ITS-Berlin
Models and methods for strategic studies of GSM networks
oriented to techno-economical analysis
by
K.- D. Hackarth, J. A. Portilla, D. Finaña
Telematic Engineering Group G.I.T. University of Cantabria
G. Kulenkampff ,
WIK: Scientific Institute for Telecom Services Studies, Bad Honneff
Germany
In collaboration with
Telematic Engineering Group
University of Cantabria
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Index
•
•
•
•
•
•
•
Cost models in telecommunication networks.
FL-LRAIC applied to mobile networks.
Network reference model for GSM network.
Mobile network design for cost studies.
Implementation of the model.
Example
Conclusions.
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Cost Models in Telecommunication Networks I
• There are several cost models which are applied to economical
studies in Telecommunication Networks
– Fully Allocated Cost (FAC) or Fully Distributed Cost (FDC): It is
mainly based on the financial accounting and hence on the historic cost of
the existing network. Allocates the total costs to the services.
– Activity Based Costs (ABC): Is a version of the FAC which looks closely
to the activities undertaken by the network operator. Therefore it results a
reduction of the arbitrarily of the FAC/FDC method.
– Current Cost Accounting (CCA): Estimates the cost of replacing
embedded facilities with modern facilities or functionalities at current
prices.
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Cost Models in Telecommunication Networks II
• Short Run Marginal Cost: It calculates the cost of supplying the NEXT unit
of output holding capital investment constant.
• Long Run Marginal Cost: The same as the previous method but allowing the
capital investment to change.
• Long Run Incremental Cost (LRIC): This method represents the costs
which would be incurred by a hypothetical firm if this firm provided the same
service as the established operator. It considers the unit cost of supplying a
large increment of additional output. These model is mapped into two lines
– Total Service Long Run Incremental Cost (TSLRIC): Estimates the forward
looking LRIC of providing an entire service.
– Total Element Long Run Incremental Cost (TELRIC): It calculates the costs of
unbundled network elements. TELRIC is based on engineering cost of the network
elements.
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Cost Models in Telecommunication Networks III
• Applying cost models there are two different
approaches:
• Top-Down,
– Based on accounting data. The whole network is first
cost, and then costs are apportioned to individual
network elements.
Accounting
Data
Network
Utilisation
Data
Total
annualised
costs
Financial
Parameters
Annualised
cost functions
Cost
attribution
rules
Unit
annualised
costs
Inputs
Calculations
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Cost Models in Telecommunication Networks IV
• Bottom-up
– Based on demand, design and unit costs. Individual
network elements are first cost, and a network design is
assumed so that the whole network can be cost.
Network
design rules
Cost
attribution
rules
Financial
Parameters
Network
Design
Investment
and operating
costs
Unit
annualised
costs
Area
characteristic
Network
Utilisation
Data
Inputs
Calculations
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FL-LRAIC Applied to Mobile Networks
• Current cost modelling for mobile network will focus
mainly on GSM systems.
• There are several cost drivers which have to be considered.
– Coverage (Km2)
– Frequency Licenses (e.g in Spain dual band 900-1800 MHz or
single band 1800 MHz).
– Busy-hour call attempts for voice traffic
– Busy-hour traffic in Erlangs for voice traffic
– Additional traffic from supplementary services, (SMS, voicemail).
– Extensions towards enhanced technologies, GPRS, HSCSD,
EDGE UMTS.
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Network reference model for GSM
Like any Telecom Network
the GSM network is
composed by two main
parts:
NMC
HLR
VLR
D
G
OMC
AuC
C
VLR
MSC
NSS
B
•A set of access networks named
Base Station Subsystem, BSS
BSS
BSC
BSS
TRAU
•One core network named
Network Switching Subsystem
NSS
Abis
BTS
Um
Sm
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MS
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Mobile network design for cost studies I
• Bottom-up method requires a complete and optimised
network configuration this means to consider all!! cells,
all!! BTS, and all!! BSC’s.
• Configure a PLMN at a National Scale only requiere a
strong set of input data due to the number and diversity
of working scenarios.
• Therefore we propose a simplification of the whole
problem causing only a small deflection from an
optimal network configuration
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Mobile network design for cost studies II
• The problem reduction have to consider the GSM network
reference model.
• Consider the BTS’s as the basic unit. and to project the cost of the
upper network elements by the corresponding use from the BTS
• To reduce the whole national set of heterogeneous scenarios to a
limited number of different over-layered homogeneous scenarios
• Consider various representative patterns like Metropolitan City,
medium city small villages and rural areas and additional patterns
like high ways, national roads etc.
