gsm network pre planning guideline 20020918 b 2.0
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Wireless Network Planning
Department, Huawei
Technologies Co., Ltd.
Document No. Product version Confidentiality level
Internal use only
Product name: M900/1800 Total 24 pages
GSM Network Pre-Planning Guideline
(V2.0)
(For Internal Use Only)
Drafted by: Wireless Network Planning
Department
Date: 2002/9/18
Checked by: Date:
Checked by: Date:
Approved by: Date:
Huawei Technologies Co., Ltd.
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Wireless Network Planning Department
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Table of Contents
1 Overview....................................................................................................................................... 5
2 Pre-planning Contents................................................................................................................5
3 Basis for Pre-Planning................................................................................................................7
3.1 Confirmation of Network Construction Target.....................................................................7
3.2 Network Performance Discussion.......................................................................................8
4 Preparations for Pre-planning....................................................................................................9
4.1 Geographical Information....................................................................................................94.2 Network Planning Design Requirements.............................................................................9
4.3 Technical assumptions......................................................................................................10
4.4 Coverage Area Acquisitions..............................................................................................11
4.5 Propagation Environment Survey......................................................................................12
4.6 Link Budget....................................................................................................................... 13
4.7 Traffic Analysis..................................................................................................................13
5 Analysis of the Number of BTSs..............................................................................................15
5.1 Determining Cell Range....................................................................................................15
5.2 Determining the Number of BTSs/TRXs...........................................................................16
6 Detailed Pre-planning................................................................................................................ 17
6.1 Preparations for Wireless Pre-planning............................................................................. 17
6.2 BTS Layout Planning........................................................................................................17
6.3 Designing Network Structure.............................................................................................18
6.4 Designing BTS Engineering Parameters...........................................................................19
6.5 Coverage Prediction and Frequency Planning.................................................................. 21
7 Propagation Model Correction.................................................................................................22
8 Location Area Planning............................................................................................................. 23
9 Other Special Issues.................................................................................................................24
9.1 Dual-Band Network...........................................................................................................24
9.2 Indoor Coverage System..................................................................................................24
10 Conclusion............................................................................................................................... 25
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GSM Network Pre-Planning Guide (V2.0)
Key words: Pre-planning Coverage Network structure Capacity
Summary: Pre-planning is the first and most important stage of wireless mobile network
construction and reflects the system design level of RNP. Pre-planning
determines the layout, performance and development potential of future network.
Great importance should be attached to wireless network pre-planning. This
document is intended for domestic and overseas network planning engineers.
Reference materials
Name Writer Code Released
date
Where and how
to access
Publisher
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1 Overview
Wireless network pre-planning is essential part of mobile communications network
construction. It refers to a rational planning of engineering parameters (such as site
layout, number of BTSs, types of BTSs, etc.) of wireless networks on the basis of a
detailed analysis of the running conditions of the existing networks (if not new networks),
thus to meet the demands of operators on network coverage, capacity and quality within
the limit of construction cost.
This document introduces the pre-planning at the stage of market demand. The pre-
planning includes multiple sub-processes, which will be described in this document. To do
a good job for each sub-process is the precondition to the accuracy and reliability of
network pre-planning.
An excellent pre-planning engineer should be familiar with:
Link budget
Wireless propagation model and coverage prediction
Traffic prediction and capacity analysis
Frequency planning
Antenna and feeder, etc.
In addition, before planning, the planning engineer should get some idea of local
economic conditions, population distribution, income distribution, geographical
conditions, etc.
2 Pre-planning Contents
Pre-planning usually belongs to pre-sales work and may include the following two types
based on market demand:
Simple pre-planning
Detailed pre-planning
(Which type is to be used is commended by network pre-planning engineer and is
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decided by the marketing engineer. This procedure should be done in the form of internal
memo in advance.)
Simple pre-planning means to calculate the number of BTSs and TRXs to meet coverage
and capacity requirements as required in the bidding documents of operators, so as to
provide a reference for operators in making their investment decision. Simple pre-
planning usually does not include site location selection, with BTSs laid out according to
ideal network meshes. In determining the maximum BTS configuration of the network, it
is only to consider whether the frequency resources are enough and to decide which
frequency planning technique to be used. Seven workdays/man for overseas are needed
to work out a simple pre-planning solution of a medium-sized network (100 BTSs).
Simple pre-planning does not need the digital map.
