1. S80216maint-08_240r1.ppt
MIMO/BF in Release 1.x: Discussion on Codebook Computational Complexity
Sangwoo Lee, Jiyun Seol, Keun Chul Hwang, Mune Joon, Inseok Hwang
Samsung
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2. Purpose of this presentation
S80216maint-08_240r1.ppt
Purpose of this presentation
Share some views on how to reduce the codebook computational complexity.
Suggest a codebook generation rule based on current 16e codebook.

3. Problem statements Codebook computation example
S80216maint-08_240r1.ppt
Problem statements
Codebook computation example
In current 16e codebook for 2Tx, rank-1 codebook vectors are the first columns of rank-2 codebook matrices  MS’s codebook computation burden can be reduced by calculating only the rank-2 metric
For 4Tx codebooks, rank-1 codebook vectors are not the first columns of rank-2 codebook matrices.  MS’s should calculate the rank-1 and rank-2 metric for rank selection separately.
Rank=1
Rank=2

4. Suggestion on Codebook for Rel.1.x
S80216maint-08_240r1.ppt
Suggestion on Codebook for Rel.1.x
For 4Tx codebook, we suggest to include the rank-1 codebook vectors in rank-2 codebook matrices.
Current 16e: The codebook generated with HE operation is composed with the last M columns, with which the rank-1 codebook vectors are excluded in rank-2 codebook matrices. Note that rank-1 codebook vectors are the first columns of H(v)
Proposed : For the codebook generated with HE operation, we propose to take the first M columns to include the rank-1 codebooks
Example: Proposed V(4,2,3)
Current 16e: V(4,2,3) = H(V(4,1,3)):,3:4
Proposed : V(4,2,3) = H(V(4,1,3)):,1:2

5. Performance Simulation
S80216maint-08_240r1.ppt
Performance Simulation
Performance of proposed codebook is the same as that of current 16e codebook.
Simulation results (4X2, perfect CE, 10dB Tx SNR)
Mean PD SINR (dB)
Current 16e
Proposed
Difference
(proposed-16e)
3bits V(4,2,3)
11.58dB
11.60dB
+0.02dB

6. Computation Complexity
S80216maint-08_240r1.ppt
Computation Complexity
Assumption: 4X2
Computational Complexity (per codeword)
Reduction of complexity is about 31%
Rank=1
Rank=2
Current 16e
Proposed
35 CMs
24 CMs
(31% reduction)
Current 16e: 35 CMs are needed
Rank-1: 11 Complex Multiplication (CMs)= 8 CMs for Hvk + 2 CMs for || ||2 + 1 CMs for .
Rank-2: 24 CMs = 16 CMs for HVk + 6 CMs for VkHHHHVk + 2 CMs for det().
Proposed: Only 24 CMs are needed, since the rank-1 calculation of 1+  *||Hvk||2 can be obtained with (1,1) element of rank-2 matrix of I+  * VkHHHHVk.

7. S80216maint-08_240r1.ppt
Conclusions
Codebook computational complexity can be reduced by including the rank-1 codebook vectors in rank-2 codebook matrices without performance degradation.

8. Appendix: Proposed V(4,2,6)
S80216maint-08_240r1.ppt
Appendix: Proposed V(4,2,6)
V(4,2,6) in current 16e is generated with Householder and concatenation HC(V(4,1,3), V(3,1,3)
Current 16e: V(4,2,6) = HC(V(4,1,3),V(3,1,3))
For V(4,2,6), we propose to use H(V(4,1,6)) to reduce the computation complexity
Proposed : V(4,2,6) = H(V(4,1,6))[1 2+mod(k,3)]

9. Appendix: Performance of proposed V(4,2,6)
S80216maint-08_240r1.ppt
Appendix: Performance of proposed V(4,2,6)
Performance of proposed codebook is the same as that of current 16e codebook. (difference is less than 0.11dB)