1. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 1 VHT Frame Padding Date: 2010-05-19 Authors:

2. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 2 Changes from r4 Explain why PHY padding bits are added before tail bits Add a straw poll on adding PHY padding bits before tail bits for VHT frames

3. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 3 Outlines 802.11n (HT) frame padding VHT frame padding 802.11n (HT) A-MPDU VHT A-MPDU Early End-of-Frame indication Conclusions

4. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 4 802.11n (HT) frame padding L-SIG length/rate indicate the end of the PPDU 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

5. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 5 VHT frame padding - motivations Bits in VHT-SIG are very precious resource to signal important system parameters Length field and rate field in L-SIG already provide sufficient information to signal the duration of a VHT frame (11-10-0534-00-00ac-Duration-in-L-SIG) No need to signal PPDU length or duration again in VHT signal fields –Simplify design and save processing power

6. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 6 VHT frame padding L-SIG length and rate indicate PPDU duration (number of symbols) –No per user length (number of octets) indication in preamble MAC provides an A-MPDU that fills the frame to the last byte for each per- user stream Same preamble structure is used for both SU and MU VHT frames –Require that A-MPDU always be used with both SU and MU VHT frames PHY provides 0-7 bits of padding PHY padding bits are added before tail bits

7. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 7 802.11n (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

8. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 8 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

9. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 9 Early EOF indication The Null subframes appended to the end of a VHT A-MPDU can be special Padding Delimiters each with an EOF flag When RX MAC detects the EOF Padding Delimiter, it may inform RX PHY to stop receiving to conserve power

10. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 10 PHY pad before tail bits With multiple encoders there is no need to separately calculate the number of PHY padding bits to be added at each encoder, i.e., number of padding bits can be calculated once and added before the encoder parser. Add 0-7 PHY padding bits Encoder Parser Add Tail, Encoding & Puncturing Stream Parser AMPDU (with MAC pad) Scrambler

11. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 11 Conclusions L-SIG length and rate indicate PPDU duration (number of symbols) –No per user length (number of octets) indication in preamble 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 In order to maintain the same preamble structure for both SU and MU frames, all VHT frames use A-MPDU structure The Null subframes appended to the A-MPDU can include an EOF indication in the delimiter so that the receiver knows it can stop receive processing to conserve power PHY padding bits are added before tail bits

12. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 12 Reference 11-10-0534-00-00ac-Duration-in-L-SIG.ppt 11-10-0070-02-00ac-802-11ac-preamble.ppt 11-10-0548-00-00ac-80MHz Transmission Flow.ppt

13. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 13 Straw Poll 1 Should the spec framework document (09/992) be updated to include the following change? –3.2.x The Data Field R3.2.x.A: When BCC encoding is used, the Data field shall consist of the 16-bit SERVICE field, the PSDU, the pad bits and the tail bits, in that order. –Yes: –No: –Abstain:

14. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 14 Straw Poll 2 Should the spec framework document (09/992) be updated to include the changes shown on the following two slides of this presentation? Yes: No: Abstain:

15. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 15 Spec framework changes (1) Add a section on A-MPDU format under Frame Formats: 6.3 Frame formats 6.3.1 A-MPDU format The VHT A-MPDU format is an extension of the 802.11n A-MPDU as shown in Figure YY. The extension (shaded in the figure) consists of zero or more delimiters with MPDU length zero and a possible final MAC Pad of less than 4 octets. The A-MPDU of a VHT PPDU fills the available octets in the payload. Figure YY – A-MPDU format for VHT PPHU

16. doc.:IEEE 802.11-10/0064r5 Submission May 19, 2010 Yong Liu, MarvellSlide 16 Spec framework changes (2) Add a requirement to the power saving section: 6.1 Power saving R6.1.A: The delimiters with MPDU length zero that pad through the end of the frame shall include an indication that no additional MPDUs are present in the frame. This would allow the receiver to stop receive processing to conserve power.