1. doc.: IEEE 802.11-12/0696r2 SubmissionLiwen Chu Etc.Slide 1 Slot-based Power Save without PS-Poll Date: 2012-07-12 Authors: Date: July, 2012

2. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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. STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Total N time slots, each time slot duration = T … TIM bitmap 11 1 0 1001 STA10 STA1

3. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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). TBTT Group n TBTT Group n TBTT TIM for group n will be transmitted in the beacon. Group n TBTT Group n TBTT Group n TBTT STAj in Group n associates with AP With ListenInterval=3*GroupInterval GroupInterval (in BI) STAj shall wake up. TIM for STAj shall be transmitted in the beacon. Slot July be allocated to STAj. STAj ListenInterval STAj July wake up. Slot for STAj will not be allocated.

5. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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…) TBTT Group n TBTT Group n TBTT TIM for group n will be transmitted in the beacon. Group n TBTT Group n TBTT Group n TBTT STAj in Group n associates with AP With ListenInterval=3*GroupInterval GroupInterval (in BI) STAj shall wake up. TIM for STAj shall be transmitted in the beacon. Slot July be allocated to STAj. STAj ListenInterval STAj July wake up. Slot for STAj will not be allocated.

6. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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. STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Total N time slots, each time slot duration = T TIM bitmap 1 0 01 STA12 11 11 11 11 STA1

7. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 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. STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Total N=10 time slots, each time slot duration = T Beacon STA 1, 3, 6, 8 TIM frame The AP does not receives ACKs from STA 1, 3, 6, 8. TIM bitmap 1 0 01 STA12 11 11 11 11 STA1

8. doc.: IEEE 802.11-12/0696r2 Submission Date: July, 2012 Slide 8 Reference [1] 802.11-12/606r0, Uplink Channel Access.