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Slot-based Power Save Improvement

Date: July, 2012. Slot-based Power Save Improvement. Date: 2012-07-12. Authors:. Slot-Based Power Save in [1]. The time slot duration T may 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 Improvement

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  1. Date: July, 2012 Slot-based Power Save Improvement Date: 2012-07-12 Authors: Liwen Chu Etc.

  2. Slot-Based Power Save in [1] • The time slot duration T may 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, or an AP can assign a time slot for a STA. • Each STA starts to access the channel at the assigned time slot following EDCA. • STAs do not collide with each other during slot-based access period. This can solve hidden-node problem. • Issues: • Group frames may transmitted before the slot-based transmission. The flexibility should be provided to when to start the slot-based transmission. • Each STA in the BSS should be able to decide the slot-based access period. Otherwise, there may be collision. • OBSS STAs can collide with the slot transmission. • It is difficult to harmonize slot-based PS-Poll access and non-slot-based PS-Poll access. 1 1 1 1 1 1 1 1 TIM bitmap Total N time slots, each time slot duration = T 0 1 1 0 STA12 STA1 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

  3. Collision Avoidance in the Same BSS • With slot-based access, to avoid hidden node problem in the BSS, a non-power-save STA needs to be able to figure out the slot-based access period start time and length. • Solution: • In the beacon frame, slot-based access period is indicated by the AP implicitly or clearly. • Start time of slot-based access period (if slot-based access period always starts after beacon transmission, this is not required), • length of slot-based access period (in ms/TU etc). • During slot-based access period in the received beacon, a STA shall set its NAV and does not try to access the wireless medium. TIM bitmap Total N time slots, each time slot duration = T 1 1 1 1 1 1 1 1 0 1 1 0 STA12 STA1 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Slot-based access period …

  4. OBSS Collision Avoidance • OBSS STAs do not decode TIM element. They do not know the slot-based access period start time and length. • OBSS’s hidden node problem is still there. • Solution: • In the beacon frame, slot-based access period is indicated by the AP. • Start time of slot-based access period (if slot-based access period always starts after beacon transmission, this is not required), • length of slot-based access period (in ms/TU etc). • During slot-based access period in the received beacon, a STA shall set its NAV and does not try to access the wireless medium. TIM bitmap Total N time slots, each time slot duration = T 1 1 1 1 1 1 1 1 0 1 1 0 STA12 STA1 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Slot-based access period …

  5. Harmonization of Non-slot-based and Slot-based PS-Poll • A power save STA may not support slot-based PS-Poll to simplify its design. • If the AP allocates slot for such power save STA, the slot is waste. • Solution: • A slot-based power save indication is defined. • Slot-based Power Save Indication can be in Extended Capabilities element or a new element. • An AP shall not allocate slots to power save STAs without slot-based power save capabilities. STA1 to STA10 have slot-based PS-Poll capabilities. STA11 and STA12 don’t have slot-based PS-Poll capabilities. TIM bitmap Total N time slots, each time slot duration = T 1 1 1 1 1 1 1 1 0 1 1 1 STA12 STA1 STA 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Slot-based access period

  6. Pre Motion 1 Do you support adding the following text to the specification framework document: STAs in overlapping BSS set its NAV to not try to access the wireless medium during the RAW indicated by the received beacon from an AP that they do not associate with

  7. Pre Motion 2 Do you support adding the following text to the specification framework document: A power save STA can indicate if it supports RAW operation to an AP.

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

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