Method and System for Dynamic Power Management in Wireless Local Area Networks

• US 20080130541A1
• Filed: 11/06/2007
• Published: 06/05/2008
• Est. Priority Date: 12/04/2006
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Laboratories America Inc (NEC Corporation)
• Inventors: Navda, Vishnu, Kokku, Ravidranath, Ganguly, Samrat
• Granted Patent: US 7,944,868 B2
• Time in Patent Office: Days
• US Class Current: 370/311
• CPC Class Codes: H04W 52/34 TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method and system for improving spatial reuse in a wireless local area network (WLAN) by per-client dynamic power management. Each access point of the WLAN associates each of its clients with a minimum power level. A central controller of the WLAN generates a schedule for transmission at different power levels, and each access point varies its transmission power level based on the schedule. An access point transmits data packets, at the scheduled transmission power level, to clients associated with a minimum power level that is less than the scheduled power level.

Claims

1. A method for transmitting data packets from an access point in a wireless local area network to a plurality of clients, comprising:

associating each client with one of a plurality of minimum power levels; and

transmitting data packets, at each of a plurality of scheduled power levels, to at least one client associated with a minimum power level less than or equal to the scheduled power level.

3. The method of claim 1, wherein said step of associating each client with one of a plurality of minimum power levels comprises:

associating each client with a lowest one of said plurality of minimum power levels for which a delivery ratio for the client is greater than a threshold.

4. The method of claim 1, wherein said step of transmitting data packets comprises:

assigning data packets to queues corresponding to the minimum power levels associated with destination clients of the data packets; and

transmitting, at the scheduled power level, data packets from a non-empty queue corresponding to highest minimum power level equal to or less than the scheduled power level.

5. The method of claim 1, wherein said step of transmitting data packets comprises:

receiving a schedule specifying a sequence of said plurality of power levels and an amount of time for transmitting at each of said plurality of scheduled power levels;

sequentially transmitting data packets, at each of said plurality of scheduled power levels in the specified sequence for the amount of time specified for each scheduled power level.

6. The method of claim 1, further comprising:

generating refinement hints for adjusting a schedule of said scheduled power levels; and

transmitting said refinement hints to a central controller.

7. The method of claim 6, wherein said step of generating refinement hints comprises:

calculating an arrival rate for each of said scheduled power levels; and

determining an adjusted time for each of said scheduled power levels, such that the adjusted time for each of said scheduled power levels is proportional to the arrival rate for the scheduled power level.

8. The method of claim 1, further comprising:

detecting when a delivery rate of a client is less than a threshold; and

when the delivery rate of a client is less than the threshold, upgrading the minimum power level associated with the client to a next highest one of said plurality of minimum power levels.

2. The method of claim 2, further comprising:

synchronizing an internal clock of said access point to a global clock, wherein said plurality of scheduled power levels are scheduled with respect to the global clock.

9. A method for transmitting data packets from a plurality of access points in a wireless local area network to clients of each of said plurality of access points, comprising:

for each of said plurality of access points, associating each client with one of a plurality of minimum power levels;

generating a global schedule for transmission at each of a plurality of transmission power levels for a corresponding transmission time; and

transmitting from each of said access points, at each of said plurality of transmission power levels for the corresponding transmission time according to said global schedule, data packets to at least one client associated with a minimum power level less than or equal to the transmission power level.

10. The method of claim 9, further comprising:

synchronizing each of said access points to a global clock, wherein said global schedule is followed simultaneously by each of said access points based on said global clock.

11. The method of claim 9, wherein said step of associating each client with one of a plurality of minimum power levels comprises:

associating each client with a lowest one of said plurality of minimum power levels for which a delivery ratio for the client is greater than a threshold.

12. The method of claim 9, further comprising:

for each of said plurality of access points, generating refinement hints for adjusting said global schedule based on performance data for the access point; and

refining said global schedule based on said refinement hints for all of said plurality of access points.

13. The method of claim 12, wherein said step of generating refinement hints comprises for each of said plurality of access points:

calculating an arrival rate for each of said transmission power levels; and

determining an adjusted time for each of said transmission power levels, such that the adjusted time for each of said transmission power levels is proportional to the arrival rate for the transmission power level.

14. The method of claim 12, wherein said step of refining said global schedule comprises:

calculating minimum time allocation for each of said plurality of transmission power levels based on said refinement hints; and

distributing remaining time among transmission power levels that require more than the minimum allocation based on said refinement hints.

15. The method of claim 9, further comprising:

for each of said plurality of access points, detecting when a delivery rate of a client is less than a threshold; and

when the delivery rate of a client is less than the threshold, upgrading the minimum power level associated with the client to a next highest one of said plurality of minimum power levels.

16. An access point for transmitting data packets to a plurality of clients in a wireless local area network, comprising:

means for associating each client with one of a plurality of minimum power levels; and

means transmitting data packets, at each of a plurality of scheduled power levels, to at least one client associated with a minimum power level less than or equal to the scheduled power level.

17. The access point of claim 16, further comprising:

means for synchronizing an internal clock to a global clock, wherein said plurality of scheduled power levels are scheduled with respect to the global clock.

18. The access point of claim 16, wherein said means for transmitting data packets comprises:

a plurality of queues, each corresponding to one of the plurality of minimum power levels for storing data packets destined for clients associated with said one of the plurality of minimum power levels; and

a wireless transmitter for transmitting, at the scheduled power level, data packets from a non-empty queue corresponding to highest minimum power level equal to or less than the scheduled power level.

19. The access point of claim 16, further comprising:

means for generating refinement hints for adjusting a schedule of said scheduled power levels; and

means for transmitting said refinement hints to a central controller.

20. The access point of claim 16, further comprising:

means for detecting when a delivery rate of a client is less than a threshold; and

means for upgrading the minimum power level associated with a client to a next highest one of said plurality of minimum power levels when the delivery rate of the client is less than the threshold.

21. A system for transmitting data packets to a plurality of clients in a wireless local area network, comprising:

a central controller configured to generate a global schedule for transmission at each of a plurality of transmission power levels for a corresponding transmission time; and

a plurality of access points, each access point configured to associate each of a plurality of clients with one of a plurality of minimum power levels, and each access point configured to transmit, at each of said plurality of transmission power levels for the corresponding transmission time according to said global schedule, data packets to at least one client associated with a minimum power level less than or equal to the transmission power level.

22. The system of claim 21, wherein each of said plurality of access points is synchronized to a global clock.

23. The system of claim 21, wherein:

each of said plurality of access point is configured to generate refinement hints for adjusting said global schedule based on performance data for the access point, and transmit said refinement hints to said central controller; and

said central controller is configured to receive said refinement hints from each of said access points, and refine said global schedule based on said refinement hints.

24. The system of claim 21, wherein:

each of said plurality of access points is configured to detect when a delivery rate of a client is less than a threshold, and upgrade the minimum power level associated with a client to a next highest one of said plurality of minimum power levels when the delivery rate of the client is less than the threshold.