11-11-0378-04-00ac-comment-resolution-sounding-poll-mimo-control-frame

IEEE P802.11

Wireless LANs

Abstract

Submission for Draft P802.11ac_D0.1 comment resolution.

In sounding procedures, VHT Compressed Beamforming Report field and MU Exclusive Beamforming Report

field can grow up to approximately 26kByts, which makes the MMPDU of VHT Compressed Beamforming frame be segmented and carried in the form of A-MPDU. This enables advanced features such as selective retransmission of segments in a VHT Compressed Beamforming frame to increase transmission

efficiency. In return for that, this submission provides modified VHT MIMO Control field including new subfields for segment identification and modified Sounding Poll frame including new subfield for indication of selective segment retransmission. Also, the sounding protocol regarding selective retransmission of segments is described.

Submission addresses Draft P802.11ac_D0.1 technical comments 28, 32, 141, 222, 763, 914, 1012, 1243, 1446, 1474, 223, 764, 1013, 1121, 1519, 1079, 1539, 960, 1194, 919, 1123, 101, 1124, and 1125

Introduction

Interpretation of a Motion to Adopt

A motion to approve this submission means that the editing instructions and any changed or added material are actioned in the TGac Draft. This introduction is not part of the adopted material.

Editing instructions formatted like this are intended to be copied into the TGac Draft (i.e. they are instructions to the 802.11 editor on how to merge the text with the baseline documents).

TGac Editor: Editing instructions preceded by “TGa c Editor” are instructions to the TGa c editor to modify existing material in the TGac draft. As a result of adopting the changes, the TGac editor will execute the instructions rather than copy them to the TGac Draft.

Submission Note: Notes to the reader of this submission are not part of the motion to adopt. These notes are there to clarify or provide context.

General Discussion:

In sounding procedures, VHT Compressed Beamforming Report field and MU Exclusive Beamforming Report field can grow over the limit of the maximum MPDU limit of a STA. The feedback needs to be segmented in this case and carried in the form of A-MPDU.

As a worst case example, when 8x8 MU-MIMO, 160MHz bandwidth, subcarrier grouping of 1, and maximum resolution quantization of 9 and 7 is considered. The size of VHT Compressed Beamforming Report field is 26,216 bytes Also, the size of MU Exclusive Beamforming Report field is 936. The total size of Beamforming Report field is 27,152 bytes. Assuming the maximum MPDU size of 3,895 bytes and considering other overhead, the number of segmentation can grow up to 8.

According to the current draft, a transmission failure in one of the segments in an A-MPDU results in entire retransmission of the VHT Compressed Beamforming frame, which makes the sounding procedure very inefficient when link quality is not good. Thus, the selective retransmission of segments in a VHT Compressed Beamforming frame would be a quite reasonable solution.

To support this, the segments in A-MPDU of VHT Compressed Beamforming frame need to be identified individually. This can be simply accomplished by introducing new fields for segment identification in a VHT MIMO Control field. This new field can also be utilized for the indication that a STA doesn’t have a valid feedback. On the other hand, Sounding Poll frame defined in 7.2.1.12 may include new additional fields for advanced sounding procedures. Thus, a new field can be introduced to indicate the selection of segments for retransmission. Considering the individual indication of segments with minimum additional overhead, a bitmap-type definition would be efficient for the new field.

A beamformer can determine which segment is not correctly received using the segment identification in a VHT MIMO Control field of the received VHT Compressed Beamforming frame. The beamformer may request the retransmission of all the segments or may request only the selected segments which have not correctly received using segment retransmission bitmap in Sounding Poll frame. Upon the reception of the Sounding Poll frame with the segment indication, a STA may feedback only selected segments in a VHT Compressed Beamforming frame or STA may retransmit all segments in a VHT Compressed Beamforming frame.

Proposed Resolution:

?TR CID 28 and 32: The comments are mentioning a missing subtype of Sounding Poll and NDPA frames. ? Proposed Response: Agree in principle.

?TR CID 141, 222, 763, 914, 1012, 1243, and 1474: The comments are mentioning missing instructions on Duration field which is left TBD.

? Proposed Response: Agree in principle. The Duration field can be set as described in Clause 7.1.4.2 (as described in IEEE802.11-11/0346)

?TR CID 1446, 223, 764, 1013, 1121, 1519, 1079, 1539, and 960: The comments are any mentioning possible additional field in Sounding Poll frame which is left TBD.

? Proposed Response: Agree in principle. One suggestion from comments is to add segment information to enable selective retransmission of segments. Discussions are given above. More details can be found in IEEE802.11-11/0411.

?TR CID 1194: The comment is mentioning the clarification of the sentence.

?TR CID 919 and 1123: The comments are mentioning the necessity indication of the feedback without VHT Compressed Beamforming Report.

