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UEC Tokyo
SISA 2010(Sept. 9, 2010)
Effect of . Base-Station Cooperationin MIMO Cellular Systems
Y. Karasawa T. Taniguchi N. Nakajima
The Univ. Electro-Communs. (UEC Tokyo)Advanced Wireless Communication research Center(AWCC)
UEC Tokyo
Contents
1) What is the Base Station Cooperation
in a MIMO Cellular System
2) Specific Method for Base Station Cooperation
3) Effect of Base Station Cooperation
4) Consideration from Propagation Viewpoint
2
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基地局A(送信側) 基地局B(送信側)移動局(受信側)
自セル 隣接セル
ユーザ信号
チャネル状態情報 チャネル状態情報コアノード
2つの基地局による仮想アレーアンテナ
エリア全体での通信路容量の最大化
Image of Base Station Cooperation (CoMP)in the Era of IMT-Advanced
User signal
Channel StateInformation
and both transmission data
CSI and data Virtual arraywith two base stations
Core node
Adjacent cell
Maximization of channel capacity
Base Station A (Tx) Base Station B (Tx)Mobile Station A (Rx)
3CoMP: Coordinated Multi-Point transmission/reception
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Image of Base Station Cooperation (2)
4
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withoutBS cooperation
A B
A+B A+B
A B
A B
BA BA
with BS cooperation
Type 1: CSI sharing
Type 2:CSI & Tx signal sharing
A B
Classifications of base station cooperation (types 1 and 2)
5Case 3 Case 4 Case 5
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BS-1 BS-2
H11 H22H21 H12
UT-1 UT-2
Data 1 Data 2
Data 1 Data 2
⎥⎦
⎤⎢⎣
⎡=
2221
1211
HHHH
H
CSI
- distance dependence: d-3.5- Shadowing: log-normal (6dB)- Short term: Rayleigh
Transmission datasharing
Data 1 Data 2
CSI sharing
6
We deal with the ideal casesuch that- Obtained CSI is perfect.- Antenna beamforming is done instantaneously.
Type 2 (= Case 5)
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Classification of cases for assessing cooperation effectiveness
8
BS-A BS-B
UT-A UT-B
BS-A BS-B
UT-A UT-B
BS-A BS-B
UT-A UT-B
BS-A BS-B
UT-A UT-B
[Case 1: No interference](MRC transmission)
[Case 2: with interference & without countermeasure](Antenna weights are the same as Case 1)
[Case 4:BS cooperationwith CSI (Type 1)]
[Case 3:with interference ](controlled at UT)
CSI BS-A BS-B
UT-A UT-B
Tx data A & B
CSI
[Case 5:BS cooperation withCSI and Tx data(Type 2)
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Expected trend in channel capacity for the different cases
9
1
2
3
4
5
1 2 3 4 5
Case
Cha
nnel
cap
acity
MRCwithoutinterference
Interference reduction at UT
Net effect ofType 1 BS cooperation
Net effect ofType 2
with Interference
without countermeasure
CSI sharing
CSI & inputData sharing
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2
wt2(1)
wr2 (1)
2
Case 1: Beamforming without considering Interference
1
wt1(1)
wr1 (1)
1
3
wt3(1)
wr3 (1)
3
Beamforming(MRC for Tx&Rx)
10
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2
wt2(1)
wr2 (2)
Case 3: Interference Reduction based on MMSE at each UT
1
wt1(1)
wr1 (2)
1+2+3
3
wt3(1)
wr3 (2)MMSE
1+2+3 1+2+311
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wt2(2)
wr2 (2)
2
Case 4: Interference Reduction based on MMSE at each BS
wt1(2)
wr1 (2)
1
wt3(2)
wr3 (2)
3
MMSE
1+2+31+2+3 1+2+3
12
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In Case 4, the weight determination algorithm is as follows:
⎟⎟⎠
⎞⎜⎜⎝
⎛+
+= )()()(
2 1log mN
mI
ms
m PPPC
)(0
2)(H)()( }{ mmtmmm
rm
s PP wHw=
∑≠=
=M
mmm
mmtmm
mr
mI PP
'1'
)'(0
2)'('
H)()( }{ wHw
)(0
)(0)(m
t
mtm
t www =
{ } )(1)()(0 mxdmxxmt rRw −=)(
0*)(T*)( )()( mmrmmmm
mxd Ptst wHxr ==
IHwwHxxR 0)'(
01'
*'
T)'()*'(T'
)(N
mM
mmm
mr
mrmm
Hmxx PP +== ∑
=
⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢
⎣
⎡
=
MMMM
M
M
HHH
HHHHHH
H
L
MOMM
L
L
21
22221
11211
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
=
)'()'(2
)'(1
)'(2
)'(22
)'(21
)'(1
)'(12
)'(11
'
mmNN
mmN
mmN
mmN
mmmm
mmN
mmmm
mm
trrr
t
t
hhh
hhhhhh
L
MOMM
L
L
H
Rayleighshadowdistmm
uv bbbh ⋅⋅=)'(
nmmmdist ddPb
−= )/( 0)'()(
0
[Propagation Channel]
13
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wt2(2)
wr2 (2)
2
Case 4 Case 5: Further Interference Reductionby adding Interference signals into Transmitting signals
wt1(2)
wr1 (2)
1
wt3(2)
wr3 (2)
3
12 3
+ 0(2+3)+ 0 (1+3) + 0(1+2)14
Suppressed but not perfect
