Capacity Allocation in Multi-Cell UMTS

7/31/2019 Capacity Allocation in Multi-Cell UMTS

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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!!

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Capacity Allocation in Multi-Cell UMTS

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