Method and computer program for handoff of mobile devices between wireless systems

• US 7,904,086 B2
• Filed: 10/02/2006
• Issued: 03/08/2011
• Est. Priority Date: 10/02/2006
• Status: Expired due to Fees

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Basu, Kalyan, Das, Sajal K, Pal, Sourav, Kundu, Sumantra R.
• Primary Examiner(s): Bost; Dwayne D
• Assistant Examiner(s): DEAN, JR, JOSEPH E
• Application Number:
  US11/541,886
• Publication Number:
  US 20080080462A1
• Time in Patent Office: 1,618 Days
• Field of Search: 455/436
• US Class Current: 455/436
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 36/362 Conditional handover

Abstract

A method and computer program are provided for handing off a mobile device in communication with a first wireless system having a first network address to one or more other wireless systems within communication range of the mobile device. The method and computer program include periodically monitoring by the mobile device of communications from the first wireless system and the other wireless systems, calculating a signal strength associated with each of the monitored communications, selecting one of the other wireless systems, and transferring communication to the selected wireless system upon detection of a predetermined threshold of the signal strength associated with the first wireless system.

Claims

1. A method for managing handoff of a mobile device between wireless access points, the method comprising:

during a networking initialization phase for a mobile device, scanning channels from the mobile device to detect wireless access points, building a candidate list in the mobile device, wherein the candidate list contains entries representing candidate wireless access points from among the detected access points, reserving Internet protocol (IP) addresses for the mobile device on the access points in the candidate list, and establishing a communication connection between the mobile device and a first access point among the access points in the candidate list via a first IP address among the reserved IP addresses, wherein the first access point belongs to a first sub-network and a first channel;

after the networking initialization phase, switching the mobile device to a normal processing mode;

periodically switching the mobile device from the normal processing mode to a background monitoring phase;

during the background monitoring phase, performing monitoring operations by the mobile device, the monitoring operations comprising;

instructing the first access point to begin buffering packets by sending a first power saving mode (PSM) message from the mobile device to the first access point;

after sending the first PSM message to the first access point, switching the mobile device from the first channel to a different channel, detecting signal strength on the different channel for at least one access point from the candidate list, and then switching the mobile device back to the first channel;

after switching the mobile device back to the first channel, instructing the first access point to release the buffered packets to the mobile device by transmitting a second PSM message to the first access point, wherein the second PSM message comprises a PSM awake message;

determining whether any access points should be removed from the candidate list, based on the signal strength detected in the background monitoring phase;

in response to a determination that one or more access points should be removed from the candidate list, removing said one or more access points from the candidate list;

determining whether an additional access point should be added to the candidate list, based on a threshold number of access points;

in response to a determination that an additional access point should be added to the candidate list, performing candidate list replenishment operations comprising;

instructing the first access point to begin buffering packets by sending a third PSM message from the mobile device to the first access point;

after sending the third PSM message to the first access point, (a) switching the mobile device from the first channel to a new channel, (b) determining whether an access point on the new channel has an acceptable signal strength, (c) in response detecting an access point on the new channel with an acceptable signal strength, reserving an IP address for the mobile device on the detected access point and adding the detected access point to the candidate list, and (d) switching the mobile device back to the first channel;

after switching the mobile device back to the first channel, instructing the first access point to release the buffered packets to the mobile device by transmitting a fourth PSM message to the first access point, wherein the fourth PSM message comprises a PSM awake message; and

outside of the background monitoring phase, upon detection of a predetermined threshold of signal strength associated with a need to handoff from the first access point, selecting a second access point from the candidate list, and transferring communication to the second access point in association with a second IP address that was reserved on the second access point for the mobile device before the mobile device detected the need to handoff from the first access point.

2. The method of claim 1, wherein the IP addresses are reserved from DHCP servers.

3. The method of claim 1, wherein the IP addresses are self configured in IPV6.

4. The method of claim 1, further comprising buffering communications between the mobile device and the first access point during the transfer.

5. The method of claim 1, wherein the transferring communication occurs prior to a loss of signal between the mobile device and the first access point.

6. The method of claim 1, wherein the predetermined threshold pertains to deterioration of the signal strength associated with the first access point.

7. The method of claim 5, wherein the communications from the first access point are monitored beyond the predetermined threshold.

