MECHANISMS TO IMPROVE MOBILE DEVICE ROAMING IN WIRELESS NETWORKS

• US 20130150012A1
• Filed: 12/08/2011
• Published: 06/13/2013
• Est. Priority Date: 12/08/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: CHHABRA, Kapil, Balasubramaniyan, Saravanan, Thomas, Tito
• Granted Patent: US 9,026,099 B2
• Time in Patent Office: Days
• US Class Current: 455/418
• CPC Class Codes: H04W 36/36 by user or terminal equipment
• CPC Class Codes: H04W 36/362 Conditional handover
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A mobile wireless device adapts roaming parameters used to determine searching for and switching among access points. The roaming parameters are adjusted based on a wireless network characterization for access points that includes a detected wireless network type. In an embodiment, the wireless network type is characterized by a service set identifier and a number of unique basic service set identifiers associated with the service set identifier per radio frequency band. Roaming parameters include a scan threshold, a roam threshold and a time interval between successive scans.

Claims

1. A method of adapting roaming in a mobile wireless device in communication with a wireless network, the method comprising:

in the mobile wireless device;

detecting a wireless network type for the wireless network to which the mobile wireless device is connected; and

adjusting one or more roaming parameters based on the detected wireless network type;

wherein the wireless network type is characterized by a service set identifier and a number of unique basic service set identifiers associated with the service set identifier per radio frequency band.

2. The method as recited in claim 1, wherein

when the number of basic service set identifiers associated with the service set identifier is one per radio frequency band, the adjusting one or more roaming parameters causes the mobile wireless device to scan for and roam to alternative access points less frequently;

and

when the number of basic service set identifiers associated with the service set identifier is more than one per radio frequency band, the adjusting one or more roaming parameters causes the mobile wireless device to scan for and roam to alternative access points more frequently.

3. The method as recited in claim 2, further comprising:

adjusting to scan for alternative access points less frequently including reducing a receive signal strength threshold; and

adjusting to scan for alternative access points more frequently including increasing the receive signal strength threshold;

wherein when a receive signal strength of an access point in the wireless network to which the mobile wireless device is connected falls below the receive signal strength threshold, the mobile wireless device searches for alternative access points to which to connect.

4. The method as recited in claim 3, further comprising:

adjusting to roam to alternative access points less frequently including increasing a receive signal strength difference threshold; and

adjusting to roam to alternative access points more frequently including decreasing the receive signal strength difference threshold;

wherein when a difference between a receive signal strength of an alternative access point and the receive signal strength of the access point in the wireless network to which the mobile wireless device is connected exceeds the receive signal strength difference threshold, the mobile wireless device roams to the alternative access point.

5. The method as recited in claim 4, further comprising:

adjusting a time interval between successive scans for alternative access points based on the detected wireless network type.

6. The method as recited in claim 1, wherein the one or more roaming parameters depend on a radio frequency band in use by the mobile wireless device.

7. The method as recited in claim 1, wherein detecting the wireless network type for the wireless network to which the mobile wireless device is connected includes

transmitting a query request;

and

listening for one or more query replies from alternative access points, each query reply including the basic service set identifier of the alternative access point.

8. A method of adapting roaming in a mobile wireless device, the method comprising:

when the mobile wireless device is connected to a wireless network having a unique basic service set identifier associated with a service set identifier on a current radio frequency channel;

scanning for and roaming to an alternative radio frequency channel in a higher radio frequency band when a received signal strength for the current radio frequency channel is in a lower radio frequency band and exceeds a first predetermined threshold; and

scanning for and roaming to an alternative radio frequency channel in a lower radio frequency band when the received signal strength for the current radio frequency channel is in a higher radio frequency band and falls below a second pre-determined threshold;

wherein the first predetermined threshold exceeds the second predetermined threshold by a predetermined difference.

9. The method as recited in claim 8, wherein the predetermined difference is greater than 10 dB.

10. The method as recited in claim 8, wherein the lower radio frequency band is a 2.4 GHz radio frequency band, and the higher radio frequency band is a 5.0 GHz radio frequency band.

