1. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 1 Some thoughts on power saving functionality Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2006-05-15 Authors:

2. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 2 Abstract Review what the power saving is needed for. Review the power saving functionality in the current draft spec. –The power saving functionality is designed based on : Reuse the mechanism of ATIM for IBSS, TIM IE in the beacon frame and PS-Poll for BSS, and APSD. Strict synchronization throughout the mesh. Beacon broadcaster rotation is coupled with power saving. Motivation of these slides is to check how the current draft spec treats power saving functionality. A suggestion is made at the latter part of the slides.

3. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 3 What the power saving is for ? The benefit of power saving mechanism are : –Introduce the low power consumption capability by reducing the active duty cycle of PHY/MAC. Reducing power consumption is one of the mandatory requirement for battery- powered devices. Longer battery life, such as cell-phone, laptop PC, etc... Low power capability is going to be an important requirements even for AC- powered devices, at least in the area of CE devices. Energy saving motivation, accelerated by ecology oriented consensus, conformance to Kyoto Protocol, etc... –Devices for infrastructure may not leverage the power saving functions. The cost of power saving mechanism are : –Add the extra complexity to support the PS functionality. –Introduce some inflexibility in terms of the frame delivery. (Transmitter shall make sure that receiver STA is in awake state prior to the transmission of the frame.)

4. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 4 What the power saving is for ? (Cont’d) Residential scenario

5. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 5 What the power saving is for ? (Cont’d) Residential scenario –Let the battery-powered device save the power.

6. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 6 What the power saving is for ? (Cont’d) Residential scenario –If the player is on the cradle, use this route and let other devices to fall in sleep.

7. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 7 What the power saving is for ? (Cont’d) Residential scenario –In night time, most of the applications are not running. –Let all the devices save power. –The mesh have to be capable to re-activate the operation in the morning.

8. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 8 What the power saving is for ? (Cont’d) Public safety / Military scenario –Some/many of the MPs are mobile terminal. –Longer battery life is preferred. Portable battery-powered devices would like to save the power.

9. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 9 What the power saving is for ? (Cont’d) Public safety / Military scenario –Some MPs could save power while other MPs are communicating.

10. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 10 What the power saving is for ? (Cont’d) Public safety / Military scenario –Mesh might be disconnected physically for a while due to the MP’s mobility.

11. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 11 What the power saving is for ? (Cont’d) The characteristic of devices/UMs (usage models) which leverage power save mode : –The battery-powered devices exactly need power saving functionality, such as handheld devices. These devices usually have less signal processing power due to the power conservation and/or cost restraints. The battery-powered devices are usually “mobile” devices, where the device mobility leads to physical topology change in the mesh. –In some deployment scenario, the active mesh operations do not need to be maintained 24 hours a day, 365 days a year. The device should operate in the PS mode during the idle time. Users may shut down some of the MP’s power supply in order to : –Make sure to achieve the complete power save (power down). –Operate the technical maintenance or recovery from the failure. –  Topology will be changed upon the leave of MP.

12. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 12 PS mode in the current spec According to P802.11s-D0.01 : –“The mesh point will advertise its power save state to all neighboring mesh points by using it’s beacons and by sending a Null-Data frame with the PS bit active.” “Mesh point waking to receive a beacon will stay awake for a minimum period of ATIM window” “Mesh points in power save mode shall also wakeup according to any negotiated schedule as part of TSPEC setup with other mesh points....” “The PS operation of an unsynchronizing MAP is based upon IEEE 802.11 infrastructure power management operation.” [quoted from subclause 11A.13.1]. –“All non-AP MPs that support the mesh power save mechanism shall support synchronization” [in subclause 11A.13.1], –“MPs that support power save operation must also support the deterministic beacon broadcasting selection as described in this section” [in subclause 11A.13.8] The power saving is designed based on : –Reuse the mechanism of ATIM for IBSS, TIM IE in the beacon frame and PS-Poll for MAP, and APSD. –Strict synchronization throughout the mesh. –Beacon broadcaster rotation is coupled with power saving.

13. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 13 PS mode in the current spec (Cont’d) May contradict with the device characteristic –Power Saving MP have to be synchronized, and maintain the mesh TSF, where PS operation may cause the confusion of mesh TSF maintenance (during the stand-by state), depending on the topology.* –Mobile MP may cause the topology change, which may cause the confusion of mesh TSF maintenance.* –BB rotation have to be implemented, where BB rotation costs additional complexity for MP. Handheld devices have limited processing power, in general. Treated as an option of options –Power saving is optionally defined above the optional synchronization feature, whereas the power saving is close to a mandatory feature for battery-powered devices. * Refer to “IEEE802.11-06/581r0” for details.

14. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 14 A suggestion for power saving mechanism Allow unsynchronizing MPs to enter the PS mode –Although the active duty cycle reduction may not be optimized compared to that of the synchronizing MPs, it could be reasonably effective and useful in some scenarios. –Provides both the power save functionality and higher operational flexibility and reliability, with less complexity. –Could be added easily using the existing mechanisms defined in P802.11-REVma/D5.2 and P802.11s-D0.01.

15. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 15 Power Saving for unsync MPs Procedure for unsync power saving MP 1.Run its own TSF just as unsynchronizing MAP, and define its own DTIM period.  as defined for all the MP 2.Return to the active state prior to the mesh DTIM beacon (and BSS DTIM beacons of unsync MAP) of neighbors.  MP will wake up prior to all the DTIM beacons of the neighbor MPs. 3.Wake up until the end of ATIM window of neighboring MPs, and may return to the doze state if nothing is received during the ATIM window.  as defined for sync MP If the beacon containing TIM indicating the existence of buffered traffic to it is received from neighboring MAP, it will try to receive the frames by sending PS- Poll frames.  as defined in 802.11 infrastructure mode 4.Transmit beacons every mesh DTIM period, and operate ATIM process as defined.  as defined for sync MP 5.Conform to APSD operations, referring the TSF timer value of transmitter.  Use the TSF timer value of transmitter instead of commonly defined TSF.

16. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 16 Power Saving for unsync MPs (Cont’d) Procedure for neighboring MPs 1.Neighbor MPs perform as described in P802.11s-D0.01. 2.Neighbor MAPs perform as described in P802.11-REVma/D5.2, dealing as neigboring MPs in PS mode as associating STA in PS mode. 3.Or optionally may transmit ATIM frame during the ATIM window of the power saving MP to let the power saving MP know if it has a packet to send to this power saving MP.

17. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 17 Power Saving for unsync MPs (Cont’d) Example processing flow (current spec)

18. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 18 Power Saving for unsync MPs (Cont’d) Example processing flow (a suggestion)

19. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 19 Summary Power saving is a quite important feature for some of the 802.11 devices. Speculated the usage scenario utilizing power saving functionality, and introduced the potential risk of power saving MPs in the current spec. Suggested to define a power saving capability for unsynchronizing MPs. Recommended change in the draft text is provided by comment sheet.

20. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 20 References [1] P802.11-REVma/D5.2 [2] P802.11s-D0.01 [3] 11-04/662r16 “IEEE 802.11 TGs Usage Models” [4] “Some thoughts on potential issue in mesh operation”, IEEE802.11-06/581r0.

21. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 21 End of slides Comments/Questions/Suggestions/Corrections are purely welcomed.

22. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 22 Backup (1) Alternative approach for unsync MP PS –PS mode in the current draft is mostly designed based on IBSS operation and APSD. –IBSS based approach is mainly used to enhance longer “stand-by time”. –APSD based approach is mainly used to enhance longer “talk time”. –Alternative approach is possible to enhance longer “stand-by time”, based on BSS infrastructure mode power saving. Use TIM IE in the beacon, Use PS-poll frame, Use PS-bit in the frame control field, Conform to power-save operation defined for BSS infrastructure mode.

23. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 23 Backup (2) Procedure for unsync power saving MP (alternative approach) 1.Run its own TSF just as unsynchronizing MAP, and define its own DTIM period.  as defined for all the MP 2.Return to the active state prior to the DTIM beacon of all the neighbors.  MP will wake up prior to all the DTIM beacons of the neighbor MPs. 3.If the beacon containing TIM indicating the existence of buffered traffic to it is received from neighboring MP, it will try to receive the frames by sending PS-Poll frames.  as defined in 802.11 infrastructure mode 4.Transmit beacons every mesh DTIM period, even if it is in the PS mode. And may return to the doze state if nothing is received during the ATIM window.  as defined for sync MP 5.MP shall transmit beacons containing TIM at every TBTT, if it buffers the transmitting frames, and remain in the active state. 6.MP may return to the doze state if it does not buffer transmitting frames and the PS- bit received from neighbors indicate the buffered frame delivery is finished. 7.Conform to APSD operations, referring the TSF timer value of transmitter.  Use the TSF timer value of transmitter instead of commonly defined TSF.

24. doc.: IEEE 802.11-06/582r0 Submission May 2006 Kazuyuki SakodaSlide 24 Backup (3) Example processing flow (alternative approach)