8. The method of claim 1, wherein the mobile device performs the candidate list replenishment operations in response to the candidate list being depleted of candidate access points other than the first access point.

9. The method of claim 1, wherein the operation of selecting a second access point from the candidate list comprises:

comparing the sub-network of the first access point and other access points from the candidate list; and

automatically selecting one of the other access points in the first sub-network, in preference to one of the other access points in a different sub-network from the first sub-network.

10. The method of claim 1, further comprising updating routing table information associated with the second access point.

11. The method of claim 9, further comprising keeping sub-network addresses alive using control messages.

12. The method of claim 1, wherein the monitoring operations performed during the background monitoring phase by the mobile device do not have a substantial negative affect on the performance of the mobile device.

13. The method of claim 1, further comprising buffering communications between the mobile device and the network associated with the first access point during the monitoring operations, wherein buffering communications comprises utilizing inline buffering at the mobile node.

14. An article of manufacture comprising:

machine-readable storage medium; and

instructions in the machine-readable storage medium, which, when executed by a mobile device, cause the mobile device to perform operations comprising;

during a networking initialization phase for the mobile device, scanning channels from the mobile device to detect wireless access points, building a candidate list in the mobile device, wherein the candidate list contains entries representing candidate wireless access points from among the detected access points, reserving Internet protocol (IP) addresses for the mobile device on the access points in the candidate list, and establishing a communication connection between the mobile device and a first access point among the access points in the candidate list via a first IP address among the reserved IP addresses, wherein the first access point belongs to a first sub-network and a first channel;

after the networking initialization phase, switching the mobile device to a normal processing mode;

periodically switching the mobile device from the normal processing mode to a background monitoring phase;

during the background monitoring phase, performing monitoring operations by the mobile device, the monitoring operations comprising;

instructing the first access point to begin buffering packets by sending a first power saving mode (PSM) message from the mobile device to the first access point;

after sending the first PSM message to the first access point, switching the mobile device from the first channel to a different channel, detecting signal strength on the different channel for at least one access point from the candidate list, and then switching the mobile device back to the first channel;

after switching the mobile device back to the first channel, instructing the first access point to release the buffered packets to the mobile device by transmitting a second PSM message to the first access point, wherein the second PSM message comprises a PSM awake message;

determining whether any access points should be removed from the candidate list, based on the signal strength detected in the background monitoring phase;

in response to a determination that one or more access points should be removed from the candidate list, removing said one or more access points from the candidate list;

determining whether an additional access point should be added to the candidate list, based on a threshold number of access points;

in response to a determination that an additional access point should be added to the candidate list, performing candidate list replenishment operations comprising;

instructing the first access point to begin buffering packets by sending a third PSM message from the mobile device to the first access point;

after sending the third PSM message to the first access point, (a) switching the mobile device from the first channel to a new channel, (b) determining whether an access point on the new channel has an acceptable signal strength, (c) in response detecting an access point on the new channel with an acceptable signal strength, reserving an IP address for the mobile device on the detected access point and adding the detected access point to the candidate list, and (d) switching the mobile device back to the first channel;

after switching the mobile device back to the first channel, instructing the first access point to release the buffered packets to the mobile device by transmitting a fourth PSM message to the first access point, wherein the fourth PSM message comprises a PSM awake message; and

outside of the background monitoring phase, upon detection of a predetermined threshold of signal strength associated with a need to handoff from the first access point, selecting a second access point from the candidate list, and transferring communication to the second access point in association with a second IP address that was reserved on the second access point for the mobile device before the mobile device detected the need to handoff from the first access point.

15. The article of manufacture of claim 14, wherein:

the operation of reserving an IP address for the mobile device on the detected access point during the candidate list replenishment operations comprises reserving the IP address for the mobile device on a second sub-network; and

when the second access point operates on the second sub-network, the operation of transferring communication to the second access point comprises using the IP address that was reserved for the mobile device on the second sub-network during the candidate list replenishment operations to transfer communication from the first sub-network to the second sub-network, such that no IP address need be allocated for the mobile device on the second sub-network during handoff processing.

16. The article of manufacture of claim 14, wherein the operation of selecting the second access point comprises:

comparing the sub-network of the first access point and other access points in the candidate list; and

automatically selecting one of the other access points in the first sub-network, in preference to one of the other access points in a different sub-network from the first sub-network.