Source: http://www.google.fr/patents/US8737351
Timestamp: 2017-11-22 02:07:31
Document Index: 611812159

Matched Legal Cases: ['§119', 'Application No. 60', 'Application No. 05724477', 'Application No. 94106480', 'Application No. 2005219974', 'Application No. 5009', 'Application No. 05724477', 'Application No. 094106480']

Brevet US8737351 - Methods and systems for reducing MAC layer handoff latency in wireless networks - Google Brevets
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...http://www.google.fr/patents/US8737351?utm_source=gb-gplus-shareBrevet US8737351 - Methods and systems for reducing MAC layer handoff latency in wireless networks
Numéro de publication US8737351 B2
Numéro de demande US 12/626,738
Date de dépôt 27 nov. 2009
Autre référence de publication CA2557762A1, EP1721477A1, EP1721477A4, EP1721477B1, US7636336, US20060062183, US20100135252, WO2005086503A1
Numéro de publication 12626738, 626738, US 8737351 B2, US 8737351B2, US-B2-8737351, US8737351 B2, US8737351B2
Inventeurs Andrea Giuseppe Forte, Henning G Schulzrinne, Sangho Shin, Anshuman S Rawat
Citations de brevets (82), Citations hors brevets (27), Référencé par (4), Classifications (9)
US 8737351 B2
associating with a first access point;
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, wherein information that identifies the second access point is stored in the mobile station; and
removing a channel corresponding to the second access point from the channel mask.
2. The method of claim 1, wherein the determining that the handoff is necessary based on any one of signal strength, signal-to-noise ratio, distance from the first access point, and available bandwidth.
3. The method of claim 1, wherein the 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, further comprising selecting particular channels for inclusion in the channel mask based on type of wireless network.
inverting the channel mask if the mobile station does not detect the one or more access points using the channel mask; and
detecting the one or more access points using the inverted channel mask.
6. The method of claim 1, wherein the selective scan further comprises performing a scan of all channels at the mobile, station in response to not detecting the channel mask.
7. The method of claim 1, further comprising updating the channel mask to remove the channel that is currently being used to connect to the second access point from the channel mask.
8. The method of claim 1, further comprising 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.
9. The method of claim 1, further comprising storing information in the mobile station relating to at least one of the first access point and the second access point, wherein the information comprises at least one of: SSID, MAC address, IP address, GPS position information, WiFi information, and location information.
10. A system for reducing handoff latency for a mobile station in a wireless network, the method comprising:
associates with a first access point;
determines whether a handoff is necessary;
performs 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;
associates with the second access point, wherein information that identifies the second access point is stored in the mobile station; and
removes a channel corresponding to the second access point from the channel mask.
11. The system of claim 10, wherein the determining that the handoff is necessary based on any one of: signal strength, signal-to-noise ratio, distance from the first access point, and available bandwidth.
12. The system of claim 10, 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.
13. The system of claim 10, wherein the processor is further configured to select particular channels for inclusion in the channel mask based on type of wireless network.
14. The system of claim 10, wherein the process& is further configured to:
invert the channel mask if the mobile station does not detect the one or more access points using the channel mask; and
detect the one or more access points using the inverted channel mask.
15. The system of claim 10, wherein the processor is further configured to perform a scan of all channels at the mobile station in response to not detecting the channel mask.
16. The system of claim 10, wherein the processor is further configured to update the channel mask to remove the channel that is currently being used to connect to the second access point from the channel mask.
17. The system of claim 10, wherein the processor is further configured to determine the second access point based on any one of: signal strength, signal-to-noise ratio, distance from the first access point, and available bandwidth.
18. The system of claim 10, wherein the processor is further configured to store information in the mobile station relating to at least one of the first access point and the second access point, wherein the information comprises at least one of SSID, MAC address, IP address, GPS position information, WiFi information, and location information.
19. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by a processor, cause the processor to perform a method for reducing handoff latency for a mobile station in a wireless network, the method comprising:
20. The non-transitory computer-readable medium of claim 19, wherein the determining that the handoff is necessary based on any one of: signal strength, signal-to-noise ratio, distance from the first access point, and available bandwidth.
