Wireless local area network supporting multiple slot times

• US 20040246932A1
• Filed: 06/13/2003
• Published: 12/09/2004
• Est. Priority Date: 11/11/2002
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Fischer, Matthew James
• Granted Patent: US 7,239,844 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• CPC Class Codes: H04W 74/02 Hybrid access
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A Wireless Local Area Network (WLAN) supports multiple slot times. A Basic Service Set (BSS)/Independent Basic Service Set (IBSS) of the WLAN services a plurality of WLAN devices (STAs) and at least one STA of the plurality of STAs supports multiple slot times. Operation is initiated using a short slot time. Then, the a determination is made that operation of the BSS/IBSS requires use of a long slot time, wherein the long slot time is longer than the short slot time. Operation of at least one of the plurality of STAs is modified to be consistent with the long slot time. In altering the operation the STA sets a local Long Slot Termination Time (LSTT). When a Target Beacon Transition Time (TBTT) is before the local LSTT, a beacon is transmitted that indicates that the long slot time is to be used and that includes the local LSTT. When the TBTT is after the local LSTT, a beacon is transmitted that indicates that the short slot time is to be used.

Claims

1. A method for operating a Basic Service Set (BSS)/Independent Basic Service Set (IBSS) of a Wireless Local Area Network (WLAN) that services a plurality of WLAN devices (STAs), wherein at least one STA of the plurality of STAs supports multiple slot times, the method comprising:

initiating operation of the BSS/IBSS of the WLAN using a short slot time;

determining that operation of the BSS/IBSS requires use of a long slot time, wherein the long slot time is longer than the short slot time; and

altering operation of at least one of the plurality of STAs to be consistent with the long slot time by;

using the long slot time;

setting a local Long Slot Termination Time (LSTT);

when a Target Beacon Transition Time (TBTT) is before the local LSTT, transmitting a beacon that indicates that the long slot time is to be used and that includes the local LSTT; and

when the TBTT is after the local LSTT, transmitting a beacon that indicates that the short slot time is to be used.

2. The method of claim 1, further comprising, by a STA of the plurality of STAs:

receiving a beacon from another STA of the plurality of STAs, wherein the beacon includes a remote LSTT;

when the remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the remote LSTT as the local LSTT.

3. The method of claim 1, further comprising, when a Timing Synchronization Function (TSF) of the BSS/IBSS is later than the LSTT, reverting to use of the short slot time.

4. The method of claim 1, wherein determining that operation of the BSS/IBSS requires use of a long slot time comprises identifying a STA that associates with the BSS/IBSS and that requires operation with the long slot time.

5. The method of claim 1, wherein determining that operation of the BSS/IBSS requires use of a long slot time comprises:

identifying a co-channel BSS that requires operation with the long slot time; and

determining that a service area of the co-channel BSS overlaps with a service area of BSS/IBSS.

6. The method of claim 1, further comprising:

receiving a beacon from a co-channel BSS/IBSS STA that includes a remote LSTT and a Timing Synchronization Function (TSF);

normalizing the remote LSTT based upon the TSF to produce a normalized remote LSTT;

when the normalized remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the normalized remote LSTT as the local LSTT.

7. The method of claim 6, wherein the beacon further comprises an indication that the long slot time is to be used.

8. The method of claim 1, wherein determining that operation of the BSS/IBSS requires use of a long slot time comprises identifying a co-channel IBSS that requires operation with the long slot time.

9. The method of claim 1, wherein setting the local LSTT includes setting the local LSTT to the sum of a Target Beacon Transition Time (TBTT) and a Minimum Long Slot Epoch (MLSE).

10. A method for operating a STA of an Independent Basic Service Set (IBSS) of a Wireless Local Area Network (WLAN), wherein the STA supports multiple slot times, the method comprising:

operating the STA using a short slot time;

determining that operation of the BSS/IBSS requires use of a long slot time, wherein the long slot time is longer than the short slot time; and

altering operation to be consistent with the long slot time by;

using the long slot time;

setting a local Long Slot Termination Time (LSTT);

when a Target Beacon Transition Time (TBTT) is before the local LSTT, transmitting a beacon that indicates that the long slot time is to be used and that includes the local LSTT; and

when the TBTT is after the local LSTT, transmitting a beacon that indicates that the short slot time is to be used.

11. The method of claim 10, further comprising:

receiving a beacon from another STA of the IBSS, wherein the beacon includes a remote LSTT;

when the remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the remote LSTT as the local LSTT.

12. The method of claim 10, further comprising, when a Timing Synchronization Function (TSF) of the IBSS is later than the LSTT, reverting to use of the short slot time.

13. The method of claim 10, determining that operation of the IBSS requires use of a long slot time comprises identifying a STA that associates with the IBSS and that requires operation with the long slot time.

14. The method of claim 10, wherein determining that operation of the IBSS requires use of a long slot time comprises:

identifying a co-channel BSS/IBSS that requires operation with the long slot time; and

determining that a service area of the co-channel BSS/IBSS overlaps with a service area of BSS/IBSS.

