January 2005 doc IEEE 802 11 051645 r

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Preambles, Beamforming, and the WWi. SE Proposal Authors: Date: 2005 -01 -17 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: // ieee 802. 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>. Submission 1 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Abstract A discussion of closed loop techniques and the WWi. SE proposal for 802. 11 n. Submission 2 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Outline • • • Background Closed loop in 802. 11 n Beamforming Simulation Results with the WWi. SE Preambles Conclusions Submission 3 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Background • Initial WWi. SE proposal did not address closed loop – Not needed for high performance • Other means, such as Space-Time Block Codes (STBC) are effective – Cost / Complexity – Mode explosion – Interoperability • WWi. SE has added provisions for closed loop (04/866 r 6) – Mode feedback – Channel estimate feedback Submission 4 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Closed Loop for 802. 11 n • There are many ways to use feedback – Rate selection – Mode selection – Beamforming • Rate and Mode selection require simple feedback – Easy to implement – Easy to standardize • Beamforming requires channel state feedback – More complicated Submission 5 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Beamforming • • • P Streams M Transmit Antennas N Receive Antennas MIMO Channel Matrix, H is N by M TX can apply a M by P Beamforming (Precoding) Matrix V Channel at RX looks like a N by P matrix Submission 6 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 SVD Beamforming • One proposed techniques is to compute V with a Singular Value Decomposition (SVD) • U and V are unitary matricies, S is a diagonal matrix. • If H is known at TX, V can be applied. • RX stations sees a new channel that looks like US. Submission 7 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Reception of SVD Beamformed Frames • Is it feasible to apply SVD beamforming to an 802. 11 n frame defined in the WWi. SE proposal? – For example • • Submission 2 TX streams 4 TX antennas Compute 4 by 2 V matrix for each sub-carrier and apply at TX Use the 2 stream frame defined in 04/866 r 6. 8 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Reception of SVD Beamformed Frames • Contrary to speculative arguments in 05/1635, you can apply SVD beamforming to WWi. SE preambles – Receiver processing works the same way – Excellent channel estimation performance • Example Simulation Results – – Submission 1000 independent 4 TX, 2 RX Model D Channels SVD beamform 2 TX Streams 25 db SNR Compute channel estimate and show error cumulative distribution function (CDF) 9 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Channel Estimation Results 1000 channels Channel Model D SNR = 25 d. B 4 Transmit Antennas 2 Transmit Streams 2 Receive Antennas Submission 10 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Channel Estimation Results • Preamble processing with or without beamforming is the same • Same benefits of the WWi. SE preamble carry forward – Good performance – Low overhead • Long preambles from other proposals are unnecessary Submission 11 C. Hansen, Broadcom

January 2005 doc. : IEEE 802. 11 -05/1645 r 0 Conclusions • WWi. SE has added provisions for closed loop to its proposal (04/866 r 6) • WWi. SE is not advocating a specific beamforming method • Some members of 802. 11 n have claimed WWi. SE preambles are not compatible with beamforming • WWi. SE preambles are fully compatible with beamforming. Submission 12 C. Hansen, Broadcom