Besides involving all the work of simple pre-planning, detailed pre-planning also includes
test and analysis of existing networks, site selection, link budget, coverage prediction,
networking structure, frequency planning, planning of key cell parameters. Model
correction may also be necessary. Fourteen working days/man are needed to work out a
detailed pre-planning solution of a medium-sized network (supposing that the digital map
has been bought, and tests of existing network and site survey are not considered).
It should be noted that consultation with operators is important to both simple pre-
planning and detailed pre-planning. Before planning, it is necessary to consult in detail
with the technical officers of operators on such issues as coverage range, coverage level,
traffic model, and frequency resources. Especially important is consultation with the
overseas market so as to ensure that the understanding of the bidding documents of both
parties is consistent.
Wireless network pre-planning mainly involves:
a) Discussion with operators on technologies
b) Preparations for pre-planning
c) Simple pre-planning
d) Using planning software simulation (coverage prediction, capacity planning and
frequency planning)
e) Test of existing network
f) Model correction
g) Application suggestion of advanced features
h) Planning of key cell parameters
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The above items may be selected based on market demand. For example, the most
common simple pre-planning may include a, b, and c. While detailed pre-planning may
include a, b, d, e, g, and h. Model correction takes a lot of labor and materials and is
usually omitted unless strongly required by operators. The propagation model for
simulation may be OKUMURA-HATA (GSM900 macrocell) or COST 231-HATA
(DCS1800 macrocell) model. For the micrococell with coverage radius less than 1 km,
Walfish-Ikegami model can be used. If the propagation environment to be simulated is
similar to any model that Huawei has corrected, the simulated propagation models can
be used.
3 Basis for Pre-Planning
Technical exchange with customers is prior to all other work in pre-planning. Discussion
with customers enables radio network planners to know customers’ requirements for
technology and their expectations for network construction, so as to reach an agreement
on technical indices like coverage and service quality according to network construction
scale and make detailed work division interface between customer and manufacturer.
This process is described in the following two aspects.
3.1 Confirmation of Network Construction Target
First make conventions with customers about some technical conditions in network
construction, including:
Definition of coverage area
Detailed specifications of service quality in the coverage area
Busy hour traffic per subscriber
Um interface service grade (GOS)
Network capacity and prediction of subscriber increase
Available frequency bands and application restrictions
The number of sites or TRXs
Indoor or in-car penetrating loss
Antenna and propagation environment analysis
BTS performance (output power, sensitivity, and combiner, etc.)
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Wireless planning tools
Site naming and numbering specifications
BTSs documents of the existing network
According to the above technical conditions and assumptions, the radio network planners
carry out network planning and guide subsequent project construction. Any change of
these technical assumptions may have chain effects on network construction, so it is
necessary to record the above discussion results in writing form.
3.2 Network Performance Discussion
The bidding documents contain operators’ expectations for network quality. These
expectations are usually presented either in clear, checkable, numerical forms. Therefore,
radio network planners should discuss in detail with operators on such expectations
before network planning.
Network performance evaluation usually involves the following:
Key performance indices (KPI)
KPI acceptance
Wireless network optimization service requirement and how to serve
Common KPIs are listed in Table 1:
Table 1 KPIs
KPI Description Test
method
Reference
value
1 TCH congestion rate OMC <2%
2 SDCCH congestion rate OMC <1%
3 Call drop rate OMC <2%
4 Handover success rate OMC >92%
5 Call setup time Average call setup time drive test <10S
6 Coverage rate Receiving level>percentage of
–90dBm
drive test >90%
7 Subjective voice quality
evaluation (MOS)
Divided into five levels from
perfect to inaudible
drive test >=3
Note 1: See Traffic Statistics Manual for traffic statistic index definition
Note 2: The KPI and their reference values come from the operator “China Mobile”.
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In the above table, subjective voice quality evaluation refers to the five levels from
inaudible to completely clear, divided according to mobile communications industry
standards:
Table 2 Subjective voice quality evaluation (MOS)
Quality grade Quality evaluation standard
Grade 5 Excellent
Grade 4 Good
Grade 3 Fair
Grade 2 Poor
Grade 1 Bad
Voice as good as or better than grade 3 can enter mobile communications networks and
voice as good as or better than grade 4 can enter PSTN.
4 Preparations for Pre-planning
4.1 Geographical Information
Subscriber distribution and geographical conditions are basic references in network
planning. The first thing to do is obtain paper map and digital map of the coverage area.
