Methods and systems for reducing MAC layer handoff latency in wireless networks

• US 7,636,336 B2
• Filed: 03/03/2005
• Issued: 12/22/2009
• Est. Priority Date: 03/03/2004
• Status: Active Grant

• Current Assignee: Trustees Of Columbia University In The City Of New York (Columbia University)
• Original Assignee: Trustees Of Columbia University In The City Of New York (Columbia University)
• Inventors: Schulzrinne, Henning G., Forte, Andrea G., Shin, Sangho, Rawat, Anshuman S.
• Primary Examiner(s): WASHINGTON, ERIKA ALISE
• Application Number:
  US11/070,936
• Publication Number:
  US 20060062183A1
• Time in Patent Office: 1,755 Days
• Field of Search: None
• US Class Current: 370/331
• CPC Class Codes: H04W 36/0016 Hand-off preparation specially adapted for end-to-end data sessions
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/36 by user or terminal equipment

Abstract

In accordance with the present invention, computer implemented methods and systems are provided for reducing handoff latency in a wireless network. In response to detecting that a handoff is necessary, the present invention uses a selective scanning algorithm that includes the use of a channel mask and/or a caching algorithm for detecting one or more new access points.

Claims

1. A method for reducing handoff latency for a mobile station in a wireless network, the method comprising:

associating with a first access point, wherein key information that identifies the first access point is stored into a cache located at the mobile station;

determining whether a handoff is necessary;

querying the cache to determine whether another access point is associated with the key information in response to determining that the handoff is necessary;

performing a selective scan of channels at the mobile station upon determining that another access point is not associated with the key information, wherein the selective scan comprises;

accessing a channel mask that is associated with the mobile station;

detecting one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

determining a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

storing information relating to the second access point into the cache located at the mobile station, wherein the information identifies the second access point and is associated with the key information;

transmitting one or more messages to the second access point for association with the second access point; and

associating with the second access point in response to receiving an indication from the second access point.

2. The method of claim 1, wherein the step of determining whether the handoff is necessary further comprises determining that the signal strength of the first access point has decreased below a given threshold value.

3. The method of claim 1, wherein the step of determining whether the handoff is necessary further comprises determining that the signal-to-noise ratio of the first access point has decreased below a given threshold value.

4. The method of claim 1, wherein the selective scan further comprises:

inverting the channel mask if the mobile station does not detect one or more access points using the channel mask; and

detecting one or more access points using the inverted channel mask.

5. The method of claim 1, wherein the selective scan further comprises:

determining whether the channel mask is associated with the mobile station; and

performing a scan of all channels at the mobile station upon determining that the channel mask is not associated with the mobile station.

6. The method of claim 1, further comprising transmitting one or more requests to the first access point for information regarding neighboring access points.

7. The method of claim 1, wherein the wireless network is an 802.11b wireless network, the method further comprising adding channel 1, channel 6, and channel 11 to the channel mask.

8. The method of claim 1, further comprising removing the channel that is currently being used to connect to the second access point from the channel mask.

9. The method of claim 1, wherein the step of determining the second access point based at least in part on the responses from the one or more access points, further comprises determining the second access point based on any one of:

signal strength, signal-to-noise ratio, distance from the first access point, and available bandwidth.

10. The method of claim 1, wherein the key information comprises at least one of:

SSID, MAC address, IP address, GPS position information, WiFi information, and location information.

11. The method of claim 1 further comprising configuring the mobile station to set a timer for accessing the second access point.

12. A method for reducing handoff latency for a mobile station in a wireless network, the method comprising:

associating with a first access point, wherein key information that identifies the first access point is stored in a cache located at the mobile station;

determining whether a handoff is necessary;

performing a selective scan of channels at the mobile station in response to determining that the handoff is necessary, wherein the selective scan comprises;

accessing a channel mask that is associated with the mobile station;

detecting one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

determining a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

associating with the second access point in response to receiving an indication from the second access point; and

updating the channel mask to remove the channel that is used to connect to the second access point.

