points AP 1  through AP 4 , can be associated with a grid detection probability 0.3; set  1108 , including wireless access points AP 1  through AP 8 , can be associated with a grid detection probability 0.8. 
     In some implementations, mobile device  100  can select the set of candidate wireless access points to monitor a geofence based on improvement of detection probability over selecting another set of candidate wireless access points. For example, mobile device  100  can select a set (e.g., set  1108 ) that provides most improvement in detection probability per additional wireless access point added. 
       FIG. 12  is a diagram illustrating exemplary techniques of selecting wireless access points for multiple geofences from sets of candidate wireless access points. A mobile device, such as mobile device  100  as described above, can monitor multiple geofences. Monitoring multiple geofences can include scanning for signals from multiple wireless access points designated for monitoring each geofence. 
     For example, mobile device  100  can be configured to monitor a first, a second, and a third geofence. Using the operations described above (e.g., in reference to  FIGS. 8A-11 ), mobile device  100  can identify sets of candidate wireless access points  1104 ,  1106 , and  1108  for monitoring the first geofence. Mobile device  100  can identify sets of candidate wireless access points  1204 ,  1206 , and  1208  for monitoring the second geofence. Mobile device  100  can identify sets of candidate wireless access points  1214 ,  1216 , and  1218  for monitoring the third geofence. When selecting wireless access points to monitor, mobile device  100  can ensure that the total number of wireless access points to monitor the first, second, and third geofences satisfy (e.g., do not exceed) an access point threshold. The access point threshold can be determined based on a configuration of a wireless processor (e.g., a maximum scan capacity of a WiFi™ chip) of mobile device  100 . Further details of selecting wireless access points that satisfy the access point threshold will be described below in reference to  FIG. 13A . 
       FIG. 13A  is a flowchart illustrating exemplary operations  1300  for selecting wireless access points for monitoring multiple geofences. The operations can be performed by a mobile device such as mobile device  100  as described above. 
     Mobile device  100  can initialize ( 1302 ) an access point budget and fence scores. The access point budget can be a value indicating how many more wireless access points can be selected, for example, based on a scanning capacity of a wireless processor, and wireless access points already selected. Initializing the access point budget can include setting the access point budget to an initial value based on the scanning capacity. A fence score of a geofence can be a detection probability (e.g., a grid detection probability) determined based on wireless access points already selected for the geofence. Initializing the fence score can include setting the fence scores of all geofences being considered to zero. 
     Mobile device  100  can iterate ( 1304 ) through the geofences and select the wireless access points. Iterating through the geofences can include selecting wireless access points for monitoring each geofence. During the iteration, mobile device  100  can determine ( 1306 ) if the access point budget remains greater than zero. If the access point budget reaches zero, mobile device  100  can stop selecting wireless access points. Otherwise, mobile device  100  can continue the iterations. 
     If the access point budget remains greater than zero, mobile device  100  can add ( 1308 ) one or more wireless access points to the geofence currently being iterated upon and determine a current fence score. 
     Iterating ( 1304 ) through the geofences can include performing the following operations based on the geofences to be monitored. Mobile device  100  can select one or more wireless access points for geofence  110  being iterated upon when iteration conditions are satisfied. The iteration conditions can be satisfied when:
         (1) The fence score of geofence  110  has room of improvement (e.g., the fence score of geofence  110  is less than a maximum fence score);   (2) A next fence score is significantly better than the current fence score. The next fence score is a detection probability of geofence  110  if the one or more wireless access points being considered are indeed selected. The next fence score is significantly better than a current fence score if the difference between the fence score and the current fence score satisfies a threshold; and   (3) The access point budget is greater than zero.       

     Upon selecting the one or more wireless access points, mobile device  100  can assign the above-calculated next fence score as a new current fence score of the geofence being iterated upon, and decrease the access point budget by the number of wireless access points selected. 
