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11ac Explicit Feedback Format

11ac Explicit Feedback Format. Date: 2010-11-11. Authors:. Outline. Beamforming feedback frame format VHT MIMO control field Angle resolution in Codebook info Compressed beamforming report Tone mapping and grouping MU-Exclusive beamforming report Per-Tone SNR subfield.

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11ac Explicit Feedback Format

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  1. 11ac Explicit Feedback Format Date: 2010-11-11 Authors:

  2. Outline • Beamforming feedback frame format • VHT MIMO control field • Angle resolution in Codebook info • Compressed beamforming report • Tone mapping and grouping • MU-Exclusive beamforming report • Per-Tone SNR subfield

  3. Feedback Frame Format Proposal • Propose to define compressed V matrix FB, which is based on the 802.11n subclause20.3.12.2.5, 7.3.1.29, and 7.4.10.8, with appropriate changes for 11ac [1]. • Propose to define the 11ac compressed V FB frame for SU and MU be the Action-No-ACK format based on 7.4.10.8, with appropriate extensions: • Category: VHT • Action: Compressed Beamforming • Define VHT MIMO Control Field, as in the next slide • Define MU exclusive beamforming report that contains per-tone SNR • Per-tone SNR details TBD Needs codebook info definition Needs tone mapping/grouping Needs to define TBD subfields for MU

  4. VHT MIMO Ctrl Field Bit definition: Nc: 0~7 correspond to 1~8 columns of V The number of maximum space-time streams that beamformer can use for beamforming. If the SU-type feedback frame (indicated by MU-type bit = 0 in VHT MIMO CTRL field) includes MFB, Nc shall be the same as Nsts in MFB field Nr: 0~7 correspond to 1~8 rows of V The number of the transmit antennas to be used for beamforming BW: 0: 20MHz 1: 40MHz 2: 80MHz 3: 160MHz Ng: 0: Ng=1 1: Ng=2 2:Ng=4 for tone grouping Codebook Info: Bit resolution for angles, (by, bf) : (In SU Mode, when MU-type bit is not set): 0: (2,4), 1: (4,6) (In MU Mode, when MU-type bit is set): 0: (5,7), 1: (7,9) MU-type: 0: SU-FB 1: MU-FB Sounding Sequence Number 3 Octets in total 3 3 2 2 1 1 4 8 Nc Nr BW Ng Codebook Info MU-type TBD Sounding Seq #

  5. Codebook Info- Angle Resolution -

  6. Samples of Simulation with SU-BF for Codebook Info (1)

  7. Samples of Simulation with SU-BF for Codebook Info (2)

  8. Samples of Simulation with SU-BF for Codebook Info (3) 4x3, Nss=2, Ng=2, MCS9, DNLOS 40MHz

  9. Samples of Simulation with MU-BF for Codebook Info (1)(2 users: Each user has 4x4 H with 2 streams) • H feedback • 16 elements • Each element has Q and I. • Feedback bits = 16 x 2 x B + 3 • HHH feedback • 4 + 6 elements • 4 elements are real, but 6 elements has I and Q • Feedback bits = (4 + 6 x 2) x B + 3 • V feedback • 12 angles • Feedback bits = 12 x B

  10. Samples of Simulation with MU-BF for Codebook Info (2) Avg of 8 bits per angle are used

  11. Tone Mapping/Grouping

  12. Background • The tone location for the feedback in 11n does not differentiate data tones and pilot tones. • However, it is not trivial to estimate the channel for pilot tones in 11ac • For efficient offset tracking, pilot tones has a single stream in 11ac • We need to redefine the tone mapping for feedback, especially with tone grouping • We propose to have a uniform distribution of tone mapping when grouping is used

  13. FB Tone Mapping (20/40/80MHz) • For the case of 160MHz, the 80MHz tone mapping in the above table indicates the subcarrier indices to be fed back for each 80MHz segment.

  14. Tone Mapping Interpretation • Define the compressed V matrix FB, report field, which is based on the 802.11n subclause20.3.12.2.5 and 7.3.1.29, with appropriate changes for 11ac: • Sub-Channel Feedback Tone Interpretation at the AP/BFMer: • In 40/80/160 MHz BSS, when receiving a feedback with BW=20MHz, the AP/BFMer interprets the FB to correspond to the tones in the Primary channel. • In 80MHz and 160MHz BSS, when receiving a feedback with BW=40MHz, the AP/BFMer interprets the FB to correspond to the tones in the Primary and Secondary channels. • In 160MHz BSS, when receiving a feedback with BW=80MHz, AP/BFMer interprets the FB to correspond to the tones in the Primary, Secondary and Secondary 40 channels.

