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80MHz/160MHz Protection

This paper discusses the implementation of HT and VHT TXOP protection mechanisms in the 802.11n and 802.11ac standards. It covers the concepts of frame aggregation, short GI, non-HT duplicate modes, and EDCA backoff procedures for different channel widths. The protection and truncation methods using Non-HT duplicate frames are detailed for 40MHz, 80MHz, and 160MHz channels. The text delves into the support for legacy STAs and the use of duplicate frames to establish protection and truncate the TXOP.

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80MHz/160MHz Protection

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  1. 80MHz/160MHz Protection Date: 2010-09-07 Authors: L. Chu et al

  2. HT TXOP Protection and Truncation • 802.11n introduces features that a legacy 802.11 STAs can not understand: 40MHz transmission, frame aggregation, short GI etc. • 40MHz non-HT duplicate mode is used to protect the 11n transmission: • Non-HT duplicate frames (e.g. RTS/CTS) are used to establish protection of its TXOP in two 20MHz channels, and • Non-HT duplicate CF-End frame are used to truncate the protect TXOP protected by non-HT duplicate frames. • To get a 40MHz EDCA based TXOP, a STA does EDCA backoff procedure in the primary channel, and detects the second channel being idle during PIFS interval before the TXOP. FC HT-STA1 RTS ch0 A-MPDU (HT frame) FC HT-AP1 ch0+ch1 RTS ch1 CTS ch0 BLKACK 11a-STA3 ch0+ch1 FC HT-AP1 11a-AP2 FC HT-STA1 11a-AP3 CTS ch1 11a-STA2 ch0 ch1 ch0+ch1 11a –STA2 NAV ch0 “ch0(primary channel)+ch1” is a 40MHz channel. ch0 is a 20MHz channel. 11a –STA3 NAV ch1 ch1 is a 20MHz channel.

  3. 802.11ac TXOP Protection and Truncation • 802.11ac uses 80/160 MHz channels. • 802.11ac introduces new features that legacy 802.11a STAs and 802.11n STAs can not understand: DL-MU MIMO, new 802.11ac preamble etc. • 802.11ac TXOP should be protected by frames which can be understood by 802.11a STAs and 802.11n STAs in each 20MHz channel. • 80MHz/160MHz non-HT duplicate frames are used for such TXOP protection/truncation: • 80MHz/160MHz non-HT duplicate frame duplicates 20 MHz non-HT transmission in each 20 MHz channel of a 80MHz/160MHz channel. • 80MHz/160MHz Non-HT duplicate frames (e.g. RTS/CTS) are used to establish protection of its TXOP in four 20MHz channels or in eight 20MHz channels, and • 80MHz/160MHz Non-HT duplicate CF-End frame is used to truncate the protect TXOP protected by non-HT duplicate frames in four 20MHz channels or in eight 20MHz channels.

  4. 802.11ac TXOP Protection and Truncation (Cont’d) • To get a 80MHz/160MHz EDCA based TXOP, a STA does EDCA backoff procedure in the primary channel, and detects the other 20MHz channels being idle during PIFS interval before the TXOP. CTS ch3 CTS RTS A-MPDU (VHT frame) ch2 ch3 CTS ch1 RTS ch2 ch0+ch1+ch2+ch3 CTS ch0 RTS ch1 VHT-AP1 RTS ch0 VHT-STA1 BLKACK FC HT-STA3 Ch0+ch1+ch2+ch3 VHT-STA1 VHT-AP1 11a-AP2 FC HT-AP3 11a-STA2 ch3 ch0+ch1 ch0+ch1+ch2+ch3 11a–STA2 NAV “ch0(primary channel)+ch1+ch2+ch3” is a 80MHz channel. ch3 “ch0(primary channel)+ch1” is a 40MHz channel. FC HT–STA3 NAV ch0 ch3 is a 20MHz channel.

  5. 80MHz/160MHz non-HT Duplicate Transmission • 80MHz/160MHz Non-HT duplicate transmission is used to transmit to 802.11a, 802.11n STAs that nay be present in a 20MHz/40MHz channel covered by 80MHz/160MHz channel. • The L-STF, L-LTF and L-SIG shall be transmitted in the same way as in the 802.11ac 80MHz/160MHz VHT transmission. • The VHT-SIG, VHT-STF, VHT-LTF are not transmitted.

  6. Straw Poll • Do you support adding the following item into the specification framework document, 11-09/0992? • R5.X: 80MHz/160MHz duplicate mode shall be included in the specification to protect 80MHz/160MHz transmission.

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