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Expanding Power Save Efficiency in IEEE 802.11 Networks

Discussing strategies to achieve deeper power saving capabilities for UHR STAs in IEEE 802.11 networks, focusing on critical traffic service considerations. Introducing concepts like cross-link wake-up to enable STAs to enter deep doze states efficiently while ensuring timely activation for critical traffic scenarios.

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Expanding Power Save Efficiency in IEEE 802.11 Networks

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  1. May 2024 doc.: IEEE 802.11-24/0737r0 Cross-link Wake-up to Go Deeper in Power Save Date: 2024-05-08 Authors: Name Yuxin Lu Affiliations Address Phone email eeluyx@gmail.com Pei Zhou TCL Industries Zhanjing Bao Submission Slide 1 Yuxin Lu, TCL Industries

  2. May 2024 doc.: IEEE 802.11-24/0737r0 Abstract In this contribution, we discuss promising solutions into a deeper power save for UHR STAs considering impact on the critical traffic service Submission Slide 2 Yuxin Lu, TCL Industries

  3. May 2024 doc.: IEEE 802.11-24/0737r0 Background • UHR Proposed PAR [1] states • Reducing power consumption of WLAN devices is required to prolong the battery life of untethered devices (e.g., non-AP STA, Mobile APs), reduce device cost, and lower energy bills of customers deploying non-AP and AP STAs in most scenarios (e.g., residential, enterprise, industrial, venues) • AP Power Save encompasses different scenarios, including periods of low utilization while minimizing the impact on the service • Several contributions have made efforts to improve power efficiency for different types of UHR STAs Submission Slide 3 Yuxin Lu, TCL Industries

  4. May 2024 doc.: IEEE 802.11-24/0737r0 Re-cap: Power Save Mode Transition • [2-6] proposed to define a power save mode for a STA that is a UHR Mobile AP or a UHR non-AP STA wherein the STA may transition from a lower capability mode to a higher capability mode upon reception of an initial control frame (ICF) • Lower capability mode (e.g., 20 MHz BW, one SS, limited data rates, PPDU format) • Higher capability mode (e.g., operating BW, NSS and MCSs, with at least one higher capability than that in the lower power capability mode) • Whether that applies for a non-mobile AP is TBD • ICF still requires STA to keep certain “lower” capability Submission Slide 4 Yuxin Lu, TCL Industries

  5. May 2024 doc.: IEEE 802.11-24/0737r0 Re-cap: Cross-link Power Save with MLO • [6,7] proposed to define cross link power save signaling mechanism • Allowing a non-AP MLD to indicate to its associated AP MLD that supports the mechanism, in a frame sent on one enabled link, the power management mode for one or more of its affiliated non-AP STAs • Scheduled PS cannot handle certain case when sudden/unscheduled critical traffic arrives during doze time, may impact service performance critical traffic arrives at STA1 for STA2: STA1 can wake up to deliver, but not sure whether STA2 is available critical traffic arrives at STA2 for STA1: delivery would be postponed STA1 in scheduled power save (doze/sleep) STA1 in scheduled power save (doze/sleep) STA1 STA2 STA1 STA2 Case b Case a Submission Slide 5 Yuxin Lu, TCL Industries

  6. May 2024 doc.: IEEE 802.11-24/0737r0 Problem Statement: Can We Go Deeper in PS? • Deep Doze: to save power to more extent • Need not to maintain ability to receive ICF or simply become unavailable for certain period • Whether to maintain NAV timer is TBD • Can resume service in case sudden/unscheduled critical traffic arrives • Such as using on-hand tool: TID-to-link mapping (TTLM) • To save power to more extent, a link may be disabled (link disablement) • If used by AP, associated LL STAs have to “move” to ensure LL performance • Even if such doze could be temporary for AP, the associated STAs cannot know that • To re-enable, perform TTLM again, which could be sophisticated or time consuming • Overall, TTLM is not a high efficiency solution to deeper PS • Such as using intra-PPDU power save • Per PPDU enabled, shall transition to the awake state at the end of the PPDU • May be quite frequent, per-PPDU based state transition could be power consuming • Not sure it indeed can save power Submission Slide 6 Yuxin Lu, TCL Industries

  7. May 2024 doc.: IEEE 802.11-24/0737r0 Problem Statement: Can We Go Deeper in PS? Critical Traffic Consideration • During scheduled PS period, STA cannot handle sudden/unscheduled arrival of critical traffic either DL/UL • Such critical traffic has to wait until the scheduled PS period comes to an end • A wake-up call is in need, in case of critical traffic arrival • If through ICF, the STA has to maintain certain “lower” MAC and PHY capability and cannot enter deep doze to save more power critical traffic arrives at STA1 for STA2: STA1 can wake up to deliver, but not sure whether STA2 is available critical traffic arrives at STA2/STA1 for STA1/STA2: wake up/notify STA1/STA2 via MLO STA1 in scheduled power save (doze/sleep) STA1 STA2 critical traffic arrives at STA2 for STA1: delivery would be postponed STA1 in scheduled power save (doze/sleep) STA1 STA2 STA1 in scheduled power save (doze/sleep) STA1 STA2 Submission Slide 7 Yuxin Lu, TCL Industries

