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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Slide 1 Complexity reduction for time domain H matrix feedback Authors: Date: 2010-11-09

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Time domain H matrix compressed feedback Time domain H matrix feedback is without any objection the best method for feedback compression for 802.11ac –Combines feedback compression and improvement of channel estimation –Time domain feedback with TiDFT presents the best CSI feedback accuracy (6dB MSE over uncompressed, way more over legacy compressed V matrix): the best compression gain (4x or 8x) Arguments against this technique: –not a legacy scheme –complexity Slide 2

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Time domain H matrix compressed feedback: discussion around legacy Objective: reduce the technological step between 11n (beamforming) and 11ac (MU-MIMO) –option 1 (ACcord): choose compressed V-matrix for 11n (beamforming) and push for compressed V-matrix in 11ac (beamforming and MU-MIMO) this would lead to the non-selection of the best compression scheme for 11ac, which would potentially reduce the use of MU-MIMO (average by the bottom) –option 2: choose H-matrix feedback for 11n (beamforming) and choose time domain H matrix for 11ac (MU-MIMO and beamforming) H matrix already favored by a majority of 11n client companies selection of the best compression scheme for 11ac to have the best MU-MIMO Slide 3

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Time domain H matrix compressed feedback: discussion around complexity time domain H feedback with TiDFT or DCT has a reasonable complexity: transfer matrix multiplication in STA for TiDFT (only 16kB ROM storage for all matrices), simple fast DCT for DCT FFT or iDCT in AP (FFT already implemented in chipsets) No additional channel estimation improvement schemes needed Compressed V matrix also have an important complexity in receiver Note that the compressed V matrix process is so long that after SIFS, the process isnt completed: the preamble time of the CSI feedback is needed to end the process In this condition, there is no way that better channel estimation will be performed on top of compressed V matrix (stay with LS estimation): that means that the quality of CSI feedback will be of the worst quality (see Celenos results in annex) For all these reasons, we believe time domain H matrix feedback should be added to the spec framework. –and we show in this presentation that the complexity can even be further reduced Slide 4

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Proposition to reduce the complexity of time domain H feedback Instead of generating the impulse response of the complete channel (all subcarriers) generate time domain response based on the all Np subcarriers feedback of the CP first elements in the time domain We propose to generate multiple partial impulse responses corresponding to multiple groups (B groups) of subcarriers generate B time domain responses each based on a group of N FFT /B subcarriers The feedback includes multiple fields of the B partial impulse responses, each constituted of CP/B elements (note that we have demonstrated that all the usefull energy is gathered in the CP/B first elements) –The two next slides illustrate the classical and the new proposition with B=2 groups of subcarriers. Slide 5

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Slide 6

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Slide 7 Two fields in CSI feedback

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Conclusion Time domain H matrix provides the best compression with the best quality of CSI feedback –especially when considering both compression and channel estimation –Improve the efficiency of MU-MIMO and reduce the overhead Technological gap between 11n and 11ac and between beamforming and MU- MIMO is not higher with time-domain H matrix if the feedback issue is solved by taking into account 11n and 11ac jointly. The complexity of the time domain H matrix can be even reduced by applying the process to 2 groups of subcarriers with TiDFT : –it enables to reduce by a factor of 2 the complexity of the compression scheme and the size of the storage for TiDFT matrices, both in STA and in AP –Note that this proposition can also be applied to the DCT-based time domain feedback (which provides a lower compression gain). in this condition, up to 8 groups can be defined with overlapping between subcarriers groups Slide 8

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Pre-motion Do you support updating the spec framework to require that time domain H matrix feedback, be one feedback format for both VHT SU beamforming and DL MU-MIMO? –Yes –No –Abstain

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 References [1] Hongyuan Zhang and all, 11ac explicit sounding and feedback, IEEE 802.11-10/1105r0, Sept 2010. [2] L. Cariou and M. Diallo, Time Domain CSI report for explicit feedback, IEEE 802.11-10/0586r1, May 2010. [3] K. Ishihara and al., CSI Feedback Scheme using DCT for Explicit Beamforming, IEEE802.11- 10/0806r1, july 2010. [4] Nir Shapira, Yaron shany, Doubling Number of VHT-LTFs in MU-MIMO Operation, IEEE802.11- 10/1113r0, Sept 2010. Slide 10

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Annex Slide 11 1 Illustration of the process with DCT-based time domain feedback 2 Simulation results from Celeno showing the performance degradation using compressed-V matrix with LS estimation instead of time domain H matrix.

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Slide 12

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doc.:IEEE 802.11-10/1275r0 Submission Laurent Cariou Nov, 2010 Simulation Results from Celeno [4] 8 AP antennas, 4 users, each with 3 antennas. Channel model D. 20ms aging Compare the case of 1,2,3,4 or (perfect CSI) LTFs per stream in NDP –Results reflect impact of the quality of the feedback (independent of the channel estimation during Data transmission) –Results equivalent to comparing a channel estimation noise reduction scheme of 0dB, 3dB, 4.5dB, 6dB and (perfect CSI) Slide 13 Curve in blue: LS channel estimation (equivalent to what is feasible with compressed V matrix feedback) Curve in red: equivalent to channel estimation improvements embedded in time domain compressed CSI feedback starting from LS channel estimation Channel estimation results embeded in Time domain compressed feedback Channel estimation results with LS channel estimation (only estimation feasible with compressed V matrix)

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