Transcript IEEE C802.16m-09/0528r1

Comparison of Two Differential Feedback Schemes for Beamforming
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE C80216m-09_0528
Date Submitted:
2009-03-07
Source:
Qinghua Li, Yuan Zhu, Eddie Lin, Shanshan Zheng,
Jiacheng Wang, Xiaofeng Liu, Feng Zhou, Guangjie Li,
and Yang-seok Choi
Intel Corporation
Venue:
Session #60, Vancouver , Canada
Re:
TGm AWD
Base Contribution:
None
Purpose:
Discussion and adoption by TGm AWD
Notice:
E-mail:
[email protected]
[email protected]
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Outline
•
•
•
•
•
•
Background
Two differential schemes
Performance comparison
Complexity comparison
Conclusions
Proposed text
Background
• SDD supports differential feedback mode for SU
and MU-MIMO precoding.
• Only “rotation based schemes” are supported.
• Two rotation based, differential schemes were
proposed.
– Scheme I: C80216m-09_0058r4.doc
– Scheme II: C80216m-08_1187.doc
• Comparisons in throughput and complexity are
made.
System Model
y
=
H
V̂
• H is channel matrix of dimension
s
+ n
N r  Nt .
•
V̂
is beamforming matrix of dimension N t  N s.
•
s
is transmitted signal vector of dimension N s 1.
One-shot reset and differential
feedback
SS:
Initial feedback V̂ 1

Differential
feedback D̂
2
...
Differential
feedbackD̂ 10
 
Initial feedback V̂ 11
 
Differential
feedback D̂ 12
 
...
Time
Reset period
BS:
Beamforming
using V̂ 1

...
Beamforming
using V̂ 9

...
Time
Differential codebook
Polar cap
Cd
Set of ideal
beamforming matrixes
ˆ t  1
V
ˆ t  1
V
V̂ t 
V t 
Scheme I
• Actual quantization at SS:


 H
H
H
ˆ
D  arg max det I 
Di Qt  1 H HQt  1 Di 
Ns
Di Cd


• Beamforming matrix reconstruction at BS:
ˆ t   Qt  1 D
ˆ
V
• Beamforming at BS:
ˆ t s  n
y  HV
Scheme II
• Actual quantization at SS:


 ˆH
H
H
ˆ
ˆ
D  arg max det I 
V t  1Di H HDi Vt  1
Ns
Di Cd


• Beamforming matrix reconstruction at BS:
ˆ t   D
ˆV
ˆ t  1
V
•Beamforming at BS:
ˆ t s  n
y  HV
Codebook of Scheme I is compacter than Scheme
II’s because of reduced dimension.
• Scheme I’s feedback matrix is NtxNs e.g. 4x1 while Scheme II’s is
always NtxNt e.g. 4x4 regardless of rank.
• Scheme I has a codebook for each rank while Scheme II has a
constant codebook.
Scheme II’s differential
codebook
Scheme I’s differential
codebook
Unused codewords
Polar cap
Differential matrix space
Complexities
3-bit Scheme I (No.
4-bit Scheme II (No. of
of real multiplications) real multiplications)
4x1
314
960
4x2
516
2352
• Scheme II’s complexity is more than triple of Scheme I’s.
– Matrix dimensions of Scheme II’s is greater than Scheme I’s.
System Level Simulations
• Isolate effect of reset (or initial) feedback
– No reset feedback
– Only measure performance of differential feedbacks
• No feedback error
• Scheme I’s 3-bit vs. Scheme II’s 4-bit
Simulation Parameters
Parameter Names
Parameter Values
Network Topology
57 sectors wrap around, 10 MS/sector
MS Channel
ITU PB3km/h
Frame Structure
TDD, 5DL, 3 UL
Feedback Delay
5ms
Inter cell Interference Modeling
One tap fading
Antenna Configuration
4Tx, 2 Rx
Code book configuration
16e (4,1,3), TF with Rtx, Diff(4,1,3,Ф)
Tx Channel Correlation Matrix (only for TF
code book)
Ideal known to both MS and BS
Q matrix update frequency
Once for the whole simulation
PMI error
free
PMI calculation
ML with SVD precoding vector
System bandwidth
10MHz, 864 data subcarriers
Permutation type
AMC, 48 LRU
CQI feedback
1Subband=4 LRU, ideal feedback
4 Tx (0.5λ), 2Rx, 1 Stream
4Tx 0.5L, 2Rx, user Rx SE CDF
1
Scheme I:
3-bit, 5o
SE gain
over 16e
5%-ile SE
gain over
16e
10.94%
32.87%
0.8
0.7
0.6
Scheme II: 7.09%
4-bit, 0.9
25.65%
0.5
0.4
ρ
Scheme I
over
Scheme II
0.9
0.3
3.60%
5.75%
0.2
16e(413)
Intel
Diff(413,5)
Scheme
I No Polar cap reset
Samsung
Diff(414,0.9)
No Polar cap reset
Scheme
II
0.1
0
0
1
2
3
4
user RX SE (b/s/Hz)
5
6
7
4 Tx (4λ), 2Rx, 1 Stream
4Tx 4L, 2Rx, user Rx SE CDF
SE gain
over 16e
Scheme I:
3-bit, 20o
6.08%
5%-ile SE
gain over
16e
1
0.9
0.8
18.86%
0.7
0.6
Scheme II: 5.86%
4-bit, 0.9
15.12%
ρ
0.5
0.4
0.3
Scheme I
over
Scheme II
0.2%
3.25%
16e(413)
IntelScheme
Diff(413,20)
I No Polar cap reset
Samsung
Diff(414,0.9)
No Polar cap reset
Scheme II
0.2
0.1
0
0
1
2
3
4
user RX SE (b/s/Hz)
5
6
7
4 Tx (Uncorrelated), 2Rx, 1 Stream
4Tx U, 2Rx, user Rx SE CDF
1
SE gain
over 16e
Intel: 3-bit,
20o
4.2%
5%-ile SE
gain over
16e
0.9
14.06%
0.7
0.8
0.6
Samsung:
4-bit, 0.9
4.31%
12.48%
0.4
ρ
Intel over
Samsung
0.5
0.3
-0.1%
1.41%
16e(413)
Intel
Diff(413,20)
Scheme
I No Polar cap reset
Samsung
Diff(414,0.9)
No Polar cap reset
Scheme
II
0.2
0.1
0
0
1
2
3
4
user RX SE (b/s/Hz)
5
6
7
Conclusions
• In all cases, both SE and 5%-SE Scheme I
outperforms Scheme II, except 0.1% SE
loss in uncorrelated channel.
– Scheme I’s overhead is less than Scheme II’s by 25%.
– Scheme II’s codebook has unused codewords.
– Since Scheme II’s codebook doesn’t have identity
matrix, it often vibrates around optimum point.
• Scheme I’s complexity is three times less
than Scheme II’s.
Proposed Text
• Adopt text in AWD.
Backup
• Transition from reset feedback to differential feedback.
4x2, 2 streams, 4 lambda
2.75
2.7
Channel capacity (b/s/Hz)
2.65
2.6
2.55
2.5
2.45
2.4
2.35
0
2
4
6
8
10
12
Feedback step index
14
16
18
20