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Slot-based Power Save without PS-Poll

Date: July, 2012. Slot-based Power Save without PS-Poll. Date: 2012-07-12. Authors:. Slot-Based Power Save in [1]. The time slot duration T July be chosen to be large enough to complete PS-Poll/trigger+SIFS+DATA+SIFS+ACK (e.g. 20 ~ 40 mS) .

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Slot-based Power Save without PS-Poll

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  1. Date: July, 2012 Slot-based Power Save without PS-Poll Date: 2012-07-12 Authors: Liwen Chu Etc.

  2. Slot-Based Power Save in [1] • The time slot duration T July be chosen to be large enough to complete PS-Poll/trigger+SIFS+DATA+SIFS+ACK (e.g. 20 ~ 40 mS). • A STA randomly chooses a time slot to start its uplink channel access. And, an AP can assign a time slot for a STA. • Both randomly selecting time slot and deterministic time slot need to synchronize to slot edge. • But deterministic time slot has higher efficiency. • Each STA starts to access the channel at the assigned time slot following EDCA. • Issues: • If a STA in the BSS can not receives the Beacon frames, It July still create hidden node problem. • OBSS STAs can collide with the slot transmission. • PS-Poll creates overhead. TIM bitmap Total N time slots, each time slot duration = T … 1 1 0 1 0 0 1 1 STA1 STA10 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

  3. Wake up BI of PS-Poll STA • STAs operating in PS modes shall periodically listen for Beacon frames, as determined by the STA's ListenInterval and the ReceiveDTIMs parameter in the MLME-POWERMGT.request primitive. • The STA shall wake up early enough to receive the first Beacon scheduled for transmission at the time corresponding to the last TBTT plus the ListenInterval. • A STA doesn’t need to wake up at each TBTT, but the AP knows when a STA shall wake up. • A STA in PS modes July not receive DTIM Beacon if ReceiveDTIMs is 0. • A STA July not receive DTIM Beacon When dot11MgmtOptionFMSActivated is false. • A WNM sleep STA needs not wake up every DTIM interval. • A WNM sleep STA wakes up every SleepInterval to check the TIM.

  4. Slot-based PS-Poll ListenInterval • STAs operating in PS modes shall periodically listen for Beacon frames, as determined by the STA's ListenInterval/SleepInterval and the ReceiveDTIMs parameter. • The STA sends ListenInterval/SleepInterval to the AP through Association Response or other method. • The AP knows when a STA shall wake up. • GroupInterval (in BI) of a slot-based PS-Poll STA is the interval between two adjacent TBTT that the AP sends the TIM of the STA’s group (Group TBTT). TIM for group n will be transmitted in the beacon. STAj July wake up. Slot for STAj will not be allocated. Group n TBTT Group n TBTT Group n TBTT Group n TBTT Group n TBTT GroupInterval (in BI) TBTT TBTT STAj ListenInterval STAj in Group n associates with AP With ListenInterval=3*GroupInterval STAj shall wake up. TIM for STAj shall be transmitted in the beacon. Slot July be allocated to STAj.

  5. Slot-based PS-Poll ListenInterval (Cont’d) • A slot is allocated to a STA in the BI whose TBTT is the last TBTT plus the ListenInterval. • During other BIs corresponding to a group’s TBTT, slot is not allocated to the STA. Normal PS Poll can be used. • The STA shall wake up early enough to receive the first Beacon scheduled for transmission at the time corresponding to the last TBTT plus the ListenInterval/SleepInterval. • The last TBTT is the TBTT for the group (Group TBTT) that the STA belongs to after its association plus N* ListenInterval/SleepInterval (e.g. N=1, 2, 3…). • The ListenInterval/SleepInterval is GroupInterval*M (e.g. M=1, 2, 3…) TIM for group n will be transmitted in the beacon. STAj July wake up. Slot for STAj will not be allocated. Group n TBTT Group n TBTT Group n TBTT Group n TBTT Group n TBTT GroupInterval (in BI) TBTT TBTT STAj ListenInterval STAj in Group n associates with AP With ListenInterval=3*GroupInterval STAj shall wake up. TIM for STAj shall be transmitted in the beacon. Slot July be allocated to STAj.

  6. Slot-Based Power Save Without PS-Poll • When the AP knows which slot (or which slots) that a STA uses, the AP knows that the STAs will wake up at the corresponding slot (or slots). • The AP can transmit the buffer frame to the STA without using PS-Poll. • With this improvement: • An AP can select to send a CTS-to-Self with the Duration value covering whole Slots. Only one backoff before CTS-to-Self is required. • An OBSS STA will set its NAV after receiving the CTS-to-Self. Collision from OBSS can be avoided. • A STA in the BSS which does not receive the beacon will set its NAV after receiving the CTS-to-Self. • When no CTS-to-Self is used, the AP starts to access the channel at the each time slot following EDCA. • The AP can select one backoff before the first time slot. • All slots are shorter, because the backoff and PS-Poll overhead is eliminated. 1 1 1 1 1 1 1 1 Total N time slots, each time slot duration = T TIM bitmap 0 1 1 0 STA1 STA12 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

  7. Slot-Based Power Save Without PS-Poll (Cont’d) • When some STAs in power save mode do not receive frames correctly, then: • After finishing the total time slot access, the AP July transmit another TIM frame to start another slot based access. Beacon TIM frame 1 1 1 1 1 1 1 1 TIM bitmap 0 1 1 0 STA1 STA12 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 STA 1, 3, 6, 8 The AP does not receives ACKs from STA 1, 3, 6, 8. Total N=10 time slots, each time slot duration = T

  8. Reference [1] 802.11-12/606r0, Uplink Channel Access.

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