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Preamble Requirements for Beamforming
March 2005 doc.: IEEE /0183r0 March 2005 Preamble Requirements for Beamforming Date: Authors: 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 < 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 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 John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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March 2005 doc.: IEEE /0183r0 March 2005 Abstract Smoothing of steered MIMO channel estimates can result in severely degraded performance Mathematical basis for the problem is presented Empirical results illustrating the problem are presented Amplifies on material presented in Monterey (IEEE /1635r1) John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Requirements and uses for HT-LTF in Beamforming System
March 2005 doc.: IEEE /0183r0 March 2005 Summary Requirements and uses for HT-LTF in Beamforming System Perturbation theory and smoothing of steered channels Phase coherence and steering vectors Performance and smoothing of steered channels John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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March 2005 doc.: IEEE /0183r0 March 2005 Observations Availability of accurate and timely Channel State Information is essential for robust high throughput operation using Transmit Beamforming and Spatial Multiplexing Provision of appropriate CSI requires transmitting a full set of HT-LTF, N_LTF = N_TX, or N_LTF = min(N_TX, N_RX) It is essential to define a flexible approach to HT-LTFs that supports frequent and efficient exchange of reference that enables full CSI updates John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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More Observations Three applications for channel measurement/sounding
March 2005 doc.: IEEE /0183r0 March 2005 More Observations Three applications for channel measurement/sounding Equivalent channel estimate (HV) For calculating optimum receiver For calculating rate feedback/stream control N_LTF = N_SS Direct channel estimation (H) for channel calibration N_LTF = N_TX Channel covariance matrix estimation for Tx steering N_LTF = N_TX or N_LTF = min(N_TX,N_RX) All packets are sounding packets: used to measure channel Some channel sounding requires N_LTF > N_SS (currently referred to as sounding packets) Should be possible for any PPDU to enable any type of channel sounding John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Perturbation Theory and Smoothing of Steered Channels
March 2005 doc.: IEEE /0183r0 March 2005 Perturbation Theory and Smoothing of Steered Channels Question: Can conventional smoothing techniques be employed at the receiver when eigenvector steering is used over the MIMO channel? Answer: Must consider the effects of small perturbations on a MIMO channel on the resulting eigenvalues and eigenvectors. What happens when steered channel at subcarrier k is estimated from steered carriers at subcarriers k-1 and k+1? John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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A Little Perturbation Theory
March 2005 doc.: IEEE /0183r0 March 2005 A Little Perturbation Theory John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Perturbation Theory (2)
March 2005 doc.: IEEE /0183r0 March 2005 Perturbation Theory (2) John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Perturbation Theory Conclusion
March 2005 doc.: IEEE /0183r0 March 2005 Perturbation Theory Conclusion Estimation error when estimating effective steered channel can be arbitrarily large when channel eigenvalues are repeated or are closely spaced Note: While these effects are not always apparent in simulations based on TGn channel models, they are real effects that can have catastrophic results. Presentation n-wwise-preambles-and-mimo-tx-beamforming.ppt showed examples of where this is a problem John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Phase Coherence in Transmit Steering Vectors
March 2005 doc.: IEEE /0183r0 March 2005 Phase Coherence in Transmit Steering Vectors Problem: Right singular vectors of channel matrix are unique up to an arbitrary phase. Random phase differences between transmit steering vectors in adjacent tones limit coherence bandwidth of effective steered channel. Extra computations are required in SVD or EVD (eigenvalue decomposition) to maximize phase coherence of steering vectors across the band. This in turn maximizes coherence bandwidth of resulting effective steered channel John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Effect of Steering on Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Effect of Steering on Estimation Effective channel resulting from transmit steering has increased delay spread. Receiver channel estimation procedure must accommodate increased delay spread. Following material shows effects of smoothing on CDF of post-detection snr when using beamforming. John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Effective Channel March 2005 March 2005 doc.: IEEE 802.11-05/0183r0
John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Effective Channel March 2005 March 2005 doc.: IEEE 802.11-05/0183r0
John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Channel Estimation Plots
March 2005 doc.: IEEE /0183r0 March 2005 Channel Estimation Plots Following graphs show CDF of SNR Difference per Mode per Sub-Carrier between known steered channel and 3 different noisy channel estimates . Noisy channel estimate derived from orthogonal long training (dashed line). Noisy channel estimate derived from WWiSE LS and MMSE Tx Div channel estimate procedure (Li) (solid line). Delay interval was -400 ns to 800 ns unless otherwise indicated. Noisy channel estimate derived from WWiSE LS and Ad Hoc channel estimate procedure (dashed-dot line). For sub-carriers with two adjacent sub-carriers use 0.5H(k) (H(k-1) + H(k+1)). For sub-carriers with only one adjacent sub-carrier use 0.5H(k) + 0.5H(k-1) or 0.5H(k) + 0.5H(k+1). John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation TGn Sync training WWiSE training with LS estimator WWiSE training with ad hoc estimator John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation TGn Sync training WWiSE training with LS estimator WWiSE training with ad hoc estimator John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation TGn Sync training WWiSE training with LS estimator WWiSE training with ad hoc estimator No steering vector phase continuity imposed. John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation No steering vector phase continuity imposed. John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation TGn Sync training WWiSE training with LS estimator WWiSE training with ad hoc estimator John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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Steered Channel Estimation
March 2005 doc.: IEEE /0183r0 March 2005 Steered Channel Estimation John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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March 2005 doc.: IEEE /0183r0 March 2005 Conclusion Mathematical basis for performance degradation when receiver channel estimation smoothing is used with transmit steering has been established. Performance degradation when smoothed WWiSE preamble is used has been demonstrated Both simple frequency-domain smoothing and “optimal” LS smoothing have been shown to demonstrate the problem. TGn should not adopt a training mechanism with demonstrated performance issues. Beamforming MIMO is demonstrably the highest throughput approach under consideration by TGn John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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March 2005 doc.: IEEE /0183r0 March 2005 References Sadowsky, Yamaura, and Ketchum, “WWiSE Preambles and MIMO Beamforming?” IEEE /1635r1, January 2005. John Ketchum, Qualcomm Inc., et al John Ketchum et al, Qualcomm Inc.
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