Capability on Doppler Mode for IEEE 802.11-17
This document discusses the proposed modifications related to Midamble in IEEE 802.11-17, specifically focusing on issues such as Midamble duration, Rx processing time, and Max NSTS. The content also addresses the processing time for HE-LTF types in Doppler mode scenarios, emphasizing the importance of adequate time for FFT, channel estimation, and pre-processing. Additionally, it proposes a capability bit for 1X/2X HE-LTF in Doppler mode to ensure efficient data symbol processing. Various considerations and solutions are presented for optimizing the performance in Doppler scenarios.
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3/9/2025 doc.: IEEE 802.11-17/1357r3 Capability on Doppler Mode Date: 2017-09-13 Authors: Affiliations Address Phone email Name Ross Jian Yu Huawei ross.yujian@huawei.com Ming Gan Huawei ming.gan@huawei.com David Xun Yang Huawei david.yangxun@huawei.com Shimi Shilo Huawei Sungeun Lee Cypress Submission Slide 1 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 Introduction Midamble was proposed in [1-4] to address the Doppler scenario for 11ax. This presentation discusses several issues with the proposed design and propose the suggested modifications: Midamble duration and Rx processing time Midamble Rx Max NSTS Submission Slide 2 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 Capability on HE-LTF Type Processing Time 4X data symbol sometimes needs another 4X data symbol duration processing time after the reception, e.g., 4X Data-9 in the figure below. When Midamble duration is comparably short, e.g., Two 1X HE-LTF with 0.8us GI (8us in total), there may not be enough time for FFT, channel estimation and pre-processing before the processing of 4X Data-10. Further averaging the CHEST of the midabmle and previous CHEST may take more time. May not be enough for channel estimation and pre-processing (8us) Preamble Midamble ... 1X HE- STF 1X HE- LTF 1X HE- LTF 1X HE- LTF 1X HE- LTF 4X Data-0 4X Data-9 4X Data-10 4X Data-11 Time needed to decode the 4X Data-9 (within 16us) Time needed to do FFT, channel estimation and MIMO pre-processing (16~24us) Time needed to do FFT, channel estimation and MIMO pre-processing (16~24us) Hence, the midamble duration should be longer than some threshold so that the Rx has enough time to proceed the channel estimation and pre-processing before the decoding of the next symbol after the midamble: = + ( ) , 2 Midamble T N HE-LTF T T T N HE-LTF GI M sts Submission Slide 3 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 Capability on HE-LTF Type - FFT Size Switch For simplicity, another option is to restrict 1X/2X HE-LTF type, for example, forbid using 1X/2X HE-LTF for Doppler mode. Becuz 4X HE-LTF will ensure at least 13.6us duration for midamble field. Whilst we do see gains for using short HE-LTF with the simulation results in [2][3], hence here we propose to have a capability bit for 1X/2X HE-LTF in Doppler mode. Another factor we need to consider is FFT size switch between midamble and data when midamble has 1X/2X HE-LTF. The Rx needs to switch between large FFT size (4X) and small FFT size (1X/2X), which leads to complexity for the Rx. May still use 4X FFT size for 1X/2X HE-LTF, whilst it depends on implementation and will leads to more delay and leads to the issues discussed in slide 3. Considering both reasons, here we propose to have a capability bit for 1X/2X HE-LTF in Doppler mode as shown in slide 5: B68 of HE PHY Capabilities Information field changes from Reserved to Midamble with 2x and 1x HE-LTF Support: When Doppler Rx field is set to 1, indicates support for receiving Midambles with 2x HE- LTF, 1x HE-LTF in HE SU PPDU if the HE SU PPDU With 1x HE-LTF And 0.8 us GI subfield is set to 1, and 1x HE-LTF in HE ER SU PPDU if the HE ER SU PPDU With 1x HE-LTF And 0.8 us GI subfield is set to 1. Submission Slide 4 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 Midamble with 2x and 1x HE-LTF Support Detail Capability Bit Setting Midambl e with 2x and 1x HE-LTF Support Subfield Midamble HE-LTF support HE ER SU PPDU With 1x HE- LTF And 0.8 us GI Subfield HE SU PPDU With 1x HE- LTF And 0.8 us GI Subfield Doppler Rx Subfield 1x HE-LTF for HE SU PPDU 1x HE-LTF for HE ER SU PPDU 1x HE-LTF for HE TB PPDU 1x HE-LTF for HE MU PPDU 2x HE-LTF for HE PPDU AP 1 1 0 0 Supported Not supported Not supported implementati on AP implementati on AP implementati on AP implementati on AP implementati on N/A 1 1 0 1 Supported Not supported Supported N/A 1 1 1 0 Supported Supported Not supported N/A 1 1 1 1 Supported Supported Supported N/A Not 1 0 0 0 Not supported Not supported N/A supported Submission Slide 5 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 Capability on Midamble Rx Max NSTS Another factor that affects the Rx s complexity handling the midamble is the number of space-time streams (Nsts). Larger Nsts needs either more processing time or more buffer/hardware. Moreover, from the STA s type or application point of view, some Rx may prefer a more robust transmission with low Nsts (mobile phone, IoT devices), whilst some Rx may need a higher data rate with high Nsts (backhaul, TV etc.). Hence it is better to have a capability field so that when Doppler Rx field is set to 1, the STA can indicate the maximum number of space- time streams supported for reception when midamble is used in the Data field. Submission Slide 6 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 SP1 Do you support to have a capability bit for 1X/2X HE- LTF in Doppler mode as shown in slide 5: B68 of HE PHY Capabilities Information field changes from Reserved to Midamble with 2x and 1x HE-LTF Support: When Doppler Rx field is set to 1, indicates support for receiving Midambles with 2x HE-LTF; and 1x HE-LTF in HE SU PPDU if the HE SU PPDU With 1x HE-LTF And 0.8 us GI subfield is set to 1; and 1x HE-LTF in HE ER SU PPDU if the HE ER SU PPDU With 1x HE-LTF And 0.8 us GI subfield is set to 1. Y N Abs Submission Slide 7 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 SP2 Do you support to have a capability bit for Midamble Rx Max NSTS: B15-16 of HE PHY Capabilities Information field changes from Reserved to Midamble Rx Max NSTS: When Doppler Rx field is set to 1, indicates the maximum number of space- time streams supported for reception when midamble is used in the Data field. Set to 0 for 1 space-time stream Set to 1 for 2 space-time streams Set to 2 for 3 space-time streams Set to 3 for 4 space-time streams Y N Abs Submission Slide 8 Ross Jian Yu, Huawei, et al
3/9/2025 doc.: IEEE 802.11-17/1357r3 References [1] 11-17-0995-00-00ax-Doppler-comment-resolutions [2] 11-17-0734-01-00ax-doppler-discussions [3] 11-17-0773-02-00ax-thoughts-on-doppler-design-in- 802-11ax [4] 11-17-1021-00-00ax-usage-of-doppler-bit-in-11ax Submission Slide 9 Ross Jian Yu, Huawei, et al
