Cell- And Frequency Planning
Transcript of Cell- And Frequency Planning
1/31/20081 May 2004 Cellular Network Planning – CE at UP 1
Cell- and Frequency Planning
Magdaleen Snyman
1/31/20081 May 2004 Cellular Network Planning – CE at UP 2
References
�GSM, GPRS and EDGE Performance: evolution towards 3G/UMTS o T.Halonen, J. Romero, J. Melero
o Second Edition
o John Wiley & Sons
o ISBN 0-470-86694-2
�The Mobile Radio Propagation Channelo J.David Parsons,
o Second Edition,
o John Wiley & Sons
o ISBN 0 471 98857 X
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Course Overview
�Conventional Cell and Frequency Planning
o You work, I watch ;-)
�Radio Network Features and their impact
�Investigating the principles
o We all think a bit ;-)
�“Real” Cell and Frequency Planning
�Setting up an AFP
�Site selection – discussion
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The inputs to Cell Planning
Traffic: (T
raffic distribution maps)
Spe
ctru
m A
vaila
ble
Cost / Money
GoS
QoS
Quality
Coverage
Speech Quality
System Choice - C/I
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4/12 Cell Pattern
Frequency Groups
A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
Channels 1 2 3 4 13 14 15 16
5 6 7 8 17 18 19 20
9 10 11 12 21 22 23 24
A3 A2
D3
D1 D2 C1
C3C2
B1
B3 B2
1721
13
9
10
5
22
16
12
24
8
20
3
15
711
1923
2
14
6
18
A1
1
4
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Prediction algorithms
�Lee’s model and other empirical models
o Ploss = PR1 + γ10log(d / d1) + n10 log( f / f0) - α0
o PR1 is the reference loss at d1(normally 1 mile)
� (e.g. -84dBm in a city like Tokyo and -49dBm for open areas)
o γ depends on the type of terrain
� (value between 2 and 4)
o n is between 2 and 3
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Co-channel interference
# Info
bits
# Coding
bits
Code
Rate
Max data rate
(kbs) /TSRequired C/I (dB)
(BLER <10%; TU3 FH)
Modul
ation
GSM 260 196 0.5 13.3 9 GMSK
CS-1 181 275 0.45 9.05 9 GMSK
CS-2 268 188 0.65 13.4 13 GMSK
CS-3 312 144 0.75 15.6 15 GMSK
CS-4 428 28 21.4 23 GMSK
MCS-1 176 0.53 8.4 9 GMSK
MCS-2 224 0.69 11.2 13 GMSK
MCS-3 296 0.89 14.8 15 GMSK
MCS-4 352 1 16.8 23 GMSK
MCS-5 448 0.38 22.4 14.5 8PSK
MCS-6 592 0.5 29.6 17 8PSK
MCS-7 896 0.78 44.8 23.5 8PSK
MCS-8 1088 0.92 54.4 29 8PSK
MCS-9 1184 1 59.2 32 8PSK
1/31/20081 May 2004 Cellular Network Planning – CE at UP 8
Adjacent Channel interference
�for co-channel interference C/Ic=9 dB
�for adjacent (200 kHz) interference C/Ia1=-9 dB
�for adjacent (400 kHz) interference C/Ia2=-41 dB
�for adjacent (600 kHz) interference C/Ia3=-49 dB
1/31/20081 May 2004 Cellular Network Planning – CE at UP 9
Adjacent channel interferenceRelativepower(dB)
0
-10
-20
-30
-50
-40
-60
-70
-80
0 200 400 600Frequency from the carrier (kHz)
measurement bandwidth 30 kHz measurement bandwidth 100k Hz
1200 1800 60003000
0
-10
-20
-30
-40
-50
-60
-70
-80
Relative
power
(dB)
0 200 400 600 1200 1800 6000
Frequency from the carrier (kHz)
measurement bandwidth 30 kHz
measurement bandwidth 100 kHz
Edge of TX
band + 2 MHz3000
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Co-channel interference
D
�The total co-channel
interference experienced at the yellow spot is the sum of
interference of all six cells with the same frequency
�The interference from one co-channel interferer can be
written as I =KD-γ
�The carrier level is
C= KR-γ
C/I = (D/R)γ /6
R
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Re-use distance
v
30°
u
D
D = (i2 + ij + j2)½2Rcos 30°
D = (i2 + ij + j2)½ (3) ½ R
Number of cells in the
re-use pattern
N = i2 + ij + j2
i in (1,2,3,4 …..)
j in (0,1,2,3,4 …..)