  8. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Exploit Cross-link Wake-up to Go Deeper in PS • Introduce cross-link wake-up, such that • STA22 on link2 can enter deep doze considering its power status • In case STA22 enters deep doze, it can still be woken up by STAs on link1 • Even if STA22 is in scheduled PS, critical traffic arrived at STA12 can notify MLD2 ASAP, would not need to wait until the scheduled PS period ends • Link2 need not to be disabled to enter deep doze, nor re-enabled to be active MLD 1 • The cross-link wake-up frame can be a cross-link variant of a Control frame • such as a cross-link Trigger frame, a cross-link PS- Poll frame • frame format detail is TBD • It can indicate whether carrier sense is required when STA22 wakes up, since STA12 may be TXOP holder on link2 • Since cross-link message may introduce additional processing time and delay, the lifetime of such message may be included • In case STA23 is also in deep doze, the wake up frame can wake up both STA22 and STA23 STA 11 STA 12 STA 13 Cross-link wake up frame: wake up STA22 (TA=STA11,RA=STA21) Link 1 Link 2 Link 3 STA 22 (Deep doze) STA 21 STA 23 MLD 2 Submission Slide 8 Yuxin Lu, TCL Industries

  9. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Example 1 • When STA22 on link2 goes into deep doze mode with limited capability, it can still be up via cross-link frame by STA11 on link1 TXOP obtained by STA22 SIFS • e.g. in case STA22 (on 5GHz link) is in doze of scheduled PS (such as TWT), STA12 has LL traffic arrived for STA22 Data Link 2 STA12 TXOP obtained by STA11 MLD1 Cross-link wake up frame: wake up STA22 (TA=STA11,RA=STA21) • This wake-up frame can indicate the PM mode for MLD1’s affiliated non-AP STAs STA11 Link 1 SIFS Ack • STA22 can indicate its availability using frames such as PS-Poll Link 1 STA21 STA21 notifies STA22 SIFS MLD2 PS-Poll Ack STA22 Transition to higher capability/active state Deep doze with limited capability Link 2 Submission Slide 9 Yuxin Lu, TCL Industries

  10. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Example 2 • If STA22 is AP, it can perform DL MU gathering associated STAs’ PM modes and considering DL buffer status TXOP obtained by STA22 SIFS CTS Link 2 STA12 TXOP obtained by STA11 MLD1 Cross-link wake up frame: wake up STA22 (TA=STA11,RA=STA21) • e.g. AP can use MU-RTS to initiate DL MU • Not required to wake up immediately, leaving the choice to AP STA11 Link 1 SIFS Ack Link 1 STA21 STA21 notifies STA22 SIFS MLD2 MU-RTS Data STA22 Transition to higher capability/active state Deep doze with limited capability Link 2 Submission Slide 10 Yuxin Lu, TCL Industries

  11. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Example 3 • If STA12 is TXOP holder on link 2, it can indicate carrier sense is not required when STA22 wakes up to reply TXOP obtained by STA12 SIFS Data STA12 TXOP obtained by STA11 MLD1 Cross-link wake up frame: wake up STA22 STA11 Link 1 • e.g. STA12 can use CTS-to-Self to protect/reserve the TXOP • STA12 can use padding if needed • STA22 replies CTS frame a certain time after receiving the wake-up frame, to retrieve data from STA12 STA21 Link 1 STA21 notifies STA22 MLD2 SIFS CTS Ack Transition to higher capability/active state Deep doze with limited capability STA22 Submission Slide 11 Yuxin Lu, TCL Industries

  12. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Example 4 TXOP obtained by STA12 TXOP obtained by STA12 SIFS SIFS Ack Ack STA12 STA12 TXOP obtained by STA11 TXOP obtained by STA11 MLD1 Cross-link wake up frame: wake up STA22 MLD1 Cross-link wake up frame: wake up STA22 STA11 STA11 Link 1 Link 1 STA21 Link 1 STA21 Link 1 STA21 notifies STA22 STA21 notifies STA22 MLD2 MLD2 SIFS Data Transition to higher capability/active state Deep doze with limited capability QoS Null Data Transition to higher capability/active state Deep doze with limited capability STA22 STA22 • e.g. STA12 can use CTS-to-Self to protect/reserve the TXOP • STA12 can use padding if needed • STA22 replies QoS Null or data frame a certain time after receiving the wake-up frame, transmitting data to STA12 Submission Slide 12 Yuxin Lu, TCL Industries

  13. May 2024 doc.: IEEE 802.11-24/0737r0 Proposal: Summary • Proposed a cross-link wake-up call for deeper power save on MLD-level • Benefits: • To save power to more extent, a link need not to be disabled to enter deep doze, nor re- enabled to be active • (Unscheduled) critical traffic arrival can be alerted ASAP via another link, limiting impact on service performance Submission Slide 13 Yuxin Lu, TCL Industries

  14. May 2024 doc.: IEEE 802.11-24/0737r0 References 1. 11-23/480r3, UHR Proposed PAR 2. 11-23/0010r0, Considerations for enabling AP power save 3. 11- 23/1875r1, Power save proposal for non-AP/mobile AP 4. 11- 23/1936r0, AP MLD Power Save Follow-up 5. 11- 23/1965r2, Dynamic Power Save – follow up 6. 11- 23/2003r1, Client power save 7. 11-24/0602r0, Multi Link Power Management for MLO Submission Slide 14 Yuxin Lu, TCL Industries

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