1. Proposed solution for comments on Beam modes
June 2007
doc.: IEEE /2402r0
Sept 2007
Proposed solution for comments on Beam modes
Date:
Authors:
Notice: This document has been prepared to assist IEEE It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Joonsuk Kim, Broadcom Corp.
Joonsuk Kim, Broadcom Corp.

2. June 2007
doc.: IEEE /2402r0
Sept 2007
Abstract
This presentation provides resolutions for 5 comments in LB 97 (CID 606, CID 803, CID 1648, CID 1919, CID2912).
Joonsuk Kim, Broadcom Corp.
Joonsuk Kim, Broadcom Corp.

3. Comments on Beam modes Sept 2007 Joonsuk Kim, Broadcom Corp. 606
281.00
There is a proliferation of options regarding all the "spatial mapping" categories, including both spatial expansion methods and beamforming. In particular, too many options for beamforming are not justified. We move to keep implicit beamforming, and explicit beamforming limitedly to full CSI feedback ( ).
Simplify this section by removing the non-compressed and compressed beamforming matrix feedback options, and amend the draft consequently.
803
148.13
9.17
There are too many non-interoperable beamforming operating modes/features
Define a subset of beamforming features that supports both implicit and explicit operation, and that is required of any device doing any form of beamforming.
1648
68.51
4 different modes of beamforming are currently in the spec. That has been the case for over a year. When so many options are available, it makes it unlikely that semiconductor vendors will develop a common beamforming method.
Cut down the number of beamforming methods. Choose 1 explicit method so that everyone can start work on implementing it.
1919
There is currently a proliferation of options regarding all the "spatial mapping" categories, including both spatial expansion methods and beamforming. This will make difficult to guarantee interoperability among different vendors and will thus harm standard effectiveness. In particular, too many options for beamforming are not justified. We move to keep implicit beamforming, and explicit beamforming limitedly to full CSI feedback ( ). Note that this comment was not really addressed during the first comment resolution process; we solicit a more serious discussion on this point.
2912
Too many beamforming options
Pick one beamforming approach or make sure they interoperate
Joonsuk Kim, Broadcom Corp.

4. Sept 2007
Summary of 5 comments
Most of comments in Beam mode have a concern on the number of beamforming modes and their interoperability issue
In this presentation, we show the benefits of each BF mode and the reason why we want to keep them all.
Joonsuk Kim, Broadcom Corp.

5. Where does the draft stand today?
Sept 2007
Where does the draft stand today?
Two general feedback mechanisms, with subordinate options
Explicit – feedback of:
Cartesian-coordinate-quantized channel matrices (“CSI feedback”)
Cartesian-coordinate-quantized steering matrices (“Non-compressed beamforming matrix feedback”)
Steering matrices compressed using Givens rotations (“Compressed beamforming matrix feedback”)
Implicit
Reciprocity of the channel is assumed
Calibration of transmitter and receiver arrays enables assumption
Joonsuk Kim, Broadcom Corp.

6. Explicit Feedback CSI Feedback
Sept 2007
Explicit Feedback
CSI Feedback
In spite of relatively large overhead, this option is useful for Beamformer to choose the steering matrix with all information it needs
It is also used for Calibration when necessary for Implicit feedback.
Joonsuk Kim, Broadcom Corp.

7. Explicit Feedback Non-compressed Beamforming feedback
Sept 2007
Explicit Feedback
Non-compressed Beamforming feedback
May be useful when AP/STA do not want to do extra signal processing for compressing/decompressing beamforming matrix V in the form of angles.
Joonsuk Kim, Broadcom Corp.

8. Explicit Feedback Compressed Beamforming feedback
June 2007
doc.: IEEE /2402r0
Sept 2007
Explicit Feedback
Compressed Beamforming feedback
With compressed format in angles, the feedback overhead is reduced as much as 95% compared to Cartesian format.
Compression and decompression process does not suffer from significant computation load due to its nice structure of rotation and phase shift (only around 40 complex multipliers for 4x4 configuration for the worst case)
This compressed format is generic so any arbitrary unitary beamforming matrix can be fedback which is found by any beamforming algorithm from Beamformee.
In simulations, the feedback overhead is about 100 bytes for the worst case (4x4 configuration with Chennel E) to achieve the performance of full resolution feedback within marginal gap [reference: 07/666r0].
Joonsuk Kim, Broadcom Corp.
Joonsuk Kim, Broadcom Corp.

9. Sept 2007
Implicit Feedback
It does not require the extra feedback overhead to deliver either CSI or beamforming matrix information from the recipient, assuming the channel is reciprocal.
Joonsuk Kim, Broadcom Corp.

10. Conclusions Each of Beamforming modes has its own benefits.
Sept 2007
Conclusions
Each of Beamforming modes has its own benefits.
Interoperability would not a big issue since we have Capability field which specifies the beamforming modes it can operate with.
We believe the n spec should not limit the choice of architecture in implementation, so we like to keep the all of current beamforming modes as they are.
Therefore, we propose to reject these 5 comments.
Joonsuk Kim, Broadcom Corp.