Coordinated Medium Access for Multi-AP Deployments in IEEE 802.11 Networks

The document discusses a solution to reduce latency, increase throughput, and improve reliability in networks with latency-sensitive traffic by introducing coordination between access points (APs). This involves leveraging mechanisms like Restricted TWT (rTWT) and Coordinated rTWT (C-rTWT) to facilitate reliable transmission of latency-sensitive data. Challenges like overlapping transmissions and hidden nodes are addressed through coordinated medium access strategies.

• Medium Access Control
• Multi-AP Deployments
• Latency-Sensitive Traffic
• IEEE 802.11 Networks
• Network Reliability

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1. Jan 2024 Coordinated Medium Access for Multi-AP Deployments Date: 2024-01-15 doc.: IEEE 802.11-23/1887r0 Authors: Name Affiliations Address Phone email Giovanni Chisci Qualcomm Technologies Inc. 5665 Morehouse Dr., San Diego CA 92121 gchisci@qti.qualcomm.com Duncan Ho Alfred Asterjadhi Abhishek Patil George Cherian Gaurang Naik Submission Slide 1 Giovanni Chisci et Al., Qualcomm

2. Jan 2024 doc.: IEEE 802.11-23/1887r0 Problem Statement Objective: reduce the latency, increase the throughput, and improve the reliability in networks with latency-sensitive traffic with some degree of predictability Problem: today, in most deployments, APs don t coordinate which leads to the inability of effectively serving latency-sensitive traffic, this is due to Delayed access due to ongoing OBSS TXOP(s) Overlapping transmissions between different BSSs resulting in high PER and increased latency due to collisions, retransmissions, hidden nodes, etc. Solution: introduce coordination between APs Submission Slide 2 Giovanni Chisci et Al., Qualcomm

3. Jan 2024 doc.: IEEE 802.11-23/1887r0 Design Principles Coordinated Medium Access for APs in UHR can leverage hooks introduced in EHT as Restricted TWT (rTWT) In rTWT, STAs terminate their TXOP before the start time of an rTWT service period (SP) so that the AP can access the medium to serve latency-sensitive traffic rTWT is an intra-BSS mechanism For UHR, a set of APs could coordinate to respect each others rTWT Consider a Coordinated rTWT (C-rTWT) between APs Consider Coordinated APs (C ed APs) to behave similarly to STAs in EHT rTWT Consider Coordinating AP (C ing AP) to behave similarly to AP in EHT rTWT Coordinated APs terminate their TXOP before the start time of the C-rTWT SP An AP can be a C ed AP in a given C-rTWT and a C ing AP in another C-rTWT The coordination scheme between APs will facilitate the transmissions of participating APs at the start of the respective SPs to reliably serve latency-sensitive traffic Submission Slide 3 Giovanni Chisci et Al., Qualcomm

4. Jan 2024 doc.: IEEE 802.11-23/1887r0 TXOP rules visualization 11bn C-rTWT 11be rTWT Issue2: clients of AP1 (e.g., STA1 hidden from AP2) will unnecessarily terminate their TXOP before AP1 s rTWT SP Issue1: TXOP of AP2 is ongoing and AP1 cannot access to serve latency-sensitive traffic during its rTWT SP STA1 and AP2 will terminate their TXOP and facilitate AP1 s medium access at the start of the C-rTWT C C- -r rTWT SP TWT SP r rTWT SP TWT SP TXOP STA1 TXOP STA1 BSS1 BSS1 t t TXOP AP2 TXOP AP2 BSS2 BSS2 t t Issue3: If both APs manage to access the medium (e.g., beyond ED range) overlapping transmissions may degrade PER APs end their BSS transmissions before the C-rTWT SPs Avoid delayed access at the start of the coordinated SP Reduces overlapped transmissions between APs R R- -TWT SP TWT SP TXOP BSS1 t R R- -TWT SP TWT SP TXOP BSS2 t Submission Slide 4 Giovanni Chisci et Al., Qualcomm

5. Jan 2024 doc.: IEEE 802.11-23/1887r0 Levels of coordination Two options for the levels of coordination: Level 1: Only C ed APs terminate their TXOP before the C ingAP s SP C ing AP can setup rTWT SPs for its STAs and use MU EDCA to reduce contention Level 2: C ed APs and their associated STAs terminate their TXOP before the C ingAP s SP C ed APs announce the SP of the C ing AP to their associated STAs (e.g., as an EHT rTWT SP) EHT rTWT supporting STAs will also end the TXOP before the C ingAP s SP Submission Slide 5 Giovanni Chisci et Al., Qualcomm