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Mobile network design for cost studies III
• Divide a city into three main areas
– Dense Urban
– Sub Urban area
– Residential - Open area
• Generate an equivalent generic city
which consists of a circle kernel and
two concentric rings
• The cell type is the same in each of
these concentric rings and hence only
three cell-radios has to be calculated
• Subdivide large cities into districts
and handled each district separately
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Mobile network design for cost studies IV
• Once time obtained the cell radius, the number of BTS’s is
calculated by a single division between the size of the
specific area and the corresponding cell coverage area
• The cell radius calculation takes into account several topics
with corresponding models:
Propagation (Okumura –Hata with COST213 extension)
Mobility (meanvalue model)
Traffic, original and handover (S. Rapaport )
Type of BTS and consider sectoring in case of high user density
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Mobile network design for cost studies V
• Once the cell deployment are calculated consider the upper
part resulting from the BSC by projection
• calculate for each cell type BTS_i the maximum number of
BTS (Nº_BTS’s_i) that a BSC can handle and project the
BSC-use for each BTS_i by the following expression
FUSE BSC BTS _ i 
1
N º BTS ´s _ i
• repeated this calculation for all BTS’s types resulting the
number of BSC’s which provides service to a determined
city or region from the following equitation
 I

N º BSC ' s   N º BTS i  FUSE BSC BTS _ i 
 i 1

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Mobile network design for cost studies VI
• maximum number of BTS’s to a
BSC depends on several issues
– Number of Carriers
– Distance
– Total traffic...
• We use a tree-star topology,
connecting all BTS’s to the BSC
which are the same type.
• Corresponding algorithms calculate
the number of BTS’s assigned to a
BSC.
• consider transmission topology are
point to multipoint radio link system
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BTS
f=1
f=1
f=3
f=2
f=6
f=3
f=1
f=2
f=1
f=10
BSC
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Mobile network design for cost studies VII
• To consider the MSC we repeat
the projection method calculation
the maximal number of BSC to be
served from a MSC and its
corresponding data base
• We consider that the BSC
corresponding to a MSC are
connected via so called self
healing rings with transmission
equipment from the SDH (Add
and Drop Multiplexer)
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Implementation of the model
• The design models described in previous slides are being
implemented on a software tool named GSM-connect.
City Parameters
Main Window of the Tool
Percentages
of
the different types
of areas in the
city
Service Parameters
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Example of a district from Berlin I
A pure academic example type to illustrate
mainly the performance of GSM connect but
not to determine real cost values
example represents the northern part of the
district of Spandau (up to 1932 proper village)
We consider the four most important Mobile
operators with the following general data
Operator
Frequency
Nº of customer
T-Mobile
900
26,7
32
Vodafone
900
23,3
28
E plus
1800
8,0
10
O2
1800
5,6
7
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(Mill.)
Penetration %
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Example of a district from Berlin II
We divided the area of north
Spandau into eleven zones,
estimated for each of them the
population density and projected
these zones into the three level
model
Zone
Extension Km2
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
0.554
2.966
1.36
2.44
1.425
2.575
3.31
5.555
6.447
1.554
6.824
Relative User
Density
10
6
3
1
7
5
5
4
6
5
3
Area
Area Code
Extension
%
Population
%
Dense Urban
1
1.979
5.65
22201
9.79
Suburban
2
14.77
40.78
115621
51.01
Residential
3
18.754
53.57
88846
39.20
Population
Area Code
7928
25466
5838
3492
14274
18424
263683
31797
55354
11119
29295
1
2
3
3
1
3
2
3
2
2
3
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Example of a district from Berlin III
The results confirms a good cell performance for T-Mobile and Vodafone due to
the use of high capacity BTS, sectoring in urban area
For the E plus a worse propagation due to 1800 Mhz licence and smaller number
of high capacity BTS with sectoring in urban area
For O 2 also a worse propagation due to 1800 Mhz licence and a high number of
BTS due to the absence of high capacity BTS with sectoring
Nº of BTS
Operador
Urban Suburban Res. Total
T-Mobile
8
41
32
81
Vodafone
7
36
28
71
E plus
9
21
35
65
O2
9
27
35
71
User/
BTS
895,5
893,9
348,7
223,5
r.c.t.c./min
100
100,4
192
210
r.c.t.c./min relative call termination cost per minute
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Conclusions
• FL-LRAIC, with bottom – up approach requires a deep
study of the network.
• For a regulator or a consulting entity it is almost
impossible to provide a complete and optimal GSM
network design on a National scale.
• Therefore we proposed and implemented some
simplifications and approximations.
• Specially we represent BTS areas by a limited set of
pattern and project the upper network elements by a
corresponding use-factor for each type of BTS
• Under real life demand- equipment- and cost scenarios
GSM-connect can calculate an estimation for the call
termination cost in GSM network
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