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Extended Block Ack

Extended Block Ack. Date: 2013-03-27. Authors:. Propose to extend the maximum BA window from 64 to 256 to support greater efficiency of operation at high PHY rates – see LB193 CID 278:

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Extended Block Ack

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  1. Extended Block Ack Date: 2013-03-27 Authors: Matthew Fischer (Broadcom)

  2. Propose to extend the maximum BA window from 64 to 256 to support greater efficiency of operation at high PHY rates – see LB193 CID 278: • The highest indicated modulation and stream combinations for some PHYs result in PHY rates that will reduce throughput efficiency to exceedingly low levels if the maximum Block Ackwindow size is not allowed to increase beyond the existing 64. • Increase the maximum allowed MPDUs in the Block Ack frame to 256 by creating a new form of Block Ack that supports a longer BA window and a longer BA bitmap Abstract Matthew Fischer (Broadcom)

  3. AMPDU, max window = 64 MPDU AMSDU, max size = 11454 B Existing Limitations Matthew Fischer (Broadcom)

  4. E.g. Assume BER = 9e-6: • MPDU, No AMSDU: • UDP payload = 1460 B => MPDU payload = 1508 B • PPDU payload = 1566 B • PER = 1-(1-9e-6)^(1566*8) = 10.7% PER • MPDU, With AMSDU = 4xMSDU: • UDP payload = 1460 B MPDU payload = 6088 B • PPDU payload = 6146 B • PER = 1-(1-9e-6)^(6146*8) = 35.8% PER AMSDU has higher PER at same SNR Matthew Fischer (Broadcom)

  5. Which term dominates? Increasing PER vs Decreasing MPDU count But AMSDU has fewer MPDUs per PPDU Matthew Fischer (Broadcom)

  6. RAW PHY Rate Comparison Matthew Fischer (Broadcom)

  7. UDP Throughput (1.0 dB/dec AWGN) Matthew Fischer (Broadcom)

  8. UDP Throughput (1.0 dB/dec AWGN) Matthew Fischer (Broadcom)

  9. UDP Throughput (1.0 dB/dec AWGN) Matthew Fischer (Broadcom) Broadcom

  10. UDP Throughput (1.0 dB/dec AWGN) Matthew Fischer (Broadcom) Broadcom

  11. UDP Throughput (AWGN) Matthew Fischer (Broadcom)

  12. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  13. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  14. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  15. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  16. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  17. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  18. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  19. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  20. UDP Throughput (Channel D) Matthew Fischer (Broadcom)

  21. Do you support the concept of allowing a longer BA window than the current value of 64 consecutive MAC Seq numbers? Straw poll #1 Matthew Fischer (Broadcom)

  22. The next slides describe a proposal for increasing the BA window by creating a new variant of the BA frame = ExtendedBA (EBA)which supports a BA window of 256 MPDUs • LB193 CID 278 [1] • Increase the maximum allowed MPDUs in the Block Ack frame to 256 by creating a new form of Block Ack. • Rationale: need to enable greater throughput and efficiency at the higher rates that are created by the 11ac amendment A New Block Ack Format Matthew Fischer (Broadcom)

  23. New bit in the BAR Control field EB = Extended Bitmap BAR Control Field B11 TID_INFO B0 1 1 B1 B2 1 B3 1 B4 7 B10 1 4 B12 B15 Bits: BA Ack Policy Multi-TID Compressed Bitmap GCR Reserved EB Matthew Fischer (Broadcom)

  24. Within a DATA frame • Redefine the meaning of Ack Policy=11b • ACK Policy = 00b indicates CBA within an AMPDU • Outside of an AMPDU, 00b means Normal ACK • ACK Policy = 11b indicates EBA within an AMPDU • Outside of an AMPDU, 11b means Block Ack • Conflict with HT-Delayed BA? • Does anyone care? Determining Response Type (option 1) Matthew Fischer (Broadcom)

  25. Option 2: Set BSSID I/G bit = 1 in DATA frame • Requests an EBA response • Option 3: Use reserved bit within MPDU delimiter • Option 4: Frag=1111b with MoreFrag=1 • Option 5: Use NEW Data Subtype = 1101 • Requires EBA response when Ack Policy = 00b • Option 6: VHT Control field 1 reserved bit • Would prefer to align this bit with HTC field reserved bit • Option 7: Responder choice, NAV issue not serious Determining Response Type (option 2-7) Matthew Fischer (Broadcom)

  26. EBA can also be transmitted • When explicitly requested within a BAR that has the value CB, EB = 01b Additional Request for EBA Matthew Fischer (Broadcom)

  27. New Extended Capability bit advertises support • Pair of supporting STAs can negotiate use of EBA • Use of EBA is implied by 64 < Buffer size value < 257 within ADEBA • Actual use of EBA is determined by Ack Policy settings in DATA frames of AMPDU and by CB, EB bit settings in BAR frames Negotiating Use of EBA Matthew Fischer (Broadcom)

  28. Related to CID 278: • Do you support making changes to the BA protocol to support an increased maximum BA window size of 256? • Yes • No • Abs Straw Poll #2 Matthew Fischer (Broadcom)

  29. Which option do you support for signaling a request for an EBA response in a DATA frame? 1: 2: 3: 4: 5: 6: 7: Straw Poll #3 Matthew Fischer (Broadcom)

  30. [1] 11-13-0233-07-000m-revmc-wg-ballot-comments.xls References Matthew Fischer (Broadcom)

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