1. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 1 Preambles, Beamforming, and the WWiSE Proposal 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, 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 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.http://stuartpatcom Date: 2005-01-17 Authors:

2. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 2 Abstract A discussion of preambles, closed loop techniques, and the WWiSE proposal for 802.11n.

3. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 3 Outline Background Closed loop in 802.11n Beamforming Simulation Results with the WWiSE Preambles Conclusions

4. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 4 Background Initial WWiSE proposal did not address closed loop –We preferred the simplicity of Open Loop Space-Time Block Codes (STBC) are very effective –Cost / complexity concerns –Mode explosion –Interoperability WWiSE has added provisions for closed loop (04/866r6) –Mode feedback –Channel estimate feedback

5. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 5 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

6. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 6 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

7. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 7 SVD Beamforming Qualcomm and TGnSync have proposed to compute V with a Singular Value Decomposition (SVD) U and V are unitary matrices, S is a diagonal matrix. If H is known at TX, V can be computed and applied to the TX signal. RX stations sees a new channel that looks like US.

8. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 8 Reception of SVD Beamformed Frames Arguments from Qualcomm/TGnsync (05/1635r0) –“The WWiSE preamble is a barrier for MIMO BF” –“WWiSE is a dead end for Tx MIMO BF” In Reality –WWiSE preambles are preferable for beamforming

9. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 9 Reception of SVD Beamformed Frames How could one 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.

10. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 10 Reception of Beamformed frames V Matrix 802.11n RX Channel H TX Streams Beamforming Transmitter

11. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 11 Reception of SVD Beamformed Frames Receiver processing for beamformed frames –Same as for frames that are not beamformed –Initial acquistion is the same –Channel estimation is the same –Processing and decoding is the same

12. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 12 Simulation of SVD Beamformed Frames Simulation Setup –Same receiver as we used for FRCC simulations –1000 independent channels –SVD beamform 2 TX Streams 2 and 4 TX antennas –25 db SNR –Compute channel estimate and show cumulative distribution function (CDF) of the mean square error

13. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 13 Channel Estimation Results 1000 channels Channel Model D SNR = 25 dB 4 Transmit Antennas 2 Transmit Streams 2 Receive Antennas

14. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 14 Channel Estimation Results 1000 channels Channel Model B SNR = 25 dB 2 Transmit Antennas 2 Transmit Streams 2 Receive Antennas

15. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 15 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 TGnsync are unnecessary

16. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 16 Why is the WWiSE Preamble Design Better? It is flexible –Legacy compatible when necessary –Shorter for highest throughput –Always shorter than the TGnsync proposal It works with open loop It works with beamforming As phy rate increases, the throughput gain increases

17. doc.: IEEE 802.11-05/1645r2 Submission January 2005 C. Hansen, BroadcomSlide 17 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 superior for beamforming.