1. VHT Link Adaptations Date: 2011-1-18 Authors: Month Year Month Year
doc.: IEEE yy/xxxxr0
doc.: IEEE yy/xxxxr0
VHT Link Adaptations
Date:
Authors:
Page 1
John Doe, Some Company
John Doe, Some Company

2. FLA Categories Solicited MFB Unsolicited MFB
MRQ with NDP Sounding that requests beamforming/MU FB, MFB sent with sounding FB frame.
MRQ that is not tied up with beamforming exchange, MFB sent in regular uplink frame.
Unsolicited MFB
Unsolicited MFB with Sounding FB.
Unsolicited MFB sent in regular uplink frame.

3. Solicited Link Adaptation in 11n
MRQ shall be sent in HTC along with sounding (see ).
+HTC MRQ=1
NDPA
NDP
MFB
MRQ is sent with sounding, so that the Rx can fully derive MIMO channel est and compute appropriate Mod/rate/Nss.
Slide 3

4. Difference in 11ac
NDPA+NDP sequence is tied up with SU-BF or MU-MIMO sounding.
Refer to NDPA frame definition
Therefore it is not possible to send a VHT MRQ in NDPA that only requests MFB and not request BF feedback.
i.e. MRQ in NDPA has to be tied up with BF.
Note that MRQ in NDPA means MFB has to be measured based on NDP.

5. MCS versus SNR FB
It is arguable whether the Rx or Tx should compute the MCS.
Tx needs to offset its power difference on sending different MCSs, the Rx does not know the Tx power control.
Rx does not know whether Tx will apply optional PHY modes such as STBC, LDPC, TxBF, or other proprietary technology.
Desirable to feedback both MCS and SNR.
SNR is defined as 8bit 2’s complement number, averaged over all the tones and all the space-time streams
Represent [-10, 53]dB, same as SNR report in Compressed V FB (11n, 11ac)

6. Solicited/Unsolicited
Example of VHTC Format
Details refer to [1]. B0 B1 B2
B3-B5
B6-B8
B9-B11
B12-B15
B16-B23
HT/VHT
Solicited/Unsolicited
MRQ
MSI
MFSI/GID-L
Nsts
MCS
SNR 1 4 3 8
B24-B26
B27
B28
B29
B30
B31
GID-H
Coding Type
FB TX Type
Reserved
AC Constraint
RDG/More PPDU 3 1

7. Link Adaptation with SU BF
We already have rule on MFB in SU BF feedback frame: MFB+SNR assumes the same CV will be applied, and Nsts=Nc.
Need a rule for responding MRQ with NDPA.
Proposal: if the MRQ is in NDPA that requests SUBF feedback, BFMee SHALL include the MFB only in SU-BF feedback.
Reason: SU-BF FB already has SNR and Nsts ready, it is just one step from computing MCS, easy to implement. Delayed MFB in this case will complicate the situation.
MRQ
NDPA
NDP
MFB+SNR
SUBF FB
Slide 7

8. Pre-Motion 1
Do you agree to add the following sentence in spec frame work
6.x VHT Link Adaptation
MRQ in VHT Control Field could be sent with any frame (i.e. not only with NDPA).
Yes No
Abstain

9. Pre-Motion 2
Do you agree to add the following sentence in spec frame work
6.x VHT Link Adaptation
An SNR Feedback field is included in VHT Control Field, which is defined as 8bit 2’s complement number, averaged over all the tones and all the space-time streams.
Yes No
Abstain

10. Pre-Motion 3
Do you agree to add the following sentence in spec frame work
6.x VHT Link Adaptation
If the MFB requester sends MRQ in an VHT NDP announcement frame requesting only SU-BF Feedbacks, then the MFB responder shall include the corresponding MFB and SNR feedback in the VHT Compressed Beamforming frame that is the response of the same NDP-A and NDP sequence.
Yes No
Abstain

11. References
[1] ac-VHT-Control-and-Link-Adaptation.pptx