Digital map contains heights, clutters and vectors data. The 3-demension digital map in
ASSET format in current use is drawn based on satellite or airplane photos. In addition,
2-dimension digital map in MAPINFO format can be obtained from digital map providers,
who have the software to convert ASSET format to MAOINFO format. When drive test
software is used, MAPINFO background map is inserted to facilitate test and analysis.
However, the 2-dimension map has no information about height so it is not suitable to be
used for coverage prediction.
4.2 Network Planning Design Requirements
Before the network planning, the network expectation of operators should be accurately
understood. The network design target usually presents in bidding documents or comes
from the discussion with operator’s engineers. The following table gives the network
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target.
Target coverage area
Large city Small city Highway
Coverage area/length
(km2)
city centered area 9 - -
urban area 50 25 -
Suburb 100 60 -
Rural area 150 100 75
Network come into use
date (YY/MM/DD)
2002-04-02 2002-04-01 2002-05-01
Number of subscribersNetwork come into use 12000 4000 1000
+6 months 14000 6000 2000
+12 months 18000 6000 2000
+18 months 18000 6000 2000
Busy hour traffic/subscriber (mErl) 30 25 20
Traffic redundancy
percentage (%)
15 15 20
Frequencies 25 25 25
Service type Indoor X
In-car X XOutdoor X X
GOS (%) 2 2 5
Coverage probability 95 95 95
New construction/capacity expansion New New Expansion
Note1: Traffic redundancy refers to the reserved radio capacity for roaming subscribers
and handover.
Note2: The above values are from an actual project of “China Mobile” .
4.3 Technical assumptions
As technical assumptions have impact on network quality, it is necessary that these
assumptions should be confirmed by operators in the written form. The technical
assumptions, which are based on the experience of operators or radio network planners,
will be used for uplink and downlink balance calculation.
Following are the reference values for technical assumptions:
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Table 3 Reference values for technical assumptions
Coverage target
Large/medium
city
Small city Highway
Network type GSM900 GSM900 GSM900
Antenna gain (dBi) 15 17 18
Antenna height (m) city centered area 25 - -
urban area 30 30 -
Suburb 35 35 20
Rural area 45 45 45
Antenna diversity
gain (dB)
city centered area 4 - -
urban area 4 4 -
Suburb 3 3 3
Rural area 3 3 3
Construction
penetrating loss (dB)
city centered area 25 - -
urban area 20 20 -
Suburb 15 15 -
Rural area 15 15 -
car penetrating loss (dB) - - 10
Slow fading SD (dB) city centered area 8 - -
urban area 8 8 -
Suburb 8 8 8
Rural area 8 8 8
4.4 Coverage Area Acquisitions
Different areas may need different signal propagation models, thus requiring different
designs of wireless networks, network structures, service grades and frequency reuse
modes. To help determine the coverage of cells, wireless coverage areas may be divided
into large cities, medium-sized cities, towns and rural areas.
Table 4 Coverage area
Area type Area type description
Large city Area with dense population, developed economy and huge traffic,
with bustling business districts and densely built skyscrapers in the
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downtown area
Medium-sized
city
Area with fairly dense population, fairly developed economy and
large traffic, with densely built downtown area, lively business
districts and great development potential.
Town Area with a relative large population, development potential and
medium traffic, with fairly densely built central area, a relative large
business district and fairly large development potential.
Rural area Sparsely settled and less developed area with small traffic.
The above areas are connected by various main roads, including expressways, national
highways, main provincial roads, main railways, main waterways, ordinary provincial
roads, railways and waterways, and mountainside roads. It is also necessary to consider
coverage of these transportation lines.
It is recommended to use omni-directional BTS for coverage only in rural areas on plains
and on irregular terrain, and use directional BTS for small, medium-sized and large cities
and expressways.
It is necessary to collect information (including coverage area design and frequency plan
of adjacent BTSs at coverage borders) of the existing networks in related adjacent areas
so as to make preparations for planning within the region.
4.5 Propagation Environment Survey
Propagation environment survey is mainly intended to inspect the wireless propagation
environment, estimate path loss and obtain a basic wireless propagation model for
estimating the number of BTSs in coverage prediction. Propagation model correction is
not necessary.
