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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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.
S80216maint-08_240r1.ppt
Problem statements
• Codebook computation example
Rank=1
k€ = arg max 1 + g Hvk
k = 1,...,L
Rank=2
2
k€ = arg max log det (I + g VkH HH HVk )
k = 1,...,L
• 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.
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)
HE (v N , M )  H (vN ):,N  M 1:N
– Proposed : For the codebook generated with HE operation, we
propose to take the first M columns to include the rank-1
codebooks
HE (vN , M )  H (vN ):,1:M
• 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
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
CDF of Post detection SINR of V(4,2,3), TxSNR=10dB, MMSE detection
1
Proposed V(4,2,3)
Current 16e V(4,2,3)
0.9
0.8
0.7
CDF
0.6
0.5
0.4
0.3
0.2
0.1
0
-10
-5
0
5
10
Post Detection SINR (dB)
15
20
25
S80216maint-08_240r1.ppt
Computation Complexity
• Assumption: 4X2
Rank=1
k€ = arg max 1 + g Hvk
Rank=2
2
k = 1,...,L
k€ = arg max log det (I + g VkH HH HVk )
k = 1,...,L
• Computational Complexity (per codeword)
– Reduction of complexity is about 31%
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.
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.
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)]
Codebook for
Rank = 1
Procedure for rank 2
V64=
64
H64=
V63=
63
v64=
V62=
62
H63=
V61=
61
v63=
V6=
6
H62=
V5=
5
v62=
V4=
4
H61=
V3=
3
v61=
V2=
2
H6=
V1=
1
v6=
62
H5=
5
v5=
2
H4=
64
v4=
61
H3=
4
v3=
1
H2=
63
v2=
6
H1=
3
v1=
Codebook for
Rank = 2
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)
CDF of Post detection SINR of V(4,2,6), TxSNR=10dB, MMSE detection
1
Proposed V(4,2,6)
Current 16e V(4,2,6)
0.9
0.8
0.7
CDF
0.6
0.5
0.4
0.3
0.2
0.1
0
-10
-5
0
10
5
Post Detection SINR (dB)
15
20
25