Apparatus for and method of synchronization and beaconing in a WLAN mesh network

• US 7,564,826 B2
• Filed: 06/15/2006
• Issued: 07/21/2009
• Est. Priority Date: 07/13/2005
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sherman, Itay, Kangude, Shantanu
• Primary Examiner(s): Tran; CongVan
• Application Number:
  US11/424,235
• Publication Number:
  US 20070014269A1
• Time in Patent Office: 1,132 Days
• Field of Search: 370/338, 370/401, 370/352, 370/412, 370/389, 370/311, 370/348, 370/444, 370/448, 455/456.1, 455/403.2, 455/434, 455/556.2, 455/547
• US Class Current: 370/338
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04J 3/0661 using timestamps
• CPC Class Codes: H04W 48/12 using downlink control channel
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A novel and useful synchronization mechanism that functions to provide a uniform time base for mesh points in a WLAN mesh based network. The invention enables timing synchronization to a common reference clock base by advertising the common TSF within beacon transmissions. All MPs in a mesh share a common DTIM interval. The synchronization mechanism enables the mesh points to avoid collisions in the generation and transmission of beacons. The TBTT offsets of the current MP and its neighbors are advertised in beacons so that neighboring MPs that hear the beacons can select non-overlapping TBTT offsets. Each MP receives one or more beacons from its neighbors and compares the timing of its neighbors to that of itself and adopts the highest TSF (i.e. the fastest) in the mesh. Eventually, all MPs in the mesh will adjust their timing to that of the MP with the fastest clock. The reception of beacons by MPs from its neighbors is also advertised. This allows for MPs to verify that the beacons they send are actually heard and are not in collision with beacon transmissions of other MPs.

Claims

1. A method of synchronization in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points;

extracting beacon information associated with said neighbor mesh points from said beacon information messages, wherein said beacon information comprises a target beacon transmission time (TBTT) offset compared to the mesh timing synchronization function (TSF);

adopting timing of a fastest mesh point in said network in accordance with said beacon information; and

selecting a beacon interval and DTIM period such that said mesh DTIM period is an integral multiple of said beacon interval.

2. The method according to claim 1, further comprising the step of generating beacon messages incorporating beacon information associated with one or more neighbors of said mesh point.

3. The method according to claim 1, further comprising the step of generating beacon massages incorporating beacon information associated with said mesh point.

4. The method according to claim 1, wherein said beacon information is transmitted by mesh points encapsulated in a neighbor list information element.

5. The method according to claim 1, wherein said beacon information further comprises a time since the last reception of a beacon from that particular mesh point.

6. The method according to claim 1, wherein said beacon information further comprises a DTIM period of that particular mesh point.

7. The method according to claim 1, wherein said beacon information messages comprise a power save states field adapted to indicate the current power save state of each neighbor listed in said beacon information message.

8. The method according to claim 1, wherein said DTIM period comprises a single value for all mesh points in said network.

9. A method of synchronization in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points, wherein said beacon information messages comprise mesh point control information which comprises a designated beacon broadcaster field adapted to indicate that the current beacon broadcaster is a designated beacon broadcaster;

extracting beacon information associated with said neighbor mesh points from said beacon information messages

adopting timing of a fastest mesh point in said network in accordance with said beacon information; and

selecting a beacon interval and DTIM period such that said mesh DTIM period is an integral multiple of said beacon interval.

10. A method of synchronization in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points, wherein said beacon information messages comprise mesh point control information which comprises a beacon broadcaster switch field adapted to indicate a change in the designated beacon broadcaster;

extracting beacon information associated with said neighbor mesh points from said beacon information messages

adopting timing of a fastest mesh point in said network in accordance with said beacon information; and

selecting a beacon interval and DTIM period such that said mesh DTIM period is an integral multiple of said beacon interval.

11. A method of synchronization in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points, wherein said beacon information messages comprise mesh point control information which comprises a beacon broadcaster power save state field adapted to indicate whether the beacon broadcaster is using a power save mode of operation;

extracting beacon information associated with said neighbor mesh points from said beacon information messages

adopting timing of a fastest mesh point in said network in accordance with said beacon information; and

selecting a beacon interval and DTIM period such that said mesh DTIM period is an integral multiple of said beacon interval.

12. A method of synchronization and collision avoidance in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points;

extracting beacon information associated with said neighbor mesh points from said beacon information messages;

adopting timing of a fastest mesh point in said network in accordance with said beacon information;

verifying receipt of beacons generated by said mesh point at said neighboring mesh points;

if beacons generated by said mesh point are not being received at one or more neighboring mesh points, selecting a new target beacon transmission time (TBTT) offset that is not in use by other mesh points such that said mesh DTIM period remains an integral multiple of said beacon interval; and

advertising said new target beacon transmission time (TBTT) offset in beacon information messages generated by said mesh point.

13. The method according to claim 12, wherein said beacon information is transmitted by mesh points encapsulated in a neighbor list information element.

14. The method according to claim 12, wherein said beacon information comprises a time since the last reception of a beacon from that particular mesh point.

15. The method according to claim 12, wherein said beacon information comprises a DTIM period of that particular mesh point.

16. The method according to claim 12, wherein said beacon information messages comprise mesh point control information.

17. The method according to claim 16, wherein said mesh point control information comprises a beacon broadcaster switch field adapted to indicate a change in the designated beacon broadcaster.

18. The method according to claim 16, wherein said mesh point control information comprises a beacon broadcaster power save state field adapted to indicate whether the beacon broadcaster is using a power save mode of operation.

19. The method according to claim 12, wherein said beacon information messages further comprise a power save states field adapted to indicate the current power save state of each neighbor listed in said beacon information message.

20. The method according to claim 12, wherein said DTIM period comprises a single value for all mesh points in said network.

21. A method of synchronization and collision avoidance in a wireless local area network (WLAN) mesh network incorporating a plurality of mesh points and having a mesh delivery traffic indication message (DTIM) period, said method comprising the steps of:

receiving beacon information messages at a mesh point from one or more neighboring mesh points, wherein said beacon information messages comprise mesh point control information which comprises a designated beacon broadcaster field adapted to indicate that the current beacon broadcaster is a designated beacon broadcaster;

extracting beacon information associated with said neighbor mesh points from said beacon information messages;

adopting timing of a fastest mesh point in said network in accordance with said beacon information;

verifying receipt of beacons generated by said mesh point at said neighboring mesh points;

if beacons generated by said mesh point are not being received at one or more neighboring mesh points, selecting a new target beacon transmission time (TBTT) offset that is not in use by other mesh points such that said mesh DTIM period remains an integral multiple of said beacon interval.