1. IEEE S802.16maint-08/218 [ 3-Bit 2-Transmit and 4-bit 4-Transmit Antenna Codebooks for Closed-Loop MIMO ] IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE S802.16maint-08/218 Date Submitted: 2008-06-19 Source: Louay JalloulVoice: +1.408.387.5048 Beceem Communications Inc. E-mail: jalloul@beceem.comjalloul@beceem.com Ron Porat Nextwave * http://standards.ieee.org/faqs/affiliationFAQ.html Venue: IEEE 802.16 Session #56 Base Contribution: Purpose: For discussion and approval by IEEE802.16 Maintenance TG 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. IEEE S802.16maint-08/218 Introduction The objective of this presentation is to compare the existing IEEE 802.16e codebooks to the newly proposed codebooks: –16e: 2-transmit antenna 3-bit codebook versus the 3-bit codebook proposed by Beceem (C802.16maint-08/218). –16e: 4-transmit antenna 6-bit codebook versus the 4-bit codebook proposed by Nextwave (C80216maint- 08_093r3). The comparison is done using a simple model and using SNR as a performance metric –Previous simulation results from system level modeling are hard to reproduce and are too complex to ascertain the reason of why one codebook works better than another (PHY is abstracted, multiple users, multiple sectors, channel model, etc.)

3. IEEE S802.16maint-08/218 System Model Consider the following simple (but non-trivial) model: –Single user, No interference –Noise limited The input-output system is describe by H : channel matrix, x : data transmitted by the BS, y : vector denoting signal received at the SS, c : precoding applied at BS transmitter which is a vector for the Rate-1 beamformer, and matrix for the Rate-2 beamformer, n : vector that denotes the noised received at the SS For Rate-1 BF, the codeword index selected according to maximum SNR Here Φ is the codebook

4. IEEE S802.16maint-08/218 16e Codebook for Rate 1 BF

5. IEEE S802.16maint-08/218 Proposed 2Tx Codebook Rate 1

6. IEEE S802.16maint-08/218 Proposed 4Tx Codebook Rate 1

7. IEEE S802.16maint-08/218 Per Antenna Power Constraint Due to the per-antenna power constraint, the system model gets modified to the following The codeword is now modified to comply with the per- antenna power constraint. Per-antenna power constraint possibilities: 1.CB entries power clipped: where min denotes element wise minimum for the vectors and comparison of magnitude in case of complex values 2.Codewords are scaled for power limitation: –Entire codeword (not individual entries) is normalized so that maximum entry is 1/sqrt(2)

8. IEEE S802.16maint-08/218 2Tx Rank-1 Comparison (Uncorrelated Antennas)

9. IEEE S802.16maint-08/218 2Tx Rank-1 Comparison (Uncorrelated Antennas)

10. IEEE S802.16maint-08/218 4Tx Rank-1 Comparison (C orrelated Antennas)

11. IEEE S802.16maint-08/218 4Tx Rank-1 Comparison (C orrelated Antennas)

12. IEEE S802.16maint-08/218 4Tx Rank-1 Comparison (Non-Correlated Antennas)

13. IEEE S802.16maint-08/218 4Tx Rank-1 Comparison (Non-Correlated Antennas)

14. IEEE S802.16maint-08/218 Comments on the Results The performance of the newly proposed codebooks (2-ant and 4-ant) are close to the case of ideal beamforming The performance of the newly proposed 2-ant 3-bit codebook is ~2-3dB better than the equivalent 16e codebook The performance of the newly proposed 4-ant 4-bit codebook is ~3-7dB better than the equivalent 16e codebook

15. IEEE S802.16maint-08/218 Back of the Envelope Calculation Quick calculation of the average SNR can confirm the improvement of proposed codebooks over the existing 16e codebooks Assume that all codewords are equally probable –SNR is computed by averaging over all the codewords in the codebook The SNR loss in the 16e codebook due to the per- antenna power constraint is given by N is the number of codewords 16e CB Loss (dB) 2-ant 16e CB Loss (dB)4-ant CB power clipped34 Codeword scaling1.653

16. IEEE S802.16maint-08/218 Concluding Remarks The proposed 2-ant 3-bit codebook was shown to have substantially better performance as compared to the current 16e 2-ant 3-bit codebook The proposed 4-ant 4-bit codebook was shown to have substantially better performance as compared to the current 16e 4-ant 6-bit codebook The proposed codebooks are constant modulus, thus ensuring power amplifier balance Using the proposed codebook results in substantially lower search complexity at the MS since the codebook values are drawn from a QPSK alphabet Recommend adding the proposed 2-ant 3-bit codebook and 4-ant 4-bit codebooks to be part of Rev2/D5 for closed-loop MIMO