  15. Exclusive-MU Feedback Report- PT-SNR -

  16. Per-tone-SNR for MU-type Feedback • Unlike SU-MIMO where feedback of the pair {V,MCS} is sufficient, known MU-MIMO precoding algorithms benefit from knowledge of the transmit correlation VS2VH with more accurate S per tone. • We propose to add a new field (MU-exclusive Beamforming Report field) at the end of Compressed Beamforming Report field, in order to define the feedback of per-tone-SNR for each space time stream when MU-type feedback is indicated. • We propose to define the per-tone-SNR for each space time stream as the deviation in dB relative to the fed back average SNR per space-time stream (1 to Nc) • The new field has additional 4xNc bits per tone: • This new field (per-tone-SNR) is added in MU-exclusive Beamforming Report field • It is signaled by beamformee using MU-type bit in MIMO control field (slide 4) • Whether the report field includes per-tone-SNR depends on the SU/MU-type feedback which is requested by the beamformer.

  17. SNR per tone Calculation • For MU-BF, it is recommended to specify how to calculate SNR at BFee, so that BFer can unify the meaning of SNR to calculate the steering matrix fairly for participating MU-clients • Add following text in the spec (in 7.3.1.61) • SNR per tone for subcarrier k and space-time stream i is found by where Vk,i is the ith column of the feedback beamforming matrix at subcarrier k, and N is the noise plus interference power measured at the beamformee • [Note] PT-SNR encoding for the feedback report is presented in the next slide • [Note] How to find SNR_average using SNR per tone is already described in 7.3.1.61

  18. Per-Tone-SNR Subfield in MU-Exclusive Beamforming Report • The proposed subfield for Per-Tone-SNR Each field for Per-Tone-SNR at each tone is in the order of the columns of corresponding V matrix: Nd bits for the first column of corresponding V are followed by Nd bits for the second column and so on, up to the last Nc_th column of corresponding V at each tone. Corresponding V is reported in Compressed Beamforming field (see slide 3)

  19. Meaning of PT-SNR • Delta-SNR • The deviation in dB at each tone relative to the fed back average_SNR per space-time-stream,1 to Nc (reported in Compressed Beamforming Report field), from -8 dB to 7 dB with 1 dB granularity • Nd = 4 bits • Ng’ (grouping for PT-SNR) is 2xNg • Ng’ is not signaled in VHT MIMO control field • where is a function to find the minimum integer that is not smaller than the argument x.

  20. Simulation Results for 8x3, 4 STAs • The effects of Per-Tone-SNR for grouping are captured • Tone mapping without tone augmentation in slide 8 is used

  21. Simulation Results for 4x1, 4 STAs • The effects of Per-Tone-SNR for grouping are captured • Tone mapping without tone augmentation in slide 8 is used

  22. Summary • Propose to define explicit feedback format for 11ac SU and MU. • Codebook Info (angle resolution) is defined for SU-BF and MU-BF • Tone mapping/grouping is modified from 11n • MU-Exclusive feedback report is introduced only for MU-type feedback • SNR per tone is defined with equation

  23. Reference [1] IEEE 802.11-10/1105r1 Explicit sounding and feedback.ppt by H. Zhang and J. Kim et. al.

  24. Pre-Motion #1 • Do you support the VHT MIMO Control Field in the beamforming report frame as described in slide 5 and to update the VHT MIMO Control Field in the spec framework document accordingly? • Yes: • No: • Abs:

  25. Pre-Motion #2 • Do you support feedback tone mapping as shown on slide 14 and to define it in the spec framework document accordingly? • Yes: • No: • Abs:

  26. Pre-Motion #3 • Do you support Sub-Channel Feedback Tone Interpretation as in slide 15 and add the text in the spec framework document? • Yes: • No: • Abs:

  27. Pre-Motion #4 Do you support to include per-tone-SNR field in the MU-exclusive beamforming report as described in slide 19 and 20, and to add the proposed field in the spec framework document? Yes: No: Abs:

  28. Pre-Motion #5 Do you support to define SNR per tone for PT-SNR subfield as described in slide 18 and to add the proposed text in the second bullet in the spec framework document? Yes: No: Abs:

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