Uniform Procedure for Preemption in IEEE 802.11-24 Standard
The presentation discusses a uniform procedure for preemption in the IEEE 802.11-24 standard, focusing on different cases where a STA preempts another's TXOP to transmit low latency (LL) traffic. It proposes a simplified design and implementation approach for handling preemptions efficiently. The procedure involves preemption requests, triggers, basic service requests, and specific handling for different types of LL traffic. Various scenarios and steps involved in preemption are outlined for clarity and standardization.
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doc.: IEEE 802.11-24/0390r0 February 2024 A Uniform Procedure for Preemption Date: 2024-02-08 Authors: Name Affiliations Address Phone Email Yunbo Li Shenzhen, China liyunbo@Huawei.com Yuchen Guo Guogang Huang Huawei Yue Zhao Maolin Zhang Ming Gan Submission Slide 1 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Introduction Many presentations in UHR SG and 11bn are discussing the procedure of preemption; A TXOP holder preempts its own TXOP to send low latency (LL) traffic can be easily handled by the TXOP holder itself; There are different cases for a STA to preempt another STA s TXOP to transmit LL traffic Case 1: Preempt a DL TXOP to send UL LL traffic Case 2: Preempt a UL TXOP to send DL LL traffic Case 3: Preempt a UL TXOP to send UL LL traffic Different procedures are discussed based on different cases; A uniform procedure is proposed for all cases to simplify the design and implementation. Submission Slide 2 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 A Uniform Procedure A TXOP is obtained TXOP holder indicates preemption enabled in a PPDU In this presentation, assuming all the preempting STAs are associated STAs. Whether and how to support OBSS STA to do preemption is open for further discussion. A PR is sent by at least one preempting STA SIFS after the preemption enabled PPDU Yes No AP sends TFR to solicit BSR from preempting STA TXOP holder continue transmits PPDU PIFS after the end of preemption enabled PPDU Preempting STAs report BSR PR: preemption request frame TF: Trigger frame TFR: Trigger frame with UORA UORA: uplink OFDMA random access LL: low latency AP sends basic TF to solicit LL traffic AP returns the TXOP to TXOP holder This step is not needed if AP is the TXOP holder Preempting STA: a STA (not the TXOP holder) that buffers LL traffic TXOP holder continue transmits PPDU Submission Slide 3 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Case 1: Preempt DL TXOP to send UL LL The AP may transmit PPDU2 before transmit a BSRP if the LL traffic is carried in PPDU2; AP must be able to solicit LL BSR from preempting STAs, a simple way is to mandate UORA support for preempting STAs; When the AP sends BSRP frame with UORA, it is better only allow BSR of LL traffic be reported by non-AP STAs; E.g. a new type of random access RU that only for LL traffic The BSRP with UORA frame is optional to transmit, AP may choose other ways to know which non-AP STAs are buffering LL traffic, e.g. Use a NFRP Trigger frame Do the prediction based on historical statistics Preemption is allowed TXOP Note: The contents of PR frames from STA2 and STA3 are exactly the same, so STA1 and AP can correctly decode them. It is similar as simultaneous CTSs follow MU-RTS sent by multiple STAs PIFS BSRP with UORA Basic TF ... PPDU1 PPDU2 AP STA 1 LL Traffic BSR SIFS SIFS PR STA 2 PR LL Traffic BSR STA 3 Submission Slide 4 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Case 2: Preempt UL TXOP to send DL LL Case 2a: DL LL to TXOP holder Case 2a and Case 2b can happen in one preemption; The PR frame is needed when considering a uniform procedure for different cases; The TXOP holder will stop transmitting following PPDU after receiving a PR frame; The contents of PR frame from the AP and the non-AP STAs are same; A signaling in PPDU3 informs STA1 continues to transmit PPDU in the remaining TXOP The detail of the signaling is TBD, e.g. carried in A-Control field. End of TXOP preemption period Preemption is allowed PR PPDU2 PPDU3 SIFS SIFS AP PIFS PPDU1 BA BA PPDU4 ... STA 1 STA 2 STA 3 Case 2b: DL LL to other non-AP STA End of TXOP preemption period Preemption is allowed PR PPDU2 PPDU3 SIFS SIFS AP PIFS PPDU1 Ack PPDU4 ... STA 1 BA STA 2 STA 3 Submission Slide 5 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Case 3: Preempt UL TXOP to send UL LL After receiving a PR frame follows PPDU1 which is preemption enabled, the AP is allowed to ignore the intra-BSS NAV and send BSRP with UORA to solicit BSR from preempting STAs; The benefits to allow AP to control the preemption procedure: Avoid contention collision from multiple STAs Can serve multiple STAs in one preemption After the LL traffic transmission are finished, The AP signaling the TXOP holder continues to transmit PPDUs in the remaining TXOP. End of preemption period TXOP BSRP with UORA Preemption is allowed Basic TF PPDU2 AP PIFS PPDU3 ... Ack PPDU1 STA 1 LL Traffic BSR SIFS SIFS PR STA 2 PR LL Traffic BSR STA 3 Submission Slide 6 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Case 2 + Case 3 First to solicit UL LL traffic End of preemption period Case 2 and Case 3 can happen in one preemption; The AP that transmits PR doesn t know whether there is one or more non- AP STAs sent PR frames. The AP may transmits BSRP with UORA to test whether there is BSR from any preempting STAs; The AP can choose first to transmit DL LL traffic or first to solicit UL LL traffic. TXOP BSRP with UORA Preemption is allowed Basic TF PR PPDU2 SIFS AP PIFS PPDU3 ... BA PPDU1 STA 1 LL Traffic BSR SIFS PR STA 2 PR LL Traffic BSR STA 3 First to transmit DL LL traffic End of preemption period TXOP BSRP with UORA Preemption is allowed Basic TF PR PPDU2 PPDU3 SIFS AP PIFS PPDU4 ... Ack PPDU1 STA 1 LL Traffic BSR SIFS PR BA STA 2 PR LL Traffic BSR STA 3 Submission Slide 7 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Summary A uniform preemption procedure is proposed to cover all possible cases Case 1: preempt DL traffic to send UL LL traffic Case 2: preempt UL traffic to send DL LL traffic Case 3: preempt UL traffic to send UL LL traffic The uniform procedure will facilitate the procedure design and implementation. Submission Slide 8 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Straw Poll 1 Do you agree a TXOP holder may indicate in a PPDU that a STA in the same BSS of the TXOP holder is allowed to send a preemption request frame SIFS after the PPDU? A preemption request frame informs buffering of low latency traffic frame The detail of indication signaling is TBD The detailed design of preemption request frame is TBD Yes: No: Abstain: Submission Slide 9 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Straw Poll 2 Do you agree a TXOP holder will continue PPDU transmission PIFS after a preemption enabled PPDU if no preemption request frame is received SIFS after the preemption enabled PPDU? Yes: No: Abstain: Submission Slide 10 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Straw Poll 3 Do you agree a TXOP holder that is a non-AP STA will grant the TXOP to its associated AP if a preemption request frame is received after a preemption enabled PPDU? A preemption enabled PPDU is a PPDU that allows preemption request frame be transmitted SIFS after the PPDU Yes: No: Abstain: Submission Slide 11 Yunbo Li (Huawei)
doc.: IEEE 802.11-24/0390r0 February 2024 Straw Poll 4 Do you agree an AP that is granted a TXOP by a non-AP STA TXOP holder to do preemption operation will return the TXOP to the TXOP holder after the preemption operation? The details of returning the TXOP is TBD Yes: No: Abstain: Submission Slide 12 Yunbo Li (Huawei)