       FIG. 13B  illustrates an exemplary application of the operations of  FIG. 13A . For illustration, mobile device  100  (as described above) selects wireless access points for monitoring a first geofence (geofence  1320 ), a second geofence, (geofence  1322 ), and a third geofence (geofence  1324 ). Each of geofences  1320 ,  1322 , and  1324  can be associated with multiple sets of candidate wireless access points with corresponding fence score. For example, geofence  1320  can be associated with a first set of four candidate access points, with associating fence score 0.1, a second set of six candidate access points with associating fence score 0.5, a third set of eight candidate access points with associating fence score 0.8. 
     During initialization operations (as indicated by arrows marked “0”), the fence scores of each of geofences  1320 ,  1322 , and  1324  can be set to zero. After the initialization, mobile device  100  can iterate through geofences  1320 ,  1322 , and  1324  and the sets of candidate wireless access points associated with the geofences in the order (1-9) as specified next to the arrows, until iteration conditions are no longer satisfied. 
     Exemplary Access Point Selection System 
       FIG. 14  is a block diagram illustrating exemplary components of a system implementing techniques of selecting wireless access points for monitoring a geofence. Wireless access point selection system  1402  can be a component of a mobile device (e.g., mobile device  100  as described above) that is configured to select one or more wireless access points for monitoring a geofence. 
     Wireless access point selection system  1402  can include data store  230 , which can store a list of wireless access points. Each wireless access point can be associated with a location, a channel, and an AP score. The location of a wireless access point can be an estimated location that may or may not correspond to a physical location of the wireless access point. The locations and AP scores can be determined by a remote server, or by mobile device  100 . Data store  230  can be implemented in a database (e.g., a relational or objective database) or a flat file stored on a storage device. 
     Wireless access point selection system  1402  can include geofence data store  1404 . Geofence data store  1404  can store information on one or more geofences, including, for example, locations and dimension of the geofences. 
     Wireless access point selection system  1402  can include geofence analyzer  1406 . Geofence analyzer  1406  is a component of wireless access point selection system  1402  configured to create a geographic grid including one or more geographic regions (e.g., tiles). Each wireless access point in data store  230  can have a location corresponding to one of the geographic regions. Geofence analyzer  1406  can designate one or more points in each geographic region as probing points. Geofence analyzer  1406  can include hardware and software components. 
     Wireless access point selection system  1402  can include probability score calculator  1408 . Probability score calculator  1408  is a component of wireless access point selection system  1402  configured to calculate probing point detection probabilities for each probing point, and the grid detection probability for each set of candidate wireless access points based on the probing point detection probabilities. Probability score calculator  1408  can include hardware and software components. Output from probability score calculator  1408  can be fed to geofence analyzer  1406  according to the iterative process as described above in reference to  FIG. 13A . 
     Wireless access point selection system  1402  can include channel optimizer  1410 . Channel optimizer  1410  is a component of wireless access point selection system  1402  configured to perform channel optimization operations based on channel information from data store  230 . Channel optimizer  1410  can include hardware and software components. 
     Wireless access point selection system  1402  can include wireless access point selector  1412 . Wireless access point selector  1412  is a component of wireless access point selection system  1402  configured to perform selection operations for one or more geofences based on the probabilities calculated by probability score calculator  1408  and channel information from channel optimizer  1410 . Wireless access point selector  1412  can include hardware and software components. 
     Wireless access point selection system  1402  can include selected access point data store  1414 . Selected access point data store  1414  is a component of wireless access point selection system  1402  configured to store a list of wireless access points selected by wireless access point selector  1412 . Wireless access point selection system  1402  can send the selected wireless access points to a wireless processor of mobile device  100  for monitoring one or more geofences. 
     Exemplary Access Point Selection Operations 
       FIG. 15  is flowchart illustrating exemplary operations  1500  of wireless access point selection. Operations  1500  can be performed by mobile device  100  as described above. 
     Mobile device  100  can receive ( 1502 ) a geofence. The geofence can be defined by a fence location and a fence dimension. The geofence can be received from a user 
     Mobile device  100  can select ( 1504 ), from multiple wireless access points, one or more wireless access points for monitoring the geofence. Selecting the one or more wireless access points can include determining multiple geographic regions corresponding to the geofence, and selecting the one or more wireless access points based on a maximum total number of wireless access points to be selected and an access point allowance for each of the geographic regions. The access point allowance can indicate a maximum number of wireless access points to be selected for the geographic region. Mobile device  100  can determine the maximum number of wireless access points to be selected based at least in part on a monitoring capacity of the wireless processor. 