D/R = (3N)½
i
j
1/31/20081 May 2004 Cellular Network Planning – CE at UP 12
The Hexagon
Area of a hexagon:
A = 3 (3)½R2/2
Distance between centers
of two adjacent cells:
d = (3)½R
R
d
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Traffic calculations revision
�An Erlang
�Erlang B Table
�Examples of Traffic channels
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Problem
�The average traffic generated by one user is
10milliErlang/Subscriber
�The population density is 50 people/km2
�Assume a phone penetration of 80%
�You are implementing a GSM system.
�You have 48 (1-48)channels available
�Assume free-space propagation … i.e. γ = 2
�Draw the re-use pattern and assign frequencies to
the cells.
�Calculate the site to site distance that you will
need to implement.
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C/I = (D/R)γγγγ /2
Sectorisation
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Effect of γ and C/I
gamma 9 12 13 17 36
2 18 33 42 102 7965
2.5 12 18 21 42 1323
3 9 12 12 24 399
3.5 6 9 9 15 171
4 6 6 9 12 90
C/I (dB
Minimum
frequencies
Assuming 3 sectored sites
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Spectral Efficiency
�Erlang/Hz/km2
�Using the previous problem as starting point – calculate the spectrum density that could be achieved if the sites were sectorised. Compare with the omni-cells
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Benefits of sectorisation
�Higher gain antennas are available – better penetration
�Less cost for same traffic density
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Underlay / Overlay - MRP
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Cell Splitting
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Hierarchical Cells
�Umbrella Cell:
�Macro Cell: Antenna above average rooftop height
�Micro Cell: Antenna below average rooftop height
�Pico Cell: Indoors
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DTX- Discontinuous
Transmission
�Average Voice activity is around 50%
�DTX is a feature that allows to be transmitted only when there is something to be transmitted
o Uses VAD (Voice Activity Detector)
�It safes on battery power
�Improves the overall network quality by reducing unnecessary interference
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Dynamic Power Control
�This enable the BTS and the Mobile to transmit only the power necessary for effective communications
�Power Control Commands are via the SACCH
�This improves the battery live of Mobile Phones
�And it improve the overall network quality by reducing unnecessary interference
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Effect of DTX and PC on Quality
2.00%
3.00%
4.00%
5.00%
6.00%
7.00%
8.00%
9.00%
10.00%
0 10 20 30 40Time (hours)
Pe
rce
nta
ge
%HOIU
%HOID
DTX + PC Off
PC Off
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Base Band Frequency Hopping
Controller
CALL 2 Tx and Rx on f1
Controller
CALL 3
Controller
CALL 4
Controller
CALL 1
Tx and Rx on f2
Tx and Rx on f3
Tx and Rx on f0
“Baseband Bus”
for routing burstsC
om
bin
er f1 f2 f3 f0
f0 f1 f2 f3
f2 f3 f0 f1
f3 f0 f1 f2
Number of frequencies equal to number of transceiversNumber of frequencies equal to number of transceivers
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Synthesised Hopping
Controller
CALL 2Tx and Rx hopping
Controller
CALL 3
Controller
CALL 4
Controller
CALL 1
Tx and Rx hopping
Tx and Rx hopping
Tx and Rx hopping
f1 f2 f3 f0
f0 f1 f2 f3
f2 f3 f0 f1
f3 f0 f1 f2
Number of frequencies more or equal Number of frequencies more or equal
to number of transceiversto number of transceivers
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Frequency Diversity
�Raleigh fading is frequency dependant
f0
f1
Position
Sig
nal le
vel
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Frequency Diversity
�Diversity: combining two or more uncorrelated versions of the same signal
� For “conventional” frequency diversity the info is sent on two different frequencies at the same time.