For GSM900, formulas for the calculation of wireless path loss are as follows:
PLDU = 147 + 1.25d + 41logd
(Walfisch-Ikegami model, supposing GSM900, hBTS < hobstacle, hBTS = 25m, street width =
25m, building width = 50m, used for the estimation of loss in Dense urban areas)
PLU = 127 + 38logd
(Walfisch-Ikegami model, supposing GSM900, hBTS > hobstacle, hBTS = 25m, street width =
25m, building width = 50m, used for the estimation of loss in ordinary urban areas)
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PLSU = 126 + 35logd
(Okumura-Hata model, supposing GSM900, hBTS = 30m, used for the estimation of loss in
suburbs)
PLRU = 116 + 35logd
(Okumura-Hata model, supposing GSM900, hBTS = 30m, used for the estimation of loss in
rural areas)
If the above formulas are not enough of the requirement, CW test may be made. Note
that in CW test, the frequency that is interfered should not be used. Select a test area
according to the map or terrain type and make sure that the area selected should be
representative. See Propagation Model Correction Guide for detailed test method.
4.6 Link Budget
Link budget involves the above described coverage target parameters and technical
assumptions. There should be different link budget formulas for different types of terrain.
Downlink and uplink should be balanced. The maximum allowed link loss can be
obtained according to the calculation results of link balance.
In most cases, the link loss of uplink and downlink is the same. The BTS transmitting
powered can be set according to the link budget result.
4.7 Traffic Analysis
Economy feasibility and rationality must be taken into account in network construction.
Only a sound prediction of initial and final stage network capacity can lead to a rational
investment decision. Network capacity prediction should be based on population
distribution, family income, fixed telephone availability, national economic development,
urban construction, etc. Charging policies are key factors to affect subscribes select
network services. It is necessary to predict subscriber distribution after the total network
construction capacity is properly predicted. In view of actual project needs, BTSs are
usually located in urban areas, suburban counties and main roads, so the prediction may
be made by means of percentage. At the initial stage of network construction, subscribers
in downtown areas usually occupy a large percentage in the prediction of total
subscribers. As network construction scale increases, subscribers in suburban counties
and main roads will occupy an increasing percentage. According to the division between
downtown area and suburban counties, the traffic per subscriber is usually 0.025Erl and
0.020Erl. Thus, the number of voice channels needed by a specific BTS may be obtained
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based on traffic prediction. Note especially that the impact of cell splitting must be
considered in calculating the number of voice channels for future BTSs.
For the capacity expansion, removement, or patching networks, their network capacity
can be predicted based on the traffic statistics of the existing network.
Erlang traffic model is used in calculating the traffic load of the network (GPRS not
considered at the moment). Generally call loss is taken as 2% or 5%. Following is Erlang
Table B:
Table 5 Erlang table
TRXs per cell Number of
TCHs
Traffic (Erl)
GoS=2% GoS=5%
1 6 2.27 2.96
2 14 8.2 9.73
3 21 14.03 16.18
4 29 21.03 23.82
5 36 27.33 30.65
6 44 34.68 38.55
7 52 42.1 46.53
8 59 48.7 53.55
9 67 56.25 61.63
10 75 63.9 69.73
Channel utilization ratio, the ratio between the busy hour traffic and the theoretic traffic of
a cell, is an important index of planning design quality and reflects network operation
efficiency or the radio resources utilization ratio. High channel utilization ratio and low call
loss are the aim of network operation. It is obvious from the above table that the more
TRXs in a cell, the larger traffic each TCH will bear and the higher the TCH utilization
ratio will be. If there are too few subscribers in an area, the construction investors willgenerally postpone setting up a BTS in this area, or serving this area with a repeater.
Limitations of cell coverage and available frequency bandwidth make it necessary to
rationally plan cell capacity and maximize channel utilization ratio while ensuring good
voice quality. In the construction of dual-band networks, considering the inter-band traffic
load sharing, the relatively abundant frequency resources may serve to reduce the
interference between adjacent frequencies in the network, to reduce the impact on
channel utilization, and thus to enhance network utilization ratio.
In practical applications, it is found that if the actual traffic per line (TCH) of a cell reaches
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85%~90% of the traffic per line (TCH) (2% call loss) given in Erlang Table B, the
congestion probability in this cell will increase noticeably. Therefore, usually 85% of the
traffic given in Erlang Table B is taken as the basis to calculate the bearable traffic
density. The predicted value of these traffic capacities needs to be measured and
improved gradually in the course of network construction.
