Slot based power save without ps poll
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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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Slot based power save without ps poll

Date: July, 2012

Slot-based Power Save without PS-Poll

Date: 2012-07-12

Authors:

Liwen Chu Etc.


Slot based power save in 1

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


    Wake up bi of ps poll sta

    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.


    Slot based ps poll listeninterval

    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.


    Slot based ps poll listeninterval cont d

    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.


    Slot based power save without ps poll1

    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


    Slot based power save without ps poll cont d

    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


    Reference

    Reference

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


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