     Determining the geographic regions corresponding to the geofence can include dividing a geographic area associated with the geofence into multiple tiles. Each geographic region can correspond to a tile. Each tile can be a substantially rectangular area. 
     The wireless access points selected for monitoring the geofence can be stored on mobile device  100 . Each wireless access point can be represented by a wireless access point identifier (e.g., a MAC address). Each wireless access point can be associated with an access point location. The access point location can be associated with (e.g., located in) one of the geographical regions for monitoring. Each wireless access point can be associated with an access point score indicating a worthiness of the wireless access point in monitoring the geofence. Each wireless access point can be associated with a channel number. The channel number can indicate on which channel a wireless access point sends and receives signals. 
     Selecting the one or more wireless access points can include iteratively performing scoring operations. The scoring operations can include setting or increasing the access point allowance for each of the geographic regions. The scoring operations can include ordering, based on the access point scores, wireless access points that have not yet been added to a geographic region, where the access point location associated with the not yet added wireless access point corresponds to the destination geographic region. The scoring operations can include designating already added access points as candidate wireless access points and calculating a detection probability based on the candidate wireless access point. Selecting the one or more wireless access points can include selecting the one or more wireless access points from the candidate wireless access points based on the maximum total number of wireless access points and the detection probabilities calculated in the iterative scoring operations. 
     Mobile device  100  can select the one or more wireless access points further based on communication channels between mobile device  100  and the wireless access points. Selecting the one or more wireless access points can include determining one or more preferred wireless access points for each of the communication channels using a probability density function, and selecting the one or more wireless access points from the preferred wireless access points. Determining one or more preferred wireless access points for each of the communication channels can include determining a popularity score of each of the communication channels using a probability density function and a number of wireless access points using the communication channel. Determining one or more preferred wireless access points for each of the communication channels can include determining the one or more preferred wireless access points based on the popularity scores of the communication channels. 
     Mobile device  100  can calculate the detection probability using probability calculation operations. The probability calculation operations can include designating at least one point in each of the geographic regions as a probing point. Mobile device  100  can calculate a probing point detection probability for each probing point. The probing point detection probability can indicate a likelihood that a mobile device located at the probing point can detect any chosen access point for monitoring the geofence. Mobile device  100  can calculate the detection probability based on the probing point detection probabilities of the probing points, including calculating a probability of not detecting any of the selected access points at any of the probing points using calculation (5) as described above in reference to  FIG. 10 . 
     Operations  1500  can include selecting one or more wireless access points for monitoring another geofence, such that a total number of the selected wireless access points representing the geofence and the selected wireless access points representing the other geofence does not exceeding the maximum number of wireless access points as allowable to be monitored by mobile device  100  at one time. Mobile device  100  can iteratively determine whether to select one or more candidate wireless access points for monitoring the geofence or to select the one or more candidate wireless access points for monitoring the other geofence in each iteration based on an amount of improvement that results from each selection. 
     Mobile device  100  can determine ( 1506 ) a tentative location of the mobile device relative to the geofence, including monitoring the selected one or more wireless access points using a wireless processor and tentatively determine, for example, whether mobile device  100  is inside of the geofence or outside of the geofence. The wireless processor can be a WiFi™ chip. Monitoring the selected one or more wireless access points comprises scanning, on one or more channels, a signal from the selected one or more wireless access points. Mobile device  100  can wake an application processor of mobile device  100 . Using the application processor, mobile device  100  can determine whether mobile device  100  is located inside of the geofence. 
     Exemplary Mobile Device Architecture 
       FIG. 16  is a block diagram of an exemplary architecture  1600  for the mobile devices of  FIGS. 1-8 . A mobile device can include memory interface  1602 , one or more data processors, image processors and/or processors  1604 , and peripherals interface  1606 . Memory interface  1602 , one or more processors  1604  and/or peripherals interface  1606  can be separate components or can be integrated in one or more integrated circuits. Processors  1604  can include application processors, baseband processors, and wireless processors. The various components in mobile device  100 , for example, can be coupled by one or more communication buses or signal lines. 
