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Wideband CDMA
Radio Network Planning
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Radio Network Planning
A radio network planning consists of three phases:
1. Network Dimensioning (using link budgets)
2. Detailed capacity and coverage planning (using planning tools)
3. Network optimisation (using optimisation tool)
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Phase 1 :Network Dimensioning
Dimensioning the WCDMA radio network includes :
radio link budget and coverage analysis,
capacity estimation and
estimation of the amount of network equipment (suchas number of BSs and RNCs)
These estimations will be based on the operators
requirements on coverage, capacity and quality ofservice.
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WCDMA-specific parameters in the link budget
compared to those parameters used in a TDMA-basedradio systems are:
1. Interference margin
The value of the interference margin used in the linkbudget depends on the loading of the cell.
Higher is the value of the interference margin in theuplink, the smaller is the coverage area. Typical valuesare 1.0-3.0 dB in the coverage-limited cases,
corresponding to 20-50% loading.
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2.Fast fading margin
For slow-moving mobiles, to take care of fast fadingeffect, a fast fading margin in the range of 2.0-5.0 dBshould be included in the link budget.
3.Soft handover gain
Due to uncorrelated channels from the MS to the BSs,handover gives a gain against slow fading. Also, softhandover gives an additional macro diversity gain
against fast fading. The total handover gain can beassumed to be in the range of 2.0-3.0 dB.
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Link budget approach
Coverage requirement for a specific data rate with uniform load
Derive Link Budget
Coverage satisfied?
Input existing 2G sites that can be
Upgraded to 3G
Refine design, put new sites using
Planners individual judgment
End
No
Yes
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Uplink Link Budget Example
3.84 Mchip/sChip rateH
-169 dBm/HzReceiver noise density (E+F)G
5 dBBase station receiver noise figureF
-174 dBm/HzThermal noise densityE
18 dBmMobile EIRP (A+B-C)D
3 dBBody lossC
0 dBiMobile antenna gainB
21 dBmMobile transmit power (125 mW)A
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14 dBiBase station antenna gainP
-120.2 dBmBase station receiver sensitivity (K-M+N)O
5 dBRequired Eb/NoN
25 dBProcessing gain (10 log (H/L) )M
12.2 Kb/sData rateL
-100.2 dBmTotal effective noise & interference (I+J)K
3 dBInterference Margin (noise rise)J
-103.2 dBmReceiver noise power (G + 10log H)I
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137.2 dBMaximum path loss for cell range
(D-O+P-Q-R-S+T)
U
4 dBSoft handover gainT
8 dBIn-car lossS
9 dBLognormal shadowing marginR
2 dBCable losses in the base stationQ
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Cell range
From the link budget, the cell range Rcan be easily calculatedusing a known propagation model, for example the Okumura-Hatamodel. The Okumura-Hata propagation model for an urbanmacro-cell with base station antenna height of 30m, mobile antennaHeight of 1.5m and carrier frequency of 1950 MHz is given by:
L = 137.4 + 35.2where L is the path loss in dB and R is the cell range in Km.
For suburban areas we assume an additional area correction factorof 8 dB and therefore the path loss is:
L = 129.4 + 35.2
)(log 10 R
)(log 10 R
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Some DefinitionsRatio of other cell to own cell interference
In the uplink, it is calculated for the BS, therefore i is similar for all
connections within one cell.
However in the downlink, it is calculated for each MS and therefore
depends on the MS location.
i ranges from 0.15 (very well isolated microcells) to 1.2 (poor radio
network planning.)
own
other
I
Ii
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For the downlink, i is defined as:
i =
where is the power received from other BSs andpj is the power
received from the serving BS.
Noise rise
noise rise =
j
other
P
I
N
Notherownj
N
total
P
PIIP
P
I
otherI
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Capacity estimation
The second part of dimensining is to estimate the capacity per cell i.e.,
supported traffic per BS. The capacity per cell depends on the amount
of interference per cell, hence it can be calculated from the load equations.
- Uplink load factor equation
(1)
where W is the chiprate,pr,jis the received signal power for mobile userj,is the activity factor of userj, Rjis the bit rate of userj and the
total received wideband power including thermal noise power in the BS.totalI
jrtotal
jr
jj PI
P
RW
jo
bN
E,
,
j
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Equation (1) can be rewritten as:
(2)
we define
where is the load factor of one connection.
Using this equation and equation (2), one can obtain as:
(3)
totalI
jjR
joN
bE
wjrP
1
1,
totaljjr ILP
,
jL
jL
jjR
joN
bE
wjL
1
1
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The total received interference, excluding the thermal noise ,canbe written as:
(4)
The noise rise is defined as:
Noise rise (5)
and using (4), we can obtain
NP
NP
totalI
N
j
totalIj
LN
j
jrP
NP
totalI
11
,
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Noise rise (6)
where is defined as the uplink load factor and equals to:
(7)
when becomes close to 1, the corresponding noise rise approaches
to infinity and system has reached its pole capacity.
