1. Supporting Low Power Operation
Month Year
doc.: IEEE yy/XXXXr0
March 2012
Supporting Low Power Operation
Date:
Authors:
Shoukang Zheng et. al, I2R, Singapore
Shoukang ZHENG et. al, I2R, Singapore

2. Month Year
doc.: IEEE yy/XXXXr0
March 2012
Abstract
In this contribution, we present the scheme that AP delays the response to acknowledge the PS-Poll through TIM frame or re-scheduling doze/awake time through an indicated timer for power saving mode operation in ah networks.
Shoukang Zheng et. al, I2R, Singapore
Shoukang ZHENG et. al, I2R, Singapore

3. March 2012
Motivation
In ah 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 /1137r4, Specification framework for TGah].
Shoukang Zheng et. al, I2R, Singapore

4. March 2012
Problems
When a large number of STAs transmits PS-Poll after waking up,
STA may have to wait for DATA even if PS-Poll has been received by AP due to that AP is busy
Some STAs may not have buffered frames at the AP and should go to sleep as soon as possible
When data rate is low, STAs waste more power to contend/wait
PS-Poll transmission time may be very close to beacon/TIM transmission time
Shoukang Zheng et. al, I2R, Singapore

5. Suggested Solution (1) Delay the response to STA’s PS-Polling
March 2012
Suggested Solution (1)
Delay the response to STA’s PS-Polling
If very close to beacon/TIM transmission time, AP is busy with other transmissions, or TIM segment doesn’t include the STA, the STA accepts a longer waiting time for the acknowledgment from the AP
After receiving one/a few PS-Polls, the AP starts to reply
The time is determined by AP and STA (e.g. during association or other management frame exchange).
Before the time expires, if AP still engages other transmissions, it may continue current transmissions without immediate response
The delay may be decided by the smaller value of the difference between the time to transmit PS-Poll and next related TIM transmission time, and a timer
Shoukang Zheng et. al, I2R, Singapore

6. Suggested Solution (1) Cont’d
March 2012
Suggested Solution (1) Cont’d
Delay the response to STA’s PS-Polling
The acknowledgment
TIM segments or TIM frames (independent of beacon as in v, where TIM broadcast allows such TIM frame)
Acknowledgement may be transmitted in a higher data rate
Other STAs
no buffered frame indicated, go to sleep
buffered frame indicated, wait for DATA from AP
Shoukang Zheng et. al, I2R, Singapore

7. Suggested Solution (2) Re-scheduling doze/awake time
March 2012
Suggested Solution (2)
Re-scheduling doze/awake time
PS-Poll not followed by DATA/immediate ACK, the 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 so that the STAs are able to capture the traffic indication
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
Shoukang Zheng et. al, I2R, Singapore

8. March 2012
Conclusions
We propose a delayed response scheme for the PS-Polls by STAs with low power operation. The collective acknowledgment through TIM segment/frame may reduce the power consumption for the awaiting STA with/without buffered frames at the AP.
We also propose to support low power consumption through the re-scheduling of doze/awake time for the PS-Polling STAs.
Shoukang Zheng et. al, I2R, Singapore

9. References [1] 11-12/127r1, Low Power Medium Access. March 2012
Shoukang Zheng et. al, I2R, Singapore

10. March 2012
Straw Poll (1)
Do you agree that AP may delay the response to the PS-Poll by the STA with low power operation through collective acknowledgment? Y: N: A:
Shoukang Zheng et. al, I2R, Singapore

11. March 2012
Straw Poll (2)
Do you agree to use TIM segment or frame as the collective acknowledgment when AP delays the response to the PS-Polls by the STAs with low power operation? Y: N: A:
Shoukang Zheng et. al, I2R, Singapore

12. March 2012
Straw Poll (3)
Do you agree that AP may reply to the PS-Poll with a timer indicating the re-scheduling of doze/wake time as in slide 7? Y: N: A:
Shoukang Zheng et. al, I2R, Singapore