Supporting Low Power Operation Month Year doc.: IEEE 802.11-yy/XXXXr0 March 2012 Supporting Low Power Operation Date: 2012-03-13 Authors: Shoukang Zheng et. al, I2R, Singapore Shoukang ZHENG et. al, I2R, Singapore

Month Year doc.: IEEE 802.11-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 802.11ah networks. Shoukang Zheng et. al, I2R, Singapore Shoukang ZHENG et. al, I2R, Singapore

March 2012 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, Specification framework for TGah]. Shoukang Zheng et. al, I2R, Singapore

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

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

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 802.11v, 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

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

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

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

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

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

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