IEEE 802.11-25/745r1 Coordinated Beamforming (CBF) Open Issues in CSI
Explore the open issues in Coordinated Beamforming (CBF) regarding Channel State Information (CSI) overhearing and acknowledgement. Delve into the challenges of sequential and joint sounding methods in IEEE 802.11-25/745r1 documentation, focusing on addressing CSI transmission concerns within different AP setups.
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May 2025 doc.: IEEE 802.11-25/745r1 CSI open issues in CBF Date: 2025-05-10 Authors: Name Okan Mutgan Klaus Doppler Prabodh Varshney Mika Kasslin Juhyung Lee Mario Costa Salvatore Talarico Kerstin Johnsson Mikhail Liubogoshchev Behnam Dezfouli Eda Genc Affiliations Nokia Address Phone email okan.mutgan@nokia.com Submission Slide 1 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Abstract Coordinated Beamforming (CBF) is already in D0.2 and sounding is an important part to realize CBF. [1] Two sounding methods (sequential and joint) are defined. This presentation discusses the CSI open issues in sequential and joint sounding, namely, CSI overhearing and CSI acknowledgement. Submission Slide 2 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Recap The real transmission The overhearing transmission In sequential sounding, The intended transmission NDPA NDP BFRP NDPA BFRP NDP AP1 NDPA NDP BFRP NDPA BFRP NDP AP2 CSI CSI STA1 CSI CSI STA2 Cross-BSS UHR TB sounding Cross-BSS UHR TB sounding EHT TB sounding EHT TB sounding In joint sounding, NDPA NDP BFRP NDP AP1 NDPA NDP BFRP NDP AP2 CSI STA1 CSI STA2 Submission Slide 3 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Open issues in the current CBF sounding In Cross-BSS UHR sounding in Seq Sounding and Joint Sounding, 1) CSI overhearing CSI is technically sent from the STA (e.g. STA1) to its associated AP (e.g. AP1) but needs to be overheard by the unassociated AP (e.g. AP2). Since the channel between unassociated STA and the AP is unknown , CSI overhearing might fail, i.e. AP might not be able to overhear the CSI from unassociated STA. Submission Slide 4 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Open issues in the current CBF sounding 2) CSI Acknowledgement [2, 3, 4, 5] One AP runs the sequence but can t tell if the other AP overheard the CSI. If other AP misses the CSI, the sounding ends with bad CSI and CBF degrades. See below for seq sounding (same goes for joint sounding too) AP1 does not know whether AP2 received the CSI correctly. NDPA NDP BFRP NDPA BFRP NDP AP2 does not know whether AP1 received the CSI correctly. AP1 NDPA NDP BFRP NDPA BFRP NDP AP2 CSI CSI STA1 CSI CSI STA2 Cross-BSS UHR TB sounding Cross-BSS UHR TB sounding EHT TB sounding EHT TB sounding Submission Slide 5 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Proposal aa CSI overhearing requires CSI acknowledgement. Some possible options might be: Option 1) CSI Status Req(optional)/Resp is exchanged between APs (seq sounding shown, joint sounding similar) TBD when CSI Status Req (optional)/Resp is sent such as: after each cross-BSS/joint sounding during sounding (advantage: immediate feedback) or at the end of sounding (advantage: lower overhead) or after the sounding (advantage: faster sounding), maybe part of a frame (e.g. CBF invite/response) in CBF transmission phase CSI Status Req CSI Status Resp NDP BFRP NDPA BFRP NDP NDPA (optional) CSI Status Req CSI Status Resp NDPA NDP BFRP NDPA BFRP NDP (optional) CSI CSI CSI CSI Cross-BSS UHR TB sounding Cross-BSS UHR TB sounding EHT TB sounding EHT TB sounding Submission Slide 6 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Proposal CSI overhearing requires CSI acknowledgement. Some possible options might be: Option 2) Simple ACK is exchanged between APs (seq sounding shown, joint sounding similar) advantage: immediate feedback & relatively short overhead Note that AP not receiving ACK does not necessarily force re-sound (i.e. ACK is informative) NDPA NDP BFRP NDPA NDP BFRP ACK AP1 ACK NDPA NDP BFRP NDPA BFRP NDP AP2 CSI CSI STA1 CSI CSI STA2 Cross-BSS UHR TB sounding Cross-BSS UHR TB sounding EHT TB sounding EHT TB sounding Submission Slide 7 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Proposal CSI overhearing requires CSI acknowledgement. Some possible options might be: Option 3 (maybe)) Existing frame during sounding such as NPDA is used (seq sounding shown, joint sounding similar) Note: This requires strict order of sequences as shown as follows (CSI ACK in NDPA in EHT TB sounding after cross BSS sounding): Note: This doesn t seem to work for joint sounding. CSI ACK advantage: no extra frame is needed CSI ACK NDPA NDP BFRP NDPA BFRP NDP AP1 CSI ACK NDPA BFRP NDPA NDP BFRP NDP AP2 CSI CSI STA1 CSI CSI STA2 Cross-BSS UHR TB sounding Cross-BSS UHR TB sounding EHT TB sounding EHT TB sounding Submission Slide 8 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Summary CSI open issues (CSI overhearing and CSI Acknowledgement) are discussed for UHR sounding in CBF Some methods for CSI Acknowledgement for CSI overhearing are discussed. Submission Slide 9 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 Straw Poll Do you agree that 802.11bn will define a method for a CBF participating AP (AP1) to confirm to another CBF participating AP (AP2), the reception or lack of reception of cross-BSS CSI from a concluded joint sounding or cross-BSS sounding step of sequential sounding corresponding to CBF clients of that AP (AP2)? Yes No Abstain Submission Slide 10 Okan Mutgan, Nokia
May 2025 doc.: IEEE 802.11-25/745r1 References [1] IEEE P802.11bn/D0.2 [2] https://mentor.ieee.org/802.11/dcn/25/11-25-0553-00-00bn-cross-bss-csi-feedback-for-co-bf.pptx [3] https://mentor.ieee.org/802.11/dcn/25/11-25-0247-01-00bn-m-ap-cobf-sounding-sequence.pptx [4] https://mentor.ieee.org/802.11/dcn/25/11-25-0379-01-00bn-considerations-on-uhr-sounding-operation.pptx [5] https://mentor.ieee.org/802.11/dcn/25/11-25-0362-00-00bn-improvement-on-co-bf-sounding.pptx Submission Slide 11 Okan Mutgan, Nokia