�To be uncorrelated the two frequencies should be more than 1/(multi-path spread), where the multi-path spread is dependant on the environment.
�For urban areas the frequencies should be more than 600kHz apart
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Why does hopping work?
�Review interleaving
�If one timeslot gets completely lost during
transmission 1/8 of two speech frames are lost.
�At the receiver the speech frames are de-interleaved
�The channel coding can recover from the 12.5%
BER.
�Interleaving and Channel Coding is part and parcel
of the GSM standard - it works even without hopping.
1/31/20081 May 2004 Cellular Network Planning – CE at UP 32
Frequency Diversity Gain
Frequency Diversity Gain vs Number of Hopping Channels
0
1
2
3
4
5
6
7
8
1 2 3 4 5 6 7 8
Number of Carriers
Gain
(d
B)
Cyclic Random Poly. (Cyclic) Poly. (Random)
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Interference Diversity
�Extent of Interference diversity depends on:
o Interference load (DTX and Power Control)
o Frequency reuse: low re-use -> low gain;
Dependant on area type.
o Number of Frequencies (less -> less gain)
o Cyclic or Random
�Interference diversity gain reached with 25% load, 12 frequencies in Urban area with random hopping is 2.5dB - mostly it is less.
1/31/20081 May 2004 Cellular Network Planning – CE at UP 34
Planning for FH network
�Use separate frequency blocks for TCH and BCCH
o BCCH frequency channel must be Always On
o No hopping over BCCH.
�Plan TCH layer:
o MAL : Mobile radio frequency channel
Allocation List
o HSN: Hopping sequence number
o MAIO: Mobile Allocation Index Offset
o MAI: Mobile Allocation Index
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Selecting a BCCH block
�Why a BCCH block?
o Identifying the source of interference
o Re-evaluation of the neighbour list
o For collecting data for a measurement based
plan
�Optimum size?
o Where a change in a BCCH carrier will on
average make the same difference as a change
in a TCH carrier in the optimised plan
1/31/20081 May 2004 Cellular Network Planning – CE at UP 36
Selecting a BCCH block
BlockSize
Total Number of Carriers Available
AverageTraffic TCHlayer Scaling
BCCH
perCell DTX PCon
=
× +
_ _ _ _
( / ) ( , )8 1
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TCH layer
MAI 0 2 1A 2A 3A 1B 2B 3B 1C 2C 3C
1 1 3 1 2 3 4 5 6 7 8 9
2 2 4 10 11 12 13 14 15 16 17 18
3 3 1 19 20 21 22 23 24 25 26 27
4 4 2 28 29 30 31 32 33 34 35 36
4 1 2 3 2 4 3 1
28 1 10 19 10 28 19 1
10 19 28 1 28 10 1 19
HSN =x
TRX1 on 1A has MAIO = 0
TRX2 on 1A has MAIO = 2
MAMAIO
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Automatic Frequency
Planning Tools
Coverage
AnalysisInterference
Matrix
Propagation
Predictions
SeparationConstraints,
etc
Frequency
Plan
TRX
Requirements
etc
AFP Tool
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Automatic Frequency Planning
Model of Network
Model effect of particular assignment on quality
�Propagation Predictions �Drive Test Data
�Handover Statistics
�Live Measurements
Cost Function:Sum of remaining interference and other penalties.Quality
Change:�Frequency�BSIC�HSN, MAIO
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Interference Matrix
�The “conventional” interference matrix represent:o The Traffic that will be interfered on if two
“radios” were assigned the same frequency;
o The area that will be interfered on if two “radios”were assigned the same frequency –
o pixel by pixel.
o Need ACCURATE propagation predictions and traffic distribution maps.
o What is the cost of accurate enough predictions?
