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VHT Frame Padding

VHT Frame Padding. Authors:. Date: 2010-01-19. Outlines. 802.11n (HT) frame padding VHT frame padding 802.11n (HT) A-MPDU VHT A-MPDU Early End-of-Frame indication Conclusions. 802.11n (HT) frame padding. A length field (16 bits) is included in HT-SIGs to indicate the end of PSDU

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VHT Frame Padding

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  1. VHT Frame Padding Authors: Date: 2010-01-19 Yong Liu, Robert Stacey et al.

  2. Outlines • 802.11n (HT) frame padding • VHT frame padding • 802.11n (HT) A-MPDU • VHT A-MPDU • Early End-of-Frame indication • Conclusions Yong Liu, Robert Stacey et al.

  3. 802.11n (HT) frame padding • A length field (16 bits) is included in HT-SIGs to indicate the end of PSDU • Tail bits and PHY Pad are appended to fill in the last symbol Yong Liu, Robert Stacey et al.

  4. VHT frame padding • VHT-SIG indicates PPDU duration only (number of symbols) • No per user length (number of octets) indication in preamble • Use A-MPDU structure to provide length information for individual MPDUs • Require that A-MPDU always be used with both SU and MU VHT frames • MAC provides an A-MPDU that fills the frame to the last byte for each per-user stream • PHY provides 0-7 bits of padding Yong Liu, Robert Stacey et al.

  5. 802.11n (HT) A-MPDU • Except when it is the last A-MPDU subframe in an A-MPDU, padding octets are appended to make each A-MPDU subframe a multiple of 4 octets in length. • Any subframe may be preceded by one or more zero-length delimiters to meet the minimum MPDU Start Spacing requirement, for example Yong Liu, Robert Stacey et al.

  6. VHT A-MPDU • VHT A-MPDU subframes have the same structure as the subframes of an 802.11n A-MPDU • The QWord MAC Pad (0-3 octets) is added to reach the next 32-bit boundary of MAC octets, if such octets fit into the last PHY symbol (Note that normally, the LAST subframe is NOT padded) • Zero or more Null subframes and a Final MAC Pad (0-3 octets) are appended to extend the A-MPDU to the last octet of the last symbol of a VHT frame • Null subframes are absent if last PHY symbol is full with 0-3 octets of Final MAC Pad after the QWord MAC Pad Yong Liu, Robert Stacey et al.

  7. Early EOF indication • The Null subframes appended to the end of a VHT A-MPDU can be a special Padding Delimiter with an EOF flag • When RX MAC detects the EOF Padding Delimiter, it may inform RX PHY to stop receiving to conserve power Yong Liu, Robert Stacey et al.

  8. Conclusions • VHT-SIG indicates PPDU duration only (number of symbols) • All VHT frames, including both SU and MU frames, use A-MPDU structure • Zero or more Null subframes and a Final MAC Pad can be appended to a VHT A-MPDU to extend the A-MPDU to the last byte of the VHT frame • The Null subframes appended to the A-MPDU may include an EOF indication in the delimiter so that the receiver knows it can stop receive processing to conserve power Yong Liu, Robert Stacey et al.

  9. Reference • 11-10-0070-00-00ac-802-11ac-preamble.ppt Yong Liu, Robert Stacey et al.

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