13. A system for reducing handoff latency for a mobile station in a wireless network, the system comprising:

means for associating with a first access point, wherein key information that identifies the first access point is stored into a cache located at the mobile station;

means for determining whether a handoff is necessary;

means for querying the cache to determine whether another access point is associated with the key information in response to determining that the handoff is necessary;

means for performing a selective scan of channels at the mobile station upon determining that another access point is not associated with the key information, wherein the selective scan comprises;

means for accessing a channel mask that is associated with the mobile station;

means for detecting one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

means for determining a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

means for storing information relating to the second access point into the cache located at the mobile station, wherein the information identifies the second access point and is associated with the key information;

means for transmitting one or more messages to the second access point for association with the second access point; and

means for associating with the second access point in response to receiving an indication from the second access point.

14. A system for reducing handoff latency for a mobile station in a wireless network, the system comprising:

means for associating with a first access point, wherein key information that identifies the first access point is stored in a cache located at the mobile station;

means for determining whether a handoff is necessary;

means for performing a selective scan of channels at the mobile station in response to determining that the handoff is necessary, wherein the selective scan comprises;

means for accessing a channel mask that is associated with the mobile station;

means for detecting one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

means for determining a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

means for associating with the second access point in response to receiving an indication from the second access point; and

means for updating the channel mask to remove the channel that is used to connect to the second access point.

15. A system for reducing handoff latency in a wireless network, the system comprising:

a mobile station that is associated with a first access point, the mobile station comprising;

memory;

a processor at least partially executing a handoff application program configured to;

store key information that identifies the first access point in a cache located at the mobile station;

determine whether a handoff is necessary;

query the cache to determine whether another access point is associated with the key information in response to determining that the handoff is necessary;

perform a selective scan of channels at the mobile station upon determining that another access point is not associated with the key information, wherein processor is further configured to;

access a channel mask that is associated with the mobile station;

detect one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

determine a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

store information relating to the second access point into the cache located at the mobile station, wherein the information identifies the second access point and is associated with the key information;

transmit one or more messages to the second access point for association with the second access point; and

associate with the second access point in response to receiving an indication from the second access point.

16. The system of claim 15, wherein the processor is further configured to determine that the signal strength of the first access point has decreased below a given threshold value.

17. The system of claim 15, wherein the processor is further configured to determine that the signal-to-noise ratio of the first access point has decreased below a given threshold value.

18. The system of claim 15, wherein the processor is further configured to:

invert the channel mask if the mobile station does not detect one or more access points using the channel mask; and

detect one or more access points using the inverted channel mask.

19. The system of claim 15, wherein the processor is further configured to:

determine whether the channel mask is associated with the mobile station; and

perform a scan of all channels at the mobile station upon determining that the channel mask is not associated with the mobile station.

20. The system of claim 15, wherein the processor is further configured to transmit one or more requests to the first access point for information regarding neighboring access points.

21. The system of claim 15, wherein the processor is further configured to remove the channel that is currently being used to connect to the second access point from the channel mask.

22. The system of claim 15, wherein the processor is further configured to configure the mobile station to set a timer for accessing the second access point.

23. A system for reducing handoff latency in a wireless network, the system comprising:

a mobile station that is associated with a first access point, the mobile station comprising;

memory;

a processor at least partially executing a handoff application program configured to;

store key information that identifies the first access point in a cache located at the mobile station;

determine whether a handoff is necessary;

perform a selective scan of channels at the mobile station in response to determining that the handoff is necessary, wherein the processor is further configured to;

access a channel mask that is associated with the mobile station;

detect one or more access points using the channel mask, wherein the mobile station receives one or more responses from the one or more access points; and

determine a second access point for association by the mobile station based at least in part on the responses from the one or more access points;

associate with the second access point in response to receiving an indication from the second access point; and

update the channel mask to remove the channel that is used to connect to the second access point.