5 Analysis of the Number of BTSs
5.1 Determining Cell Range
Radio network planners can roughly figure out cell coverage in different coverage
topographies according to calculation of maximum link loss budget and the propagation
model. Suppose the maximum path loss budget of the equipment is 131dB, then for
GSM900 network in ordinary downtown areas:
131 = 127 + 38logd
⇒ d = 1.2Km.
Cell coverage area is calculated according to hexagonal cell graph, as shown in the
following diagram.
Figure 1 Site radius and coverage area
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In the above diagram, x is the side length of a sector and R is the site radius. The area of
the equilateral triangle with side x:
S = R/2(cos30°) R/4 = (R2 3 )/16,
The area of a site is 6S = 6 (R2 3 )/16 = 3 (R2 3 )/8
Then the coverage area of a BTS is 18S, about 1.95R2
For an omni-directional station, let its radius be r, then its coverage area is S = (3r 2 3 )/2
= 2.6r 2
It can be known from the above that the coverage area of a site with radius 1.2Km is
about 2.8Km2.
5.2 Determining the Number of BTSs/TRXs
According to the cell coverage area calculated in the above section, the number of BTSs
required can be obtained simply by exact division of the area to be covered. This result is
obtained from the perspective of wireless coverage.
The number of BTSs should also be calculated from the perspective of capacity. The
radio network planners calculate the maximum network capacity in this way:
According to the service grade (GoS) determined above, look up in the Erlang table and
find the configured traffic of each cell and multiply it with the number of BTSs to obtain
the maximum traffic capacity of the network. If the result is larger than the designed
target value of the network capacity, then the number of BTSs calculated from the
perspective of coverage will meet the design requirements.
If the result is smaller than the designed value of network capacity, then it is necessary to
add more BTSs or increase the number of TRXs in every BTS so as to increase the total
traffic capacity. Based on practical engineering experience, the actual traffic capacity
provided by the network should be approximately 1.3 times as the expected traffic. Such
a network is unlikely to be congested seriously.
Note: In predicting the maximum configuration of TRX, it should be consider whether
there is enough frequency resource, whether the tight frequency reuse is adopted,
whether the frequency hopping is adopted, or whether power control is used for anti-
interference. For example, under the existing technical condition, the GSM900 of an
operator has only 6MHz bandwidth. If the site configuration is larger than S4/4/4 (non-
standalone site), the network performance cannot be guaranteed (assuming 1x3
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frequency reuse is adopted).
Generally, the number of SDCCHs can be configured according to be the default
percentage of TCH/SDCCH given in SDCCH Capacity Planning Guide. If special traffic
model is required by operator, the configuration of SDCCH also can be calculated from
the above given method.
6 Detailed Pre-planning
Detailed pre-planning design is based on simple pre-planning result.
6.1 Preparations for Wireless Pre-planning
Detailed pre-planning needs relevant planning tools. ASSET planning software may serve
the purpose. For cities and areas with dense subscriber distribution, digital maps are
usually necessary. The digital maps can be bought from the digital map provider. In rural
areas or plains with sparse subscriber distribution, blank digital maps are often used.
Such maps make no distinction as regards surface clutters and heights. So the coverage
prediction based on blank digital map is not accurate enough, and only serves as
reference. But the prediction still can be used for adjacent cell planning and frequency
planning.
6.2 BTS Layout Planning
There are two ways to distribute the site location as follows:
One is to follow standard meshes. Radio network planners select locations of BTSs in the
covered area according to the intervals of standard meshes, then adjust sites’ layout
according to the coverage prediction so as to meet coverage. After a satisfactory BTS
layout design is worked out, it is also necessary to analyze the capacity of such a
structure. The final number of BTSs should meet both the coverage and capacity. The
capacity is designed by carefully calculating the number of TRXs configured for each
BTS and making relevant analysis and adjustment according to the configuration.
Adjustment of BTS configuration depends on subscriber distribution. If capacity in some
areas fails to meet the requirements, more BTSs should be added, and then repeat the
above process. Such calculation process may be represented with visual graphs and
visual data description in GIS.
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Another way is to begin pre-planning from specific areas. Planning begins from areas
with the densest subscriber distribution or the area most difficult to be planned. This
requires an in-depth knowledge of subscriber distribution, terrain and surface features
obtained from coverage area survey. First put BTSs in the center of key areas that
ensure coverage and capacity of important areas. Then plan other BTSs according to the
design targets of coverage and capacity and finally work out a satisfactory layout of sites.
