doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 1 Responses to WWiSE Points on Beamforming 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. 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 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at. Date: Authors:

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 2 Abstract The is a response to the points made on slides 40 and 41 of the WWiSE proposal presentation 05/0150r2

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 3 Points from WWiSE Presentation Slide 40 of 05/0150r2 “The TGnSync version of beamforming has many disadvantages:…..”

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 4 WWiSE Claim: “Requires channel estimation to be done by simple frequency division” Response: This is not true. Any form of orthogonal training will support beamforming cleanly. Qualcomm proposed training using time orthogonality with Walsh sequences. Qualcomm has built a prototype MIMO beamforming system around this type of training that achieves rates in excess of 200 Mbps. Further WWiSE Claim: “ “Loses the opportunity to improve channel estimation, and hence robustness. This loss is permanent.” Also not true. Smoothing can be applied to TGn Sync HT-LTF when appropriate. Smoothing gains will be commensurate with those achieved for WWiSE preamble. The difference is that smoothing is not required to make TGn Sync preamble work.

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 5 WWiSE Claim: “Requires MMSE detection at receiver” Response: This is not true. Many different forms of detection will work with Tx beamforming. However, Tx beamforming allows the implementation of very simple receivers. Qualcomm’s prototype gives high throughput with a very simple spatial matched filter receiver. Performance can be enhanced by implementing an MMSE receiver. A “generalized” receiver can be used as well, but for Tx beamforming there will be little if any performance gain from using techniques such as successive cancellation. One of the primary advantages of beamforming is that it avoids the substantial additional complexity of such receiver techniques. Furthermore, the use of generalized receiver techniques without Tx beamforming is fully supported in the TGn Sync proposal. Direct- mapped or spatial spreading can be used in conjunction with generalized receivers to provide high performance.

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 6 WWiSE Claim: “Requires longer preambles” Response: This is not true. The difference in lengths of the TGn Sync and WWiSE preamble have little to do with support for beamforming. The HT reference portion of the TGn Sync preamble is under many circumstances shorter than the equivalent portion of the WWiSE preamble. For example transmitting a single spatial stream, the TGn Sync HT-LTF is 7.2 us, compared to at least 8 us for WWiSE. Or when transmitting 3 spatial streams, the TGn Sync HT-LTF is 15.2 usec, compared to 16 usec for WWiSE

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 7 WWiSE Claim: “Requires calibration” Response: This is true. Devices that don’t have sufficiently well- matched transmit and receive chains will require an over-the-air-calibration process. However, this is a low-complexity, low-overhead background process that will have minimal impact on device complexity and network throughput. Development of devices that don’t require calibration is an area for potential innovation

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 8 WWiSE Claim: “…” “…places many burdensome constraints on receiver”Response: What burdensome constraints? Tx beamforming enables very simple receiver implementations. Equivalent performance without Tx beamforming requires much more complex receivers.

doc.: IEEE /0255r0 Submission March 2005 John Ketchum, Qualcomm IncSlide 9 Conclusion WWiSE’s objections to the TGn Sync approach to beamforming are completely without merit