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March 2005
John Ketchum, Qualcomm Inc
Slide 1
doc.: IEEE 802.11-05/0255r0
Submission
Responses to WWiSE Points on Beamforming
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Date: 2005-03-15
Name Company Address Phone email
John Ketchum Qualcomm 9 Damonmill Square Suite 2A
781-276-0915 [email protected]
Authors:
March 2005
John Ketchum, Qualcomm Inc
Slide 2
doc.: IEEE 802.11-05/0255r0
Submission
Abstract
• The is a response to the points made on slides 40 and 41 of the WWiSE proposal presentation 05/0150r2
March 2005
John Ketchum, Qualcomm Inc
Slide 3
doc.: IEEE 802.11-05/0255r0
Submission
Points from WWiSE Presentation
• Slide 40 of 05/0150r2
“The TGnSync version of beamforming has many disadvantages:…..”
March 2005
John Ketchum, Qualcomm Inc
Slide 4
doc.: IEEE 802.11-05/0255r0
Submission
WWiSE Claim:WWiSE Claim:
““Requires channel estimation to be done by simple frequency Requires channel estimation to be done by simple frequency division”division”
Response: This is not true. Any form of orthogonal training will Response: This is not true. Any form of orthogonal training will support beamforming cleanly. Qualcomm proposed training support beamforming cleanly. Qualcomm proposed training using time orthogonality with Walsh sequences. Qualcomm has using time orthogonality with Walsh sequences. Qualcomm has built a prototype MIMO beamforming system around this type of built a prototype MIMO beamforming system around this type of training that achieves rates in excess of 200 Mbps.training that achieves rates in excess of 200 Mbps.
Further WWiSE Claim: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.
March 2005
John Ketchum, Qualcomm Inc
Slide 5
doc.: IEEE 802.11-05/0255r0
Submission
WWiSE Claim:WWiSE Claim:““Requires MMSE detection at receiver”Requires MMSE detection at receiver”Response:Response:This is not true. Many different forms of detection will work with Tx This is not true. Many different forms of detection will work with Tx
beamforming. However, Tx beamforming allows the beamforming. However, Tx beamforming allows the implementation of very simple receivers. Qualcomm’s prototype implementation of very simple receivers. Qualcomm’s prototype gives high throughput with a very simple spatial matched filter gives high throughput with a very simple spatial matched filter receiver. Performance can be enhanced by implementing an receiver. Performance can be enhanced by implementing an MMSE receiver. A “generalized” receiver can be used as well, but MMSE receiver. A “generalized” receiver can be used as well, but for Tx beamforming there will be little if any performance gain for Tx beamforming there will be little if any performance gain from using techniques such as successive cancellation. One of the from using techniques such as successive cancellation. One of the primary advantages of beamforming is that it avoids the primary advantages of beamforming is that it avoids the substantial additional complexity of such receiver techniques.substantial additional complexity of such receiver techniques.
Furthermore, the use of generalized receiver techniques without Tx Furthermore, the use of generalized receiver techniques without Tx beamforming is fully supported in the TGn Sync proposal. Direct-beamforming is fully supported in the TGn Sync proposal. Direct-mapped or spatial spreading can be used in conjunction with mapped or spatial spreading can be used in conjunction with generalized receivers to provide high performance.generalized receivers to provide high performance.
March 2005
John Ketchum, Qualcomm Inc
Slide 6
doc.: IEEE 802.11-05/0255r0
Submission
WWiSE Claim:WWiSE Claim:““Requires longer preambles”Requires longer preambles”Response: This is not true. The difference in lengths of Response: This is not true. The difference in lengths of
the TGn Sync and WWiSE preamble have little to do the TGn Sync and WWiSE preamble have little to do with support for beamforming. with support for beamforming.
The HT reference portion of the TGn Sync preamble is The HT reference portion of the TGn Sync preamble is under many circumstances under many circumstances shortershorter than the equivalent than the equivalent portion of the WWiSE preamble. portion of the WWiSE preamble.
For example transmitting a single spatial stream, the TGn For example transmitting a single spatial stream, the TGn Sync HT-LTF is 7.2 us, compared to at least 8 us for Sync HT-LTF is 7.2 us, compared to at least 8 us for WWiSE.WWiSE.
Or when transmitting 3 spatial streams, the TGn Sync Or when transmitting 3 spatial streams, the TGn Sync HT-LTF is 15.2 usec, compared to 16 usec for WWiSEHT-LTF is 15.2 usec, compared to 16 usec for WWiSE
March 2005
John Ketchum, Qualcomm Inc
Slide 7
doc.: IEEE 802.11-05/0255r0
Submission
WWiSE Claim:WWiSE Claim:
““Requires calibration”Requires calibration”
Response:Response:
This is true. Devices that don’t have sufficiently well-This is true. Devices that don’t have sufficiently well-matched transmit and receive chains will require an matched transmit and receive chains will require an over-the-air-calibration process. However, this is a over-the-air-calibration process. However, this is a low-complexity, low-overhead background process that low-complexity, low-overhead background process that will have minimal impact on device complexity and will have minimal impact on device complexity and network throughput.network throughput.
Development of devices that don’t require calibration is Development of devices that don’t require calibration is an area for potential innovationan area for potential innovation
March 2005
John Ketchum, Qualcomm Inc
Slide 8
doc.: IEEE 802.11-05/0255r0
Submission
WWiSE Claim:WWiSE Claim:
“…“…places many burdensome constraints on receiver””
Response:Response:
What burdensome constraints? Tx beamforming enables What burdensome constraints? Tx beamforming enables very simple receiver implementations. Equivalent very simple receiver implementations. Equivalent performance without Tx beamforming requires much performance without Tx beamforming requires much more complex receivers.more complex receivers.
March 2005
John Ketchum, Qualcomm Inc
Slide 9
doc.: IEEE 802.11-05/0255r0
Submission
Conclusion
• WWiSE’s objections to the TGn Sync approach to beamforming are completely without merit