If the interference from the other cells is taken into account, then one
can write
N
jj
LUL1
UL
ULN
jj
N
total
LP
I
11
1
1
1
UL
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(9)
where i is the ratio of other cells to own cell interference.
The interference margin used in the link budget must be equal to the
maximum planned noise rise i.e., -10 log(1- ).
For an allvoice service network, where all N users in the cell have
a low bit rate ofR, we can write
1
RN
EW
o
b
UL
N
j
jjR
oN
bE
W
N
j
iLi
j
jUL
11
1
1
)1()1(
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and hence equation (9) is simplified to
)1( iNR
W o
NbE
UL
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- Downlink load factor
In the absence of intra- and inter- cell interferences, one can write
In the absence of interferences, we definedand hence,
NP
jrP
jRj
W
joN
bE ,
NPjLjrP ,
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when we take into account both intra- and inter- cell interferences,
we have
where is the orthogonality of the channel of mobile user j.Its value depends on the channel multipath fading ; where = 1
means no multipath fading. is the ratio of other cell to own
cell base station power, received by the mobile user j.
jR
WjoN
bEjj
ijj
L1
1
j
j
ji
jR
Wj
joNb
E
P
jrP
jLN
1,
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The downlink load factor is defined as:
since, in the uplink, i and depends on the location of the mobile
user and they should ; therefore, be approximated by their average
values across the cell, and .jji
ji
j
j
RW
joNbEN
jj
1
1
N
jj
LDL
1
j
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The average value of the downlink load can then be approximated as:
the noise rise is given by:
noise rise Interference margin
when 1 noise rise
the system approaches its pole capacity.
i
jR
W
joN
bE
N
j
jDL
1
1
DL
1log10
DL
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Total BS transmission power
The total BS transmission power can be written as:
where is the average attennation between the BS and mobile
receiver (6 dB less than the maximum path loss)
since
DL
N
jjrPL
totalP
11
,
L
Njr P
jR
W
joN
bE
jP
,
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and
then
where is the power spectral density of the mobile receiver and is
given by:
where F is the noise figure of the mobile receiver with typical values
of 5-9 dB.
WNP oN
DL
N
jjR
W
joN
bEj
LWoN
totalP
1
1
oN
FKTN oo
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Throughput per cell
whereNis the number of users per cell,R is the bit rate and
is the block error rate.
BLERRNThroughout 1
BLER
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Link budget approach
Pros
- Enables fast planning of coverage for a pre-specified uniform load
- Skilled 3G staff not a requirement
Cons
- Too simplistic for WCDMAwhere coverage/capacity/QoS are
closely related- The final performance of the network cannot be derived based on
this method
- Mix of traffic cannot be taken into account
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Phase2 :Detailed capacity and coverge planning In this phase, real propagation data from the planned area and the
estimated user density and user traffic are used.
The output of this phase are the base station locations, configuration andnetwork parameters.
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Static simulation approach
Coverage/traffic/QoS requirements
Input existing 2G sites which can be
upgraded to 3G
Refine design, put new sites using
Planners individual judgment
WCDMA static simulator
Coverage/capacity/QoS
Satisfied?
End.
No
Yes
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Static simulation approach
Pros- Average QoS, capacity and coverage may be assessed for a mix
of traffic
Cons- Can only be run on a limited area, typical figures for running time
for a 3 Km x 3 Km area is ~5-8 hours on a Unix work station
- Manual judgment must be exercised in interpreting the results and
making decisions to improve the plan.
- Plans may need to be iterated several times (on average 5 times)before the desired capacity/QoS/ coverage is achieved. This takes
total planning time for a 3 Km x 3 Km to ~1 to 2 working days at best
- Skilled 3G a prerequisite
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Phase 3 : Optimisation Phase
Network optimiser
Optimises WCDMA FDD network plan minimising the number of sites
required to achieved the coverage/traffic/QoS targets set by the user.
An Optimiser also automatically selects the most appropriate antenna
tilt, direction and sectorisation in order to achieve the required
coverage/traffic/QoS.
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Network optimiser
Feed in your site portfolio
Set optimisation criteria
Run Optimiser algorithms
End
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Optimisation phase
Coverage information
WCDMA FDD
parameters
Traffic information
Site locations
Optimisation criteria
Optimiser
Optimised site
locations
Coverage,
Capacity/QOS
statistics
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Reference
WCDMA for UMTS, Edited by Harri Holma and Antti Toskala,
Second edition, John Wiley & Son Ltd, ISBN 0-470-84467-1.
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