11. A method to adapt roaming parameters in a mobile wireless device, the method comprising:

when the mobile wireless device is connected to a current access point;

retrieving from memory information for the current access point;

selecting one or more roaming parameters for the mobile wireless device based on the retrieved information for the current access point;

scanning for alternative access points;

receiving information from one or more located alternative access points;

determining a wireless network type for the one or more located alternative access points;

storing the received information and the determined wireless network type for the one or more located alternative access points; and

updating the stored information for the current access point;

wherein the wireless network type includes at least a single basic service set identifier per service set identifier type per radio frequency band and a multiple basic service set identifier per service set identifier type per radio frequency band.

12. The method as recited in claim 11, wherein the multiple basic service set identifier per service set identifier type per radio frequency band further includes a two basic service set identifiers per service set identifier type per radio frequency band and a more than two basic service set identifiers per service set identifier type per radio frequency band.

13. The method as recited in claim 11, wherein the scanning includes passively scanning for the alternative access points by changing a receive radio frequency channel and receiving radio frequency beacons transmitted periodically by the alternative access points.

14. The method as recited in claim 11, wherein the scanning includes actively scanning for the alternative access points by transmitting a request having a specific service set identifier and subsequently listening for replies from alternative access points having a matching service set identifier.

15. The method as recited in claim 11, wherein the scanning includes actively scanning for the alternative access points by transmitting a request having a broadcast service set identifier and subsequently listening for replies from any alternative access points.

16. A mobile wireless device comprising:

at least one transceiver;

a processor to control roaming of the mobile wireless device; and

a non-volatile memory to store access point information;

wherein the processor is configured to;

scan periodically for available access points;

retrieve access point information from the non-volatile memory for one or more available access points; and

set roaming parameters for the mobile wireless device based on the retrieved access point information that includes a number of distinct basic service set identifiers associated with a service set identifier for each access point.

17. The mobile wireless device as recited in claim 16, wherein the processor is further configured to:

calculate a roaming success rate for roaming to an alternative access point; and

adjust the roaming parameters dynamically based on the calculated roaming success rate.

18. The mobile wireless device as recited in claim 17, wherein the processor is further configured to adjust the roaming parameters to achieve a roaming success rate less than approximately 90 percent.

19. The mobile wireless device as recited in claim 18, wherein the processor is further configured to adjust the roaming parameters based on a measured difference in received signal strength between a current access point to which the mobile wireless device is connected and the available access point having the highest received signal strength.

20. The mobile wireless device as recited in claim 19, wherein the processor is further configured to adjust the roaming parameters to achieve a measured difference in received signal strength to less than approximately 20 percent.

21. Non-transitory computer program product encoded in a non-transitory computer readable medium for adapting roaming in a mobile wireless device, the non-transitory computer program product comprising:

in the mobile wireless device;

non-transitory computer program code for receiving information from alternative access points including at least a service set identifier and a basic service set identifier for each alternative access point;

non-transitory computer program code for maintaining a database of basic service set identifiers associated with service set identifiers for wireless networks to which the mobile wireless device is connected presently and has connected with previously;

non-transitory computer program code for retrieving information from the database to select an initial set of roaming parameters for the mobile wireless device; and

non-transitory computer program code for updating the roaming parameters based on information received from alternative access points.

22. The non-transitory computer program product as recited in claim 21, further comprising:

non-transitory computer program code for categorizing a wireless network environment type for each service set identifier in the database based on the number of basic service set identifiers associated with the service set identifier, the wireless network environment type including a sparse environment having a number of basic service set identifiers fewer than or equal to a positive integer and a dense environment having a number of basic service set identifiers greater than the positive integer; and

non-transitory computer program code for adapting the roaming parameters based on the categorized wireless network environment type for a current access point to which the mobile wireless device is connected.

23. The non-transitory computer program product as recited in claim 22, further comprising:

non-transitory computer program code for adapting the roaming parameters based on a frequency of successful roaming to alternative access points.

24. The non-transitory computer program product as recited in claim 22, further comprising:

non-transitory computer program code for decreasing a frequency of roaming to alternative access points when the current access point is in a sparse environment; and

non-transitory computer program code for increasing the frequency of roaming to alternative access points when the current access point is in a dense environment.

25. The non-transitory computer program product as recited in claim 22, further comprising:

non-transitory computer program code for adapting the roaming parameters to achieve a frequency of successful roaming to a range between approximately 75 percent and approximately 95 percent and a difference in received signal strength between a current access point to which the mobile wireless device is connected and a previous access point to which the mobile wireless device was connected most recently to less than approximately 20 dB.