Systems and Methods for Indicating Buffered Data at an Access Point Using a Traffic Indication Map Broadcast

• US 20080225768A1
• Filed: 03/12/2008
• Published: 09/18/2008
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Wentink, Maarten Menzo
• Granted Patent: US 8,089,908 B2
• Time in Patent Office: Days
• US Class Current: 370/311
• CPC Class Codes: H04W 48/12 using downlink control channel
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Stations in standby mode periodically wake up to check for buffered data at the access points. Traditionally, the information is available by checking the periodic beacon frame for a traffic indication map (TIM). Unfortunately, the length of beacons has steadily increased with the progression of the various wireless standards requiring stations to wake up for longer periods to merely check for buffered data. Several approaches are disclosed which address this shortcoming, including the broadcast of TIM frames, the partial reception of beacon frames and the use of an embedded TIM frame within a beacon frame.

Claims

1. A method for indicating buffered data comprising:

periodically broadcasting a traffic indication map (TIM) frame outside a beacon frame;

said TIM frame comprising a bitmap control field comprising an offset and a partial virtual bitmap field indicative of the stations having buffered data awaiting; and

wherein the broadcasting takes place at a predetermined time.

2. The method of claim 1, wherein the TIM frame is a control frame.

3. The method of claim 1, wherein the TIM frame is a management action frame.

4. The method of claim 1, wherein the predetermined time is a target beacon transmission time (TBTT) plus an offset.

5. The method of claim 4, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frame plus SIFS.

6. The method of claim 4, wherein the offset is announced in a beacon frame, a probe response or both.

7. The method of claim 1, wherein the predetermined time is a delivery traffic indication time (DTIM) TBTT plus an offset.

8. The method of claim 7, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frame plus SIFS.

9. The method of claim 7, wherein the offset is announced in a beacon frame, a probe response or both.

10. The method of claim 1, wherein the TIM frame comprises a second bitmap control field and a second partial virtual bitmap.

11. The method of claim 1, wherein a second TIM frame is broadcast after a short interframe space (SIFS) after the TIM frame.

12. The method of claim 1, wherein a second TIM frame is broadcast at a lower physical layer (PHY) rate than the TIM frame.

13. The method of claim 1, wherein the TIM frame comprises a check beacon indication.

14. The method of claim 13, wherein the check beacon indication comprises means for indicating a critical change in the beacon frame.

15. The method of claim 13, wherein the check beacon indication comprises a counter which is incremented after each critical change in the beacon frame.

16. The method of claim 13, wherein the check beacon indication comprises means for indicating a significant change in the beacon frame.

17. The method of claim 13, wherein the check beacon indication comprises a counter which is incremented after each significant change in the beacon frame.

18. A method in a station for retrieving buffered data from an access point comprising:

waking up at a predetermined time;

receiving a TIM frame having a partial virtual bitmap and a check beacon indication;

if the partial virtual bitmap is indicative that the access point has buffered data for the station, receiving the buffered data; and

if the check beacon indication indicates a critical or significant change in a beacon frame, receiving the beacon frame.

19. The method of claim 18, wherein the TIM frame is a control frame or a management action frame.

20. The method of claim 18, wherein the predetermined time is a TBTT plus an offset or a DTIM TBTT plus an offset, wherein the offset is announced in a beacon frame, a probe response or both.

21. The method of claim 20, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frame plus SIFS.

22. An access point comprising:

a processor;

a wireless network interface device; and

a memory comprising instructions;

said instructions causing the processor to cause the wireless network interface device to broadcast a TIM frame outside a beacon frame at a predetermined time; and

said TIM frame comprising a bitmap control field comprising an offset and a partial virtual bitmap field indicative of the stations having buffered data awaiting.

23. The access point of claim 22, wherein the TIM frame is a control frame or a management action frame.

24. The access point of claim 22, wherein the predetermined time is a TBTT plus an offset or a DTIM TBTT plus an offset, wherein the offset is announced in a beacon frame, a probe response or both.

25. The access point of claim 24, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frame plus SIFS.

26. The access point of claim 22, wherein the TIM frame comprises a second bitmap control field and a second partial virtual bitmap.

27. The access point of claim 22, wherein a second TIM frame is broadcast after a SIFS after the TIM frame, wherein a second TIM frame is broadcast at a lower PHY rate than the TIM frame.

28. The access point of claim 27, wherein the predetermined time is a TBTT plus an offset or a DTIM TBTT plus an offset, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frames plus two SIFS.

29. The access point of claim 22, wherein the TIM frame comprises a check beacon indication, comprising a means for indicating a critical change in the beacon frame, a means for indicating a significant change in the beacon frame, or both.

30. The access point of claim 22, wherein the TIM frame comprises a check beacon indication, comprising a first counter which is incremented after each critical change in the beacon frame, a second counter which is incremented after each significant change in the beacon frame, or both.

31. A station for retrieving buffered data from an access point comprising:

a processor;

a wireless network interface device; and

a memory comprising instructions;

said instructions causing the processor to wake-up at a predetermined time and to cause the wireless network interface device

to receive a TIM frame from an access point having a partial virtual bitmap and a check beacon indication;

if the partial virtual bitmap is indicative that the access point has buffered data for the station, to receive the buffered data; and

if the check beacon indication indicates a critical or significant change in a beacon frame, to receive the beacon frame.

32. The station of claim 31, wherein the TIM frame is a control frame or a management action frame.

33. The station of claim 31, wherein the predetermined time is a TBTT plus an offset or a DTIM TBTT plus an offset, wherein the offset is announced in a beacon frame, a probe response or both.

34. The station of claim 33, wherein the offset is a negative number with a magnitude equal to the minimum, average or maximum size of the TIM frame plus SIFS.