? Proposed Response: Agree in principle. One suggestion from comments is that use the reserved bits for segment numbering and reserve one value to indicate null feedback case. The identification of segments can be utilized for advanced sounding procedures such as selective segment retransmission of VHT Compressed Beamforming frame.

?TR CID 101: The comment is mentioning the necessity of increasing the number of bits for BW indication in Figure 7-3.

? Proposed Response: Disagree. There is no reason to change. Two bits are fine as it is.

?TR CID 1124: The comment is mentioning the exact behavior for grouping of subcarriers.

? Proposed Response:

Agree in principle. Grouping is defined as “Grouping is a method that reduces the size of the VHT Compressed Beamforming Report field by reporting a single value for each group of Ng adjacent subcarriers” in 7.3.1.32. The sentence needs to be clarified with the reference. ?TR CID 1125: The comment is mentioning the undefined words “SU-BF ” and “MU-BF ”.

? Proposed Response: Agree in principle. Editorial correction required but details on different numbers of feedback bits seems not appropriate in the table. Those should be written in 7.3.1.32 if necessary.

Editing instructions:

TGac editor: Insert the following row in Table 7-1 (Draft 802.11mb-D4.0):

7 Frame formats

7.2 Format of individual frame types

7.2.1 Control frames

7.2.1.12 Sounding Poll

TGac editor: Change the name of the new control frame defined 7.2.1.12 from Sounding Poll frame to Beamforming Report Poll frame:

TGac editor: Insert the Segment Retransmission field in Table 7-16f as shown:

Octets:

TGac editor: On page 10 line 37, change the paragraph as follows:

The Duration field is set according to 7.1.4.2 Duration/ID field.

TGac editor: On page 10 line 42, insert two new paragraphs as follows:

The Segment Retransmission Bitmap field indicates the segments to be polled in a VHT Compressed Beamforming frame. The bit in position n(n=0 for LSB and n=7 for MSB) is set to 1 when the segment with the Remaining Segment subfield in VHT MIMO Control field set to n is requested. The bit in position n is set to 0 when the segment with the Remaining Segment subfield in VHT MIMO Control field set to n is not requested.

TGac editor: On page 10 line 44, put the sentence in the form of editor’s note.

7.3 Management frame body components

7.3.1 Fields that are not information element

7.3.1.31 VHT MIMO Control field

TGac editor: Change the VHT MIMO Control field in Figure 7-3 as follows:

TGac editor: Change the third row in Table 7-2 as follows:

TGac editor: Change the sixth row in Table 7-2 as follows:

TGac editor: Insert the following rows before Sounding Sequence row in Table 7-2:

9. MAC sublayer functional description

9.21 Null data packet (NDP) sounding

9.21.5 VHT sounding protocol

TGac editor: On page 59 line 13, insert three new paragraphs as follows:

In its first attempt to retrieve a VHT Compressed Beamforming frame from a beamformee that is not the one indicated by the first STA Info field, a beamformer shall transmits a Beamforming Report Poll frame to poll all possible segments of the VHT Compressed Beamforming frame from the beamformee, by setting all the bits in the Segment Retransmission Bitmap field of the Beamforming Report Poll frame to 1.

If a beamformer fails to receive some or all segments of a VHT Compressed Beamforming frame, the beamformer may request a selective retransmission of missing segments by sending a Beamforming Report Poll frame with the Segment Retransmission Bitmap field set as described in 7.2.1.12 to indicate the segments requested for retransmission. If the beamformer fails to receive the segment with the First Segment field set to 1, it may request a selective retransmission of missing segments assuming the VHT Compressed Beamforming frame is split into 8 segments. The beamformer may also request the retransmission of all segments by setting all the bits in the Segment Retransmission Bitmap field of the Beamforming Report Poll frame to 1.

A beamformee shall reply to a Beamforming Report Poll frame by either sending only the segments indicated in the Segment Retransmission Bitmap field in the Beamforming Report Poll frame or sending all the segments disregarding the Segment Retransmission Bitmap field in the Beamforming Report Poll fame.

TGac editor: On page 59 line 14, replace the paragraph with the one as follows:

A beamformer shall not transmit a Beamforming Report Poll frame to a SU only beamformee unless it has received at least one segment of the VHT Compressed Beamforming frame from the beamformee.

Premotion:

Do you agree the comment resolutions for CIDs 28, 32, 141, 222, 763, 914, 1012, 1243, 1446, 1474, 223, 764, 1013, 1121, 1519, 1079, 1539, 960, 1194, 919, 1123, 101, 1124, and 1125 as in 11/0378r2, and to be forwarded to the 11ac task group for motion?

- Yes:

- No:

- Abs: