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Channel Access Supporting Low Power Operation

Channel Access Supporting Low Power Operation. Authors:. Date: 2012-07-12. Abstract. In this contribution, we present the scheme to re-schedule doze/awake time for PS-Poll sent by STA supporting low power operation in 802.11ah networks. Motivation.

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Channel Access Supporting Low Power Operation

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  1. Channel Access Supporting Low Power Operation Authors: Date: 2012-07-12 Shoukang Zheng et. al, I2R, Singapore

  2. Shoukang Zheng et. al, I2R, Singapore

  3. Shoukang Zheng et. al, I2R, Singapore

  4. Abstract In this contribution, we present the scheme to re-schedule doze/awake time for PS-Poll sent by STA supporting low power operation in 802.11ah networks Shoukang Zheng et. al, I2R, Singapore

  5. 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]. Shoukang Zheng et. al, I2R, Singapore

  6. Example of Low Power Medium Access beacon DATA 1 DATA 1 DATA 2 beacon DATA 3 DATA 4 ACK BU=1 ACK BU=1 ACK BU=1 AP Short Ack PS-Poll awake doze STA1 Short Ack PS-Poll STA2 awake doze Short Ack PS-Poll STA3 awake doze Short Ack STA4 PS-Poll awake doze Shoukang Zheng et. al, I2R, Singapore

  7. 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 • busy processing other matters • 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 Shoukang Zheng et. al, I2R, Singapore

  8. 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 • AP determines to use the protocol [1] or this proposed scheme Shoukang Zheng et. al, I2R, Singapore

  9. July 2012 Turning into Paged STA • After non-TIM STA is switched to Power Save Mode, AP can assume that non-TIM STA is going to become paged STA and wake up in the next beacon transmission time • If the beacon carries the slot information associated with the TIM bit for it to receive downlink buffered unit, this paged STA (originally non-TIM STA) may not send PS-Poll again • The above paged STA can go to sleep till the assigned slot if there is no uplink data to transmit • In the assigned time slot, the paged STA wakes up to receive the downlink data from the AP Shoukang Zheng et. al, I2R, Singapore

  10. Example of Proposed Scheme beacon DATA 1 DATA 1 DATA 2 beacon DATA 3 DATA 4 ACK BU=1 Timer BU=1 Timer BU=1 AP Short Ack PS-Poll awake doze STA1 Short Ack PS-Poll STA2 awake doze Short Ack PS-Poll STA3 doze awake doze Short Ack STA4 PS-Poll doze awake doze Shoukang Zheng et. al, I2R, Singapore

  11. Conclusions • We propose to support low power operation through the re-scheduling of doze/awake time for the STAs. • The timer can be used to indicate the beacon transmission time to support the above rescheduling. Shoukang Zheng et. al, I2R, Singapore

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

  13. Straw Poll • Do you agree that AP may reply to the PS-Poll with a timer indicating the re-scheduling of doze/awake time as in slide 8? • Y: • N: • A: Shoukang Zheng et. al, I2R, Singapore

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