GSM Network Pre Planning Guideline 20020918 B 2.0

7/15/2019 GSM Network Pre Planning Guideline 20020918 B 2.0

http://slidepdf.com/reader/full/gsm-network-pre-planning-guideline-20020918-b-20 1/25

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.



GSM Network Pre-Planning Guideline (V2.0) Internal Use Only

Wireless Network Planning Department

2




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

3




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

4




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

5




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

6




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.)

7




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”.

8




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

9




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:

10




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)


urban area 4 4 -

Suburb 3 3 3

Rural area 3 3 3

Construction

penetrating loss (dB)


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

11




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)

12




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

13




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

14




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

15




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

16




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.

17




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.

18




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

19




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.

20




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.

21




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

22




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.

23




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.

24




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.

25

Documents

GSM Network Pre Planning Guideline 20020918 B 2.0