1/31/20081 May 2004 Cellular Network Planning – CE at UP 41
Generating the
Interference Matrix
2.5 km
2.0 km
2 m Resolution
2.5 km
2.0 km
50 m Resolution
Microcell Service Area ≈ 1 pixel
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Probability of C/I>9dB
Cummulative Probability Distribution
for C/I exceeding 9dB
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-20 -15 -10 -5 0 5 10 15 20 25 30
Calculated C/I (dB)
Pro
ba
bilit
y t
ha
t C
/I w
ill b
e b
elo
w 9
dB
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AFP
�Implements a mathematical optimisationmethod or Artificial Intelligence method to minimise
�Cost = � �Cijδij +� � Aijδij
o δij = 1 if radios i and j are assigned the same(adjacent) frequency,
o δij = 0 else
�By changing the frequency assignments to the different cells
1/31/20081 May 2004 Cellular Network Planning – CE at UP 44
What are the true aims in
Cell and Frequency Planning
�What will really give optimum quality?
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The inputs to Cell Planning
Traffic: (T
raffic distribution maps)
Spe
ctru
m A
vaila
ble
Cost / Money
GoS
QoS
Quality
Coverage
Speech Quality
System Choice - C/I
1/31/20081 May 2004 Cellular Network Planning – CE at UP 46
Quality
�Voice Quality
o Impacted by the FER (Frame Erasure Rate /
Probability
o And to some extent by the BER (Bit Error Rate /
probability)
�Dropped Calls
o Radio Link Timeout based on unsuccessful
SACCH frame - FER
1/31/20081 May 2004 Cellular Network Planning – CE at UP 47
FER and SQI vs.RxQual
-10
0
10
20
30
0 1 2 3 4 5 6 7
RxQual
SQ
I/ %
FE
R
Non-Hopping
Non-Hopping
Hopping
Hopping
FER
SQI
1/31/20081 May 2004 Cellular Network Planning – CE at UP 48
C/I to FER
Frame Erasure Rate
-30
-25
-20
-15
-10
-5
0
-5 0 5 10 15 20C/I(dB)
10
lo
g(F
ER
)
Frequency Hopping
on 8 freqquencies,
Random Hopping
Non-Hopping
1/31/20081 May 2004 Cellular Network Planning – CE at UP 49
Measurement Based
Frequency Planning�Using Mobile Measurement Reports how
will you go about generating the optimal Interference Matrix?
1/31/20081 May 2004 Cellular Network Planning – CE at UP 50
The first Measurement
Based Plan�Johannesburg’s Central Business District
�12km×12km
�65 sites (≈350 cells)
�477 carriers
�Despite questioned cluttered data and propagation
prediction models
�very low dropped call rate of about 1.4% was very
often achieved
�partly due to dedicated optimisation
1/31/20081 May 2004 Cellular Network Planning – CE at UP 51
�Cell Traffic Recordings was used to collect Mobile
Measurement Reports on all the cells
�With the mobiles measuring on all BCCH channels
�The process took about a month.
�The signal strength of the serving cell and the
reported neighbours was used to calculated the
C/I and eventually the FER.
�The average FER for each server-interferer
relation was calculate.
