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11ac Explicit Sounding and Feedback

11ac Explicit Sounding and Feedback. Date: 2010-11-09. Authors:. Overview. The following BF/MU items were accepted in Sept IEEE meeting (1105r0): Only explicit sounding and feedback are applied for SU beamforming, and MU-MIMO. NDP as the only sounding format. NDP PPDU frame format.

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11ac Explicit Sounding and Feedback

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  1. 11ac Explicit Sounding and Feedback Date: 2010-11-09 Authors:

  2. Overview • The following BF/MU items were accepted in Sept IEEE meeting (1105r0): • Only explicit sounding and feedback are applied for SU beamforming, and MU-MIMO. • NDP as the only sounding format. • NDP PPDU frame format. • Immediate feedback only: FB SIFS after NDP or polling frame. • General feedback frame format: Action-No-Ack frame as below. • This presentation continues the discussions of the compressed feedback format for both SU and MU.

  3. Compressed V Matrix Feedback • Compressed V matrix FB (as in 11n spec 20.3.12.2.5 and 7.3.1.29) is a good candidate for both SU and MU feedbacks. • Unified format between SU and MU. • Unified format between 11ac in 5GHz and 11n in 2.4GHz and 5GHz. • Reduced overhead (important for MU) compared with raw CSI feedback, by using quantized angles in V to replace raw I/Q values in H. • Overhead reduction from compressed V FB was largely discussed back in 11n—refer to [1]. • Refer to Appendix I for size comparisons. • Enables feeding back partial rank, in LOS or ill-conditioned channels.

  4. V Feedback v.s. H Feedback • Feeding back V matrix in MU performs similarly as feeding back CSI matrix, for a wide range of precoder designs. • Assume H=U.S.V*, when per-tone substream SNR (equivalent to S) is fed back with V matrix, S.V* is equivalent to H (up to a receiver side rotation matrix). • Refer to the simulations in the subsequent slides.

  5. Simulation Settings • SU-BF: • Ntx=4, Nrx=2, DNLOS 80MHz, MCS15, Compressed V FB with b_phi=4, b_psi=2, Ng=1,2. • DL-MUMIMO PER: • 2 Clients, with (Ntx, Nrx1, Nrx2) = (4,2,2), and (6,2,2) • 40MHz, DNLOS channels, equal path loss for two clients. • CV FB with (9,7) angle quantization. • Linear interpolation at AP, if Ng=2; no smoothing if Ng=1. • PER of user 1 is measured • DL-MUMIMO Throughput: • 4 Clients, with (8,3,3,3,3), and (4,2,2,2,2) • 40MHz, DNLOS channels.

  6. SU-BF PER: DNLOS 80MHz, MCS15, 4x2, b_phi=4, b_psi=2

  7. MU PER:DNLOS 40MHz, (4,2,2) Nss=1 MCS7 per user, b_phi=9, b_psi=7 Note: We may reduce the gap by more advanced interpolation/smoothing at AP.

  8. MU:DNLOS 40MHz, (6,2,2) Nss=2 MCS7 per user, b_phi=9, b_psi=7 Note: We may reduce the gap by more advanced interpolation/smoothing at AP.

  9. MU Throughput: (8,3,3,3,3) • Tables below show throughput comparison of compressed V with tone grouping of one and four and with angle quantization relative to perfect channel feedback • Further overhead reduction can be achieved with rank one feedback

  10. MU Throughput: (4,2,2,2,2)

  11. On Time Domain Compressed H FB [3][4] • Time/Transfer domain compressed H introduces a completely different feedback approach from 11n. • One additional feedback mode for 11ac devices that also support 11n BF mode(s). • Higher complexity, memory requirement and power consumption by using FFT engine to generate and decode the feedback, especially when only immediate feedback is allowed in 11ac. • Feeding back time/transfer domain H matrix doesn’t allow reduced-rank feedbacks, which is definitely sufficient in SU, and somewhat sufficient in MU (e.g. in LOS or ill-conditioned channels). • Example: In a 3x8 H channel with strong LOS, CV FB allows only feeding back 3x1 matrix, but H feedback needs to feed back the whole 3x8 matrix. • This might be a common scenario as MU-MIMO is mainly useful at low range, e.g. refer to the measurement results in [5][6]. • The CV Feedback (in frequency domain) in this proposal does not prevent the BFmer/AP to apply advanced interpolation/smoothing technology (e.g. use time domain interpolation) to improve the feedback quality.

  12. CV FB Format • 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. • 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 • Refer to [2] on detailed descriptions of VHT MIMO Control Field, Compressed Beamforming Report field, and MU-exclusive Beamforming Report field.

  13. Conclusions • Propose Compressed V Matrix Feedback as the only feedback format for SU and MU. • Unified between 11ac SU and MU • Unified between 11ac and 11n • Reduced overhead for SU and MU • Good performance in both SU-BF and MU-MIMO.

  14. Appendix I: Comparing Sizes of Raw H and CV Feedbacks

  15. H vs CV Feedback Size (Bytes) • Follow 11n CSI and CV FB Definitions. • 40MHz, Ng=1, H with Nb=8, CV with b_phi=8, b_psi=6 Nc Nr H: Nr Nc CV:

  16. Discussions • The tables are mainly for MU FB (high bit-width required). • Overhead savings are big, e.g. • 4x2: %47 reduction • 4x4: %68 reduction • 8x4: %41 reduction • Overhead saving for SU-BF is more (see [1]). • With reduced rank CV feedback, the saving could be more.

  17. Pre-Motion #1 • Do you agree to adopt compressed V matrix feedback (based on 20.3.12.2.5 and 7.3.1.29 in 11n spec) as the only feedback format for SU beamforming and MU-MIMO, and add the same statement into the spec framework? • Yes • No • Abstain

  18. References [1] 11-07-0666-00-000n-BEAM-LB97-CID2969, Joonsuk Kim, et al. [2] 11-10-1227-00-00ac-explicit-feedback-format.ppt [3] 11-10-0332-00-00ac-csi-report-for-explicit-feedback-beamforming-in-downlink-mu-mimo [4] 11-10-0586-01-00ac-time-domain-csi-report-for-explicit-feedback [5] 11-09-0345-00-00ac-indoor-channel-measurements-for-tgac [6] 11-09-0542-00-00ac_Corridor_channel_measurements_for_tgac

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