21. The non-transitory computer-readable medium of claim 19, wherein the 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.
22. The non-transitory, computer-readable medium of claim 19, wherein the method further comprises selecting particular channels for inclusion in the channel mask based on type of wireless network.
24. The non-transitory computer-readable medium of claim 19, wherein the method further comprises performing a scan of all channels at, the mobile station in response to not detecting the channel mask.
25. The non-transitory computer-readable medium of claim 19, wherein the method further comprises updating the channel mask to remove the channel that is currently being used to connect to the second access point from the channel mask.
26. The non-transitory computer-readable medium of claim 19, wherein the method 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.
27. The non-transitory computer-readable medium of claim 19, wherein the method further comprises storing information in the mobile station relating to at least one of the first access point and the second access point, wherein the information comprises at least one of: SSID, MAC address, IP address, GPS position information, WiFi information, and location information.
This application is a continuation of U.S. patent application Ser. No. 11/070,936, filed Mar. 3, 2005, now U.S. Pat. No. 7,636,336, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/549,782, filed Mar. 3, 2004, which are hereby incorporated by reference herein in their entireties.
Several attempts have been made to reduce handoff latency. One solution has been proposed that focuses on reducing the reassociation delay by using a caching mechanism located at the access point. (See, e.g., Mishra et al., “Context caching using neighbor graphs for fast handoffs in a wireless network,” Computer Science Technical Report CS-TR-4477, University of Maryland, February 2004.) This caching mechanism is based on the Inter Access Point Protocol (LAPP) and is used to exchange client context information between neighboring access points. The cache in the access point is filled using the information contained in LAPP Move-Notify messages or reassociation requests sent to the access point by mobile devices. By exchanging the client context information with the old access point, the new access point does not require the client to send its context information in order to reassociate, thereby reducing the reassociation delay.
In some embodiments, the handoff procedure is performed by the firmware or by a HostAP driver. The HostAP driver is a Linux driver for wireless LAN cards based on Intersil's Prism2/2.5/3 802.11 chipset. Wireless cards using these chipsets include, for example, the Linksys WPC11 PCMCIA card, the Linksys WMP11 PCI card, the ZoomAir 4105 PCMCIA card, and the D-Link DWL-650 PCMCIA card. The HostAP driver supports a command for scanning access points, handles the scanning results, and supports a command for joining to a specific access point. It may also be possible to disable the firmware handoff by switching to a manual mode and enabling the selective scanning algorithm.
If there are no entries associated with the key, the station performs the selective scanning algorithm (see, e.g., FIGS. 5 and 6). Upon performing the selective scanning algorithm, the station may associate the results of the selective scanning algorithm with the current key at step 725. For example, the selective scanning algorithm may determine that BESTAP1 and SECONDBESTAP2 are, based on signal strength; the two next best access points other than the current access point. In response to this determination, the station associates BESTAP1 and SECONDBESTAP2 with the current key related to the current access point. However, any other suitable number of access points may be determined and related to the current access point.
Experiment 1 2 3 4 5 6 7 8 9 10 avg
Table 1 shows handoff delay (in ms) of the 802.1 lb in the link layer (also shown in FIG. 8).
Original Handoff 36 55 32 79 37 122 134 32 69 36 63
Selective Scanning 88 24 26 19 31 28 46 26 64 18 37
Handoff time Packet loss in Handoff time Packet delay in
in mobile mobile receiver in mobile mobile sender
receiver (ms) (num of packets) sender (ms) (num of packets)
Original Handoff 182.5 63.2 201.5 210.7
Selective Scanning 102.1 37.0 141.1 161.7
Table 4 shows the handoff time, packet loss, and packet delay using the selective scanning algorithm and/or the caching algorithm in an environment without rogue access points.
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Classification aux États-Unis 370/331, 370/338, 370/329
Classification internationale H04W4/00, H04W36/36, H04W36/10
Classification coopérative H04W36/0083, H04W36/0016, H04W36/36