�and multiplied with the traffic on the serving cell
Measurement Based
Frequency Planning
1/31/20081 May 2004 Cellular Network Planning – CE at UP 52
The
Sanity
Check
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Using MMRs in
Frequency Planning
Dropped Call Rate
0.90%
1.10%
1.30%
1.50%
1.70%
1.90%
2.10%
2.30%
0 10 20 30 40
Time
Pe
rce
nta
ge
Traffic
1.29%
%Drop
DayAvg
Pla
n Im
ple
me
nte
d
1/31/20081 May 2004 Cellular Network Planning – CE at UP 54
The
Results:
Quality
Intra-cell Hand-over and TCH Dropped
due to Bad Quality
2.00%
3.00%
4.00%
5.00%
6.00%
7.00%
8.00%
0 10 20 30 40
Time
Pe
rce
nta
ge
(o
f tc
alls
fo
r H
an
d t
ca
ss
al fo
r T
) %HoBUQ
%HoBDQ
Traffic
%TBQDis*50
Pla
n Im
ple
me
nte
d
1/31/20081 May 2004 Cellular Network Planning – CE at UP 55
Data Sources for the
Interference Matrix (1)
�Propagation Predictionso Well established conventional method
o Based on Predicted Carrier to Interference
ratios that is often translated with a “C/I weights”
curve
o Integration with AFP tools eases use
o Suited for new networks with many new cells
o Dependant on elevation and clutter data that
often has limited accuracy
1/31/20081 May 2004 Cellular Network Planning – CE at UP 56
�Neighbour relations statisticso Well suited for very tight plan
o Too little information for a less tight plan
o Hand-over statistics not directly related to C/I
o Can not model interference from non-
neighbours
Data Sources for the
Interference Matrix (2)
1/31/20081 May 2004 Cellular Network Planning – CE at UP 57
�Drive Test Datao Measurements done with network set on measure on all
BCCH channels
o Independent of accuracy of elevation and clutter data
o Extensive measurements necessary for interference matrix
o Difficult to deduce interfered traffic from data
o Drives are limited to roads and does not include high rise buildings
o Effort in importing into an AFP
o Often used to supplement propagation predictions
Data Sources for the
Interference Matrix (3)
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�Live Data: Mobile Measurement Reportso Mobile Measurement Reports are collected with the cell
set to measure on all BCCHs
o Data reflect the actual traffic distribution as well as the actual C/I. (“as the customer sees it”)
o No additional neighbour relations or exceptions required
o Extensive data collection - slow process. Requires the
network to be fairly mature and stable.
o Difficult to model new sites
o Takes some effort to import into an AFP.
Data Sources for the
Interference Matrix (4)
1/31/20081 May 2004 Cellular Network Planning – CE at UP 59
Prediction vs. MMRP
�LIMITED accuracy
o Propagation predictions
o Clutter and Height data
o In building
o Traffic distribution
�Cannot represent new
sites
�MMR limitations:
o RxLev: -110 -> -48dBm
o Only integers
o Only six neighbours
o BSIC decoding
problems
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Combining Data Sources
�….one of the remaining challenges. E.g:
o How to complement the shortcomings of the
mobile measurements reports with the
propagation predictions to include new cells.
o How to combine limited measurements with
predictions.
�without
o Spoiling good data with bad data.
o Skewing the matrix, e.g. when drive test data is
available for only part of the network.
1/31/20081 May 2004 Cellular Network Planning – CE at UP 61
Penalties for AFP
�A “bare necessity” approach i.e. set penalties only when
o it is required by law or
o It is required for feasibility – e.g. filter combiner
separation
o it will assist in the improvement of network
quality
o Is penalties to avoid adjacencies required?
�The size of the penalties must reflect their importance and effect on network quality
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Examples of Scaling Factors
�Difference in interference introduced
o Traffic load on TCH channels
o Power Control
o Discontinuous Transmission (DTX)
o Over-laid Under-laid - depend on effectiveness
of implementation
o Synthesizer Hopping - dependant on fractional
load
�Difference in immunity to interference
o Frequency Diversity Gain of Hopping Networks
1/31/20081 May 2004 Cellular Network Planning – CE at UP 63
Interference Load
�The core questions:o How much interference will assigning the same
frequency to a carrier in Cell A and Cell B cause ?
o How much less will that be after DTX?
o How much less will that be after Power Control?
�Interference Loado How much signal or potential interference is
carried on a particular carrier
o Interference Load = Traffic on Cell8 * #Carriers
1/31/20081 May 2004 Cellular Network Planning – CE at UP 64
Interference Load Reduction
�For BCCH
o Interference Load = 1
�For Non-Hopping TCH without DTX and PC
o Interference Load = Traffic on TCH Carriers
o 8 * Number of TCH Carriers
�After DTX
o Voice Activity Factor 40% on TCH channels
o Interference Load = 0.4 * Traffic on TCH Carriers
o 8 * Number of TCH Carriers
1/31/20081 May 2004 Cellular Network Planning – CE at UP 65
Interference Load Reduction
�After Power Control ?
