capacity allocation in multi-cell umts
TRANSCRIPT
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College of
Engineering
Capacity Allocation inMulti-cell UMTS
Networks for DifferentSpreading Factors with
Perfect and ImperfectPower Control
Robert Akl, D.Sc.
Son Nguyen, M.S.
Department of ComputerScience and Engineering
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Outline
User and Interference Model
WCDMA Capacity with Perfect Power
Control
WCDMA Capacity with Imperfect PowerControl
Spreading Factors
Numerical Results
Conclusions
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CDMA with One Class of Users
Cell j
Cell i
jr
ir
10
2, 10 ,, /
E
jm
jj
ji mCj ji i
r x y n dA x yAr x y
I
2 ( , )( , )
( , )
ms j
ji m
iCj
nj r x ye dA x y
Aj
r x y
I
jiI Relative average interference at cell
i caused by nj users in cellj
dAln(10)10
s
where
is the standard deviation
of the attenuation for the
shadow fadingm is the path loss exponent
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WCDMA with Multiple Classesof Users
2( )
, ,
( , )( , ) ( , )
( , )
s
j
m
j
ji g g g j g mj iC
r x yeI S v n w x y dA x y
A r x y
is the user distribution density at (x,y)w(x,y)
Inter-cell Interference at cell icausedby njusers in celljof class g
2( )
,
( , )( , ) ( , ).
( , )
s
j
m
j
ji g m
j iC
r x yew x y dA x y
A r x y
is per-user (with service g) relative inter-cell interference factor
from cellj to BS i,ji g
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Total Inter-cell Interference Density
in WCDMA
inter
, ,
1, 1
1 M G
g g g j g ji g
j j i g
I S nW
M is the total number of
cells in the network
G total number of services
W is the bandwidth of the
system
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Model User Density with 2D
Gaussian Distribution
2 2
1 2
1 2
1 1
2 2
1 2
( , )2
x y
w x y e e
own
,
1
1 G
g g g i g
g
I S nW
is the total intra-cellinterferencedensity caused
by all users in cell i
means is a user density normalizing parameter
variances of the distribution for every cell
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Signal-to-Noise Density in WCDMA
is the thermal noise density,
is the bit rate for service g
0N
Rg
own inter0 ,0
g
gb
g gi g
i i
S
RE
SIN I I
W
is the minimum signal-to-noise ratio required
0 , , ,
1 1, 1
g
g
gG M G
g
i g g j g g ji g g
g j j i g
S
R
S
N n nW
g
where
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Simultaneous Users in WCDMA Must Satisfy
the Following Inequality Constraints
( )
0
1 ggeff
g g g
RWc
R S N
is the minimum signal-to-noise
ratiog
is the maximum signal
powerg
S
the number of users in BS i for
given service g,ni g
( )
, , ,
1 1, 1
G M Gg
i g g j g g ji g g eff
g j j i g
n n c
1, 2, ,( , , , )
g g M Gn n n
1, ,g G
The capacity in a WCDMA network is defined as the maximum
number of simultaneous users for all services
. This is for perfect power control (PPC).
where
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Imperfect Power Control
Transmitted signals between BSs and MSs are subject tomulti-path propagation conditions
The received signals vary according to a log-normal distribution with a standard deviation on theorder of 1.5 to 2.5 dB. Thus in each cell for every
user with service needs to be replaced
0 ,
bE
Ii g
2
, , ( )
0 0
( ) ( )cb o b b i b
i,g
E EE e
I I
, ,( ) ( )
b i b i,g b o bE E
,( )b i bE i
g
2
( )2
( )
( )
_c
g
effg
eff IPC
cc
e
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Relationship between Spreading
and Scrambling
Channelization codes: separatecommunication from a single source
Scrambling codes: separate MSs andBSs from each other
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Main differences between WCDMA
and IS-95 air interfaces
Channelization code Scrambling code
Usage Uplink: Separation of physical data(DPDCH) and control channels(DPCCH) from same MS
Downlink: Separation of downlinkconnections to different MSs within
one cell.
Uplink: Separation of MSs
Downlink: Separation ofsectors (cells)
Length Uplink: 4-256 chips same as SF
Downlink 4-512 chips same as SF
Uplink: 10 ms = 38400 chips
Downlink: 10 ms = 38400 chips
Number ofcodes
Number of codes under onescrambling code = spreading factor
Uplink: Several millions
Downlink: 512
Code family Orthogonal Variable SpreadingFactor
Long 10 ms code: Gold Code
Short code: Extended S(2)code family
Spreading Yes, increases transmissionbandwidth
No, does not affecttransmission bandwidth
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Spreading Factor
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Orthogonal Variable Spreading
Factor (OVSF) codes
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Simulations
Network configuration
COST-231 propagation model
Carrier frequency = 1800 MHz
Average base station height = 30 meters
Average mobile height = 1.5 meters
Path loss coefficient, m= 4
Shadow fading standard deviation, s= 6 dB
Bit energy to interference ratio threshold, = 9.2 dB
Activity factor, v = 0.375
Processing gain, W/R= 6.02 dB, 12.04 dB, 18.06 dB,and 24.08 dB for Spreading Factors equal to 4, 16,64, and 256.
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Numerical Results
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Numerical Results
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Numerical Results
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Numerical Results
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Results of Optimized Capacity
Calculation
The SIR threshold for the receivedsignals is decreased by 0.5 to 1.5 dBdue to the imperfect power control.
As expected, we can have many lowrate voice users or fewer data users asthe data rate increases.
The determined parameters of the 2-dimensional Gaussian model matcheswell with the traditional method formodeling uniform user distribution.
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Thank You!!
Questions?