     Sensors, devices, and subsystems can be coupled to peripherals interface  1606  to facilitate multiple functionalities. For example, motion sensor  1610 , light sensor  1612 , and proximity sensor  1614  can be coupled to peripherals interface  1606  to facilitate orientation, lighting, and proximity functions of the mobile device. Location processor  1615  (e.g., GPS receiver) can be connected to peripherals interface  1606  to provide geopositioning. Electronic magnetometer  1616  (e.g., an integrated circuit chip) can also be connected to peripherals interface  1606  to provide data that can be used to determine the direction of magnetic North. Thus, electronic magnetometer  1616  can be used as an electronic compass. Motion sensor  1610  can include one or more accelerometers configured to determine change of speed and direction of movement of the mobile device. Gravimeter  1617  can include one or more devices connected to peripherals interface  1606  and configured to measure a local gravitational field of Earth. 
     Camera subsystem  1620  and an optical sensor  1622 , e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as recording photographs and video clips. 
     Communication functions can be facilitated through one or more wireless communication subsystems  1624 , which can include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem  1624  can depend on the communication network(s) over which a mobile device is intended to operate. For example, a mobile device can include communication subsystems  1624  designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi or WiMax network, and a Bluetooth network. In particular, the wireless communication subsystems  1624  can include hosting protocols such that the mobile device can be configured as a base station for other wireless devices. 
     Audio subsystem  1626  can be coupled to a speaker  1628  and a microphone  1630  to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording, and telephony functions. 
     I/O subsystem  1640  can include touch screen controller  1642  and/or other input controller(s)  1644 . Touch-screen controller  1642  can be coupled to a touch screen  1646  or pad. Touch screen  1646  and touch screen controller  1642  can, for example, detect contact and movement or break thereof using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with touch screen  1646 . 
     Other input controller(s)  1644  can be coupled to other input/control devices  1648 , such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of speaker  1628  and/or microphone  1630 . 
     In one implementation, a pressing of the button for a first duration may disengage a lock of the touch screen  1646 ; and a pressing of the button for a second duration that is longer than the first duration may turn power to mobile device  100  on or off. The user may be able to customize a functionality of one or more of the buttons. The touch screen  1646  can, for example, also be used to implement virtual or soft buttons and/or a keyboard. 
     In some implementations, mobile device  100  can present recorded audio and/or video files, such as MP3, AAC, and MPEG files. In some implementations, mobile device  100  can include the functionality of an MP3 player, such as an iPod™ Mobile device  100  may, therefore, include a pin connector that is compatible with the iPod. Other input/output and control devices can also be used. 
     Memory interface  1602  can be coupled to memory  1650 . Memory  1650  can include high-speed random access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, and/or flash memory (e.g., NAND, NOR). Memory  1650  can store operating system  1652 , such as Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. Operating system  1652  may include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, operating system  1652  can include a kernel (e.g., UNIX kernel). 
     Memory  1650  may also store communication instructions  1654  to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers. Memory  1650  may include graphical user interface instructions  1656  to facilitate graphic user interface processing; sensor processing instructions  1658  to facilitate sensor-related processing and functions; phone instructions  1660  to facilitate phone-related processes and functions; electronic messaging instructions  1662  to facilitate electronic-messaging related processes and functions; web browsing instructions  1664  to facilitate web browsing-related processes and functions; media processing instructions  1666  to facilitate media processing-related processes and functions; GPS/Navigation instructions  1668  to facilitate GPS and navigation-related processes and instructions; camera instructions  1670  to facilitate camera-related processes and functions; magnetometer data  1672  and calibration instructions  1674  to facilitate magnetometer calibration. The memory  1650  may also store other software instructions (not shown), such as security instructions, web video instructions to facilitate web video-related processes and functions, and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions  1666  are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively. An activation record and International Mobile Equipment Identity (IMEI) or similar hardware identifier can also be stored in memory  1650 . Memory  1650  can include geofence instructions  1676  that can be used receive a geofence defined by a user, identifying one or more wireless access points for monitoring the geofence, monitoring the geofence using the identified wireless access points, and perform tasks associated with the geofence upon determining the mobile device is inside or outside the geofence. 
     Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. Memory  1650  can include additional instructions or fewer instructions. Furthermore, various functions of the mobile device may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits. 
     Exemplary Operating Environment 
       FIG. 17  is a block diagram of an exemplary network operating environment  1700  for the mobile devices of  FIGS. 1-9 . Mobile devices  1702   a  and  1702   b  can, for example, communicate over one or more wired and/or wireless networks  1710  in data communication. For example, a wireless network  1712 , e.g., a cellular network, can communicate with a wide area network (WAN)  1714 , such as the Internet, by use of a gateway  1716 . Likewise, an access device  1718 , such as an 802.11g wireless access point, can provide communication access to the wide area network  1714 . 
     In some implementations, both voice and data communications can be established over wireless network  1712  and the access device  1718 . For example, mobile device  1702   a  can place and receive phone calls (e.g., using voice over Internet Protocol (VoIP) protocols), send and receive e-mail messages (e.g., using Post Office Protocol 3 (POP3)), and retrieve electronic documents and/or streams, such as web pages, photographs, and videos, over wireless network  1712 , gateway  1716 , and wide area network  1714  (e.g., using Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP)). Likewise, in some implementations, the mobile device  1702   b  can place and receive phone calls, send and receive e-mail messages, and retrieve electronic documents over the access device  1718  and the wide area network  1714 . In some implementations, mobile device  1702   a  or  1702   b  can be physically connected to the access device  1718  using one or more cables and the access device  1718  can be a personal computer. In this configuration, mobile device  1702   a  or  1702   b  can be referred to as a “tethered” device. 
     Mobile devices  1702   a  and  1702   b  can also establish communications by other means. For example, wireless device  1702   a  can communicate with other wireless devices, e.g., other mobile devices, cell phones, etc., over the wireless network  1712 . Likewise, mobile devices  1702   a  and  1702   b  can establish peer-to-peer communications  1720 , e.g., a personal area network, by use of one or more communication subsystems, such as the Bluetooth™ communication devices. Other communication protocols and topologies can also be implemented. 
     The mobile device  1702   a  or  1702   b  can, for example, communicate with one or more services  1730  and  1740  over the one or more wired and/or wireless networks. For example, one or more access point listing services  1730  can determine one or more identifiers of wireless access points, estimate locations of the wireless access points using location data harvested from one or more location-aware device, determining AP scores for wireless access points, determine a channel for each wireless access point, and provide the information to mobile device  1702   a  or  1702   b.    
     Geofence service  1740  can, for example, provide geofence-based API such that users of mobile device  1702   a  or  1702   b  can develop geofence-based application programs The application programs can be provided for download to mobile device  1702   a  or  1702   b.    
     Mobile device  1702   a  or  1702   b  can also access other data and content over the one or more wired and/or wireless networks. For example, content publishers, such as news sites, Really Simple Syndication (RSS) feeds, web sites, blogs, social networking sites, developer networks, etc., can be accessed by mobile device  1702   a  or  1702   b . Such access can be provided by invocation of a web browsing function or application (e.g., a browser) in response to a user touching, for example, a Web object. 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. For example, geographic regions used in wireless access point selection are represented as tiles. The collection of the geographic regions is represented as a grid. The actual shape of the geographic regions can vary.

Metadata:
Filing Date: 20110603
Publication Date: 20140107
Grant Date: 20140107
Priority Date: 20110603
Inventors: GROSMAN YEFIM
MARTI LUKAS M.
GRAINGER MORGAN
MAYOR ROBERT
HUANG RONALD K.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W64/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M2250/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/72457", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M2250/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W48/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/72457", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M2250/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M2250/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M2250/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/72457", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W48/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M2250/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W48/16", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 46149738