After this step is finished, other subsequent steps are the same as those for the first way.
Different traffic distribution densities and irregular topographies and surface features
result in irregular wireless coverage and thus different intervals between BTSs. Usually
the intervals between BTSs in areas with intensive traffic are smaller. Microcells may also
be used to provide hierarchical coverage and desired capacity for some hot areas. As
frequency resources are limited, the anti-interference measures should be taken in
priority while meeting capacity requirement. There is no standard plan for BTS
distribution of a network, a better plan should be selected in consideration of the whole
network. See Site Survey Guide for site location selection.
6.3 Designing Network Structure
Make in-depth analysis of the network structure in laying out BTSs. The network structure
usually includes high-layer BTSs, middle-layer BTSs or low-layer BTSs according to the
antenna height, with the network traffic load mainly taken by middle-layer BTSs. Network
hierarchy should be supported by BSC equipment.
Middle-layer BTSs have antennas a little higher than the average height of the buildings.
The antennas are usually installed on the top floor of the building to cover several
adjacent blocks. In towns and rural areas, most BTSs are middle-layer BTSs except a
few high-layer BTSs built for such reasons as fast moving environment and specialterrain. On one hand, middle-layer BTSs can make efficient use of frequency resources
(better than high-layer BTSs), and on the other hand efficiently absorb traffic (better than
low-layer BTSs), taking a major part of traffic load in network. Middle-layer BTSs are
usually 0.6~5km from each other except in rural areas. In some areas in large cities, the
average intervals between middle-layer BTSs may be less than 0.6km. Preferably,
however, the average intervals should not be less than 0.4km even in large cities,
otherwise the impact of buildings on the signals strength of various BTSs will be
uncontrollable.
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High-layer BTSs have antennas much higher than the average height of buildings and
cover multiple middle-layer BTSs in the covered area. High-layer BTSs make less
efficient use of frequency resources and thus only apply to large cities (with many
viaducts, beltways and light railways on which subscribers may travel at 60~80km/h) or in
some areas in medium-sized cities with dense high-rise buildings. High-layer BTSs are
not suitable for other medium-sized cities, towns or rural areas except for such reasons
as fast moving environment and special terrain. Follow the principle of “few but best” in
building high-layer BTSs. High-layer BTSs may provide a satisfactory solution to the
good coverage and low frequency interference in high-rise buildings in the downtown
area.
Low-layer BTSs have antennas lower than the average height of buildings. The
antennas are usually installed on the outer walls of lower floors, skirt buildings, or on top
of low buildings or inside the buildings, covering only one block, part of a block or a
building. Low-layer BTSs make efficient use of frequency resources but behave poorly in
absorbing traffic. This is mainly because the low-layer BTSs cover a small area and if
they are slightly off the hot traffic centers it will be difficult for them to absorb satisfactory
traffic. Therefore, to build the low-layer BTSs, make clear whether the low-layer BTSs are
intended to solve inadequate coverage or cope with high traffic, which affect the decision
of the site selection and size of the low-layer BTSs.
Generally, at the initial stage of network construction, the network is designed as a single-
layer one, composed of most middle-layer BTSs. New BTSs may be added depending on
traffic and coverage demands after the basic network is completed. Low-layer BTSs
(usually using microcell layer and distributed antenna system to provide indoor coverage
and to avoid interference and difficult site location selection due to short intervals
between BTSs) are built in bustling business districts with intensive traffic. These BTSs
will gradually evolve into a hierarchical network.
Note that the hierarchical network requires a relatively many frequency resources so it isnot recommended for the network with short frequency resources.
6.4 Designing BTS Engineering Parameters
Detailed designing of BTS engineering parameters comes after the planning of the
number of BTSs, BTS configuration and BTS layout. The BTS engineering parameters
mainly include site name, longitude, latitude, downtilt, and height.
