Preambles, Beamforming, and the WWiSE Proposal January 2005 doc.: IEEE 802.11-05/1645r0 January 2005 Preambles, Beamforming, and the WWiSE Proposal Date: 2005-01-17 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>. C. Hansen, Broadcom C. Hansen, Broadcom

January 2005 doc.: IEEE 802.11-05/1645r0 January 2005 Abstract A discussion of closed loop techniques and the WWiSE proposal for 802.11n. C. Hansen, Broadcom C. Hansen, Broadcom

Outline Background Closed loop in 802.11n Beamforming January 2005 Outline Background Closed loop in 802.11n Beamforming Simulation Results with the WWiSE Preambles Conclusions C. Hansen, Broadcom

Background Initial WWiSE proposal did not address closed loop January 2005 Background Initial WWiSE 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 WWiSE has added provisions for closed loop (04/866r6) Mode feedback Channel estimate feedback C. Hansen, Broadcom

Closed Loop for 802.11n There are many ways to use feedback January 2005 Closed Loop for 802.11n 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 C. Hansen, Broadcom

Beamforming P Streams M Transmit Antennas N Receive Antennas January 2005 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 C. Hansen, Broadcom

January 2005 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. C. Hansen, Broadcom

Reception of SVD Beamformed Frames January 2005 Reception of SVD Beamformed Frames Is it feasible to apply SVD beamforming to an 802.11n frame defined in the WWiSE proposal? For example 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 04/866r6. C. Hansen, Broadcom

Reception of SVD Beamformed Frames January 2005 Reception of SVD Beamformed Frames Contrary to speculative arguments in 05/1635, you can apply SVD beamforming to WWiSE preambles Receiver processing works the same way Excellent channel estimation performance Example Simulation Results 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) C. Hansen, Broadcom

Channel Estimation Results January 2005 Channel Estimation Results 1000 channels Channel Model D SNR = 25 dB 4 Transmit Antennas 2 Transmit Streams 2 Receive Antennas C. Hansen, Broadcom

Channel Estimation Results January 2005 Channel Estimation Results Preamble processing with or without beamforming is the same Same benefits of the WWiSE preamble carry forward Good performance Low overhead Long preambles from other proposals are unnecessary C. Hansen, Broadcom

January 2005 Conclusions WWiSE has added provisions for closed loop to its proposal (04/866r6) WWiSE is not advocating a specific beamforming method Some members of 802.11n have claimed WWiSE preambles are not compatible with beamforming WWiSE preambles are fully compatible with beamforming. C. Hansen, Broadcom