Benefits of Compressed Explicit feedback to resolve CID 2969 May 2007 doc.: IEEE 802.11-07/0xxxr0 May 2007 Benefits of Compressed Explicit feedback to resolve CID 2969 Date: 2007-05-09 Authors: Notice: This document has been prepared to assist IEEE 802.11. 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. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Joonsuk Kim, Broadcom Joonsuk Kim, Broadcom

CID 2969 in LB97 comments CID 2969 says May 2007 CID 2969 in LB97 comments CID 2969 says “Since the complexity of processing the Compressed beamforming matrix is higher and the advantage in throughput is marginal (if any) when compared to non-Compressed beamforming, the Compressed beamforming matrix text should be deleted.” This presentation shows the comment is wrong. This includes a simple complexity analysis and overhead comparison for throughputs. Joonsuk Kim, Broadcom

May 2007 Complexity For example of 2x2, decomposition at Beamformee requires only 3 complex multiplies. At Beamformer, finding V with angles needs only 2 complex multiplies. Even with the worst case of 4x4, it may need only less than 40 complex multiplies, depending on how to implement it. Compared with signal processing to find the SVD beamforming matrix V for example, this process is negligible in terms of complexity. Joonsuk Kim, Broadcom

Overhead: Sample Simulations for 2x2 ch. B NLOS May 2007 Overhead: Sample Simulations for 2x2 ch. B NLOS Joonsuk Kim, Broadcom

Summary for channel E 2x2 3x3 4x2 4x4 Cartesian 280/570 504/1026 May 2007 Summary for channel E The length of feedback data [Bytes] (BandWidth = 20MHz/40MHz) 2x2 3x3 4x2 4x4 Cartesian 280/570 504/1026 448/912 896/1824 Givens 56/114 168/342 210/428 336/684 (252/513) Grouping 2 28/56 84/168 105/210 168/336 (126/252) Grouping 4 14/28 42/84 53/105 84/168 (63/126) For Givens/Grouping, 8,24,30,48(or 36) bits/tone are applied for 2x2,3x3,4x2,4x4 system, respectively, for the worst case of Channel E. For Channel D, Blue turns to Black, and Red turns to Blue. Colors: Black: PER performance penalty of 0dB~0.5dB compared to the full resolution BF Blue: PER performance penalty of 0.5dB~1dB compared to the full resolution BF Red: PER performance penalty of 1dB~1.5dB compared to the full resolution BF Joonsuk Kim, Broadcom

May 2007 Conclusions There are many benefits of compressed explicit feedback in overhead reduction with minimal aid of the beamformee to determine the angles for feedback. Compared to the complexity of finding SVD beamforming matrix V, additional process to determine angles are negligible. 95% of overhead reduction compared to Non-compressed explicit feedback is NOT “marginal”. Since the reasons for the comment in CID 2969 are wrong, it is proposed to reject CID 2969. Propose: Reject on the ground that BEAM adhoc group agreed there are many benefits of compressed explicit feedback in terms of complexity and overhead reduction compared to Non-compressed explicit feedback as shown in 07/0666r0. Joonsuk Kim, Broadcom