15. The method of claim 10, further comprising:

receiving a beacon from a co-channel BSS/IBSS STA that includes a remote LSTT and a Timing Synchronization Function (TSF);

normalizing the remote LSTT based upon the TSF to produce a normalized remote LSTT;

when the normalized remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the normalized remote LSTT as the local LSTT.

16. The method of claim 15, wherein the beacon further comprises an indication that the long slot time is to be used.

17. The method of claim 10, wherein determining that operation of the IBSS requires use of a long slot time comprises identifying a co-channel IBSS that requires operation with the long slot time.

18. The method of claim 10, wherein setting the local LSTT includes setting the local LSTT to the sum of a Target Beacon Transition Time (TBTT) and a Minimum Long Slot Epoch (MLSE).

19. A method for operating a STA of a Basic Service Set (BSS)/Independent Basic Service Set (IBSS) of a Wireless Local Area Network (WLAN), wherein the STA supports multiple slot times, the method comprising:

operating the STA using a short slot time;

determining that operation of the BSS/IBSS requires use of a long slot time, wherein the long slot time is longer than the short slot time;

receiving a beacon from another STA of the BSS/IBSS, wherein the beacon includes a remote LSTT;

when the remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the remote LSTT as the local LSTT.

20. The method of claim 19, wherein the beacon further comprises an indication that the long slot time is to be used.

21. The method of claim 19, determining that operation of the BSS/IBSS requires use of a long slot time comprises identifying a STA that associates with the BSS/IBSS and that requires operation with the long slot time.

22. The method of claim 19, wherein determining that operation of the BSS/IBSS requires use of a long slot time comprises:

identifying a co-channel BSS that requires operation with the long slot time; and

determining that a service area of the co-channel BSS overlaps with a service area of BSS/IBSS.

23. The method of claim 19, further comprising:

receiving a beacon from a co-channel BSS/IBSS STA that includes a remote LSTT and a Timing Synchronization Function (TSF);

normalizing the remote LSTT based upon the TSF to produce a normalized remote LSTT;

when the normalized remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the normalized remote LSTT as the local LSTT.

24. The method of claim 23, wherein the beacon further comprises an indication that the long slot time is to be used.

25. The method of claim 19, wherein determining that operation of the BSS/IBSS requires use of a long slot time comprises identifying a co-channel IBSS that requires operation with the long slot time.

26. A Wireless Local Area Network (WLAN) device (STA) that supports multiple slot times, the STA comprising:

a Radio Frequency (RF) interface that supports communications with at least one other STA of the WLAN;

a processor operably coupled to the RF interface; and

wherein the RF interface and the processor cooperatively operate to;

commence operations using a short slot time;

determine that operation requires use of a long slot time, wherein the long slot time is longer than the short slot time by;

using the long slot time;

setting a local Long Slot Termination Time (LSTT);

when a Target Beacon Transition Time (TBTT) is before the local LSTT, transmitting a beacon that indicates that the long slot time is to be used and that includes the local LSTT; and

when the TBTT is after the local LSTT, transmitting a beacon that indicates that the short slot time is to be used.

27. The STA of claim 26, wherein the RF interface and the processor cooperatively operate further to:

receive a beacon from another STA, wherein the beacon includes a remote LSTT;

when the remote LSTT precedes the local LSTT, ignore the remote LSTT; and

when the remote LSTT is later than the local LSTT, write the remote LSTT as the local LSTT.

28. The STA of claim 26, wherein the RF interface and the processor cooperatively operate further to:

receive a beacon from a foreign co-channel STA that includes a remote LSTT and a Timing Synchronization Function (TSF);

normalize the remote LSTT based upon the TSF to produce a normalized remote LSTT;

when the normalized remote LSTT precedes the local LSTT, ignore the remote LSTT; and

when the remote LSTT is later than the local LSTT, write the normalized remote LSTT as the local LSTT.

29. The STA of claim 26, wherein the STA is a wireless terminal.

30. The STA of claim 26, wherein the STA is an Access Point (AP).

31. A Wireless Local Area Network (WLAN) device (STA) that supports multiple slot times, the STA comprising:

a Radio Frequency (RF) interface that supports communications with at least one other STA of the WLAN;

a processor operably coupled to the RF interface; and

wherein the RF interface and the processor cooperatively operate to;

commence operations using a short slot time;

determine that operation requires use of a long slot time, wherein the long slot time is longer than the short slot time by;

using the long slot time;

receiving a beacon from another STA, wherein the beacon includes a remote LSTT;

when the remote LSTT precedes the local LSTT, ignoring the remote LSTT; and

when the remote LSTT is later than the local LSTT, writing the remote LSTT as the local LSTT.

32. The STA of claim 31, wherein the STA is a wireless terminal.

33. The STA of claim 31, wherein the STA is a Access Point (AP).