Selecting a subset of access points

1. A method for selecting a subset of access points, comprising, by a processor:

receiving, from multiple access points, time-of-flight information and signal strength information associated with a mobile device;

determining a respective mobility state of the mobile device relative to each access point based on the time-of-flight information;

identifying, based on the determined mobility states, access points that the mobile device is headed towards;

identifying a subset of the multiple access points based on the time-of-flight information, the signal strength information, and load information of each access point to minimize a number of handoffs by inclusion of an access point in the subset that has a lowest signal strength value above the minimum signal strength value from the identified access points that the device is headed towards;

instructing the subset of the multiple access points to respond to a probe request of the mobile device.

2. The method of claim 1 , further comprising instructing the access points not in the subset to refrain from responding to the probe request of the mobile device.

3. The method of claim 1 , wherein the subset of the multiple access points is identified based at least in part on:

not including at least one of the access points in the subset due to the time-of-flight information received from the at least one of the access points.

4. The method of claim 1 , wherein not including at least one of the access points in the subset due to the time-of-flight information received from the at least one of the access points comprises:

only including access points in the subset whose time-of-flight information is below a threshold.

5. The method of claim 1 , wherein the subset of the multiple access points is identified based at least in part on:

not including at least one of the access points in the subset due to the load information of the at least one of the access points.

6. The method of claim 1 , wherein the subset of the multiple access points is identified based at least in part on:

not including at least one of the access points in the subset due to the signal strength information associated with the mobile device received from the at least one of the access points.

7. The method of claim 1 , wherein identifying a subset of the multiple access points further comprises:

determining a mobility state of the mobile device relative to at least one of the access points based on the time-of-flight information received from the at least one of the access points; and

determining whether at least one of the access points should be in the subset based on the determined mobility state.

8. The method of claim 7 , wherein the mobility state of the mobile device relative to an access point comprises a velocity and a directional heading,

the velocity being determined based on the following equation:

v =ToF1−ToF2/ t 2− t 1,

where v is the velocity, ToF1 is a first time-of-flight calculated based on an elapsed period between sending a first message and receiving a first acknowledgement from the mobile device, ToF2 is a second time-of-flight based on an elapsed period between sending a second message and receiving a second acknowledgement from the mobile device, t1 is a first time at which the first message was sent, and t2 is a second time at which the second message was sent, and

the directional heading being determined to be toward the access point if the velocity is positive and away from the access point if the velocity is negative.

9. The method of claim 7 , further comprising:

after association of the mobile device with a first access point in the subset:

instructing access points in a direction of mobility of the mobile device to obtain time-of-flight information and signal strength information associated with the mobile device;

receiving time-of-flight information and signal strength information from one or more of the instructed access points;

identifying a second subset of the one or more of the instructed access points based on the time-of-flight information, signal strength information, and load information of the one or more of the instructed access points;

instructing the first access point to encourage the mobile device to perform a channel scan or to disassociate from the mobile device; and

instructing the access points in the second subset to respond to probe requests from the mobile device.

10. The method of claim 9 , further comprising instructing any access points not in the second subset that receive a probe request from the mobile device to refrain from responding to the probe request of the mobile device.

11. The method of claim 9 , wherein instructing the first access point to encourage the mobile device to perform a channel scan comprises instructing the first access point to send a BSS transition management request or reducing the transmit power of unicast packets towards the mobile device.

12. A wireless local area network controller, comprising:

a communication interface to send and receive data to and from multiple access points; and

a processor to:

receive from the access points time-of-flight information and signal strength information associated with a mobile device;

determine a respective mobility state of the mobile device relative to each access point based on the time-of-flight information;

identify, based on the determined mobility states, access points that the device is headed towards;

select a subset of the access points based on the time-of-flight information, the signal strength information, and load information of each access point to minimize a number of handoffs by inclusion of an access point in the subset that has a lowest signal strength value above the minimum signal strength value from the identified access points that the device is headed towards; and

instruct the subset of the access points to respond to a probe request of the mobile device.

13. The controller of claim 12 , wherein the processor is to choose a selection technique from a plurality of selection techniques based on bandwidth requirements of an application executing on the mobile device, based on a type of an application executing on the mobile device, or based on a pattern of mobility of the mobile device.

14. A non-transitory computer-readable storage medium storing instructions for execution by a processor, the instructions when executed causing the processor to:

receive from a plurality of access points time-of-flight information associated with a device, signal strength information associated with the device, and load information associated with the respective access point;

determine a respective mobility state of the mobile device relative to each access point based on the time-of-flight information;

identify, based on the determined mobility states, access points that the device is headed towards;

select a subset of the access points based on the time-of-flight information, the signal strength information, and the load information to minimize a number of handoffs by inclusion of an access point in the subset that has a lowest signal strength value above the minimum signal strength value from the identified access points that the device is headed towards; and

instruct access points in the subset to respond to a probe request of the device.