1. 1 Differential Feedback Scheme for Closed-Loop Beamforming IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE C80216m-09_0927 Date Submitted: 2009-03-07 Source: Qinghua Li, Yuan Zhu, Eddie Lin, Shanshan Zheng, E-mail:guangjie.li@intel.comguangjie.li@intel.com Jiacheng Wang, Xiaofeng Liu, Feng Zhou, Guangjie Li, qinghua.li@intel.comqinghua.li@intel.com Alexei Davydov, Huaning Niu, and Yang-seok Choi Intel Corporation Venue: Session #61, Cairo, Egypt Re: TGm AWD Base Contribution: None Purpose: Discussion and adoption by TGm AWD Notice: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who 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 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

2. 2 Outline Introduction Differential feedback –Scheme I: C80216m-09_0528r4, Qinghua Li, et al. –Scheme II: C80216m-08_1187, Bruno Clerckx, et al. Comparison of throughput, reliability, overhead, and complexity Conclusions Proposed text

3. 3 Signal model — a sense about matrix dimensions is channel matrix of dimension. is beamforming matrix of dimension. is transmitted signal vector of dimension.

4. 4 One-shot reset and differential feedback

5. 5 There is always correlation between adjacent precoders. Adjacent beamforming matrixes are nearby. Distance between adjacent matrixes is determined by channel variation and determines beamforming gain degradation within each feedback period.

6. 6 Differential codebook — polar cap

7. 7 Scheme I Differentiation at SS: Quantization at SS: Beamforming matrix reconstruction at BS: Beamforming at BS: Sanity check: Beamforming matrix needs to be fed back.

8. 8 Actual implementation Actual quantization at SS: Beamforming matrix reconstruction at BS: Beamforming at BS: Note that quantization criterion here is better than that in C80216m-09_0058r4.

9. 9 Computation of Q(t-1) Low computational complexity – Householder matrix for rank 1 – Gram-Schmidt for rank 2 Add no hardware – Reuse hardware of the mandatory, transformed codebook

10. 10 Scheme II Actual quantization at SS: Beamforming matrix reconstruction at BS: Beamforming at BS: Note that quantization criterion here is better than that in C80216m-08_1187.

11. 11 Updates of Scheme II Identity matrix is included into the codebook lately. Polar cap size is reduced through increased correlation 0.95.

12. 12 Scheme I and Scheme II track perturbations of e 1 and [e 1 e 2 e 3 e 4 ], respectively. Scheme I’s codewords quantize perturbations of e 1 on unit circle with 6 degrees of freedom (DOF), while Scheme II’s codewords quantize perturbations of whole identity matrix on Stiefel manifold with 12 DOF. Scheme I Scheme II

13. 13 Scheme I codebook matches to precoder delta distribution while Scheme II’s doesn’t. Differential matrix is symmetric about center [e 1 ] or identity matrix. Scheme I’s codebook is symmetric about [e 1 ], while Scheme II’s codebook is asymmetric about identity matrix with uneven quantization errors.

14. 14 Other differences Correlation adaptation – Scheme I has two codebooks for small and high correlation scenarios, respectively. The two codebooks are pre-defined and stored. – Scheme II varies codebook using measured correlation matrix and costly online SVD computation. Rank adaptation – Scheme I can change precoder rank anytime. – Scheme II can not change precoder rank during differential feedbacks and has to wait until next reset.

15. 15 The complexity of Scheme II’s 4-bit version is more than triple of Scheme I's 3-bit because Scheme II uses 4x4 matrix operation rather than 4x1 or 4x2.

16. 16 Scheme II's 4-bit complexity is more than 50% of Scheme I's 4-bit because Scheme II uses 4x4 matrix operation rather than 4x1 or 4x2.

17. 17 Summary of Differences Scheme IScheme II Principle Track perturbation of e 1 or [e 1 e 2 ]. Track perturbation of [e 1 e 2 e 3 e 4 ]. Codebook dimension 4x1 and 4x24x4 Computational Complexity LowHigh No. of codebooks One small codebook for each rank One large codebook for all ranks Codeword distribution Even distribution on Grassmannian manifold Uneven distribution on Grassmannian manifold Rank adaptation Rank can be changed at anytime. Rank changes only after reset. Correlation adaptation Two predefined codebooks for small and large correlation scenarios, respectively. Adaptive codebooks with online SVD computation for different correlation scenarios. Support of 8 antennas EasyDifficult because of wasted codewords and high complexity.

