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Low-Power PS-Poll

This contribution presents a scheme supporting low-power medium access via Low-Power PS-Poll, addressing problems and providing suggested solutions for different PS-Poll cases. Differentiation methods and AP responses to Low-Power PS-Poll are discussed.

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Low-Power PS-Poll

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  1. Low-Power PS-Poll Authors: Date: 2012-05-13 Shoukang Zheng et. al, I2R, Singapore

  2. Abstract In this contribution, we present the scheme to support low power medium access with low-power PS-Poll. Shoukang Zheng et. al, I2R, Singapore

  3. Low Power Medium Access • In 802.11ah use cases, battery-operated devices benefit from the low power operation • IEEE 802.11-11/1137r4 • 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 Shoukang Zheng et. al, I2R, Singapore

  4. Problems • When AP receives the PS-Poll sent by a STA listening to beacon/TIM, AP shall respond by ACK or buffered frame • When AP receives the PS-Poll sent by low-power-operated STA without listening to beacon/TIM, AP shall respond by ACK with BU bit (set as 1 or 0) or buffered frame Shoukang Zheng et. al, I2R, Singapore

  5. Motivation • Two types of PS-Polls • Power Saving Mode • Low Power Medium Access • There may be different protocols (e.g. four cases as follows) for the above two PS-Polls • The protocols need to know the type of PS-Poll due to different protocols • How to know which type of PS-Poll Shoukang Zheng et. al, I2R, Singapore

  6. Case 1 • For the case that TIM bit for a STA in current beacon interval is one and the STA wakes up in that interval, AP that can’t send DATA must differentiate normal PS-Poll from the PS-Poll sent by low-power-operated STA unless BU bit is also set for ACK • If PS-Poll is sent by STA without listening to beacon/TIM, AP shall respond by ACK with BU bit set as 1, and STA will check BU bit and wait for DATA after receiving ACK. Short ACK without BU bit cannot be used. • If PS-Poll is sent by STA listening to beacon/TIM, AP shall respond by ACK ignoring BU bit, and STA will wait for DATA after receiving ACK. Short ACK can be used. Shoukang Zheng et. al, I2R, Singapore

  7. Case 2 • For the case that TIM bit for a STA in current beacon interval is zero and the STA wakes up in that interval, AP doesn’t have to differentiate normal PS-Poll from the PS-Poll sent by low-power-operated STA if Short ACK is not used • If PS-Poll is sent by STA without listening to beacon/TIM, AP shall respond by ACK with BU bit set as 0, and STA will check BU bit and can go to sleep after receiving ACK. Short ACK without BU bit cannot be used. • PS-Poll will not be sent by STA listening to beacon/TIM and AP shall not expect any PS-Poll for the STA. Shoukang Zheng et. al, I2R, Singapore

  8. Case 3 • For a PS-Poll sent by low-power-operated STA, AP may respond with a timer [DCN 409] • As the acknowledgment to the STA • Other STAs can make use of this timer if RA for the ACK is broadcast address • Not required to check the status of buffered unit if BU bit is not used • Helpful when AP can’t respond by ACK with BU bit set as 1 or 0 promptly in SIFS for a STA as it takes time to find out whether the STA is low-power-operated and has buffered unit Shoukang Zheng et. al, I2R, Singapore

  9. Case 4 • For STA supporting low power operation, TIM bit is not transmitted [DCN 0343] • If PS-Poll is sent by low power STA and there is buffered frame, AP shall respond by ACK with BU = 1, and STA will check BU bit and wait for DATA after receiving ACK. Short ACK without BU bit cannot be used. • If PS-Poll is sent by power saving STA, AP shall respond by ACK ignoring BU bit, and STA will wait for DATA after receiving ACK. Short ACK can be used. • If PS-Poll is sent by low power STA and there is no buffered frame, AP shall respond by ACK with BU = 0, and STA will check BU bit and can go to sleep after receiving ACK. Short ACK without BU bit cannot be used. Shoukang Zheng et. al, I2R, Singapore

  10. Suggested Solution • We propose the method to differentiate two types of PS-Polls: (1) normal PS-Poll for Power Saving STA where the STA listens to the TIM sent by its associated AP and (2) low-power PS-Poll for STA with low power operation • defining a Low-Power-PS-Poll bit in PS-Poll (simple) • giving a new type of control frame for the low-power PS-Poll by STA with low power operation Shoukang Zheng et. al, I2R, Singapore

  11. Low-Power PS-Poll • Low-Power-PS-Poll bit in PS-Poll differentiates the normal PS-Poll from the low-power PS-Poll • If a STA supporting low power operation transmits PS-Poll without listening to the beacon/TIM, it makes use of the Low-Power-PS-Poll bit to indicate that the PS-Poll is a low-power PS-Poll Shoukang Zheng et. al, I2R, Singapore

  12. AP’s response to Low-Power PS-Poll • When AP receives the low-power PS-Poll, it follows the related protocol to handle this PS-Poll • For example, AP follows the protocol as in IEEE 802.11-11/1137r4 or • Use normal ACK rather than short ACK without BU bit • Other enhancement if applicable Shoukang Zheng et. al, I2R, Singapore

  13. Method 1 for Low-Power PS-Poll bit • Low-Power-PS-Poll bit can reuse Power Management bit • Setting it as 0 in normal PS-Poll to indicate the STA is low-power-operated and AP will handle it accordingly Shoukang Zheng et. al, I2R, Singapore

  14. Method 2 for Low-Power PS-Poll bit • Low-Power-PS-Poll bit can use the reserved case of DURATION/ID field (see table below) • Use bit 13 to indicate (for the case of bit 14=1 and bit 15=1) Shoukang Zheng et. al, I2R, Singapore

  15. Conclusions • We propose to use Low-Power-PS-Poll bit to differentiate the low-power PS-Poll sent by STA supporting low power operation from the normal PS-Poll. Shoukang Zheng et. al, I2R, Singapore

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

  17. Straw Poll (1) • Do you agree that AP shall differentiate two types of PS-Poll as in slide 5? • Y: • N: • A: Shoukang Zheng et. al, I2R, Singapore

  18. Straw Poll (2) • Do you agree to define a Low-Power-PS-Poll bit in PS-Poll to facilitate the operation at AP as in slide 11? • Y: • N: • A: Shoukang Zheng et. al, I2R, Singapore

  19. Straw Poll (3) • Do you agree that Low-Power-PS-Poll bit reuses Power Management bitas in slide 13? • Y: • N: • A: Shoukang Zheng et. al, I2R, Singapore

  20. Straw Poll (4) • Do you agree that AP shall respond to the low-power PS-Poll following the related protocol as in Slide 12? • Y: • N: • A: Shoukang Zheng et. al, I2R, Singapore

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