6. Jan 2024 doc.: IEEE 802.11-23/1887r0 TSF adjustment for LV2 coordination If AP2 announces Coordinated SP1 without correcting the Target Wake Time, then AP2 will announce a start time that is different from the correct start time of SP1 Beacon of AP1 Coordinated SP information SP 1 SP 1 SP 1 t t t1 AP2 Correct start time t1 AP1 (w.r.t AP2) (w.r.t AP1) For LV2 the TSFs may be different at different Aps, two solutions: Option 1:APs synchronize their TSF Option 2: each AP corrects the start time of SPs announced by other APs before announcing other APs Coordinated SP information to its associated STAs (e.g., in its transmitted Beacon frames) requires extensions for TWT field to support different offsets between APs when Coordinated SP is communicated through R-TWT Submission Slide 6 Giovanni Chisci et Al., Qualcomm

7. Jan 2024 doc.: IEEE 802.11-23/1887r0 Gain Analysis: Single Family Home 20 S1 Two floors with 3 APs 13 dB floor loss and 10 dB wall loss S2 Floor 2 Room 4 Room 3 15 Each AP having 2 clients 2 AP are in Floor 1, 1 AP is on Floor 2 AP and STA location are random Room 1 Room 2 10 10 S2 Traffic: STA1 DL low latency traffic (served on AC_VO) VR with 60 Kbytes at 60 fps CBR with 1500 Bytes at 60 fps STA2 DL full buffer traffic served on AC_BE Floor 1 Room 4 Room 3 5 S1 S1 S1 S2 Room 1 Room 2 0 10 5 Submission Slide 7 Giovanni Chisci et Al., Qualcomm

8. Jan 2024 doc.: IEEE 802.11-23/1887r0 Gain Analysis: Single Family Home (Cont d) 600 25 500 20 400 99 Percentile Latency (msecs) 99 Percentile Latency (msecs) 15 300 10 200 5 100 0.202 2.057 0 0 Baseline 11be R-TWT UHR C-R-TWT Baseline 11be R-TWT UHR C-R-TWT Latency Statistics for CBR traffic (1500 Bytes) scenario at STA1 (low latency traffic) Latency Statistics for VR traffic scenario at STA1 (low latency traffic) Submission Slide 8 Giovanni Chisci et Al., Qualcomm

9. Jan 2024 doc.: IEEE 802.11-23/1887r0 Next steps APs coordination will require investigating and developing additional aspects such as: Coordination setup/negotiation: In proprietary environments (e.g., enterprise) simply a network configuration can setup AP coordination In non-proprietary environments negotiation between Aps might be needed Coordinated EDCA: To improve prioritization of a C ing AP at the beginning of its C- rTWT SP aspects of coordinated EDCA may need further investigation/development Details of the above aspects will discussed in next steps. Submission Slide 9 Giovanni Chisci et Al., Qualcomm

10. Jan 2024 doc.: IEEE 802.11-23/1887r0 Conclusion We introduced the APs coordination framework for UHR The coordination framework leverages the EHT rTWT framework Two levels of coordination have been considered (LV1: for coordinated APs only and LV2: for coordinated APs and their associated STAs) APs coordination will facilitate the transmissions of a coordinating AP at the start of its SP to reliably serve latency-sensitive traffic Next steps investigations will involve negotiation between APs and coordinated EDCA. Submission Slide 10 Giovanni Chisci et Al., Qualcomm

11. Jan 2024 doc.: IEEE 802.11-23/1887r0 SP1 Do you agree to define mechanisms that enable APs to coordinate their respective rTWT schedules and/or to ensure that one AP extends the protection of the rTWT schedule of the other AP. NOTE TBD mechanisms include negotiation between 2 APs and advertisement. Submission Slide 11 Giovanni Chisci et Al., Qualcomm

12. Jan 2024 doc.: IEEE 802.11-23/1887r0 SP2 Do you agree that, if an AP extends the protection of the rTWT schedule of another AP, following negotiation or through other means, then: The AP shall ensure its TXOP ends before the start time of the corresponding OBSS rTWT SP(s) The AP shall advertise in the beacon frames it transmits the OBSS rTWT schedule so that its associated STAs supporting rTWT follow the baseline rTWT rules for the OBSS rTWT schedule. Submission Slide 12 Giovanni Chisci et Al., Qualcomm