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wt2(2)
wr2 (2)
2
Case 5: Further Interference Reductionby adding Interference signals into Transmitting signals
wt1(2)
wr1 (2)
1
wt3(2)
wr3 (2)
3
1-2-3-1+2-3 -1-2+3
+ 02(2+3)+ 02(1+3) + 02(1+2)
Addition ofinterferencesignals intensively for canceling
15
Suppressedalmost perfectly
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wt(m’) wt (m)
wr (m)
wtm(2) wt (m)
wrm (2) wr (m)
)(0
2
'1' ''
'')( mM
mmm mm
mmmmmm
ms PP ∑
≠=
−=αααα
∑ ∑≠=
≠≠=
=M
mmm
mM
mmmm
m mm
mmmmmI PP
'1'
)'(0
2
'""
1" ""
"'")(
ααα
∑≠=
−M
mmm
mmmmm
m ss"
1"""
1 αα∑
≠=
−M
mmm
mmmmm
m ss'"
1"""'
'''
1 αα
")("
H)(" }{
mtmm
mrmm wHw=α
mmα
'mmα
Overall Channel Gainincluding Tx&Rx AntennaWeights
16
Scheme realizing Case 5
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Assumed Conditions for Assessing a Base-Station Cooperation System
Parameters Setting
Cell shape Honeycomb structureTransmission stream Single streamTx antennas Nt 2, 4 Rx antennas Nr 2 Propagation model Path loss: d-3.5
Shadowing: Log-normal with SD of 6dBShort-term fading: Rayleigh (iid)
SNR at cell edge 10dB, 20dB, 30dB
17
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0 2 4 6 8 10 12 14 16
0.2
0.4
0.6
0.8
1
Channel capacity (b/s/Hz)
Cumulative probability
Case 1
Case 2
Case 3
Case 4
Case 5
M=3Nt=2, Nr=2SNR=20dBEdge/UniformSd=6dB
2x2 MIMO
Effect of Three-Cell Cooperation (CDF of Channel Capacity)
18
BS UT
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0
2
4
6
8
10
12
14
0 1 2 3 4 5 6
SNR=10dBSNR=20dBSNR=30dB
Channel capacity (b/s/Hz)
Case
M=3Nt=2, Nr=2SNR=10,20,30dBEdge/UniformSd=6dB
Effect of Three-Cell Cooperation (Average Channel Capacity)
19
2x2 MIMO
BS UT
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0
2
4
6
8
10
12
14
1 2 3 4 5
SNR=10dBSNR=20dBSNR=30dB
M=3Nt=4, Nr=2SNR=10,20,30dBEdge/UniformSd=6dB
Channel capacity (b/s/Hz)
Case
4x2 MIMO
Effect of Three-Cell Cooperation (Average Channel Capacity)
20
BSUT
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0
2
4
6
8
10
12
14
SNR=10dBSNR=20dBSNR=30dB
1 2 3 4 5
Channel capacity (b/s/Hz)
Case
M=7Nt=4, Nr=2SNR=10,20,30dBEdge/UniformSd=6dB
4x2 MIMO
Effect of Seven-Cell Cooperation (Average Channel Capacity)
21
BSUT
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Tx & Rx weight calculation(without interference)
Rx weight re-calculation(with interference)
Tx weight re-calculation(with interference)
Further interference reductionbased on Tx data sharing
Case 5 Case 7 Case 6
Tradeoff of Beamforming and Tx signal Control
Beam-forming
22
Almost perfect beamformingbut not perfect
Case 1, Case 2
Case 3
Case 4
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0
2
4
6
8
10
1 2 3 4 5 6 7
Channel capacity (bit/s/Hz)
Case
M=74x2SNR=20dBEdge/Uniform
Tradeoff of Beamforming and Tx signal Control
4x2 MIMO
Almost PerfectBeamforming
Tx Signal Control
Rough BeamformingTx Signal Control
Case 5 is the best. 23
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Necessary Timefor CSIcollection
+
Necessary Timefor Informationdistribution
+
Weightcalculationtime
BS-A BS-B
H(t)
UT-A UT-B
= Tb
Db f
T 1
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Delay spreadστ
Amplitude and phase variationdue to Doppler spread
delay
Tf = 1/ fDPropagation factor: 2Large Doppler spreading
(higher freq.high speed)
Propagation factor: 1Wide spreading of delay (outdoor)
Fading period (fD: Maximum Doppler frequency)
Less thanTf /100
Tb
Two Propagation Factorsin Block Signal Transmission
Tb : Period of blocklength
Db f
T 1
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Conclusions
BS cooperation scheme is a promising to realize high channel capacity.
The cooperation scheme is divided into two categories.One is antenna beamforming based on exchanging all propagationinformation among cooperating Base Stations (Type 1).The other is interference cancellation by adding interference signalsintentionally after the beamforming (Type 2).
The results given above are for ideal cases, but it is also importantto consider realistic cases. It seems difficult to achievehigh reliability using this control scheme in practical systems. These investigations will be performed in a future study.
26
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Thank you very muchfor your kind attention.