In the network planning, the height usually refers to the height of antenna. The height of
antennas depends on the different types of coverage areas, network structures and
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average height of buildings. Usually an antenna higher than 30 m is recommended in the
downtown area and a slightly higher (usually 40m~50m) for the BTS facing suburb on the
border between the city and suburb. The relative height between omni-directional
antennas and the target area is usually 60~70 m. The height of BTSs in removement
networking may be adjusted based on network construction conditions, target area and
installation environments. Special terrain in some mountainous areas may require that
the BTSs should be built on the summits. In this case, directional antennas had better be
used to avoid “coverage hole near the site” resulting from omni-directional antennas. In
the past, BTSs with omni-directional antennas were built only in villages in plains, in
some special topographies and along some main roads, while BTSs in other areas used
directional antennas. With the network construction target enhanced, the BTS with omni
antenna cannot meet the coverage requirement. In the areas with dense subscriber
distribution, BTSs (excluding microcells and indoors distributed antenna systems) use
65° directional antennas. To avoid mutual interference, the antenna gain should not be
too high. BTSs in the areas with small number subscribers but broad coverage being
required usually use high-gain 90° directional antennas.
To ensure standardized network structure and minimize interference, it is recommended
to keep the antennas of various BTSs and sectors in a particular area facing the same
direction, e.g. designed as 0°/120
°/240
°or 60
°/180
°/300
°(recommended). But it is
necessary to adjust the direction of antennas of BTSs near the sea, rivers, main roads or
the connecting parts between cities and suburbs, in the areas with traffic unevenly
distributed, and in downtown area with dense high-rise buildings. Note especially that
many streets in large and medium-sized cities have high-rise buildings on both sides, so
the nearby antennas should not face the streets so as to avoid waveguide effect.
The downtilt of the antennas depends on the actual situation, following a principle of
trying to reduce the interference between cells with the same frequency and to ensure
adequate coverage, thus preventing the formation of blind zone. If the downtilt is toolarge, the front/back radiation ratio must be considered to prevent the back lobe of the
antennas from interfering with the back cell or prevent the side lobe from interfering with
the adjacent sectors. Generally, cells near waters should be designed with large downtilt
to prevent interference on the cells on the opposite bank. Cells in suburbs or along main
roads are not designed with mechanical downtilt so as to enlarge coverage. See Antenna
Downtilt Planning Adjustment Guide for detailed information about the effect of antenna
downtilt on cell coverage.
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6.5 Coverage Prediction and Frequency Planning
Coverage prediction can be made based on the network engineering parameters
designed above. See ASSET User Manual for details.
If the coverage prediction result is different from the ideal condition, then it is necessary
to make adjustments in the following ways:
1) Repeater may be set up outside of the coverage area and where there is demand
but it is not suitable to build BTSs. For the area with weak signal or for the blind zone
within the coverage area, microcells may be used.
2) If adjacent cells have large coverage spacing, increase the height of antennas or
build new BTSs according to cell splitting principle.
If the cell coverage cannot meet the requirement of co-channel and adjacent frequency
interference index, then make the following adjustments:
Adjust the number of TRXs in this cell
Adjust BTS location or other design parameters (including the antenna model,
antenna height, azimuth, downtilt, and transmitting power). In this case, inter-BTS
influence must be taken into account
Frequency planning and BCC planning follow coverage prediction. See relevant
documents for the details about frequency planning. ASSET adopts intelligent local
search algorithm (ILSA) to realize automatic frequency planning. Repeated modification
of searching conditions and multiple times of search may be necessary to obtain a
desired result. This result should be checked by experienced RNP engineers to optimize
overall effect.
For the simple prediction planning, usually it is unnecessary to make the detailed
frequency planning but only to describe the frequency reuse mode and planning ideals to
be used, such as:
1) Whether the different section of frequencies should be planned for BCCH and TCH
respectively.
2) Whether BCCH adopts high or low frequencies
3) A rational number of BCCH frequencies that can guarantee both the network
performance and the frequency resource is not wasted.
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4) Number of TCH frequencies that can satisfy the capacity (or site configuration)
requirement.
5) Whether some frequencies should be reserved for microcell.
At present the commonly used frequency planning technologies in GSM network are:
4×3, 3×3, 1×3, 1×1, MRP, and IUO.
4×3: 12 cells of 4 sites form a frequency reuse cluster. The frequency inside these 12
cells cannot be reused.
3×3: 9 cells of 3 sites form a frequency reuse cluster. The frequency inside these 9 cells
cannot be reused.
1×3: 3 cells of 1 site form a frequency reuse cluster. The frequency inside these 3 cells
cannot be reused.
1×1: 1 cell of 1 site forms a frequency reuse cluster. The frequency inside this cell cannot
be reused.
