1. doc.: IEEE 802.11-12/0409r5 Submission May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 1 Supporting Low Power Operation Date: 2012-05-13 Authors:

2. doc.: IEEE 802.11-12/0409r5 Submission May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 2 Abstract In this contribution, we present the scheme to re-schedule doze/awake time through ACK timer for PS-Poll sent by STA supporting low power operation in 802.11ah networks.

3. doc.: IEEE 802.11-12/0409r5 Submission May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 3 Motivation In 802.11ah use cases, battery-operated devices benefit from the low power operation. A STA with low power operation may not listen to Traffic Indication from the AP. It may send PS-Poll any time. The AP receives PS-Poll shall immediately respond with ACK or buffered data frame to the STA [IEEE 802.11-11/1137r4].

4. doc.: IEEE 802.11-12/0409r5 Submission awake doze awake Example of Low Power Medium Access May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 4 beaconbeacon PS-Poll ACK BU=1 DATA1DATA1 AP STA1 STA2 STA3 STA4 ACK BU=1 ACK BU=1 DATA1DATA1 Short Ack DATA2DATA2 Short Ack beaconbeacon DATA3DATA3 Short Ack DATA4DATA4 Short Ack PS-Poll doze

5. doc.: IEEE 802.11-12/0409r5 Submission Problems When a large number of STAs transmits PS-Poll after waking up –STA with buffered frame has to wait for DATA when AP is unable to respond promptly due to transmitting fragmented DATA retransmitting DATA taking time to determine the status of buffered frame –AP may not complete the data transmissions for all the PS-Polls in the beacon interval –When data rate is low, STAs waste more power to contend/wait May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 5

6. doc.: IEEE 802.11-12/0409r5 Submission Suggested Solution Re-scheduling doze/awake time –PS-Poll not followed by DATA or immediate ACK, AP replies to STA with a timer indicating when it should wake up again –The timer is considered short enough without causing too much clock drift –The reply may contain traffic indication for STAs If PS-Polling STA knows no buffered frame, it goes to sleep If PS-Polling STA knows buffered frame for itself, it may go to sleep and wake up again after timer expires Other STAs may make use of this timer –STA can re-sync to the beacon with the help of the timer May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 6

7. doc.: IEEE 802.11-12/0409r5 Submission doze awake doze awake Example of Proposed Scheme May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 7 beaconbeacon PS-Poll ACK BU=1 DATA1DATA1 AP STA1 STA2 STA3 STA4 ACK Timer BU=1 ACK Timer BU=1 DATA1DATA1 Short Ack DATA2DATA2 Short Ack beaconbeacon DATA3DATA3 Short Ack DATA4DATA4 Short Ack PS-Poll doze

8. doc.: IEEE 802.11-12/0409r5 Submission ACK Timer (1/3) May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 8 Use normal ACK with a timer to reschedule doze/awake time for low-power-operated STA The timer can use the reserved case of Duration/ID field of ACK frame – bit 14=0 and bit 15=1, where bit 0-13 can be used for timer

9. doc.: IEEE 802.11-12/0409r5 Submission ACK Timer (2/3) May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 9 RA for ACK timer –Unicast address: only the STA sending the PS-Poll –Broadcast address: all STAs supporting low power operation

10. doc.: IEEE 802.11-12/0409r5 Submission ACK Timer (3/3) May 2012 Shoukang Zheng et. al, I2R, SingaporeSlide 10 The unit of the timer –Negotiated between AP and STA or determined by AP –Microsecond since the range is 1-16383, not long enough to cover a longer time –TU, fraction of beacon interval or beacon interval? TU –Absolute value, not flexible beacon interval –STA consume more power due to coarse-grained timer Fraction of beacon interval –may be suitable

11. doc.: IEEE 802.11-12/0409r5 Submission May 2012 Slide 11 Conclusions We propose to support low power operation through the re- scheduling of doze/awake time for the STAs. ACK timer is proposed to support the above rescheduling. Shoukang Zheng et. al, I2R, Singapore

12. doc.: IEEE 802.11-12/0409r5 Submission May 2012 Slide 12 References [1] 11-12/127r1, Low Power Medium Access. Shoukang Zheng et. al, I2R, Singapore