o Consider a very simplified model:
� C/I = Server SS / (6* Interferers SS)
� Reducing the signal level of the server and of the interferers by approximately 10dB:
� C/I = 0.1* Server SS / (6*0.1* Interferers SS)
� Approximately unchanged.
o Practical implementation suggest a definite interference reduction - by 60%
o Interference Load = 0.6 * Traffic on TCH Carriers
o 8 * Number of TCH Carriers
1/31/20081 May 2004 Cellular Network Planning – CE at UP 66
Inter-modulation Products
�Harmonics or Inter-modulation products results from non-linearity in the system
�May cause a problem if one of these products fall on a receiving frequency.
�IM originate from frequencies in the transmit band and cause interference in the receive band
1/31/20081 May 2004 Cellular Network Planning – CE at UP 67
Inter-modulation Products
GSM1800 Downlink -BaseTxGSM1800 Uplink - MobileTx
GSM900 Uplink - MobileTx GSM900 Downlink - BaseTx
915MHz
1785MHz 1805MHz 1880MHz1710MHz
935MHz 960MHz890MHz
Dualband
GSM1800
GSM900
1/31/20081 May 2004 Cellular Network Planning – CE at UP 68
A few terms
�Frequency Allocation Re-use
o FAR = Total Number of Frequency Channels
Number of Frequencies per Cell
�Effective Re-use
Reff= Total Number of Frequency Channels
Average number of TRX per Cell
�Fractional Load
o Lfrac= Number of TRX per Cell .
Number of Frequencies per Cell
�Hardware Load
o LHW= (Busy Hour Traffic) / (TN /TRX)
1/31/20081 May 2004 Cellular Network Planning – CE at UP 69
A few terms
�Frequency Load
o Lfreq= LHW Lfrac
�Effective Frequency Load
o EFL =. Busy Hour Traffic per Cell .
(TN per TRX for Traffic).(Total # FreqCH)
1/31/20081 May 2004 Cellular Network Planning – CE at UP 70
Optimum # carriers to
Hop over = 24/6
Optimum frequency Re-use
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9
Frequency Reuse = #TCH carriers / #TCH per cell
Erlang p
er
Site
6MHz available for TCH
1/31/20081 May 2004 Cellular Network Planning – CE at UP 71
Quality vs Capacity
100
105
110
115
120
125
130
135
140
145
150
6 7 8 9 10 11 12 13 14 15 16
Average Erlang per Cell (Capacity)
(deduced from Spectrum Utilisation)
Min
ute
Erl
an
g p
er
Dro
p (
Qu
ali
ty) The challenge: To maximize Quality * Capacity
1/31/20081 May 2004 Cellular Network Planning – CE at UP 72
Major Interferers
Effect of reducing major interferers
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00%
P er cent age of Cel l s cont r i but i ng t o I nt er f er ence
Cummulative Contribution
With 5 sites' interference removed
1/31/20081 May 2004 Cellular Network Planning – CE at UP 73
What criteria would you
use for site selection?
�Close to traffic – most effective Power Control
�Contained (high γ )
o In building
o In valleys rather than on top of mountains
�What effect will an unbalanced link have?
1/31/20081 May 2004 Cellular Network Planning – CE at UP 74
What criteria will you provide an
Automatic Cell Planning tool with?
Interference Matrix
MMR
Frequency Allocation
Propagation Predictions
Traffic distribution - GIS
Possible sites
Equipment used
Effective Frequency load
Hand over areas
Income: Coverage
of potential traffic
Cost: cost of
changes / sites
1/31/20081 May 2004 Cellular Network Planning – CE at UP 75
Evaluating automatic tools...
�Automatic Frequency Planning Toolso Must Allow various data sources to be imported
o Must model the network accurately (e.g. Model hopping accurately)
o Must be simple to use, hence most of the modelling should be integrated
�Automatic Network Optimisationo Must be reliable and accurate enough to allow it to
run free with very little manual input
�Automatic Cell Planningo Cost function is so complex it should come with
the tool... and allow manual changes
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