MRP: is a relatively complex frequency reuse technology which increases the tightness
of frequency reuse layer by layer.
IUO: IUO is not an independent frequency reuse technology. It needs to be used together
with above frequency reuse technologies.
The 1×3, 1×1, and MRP are tight frequency reuse mode, which need the support of anti-
interference measures such as frequency hopping, power control, and DTX. In addition,
BCCH carrier can use only 4×3 or looser frequency reuse mode.
7 Propagation Model Correction
All coverage predictions and frequency plans are based on calculation result of
propagation model, so the accuracy of propagation model has an impact on the quality of
the entire pre-planning solution. Huawei Radio Network Planning Department has made
correction of some propagation models in some typical areas. Due to the large amount of
work it is not recommended to made model correction. See Propagation Model
Correction Guide for details
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8 Location Area Planning
To help locate the position of a mobile station, the coverage area of GSM PLMN is
divided into many location areas (LA). The size of a location area (the coverage area of a
LAC) is a key factor in the system. LA planning follows the following principles:
1) A location area should not be too large or too small.
If the area covered by LAC is too small, then MS may need more location updatings, thus
increasing the signal flow in the system. If the location area is too large, then the same
paging message from the network to the MS will be sent to many cells, resulting in PCH
overload and increasing the signal flow at Abis interface. The calculation of location area
is related to the paging strategies of different manufacturers. See Guide to Location Area
Capacity Planning for details.
2) Try to divide LA based on the geographical distribution and behaviors of MSs so that
fewer location updatings take place on the border of the location area. For example, in
large cities with high traffic, if there are two or more location areas, terrain features such
as hills and rivers in the downtown areas can serve as the border of location areas so as
to reduce overlap between different cells in the two location areas. If there are no such
terrain features, streets should not serve as the borders of location areas and the borders
should not be set in places with high traffic (like stores). The borders of location areas
should be oblique to the streets but not vertical or parallel to them. In the downtown
areas and the connecting parts of the cities and suburbs, the borders of location areas
are usually set at BTSs on the outer of the city rather than in the connecting parts of the
cities and suburbs with intensive traffic, so as to prevent frequent location updatings of
the subscribers in these parts.
It is usually necessary to consult with operators about location area planning . CGI and CI
coding can be obtained from operators.
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9 Other Special Issues
9.1 Dual-Band Network
Dual-band network is mainly used to cope with shortage of frequency resources resulting
from the increase of subscribers. Generally, in the coverage area, GSM900 network has
provided satisfactory coverage, so GSM1800 network mainly serves to absorb traffic.
Therefore pre-planning of GSM1800 network is mainly concerned with the calculation of
traffic balance and cooperation between two bands. The numbers of BTSs and TRXs of
GSM1800 network are determined based on the traffic data of various GSM900 sites
collected through the OMC of the existing networks and together with the reference to the
prediction of the increase of subscribers. The propagation loss of 1800MHz is larger than
that of 900MHz. GSM1800 BTS and GSM900 BTS are built at the same site to save cost.
Thus, in terms of wireless coverage, cell selection and reselection and handover can
cooperate so as to avoid unnecessary signaling load. Make MSs camp in GSM1800
network as much as possible by designing cell parameters. Try to make MSs in active
status camp in GSM1800 network as much as possible through Huawei’s hierarchical
design and various handover algorithms. The careful selection of handover threshold and
handover judgement time can effectively improve the conversation quality. See Dual Band Network Planning Guide for detail.
The networking modes for dual band network planning are: co-site, BSC sharing, MSC
sharing, independent MSC. The different networking modes have different advantages
and disadvantages. See Dual Band Network Planning Guide for detail.
9.2 Indoor Coverage System
Enhancing indoor coverage is an effective means to improve network quality after the
network has been developed to a certain extent. Ordinary outdoor microcells fail to
provide the adequate coverage for the places inside buildings, basements, elevators,
tunnels, etc. In this case, some special technologies may be used, including:
Repeater
Microcell or microcell BTS
Distributed antenna system
Leakage cable
See Indoor Coverage Planning Guide and Repeater Planning Guide for detail.
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10 Conclusion
Network planning is key step to mobile communications construction. Good planning is
essential to the reliable running of future network. The network pre-planning should
combine the experience of network optimization so as the network can meet the
expectation of operator or even be better than the expectation once the network is put
into use. Then the future network optimization can be reduced.
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