18. 18 Comparison of throughput and reliability System level simulation Single-user MIMO Implementation losses are included – Feedback error and error propagation – Quantized reset feedback

19. 19 General SLS parameters Parameter NamesParameter Values Network Topology57 sectors wrap around, 10 MS/sector MS channelITU PB3km/h Frame structureTDD, 5DL, 3 UL Feedback delay5ms Inter cell interference modelingChannel is modeled as one tap wide band Antenna configuration4Tx, 2 Rx Codebook configurationBaseline 6 bits, Diff 4 bits or 3 bits Q matrix reset frequencyOnce every 4 frames PMI errorfree PMI calculationMaximize post SINR System bandwidth10MHz, 864 data subcarriers Permutation typeAMC, 48 LRU CQI feedback1Subband=4 LRU, ideal feedback

20. 20 Codebook related parameters Samsung diff. codebook Intel diff. 4-bit codebook Intel diff. 3-bit codebook Codebook size4 bits i.e. 16 codewords 3 bits i.e. 8 codewords Feedback overhead 18 bits / 4 frames / Subband including 6-bit reset 15 bits / 3 frames / Subband including 6-bit reset CQI erasure rate10%

21. 21 3-bit Scheme I vs. 4-bit Scheme II

22. 22 4 Tx, 2 Rx, 1 stream 0.5λScheme I 5 o, Samsung 0.9 4λScheme I 20 o, Samsung 0.9 Uncorrelated, Scheme I 20 o, Samsung 0.9 SE gain over 16e 5%-ile SE gain over 16e SE gain over 16e 5%-ile SE gain over 16e SE gain over 16e 5%-ile SE gain over 16e Scheme I: 3- bit 11.6%36.3%3.7%21.9% 2.5%16.2% Scheme II: 4-bit 10.7%35.3%1.3%19% -1%7.7% Scheme I over Scheme II 0.8%0.7%2.7%2.4%3.5%7.9%

23. 23 Remarks Scheme I's 3-bit scheme has higher throughput and reliability than Scheme II's 4-bit scheme. In addition, Scheme I's feedback overhead and complexity are lower than Scheme II's. Scheme II's codebook is optimized for highly correlated channels and scarifies uncorrelated/lowly correlated channels. Scheme II's codebook can not track channel variation in uncorrelated channel and performs even poorer than 16e codebook.

24. 24 Scheme I's 4-bit vs. Scheme II's 4-bit

25. 25 4 Tx (0.5λ), 2 Rx, 1 stream SE gain over 16e 5%-ile SE gain over 16e Scheme I: 4-bit, 5 o 11.7%37.7% Samsung: 4-bit, 0.95 ρ 10.6%35.4% Scheme I over Samsung 1.06%1.37%

26. 26 4 Tx(4λ), 2Rx, 1 stream SE gain over 16e 5%-ile SE gain over 16e Scheme I: 4-bit, 20 o 3.9%21.5% Samsung: 4-bit, 0.9 ρ 1.36%19% Scheme I over Samsung 2.5%2.1%

27. 27 4 Tx (uncorrelated), 2 Rx, 1 stream SE gain over 16e 5%-ile SE gain over 16e Scheme I: 4-bit, 20 o 0.2%17.4% Samsung: 4-bit, 0.9 ρ -2.9%13% Scheme I over Samsung 3.1%3.9%

28. 28 Comparison on rank-2 codebooks

29. 29 4 Tx (4λ), 2 Rx, 2 streams SE gain over 16e Scheme I: 4-bit, 20 o 10.29% Samsung: 4-bit, 0.9 ρ 10% Scheme I over Samsung 0.27%

30. 30 4 Tx (uncorrelated), 2 Rx, 2 streams SE gain over 16e Scheme I: 4-bit, 20 o 9.45% Samsung: 4-bit, 0.9 ρ 9.28% Scheme I over Samsung 0.15%

31. 31 Remarks Scheme I's 4-bit scheme has higher throughput and reliability than Scheme II's 4-bit scheme. Scheme I's complexity is lower than Scheme II's. Scheme I's 4-bit has 0.3% higher throughput than Scheme I's 3-bit. Scheme II's codebook is optimized for highly correlated channels and scarifies uncorrelated/lowly correlated channels.

32. 32 Conclusions Scheme I's 3-bit outperforms Scheme II's 4-bit in all cases in terms of throughput and reliability. Scheme I's 3-bit scheme has feedback overhead and computational complexity lower than Scheme II's 4-bit by 17% and 60%, respectively. Scheme I's 4-bit has even higher throughput than Scheme I's 3-bit. Scheme II's new design solves vibration problem by adding identity matrix but it can not track channel variation in uncorrelated channels.