Tde Final Report

8/3/2019 Tde Final Report

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Cellular Mobile Radio Base Station Network Planning for

Telecommunications

1 INTRODUCTION

This project is based on the designing of a cellular network for a real

geographical area on the software named Cell Planner. Cell Planner is the

software which provides all the functions for the design of a wireless

system and allows us to estimate the performance of the designed system

or we can say wireless system. It is essentially helpful for almost all the

frequency ranges for Analog, TDMA, CDMA, GSM and 3G. Our project is

based on the designing of GSM Public Land Mobile Network (PLMN). It is a

very supportive tool through which we can actually see the characteristic

of a particular base station under different circumstances including its

antenna, power, height and other parameters.

The project teaches us the technical concepts of a cellular network and

also provides us the understanding of terms such as co channel

interference, adjacent channel interference and composite interference.

Also we came to know how an antenna will behave in different situationsand how its pattern gets affected by the environment

1.1 Purpose

The purpose of the project is to understand the concepts of the cellular

network deeply and to learn how to tackle with the different problems

which a Base station Engineer face while installing a base station and also

what all things should be kept in mind before performing such action. As

the main aim of a Base station Engineer is to work for his desired task

efficiently and perform all the actions involved in it considering the

economic as well as the technical aspects, moreover network should

satisfy the quality of service (QoS).

1.2 Scope

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The Scope of this project includes the entire technical requirement for the

network which we can use efficiently. It provides the. Also this project

enables an engineer to create a network using all the requirements given.

It comprises of planning, designing, simulating and analysing the designed

cellular network

1.3 Report Organisation

The main aim of this project is to achieve a good coverage in a particular

area with the best possible way including the cost and maintenance of the

network. This Report presented is organised in three different sections

which are:

Network configuration including Base Station Sites.

Antenna selection criterion and assigning frequency.

Good Coverage with handling traffic easily.

2 NETWORK PLANNING APPROACH

This part of the project may be treated as the main part as planning a

network means to create the back bone of a human. If the back bone isweak then the whole system will suffer, causing the network to degrade its

performance which is not acceptable. As it has been said again and again

that for a cellular network two things are the most vital elements are

Coverage and traffic. If these two things are good enough to achieve

desired GoS then the task is accomplished. Thus the approach towards the

designing of the project should be firm and fixed in order to achieve the

task successfully.

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1.4 General Requirements:

The first thing which comes in mind before planning a network is “How to

build a cellular mobile telecommunication network for a given area

effectively and efficiently?” The answer to this will be, use all the

resources efficiently and for this the basic requirements of our project

include the antenna selection, area to covered, base station parameters

such as power, height, cell radius and frequency.

System Parameters used while proceeding with the project are given as

follows:

Adjacent channel selectivity 20 dBAcceptable C/I 12 dBBit Error Ratio 3 %Band centre frequency:

GSM 900

DCS 1800 A

DCS 1800 B

925MHz

1795 MHz

1990MHzEnvironment Standard

Attenuation

40 dB

Attenuation standard deviation 6 dBMinimum Tx output power 5 WattsMaximum Tx output power 45 Watts

The specification for the GSM-900 mobile terminal specifications weregiven as follows:

Maximum RF power 0.8 Watt

sReceiver noise figure 8 dBAntenna height (outdoor0 1.5 mAntenna nominal gain 0 dBd

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The cellular network is to be analysed under different environment and

each environment has its own affect on the signal level and are taken into

account before any conclusion. Thus the mobile environment

specifications are as follows under different conditions:

A) Pedestrian (CLASS 3)

Human body attenuation 3 dBPenetration attenuation 0 dBAverage speed 5 Km/h

r

B) In vehicle – Handheld (CLASS 2)

Human body attenuation 3 dBPenetration attenuation 3 dBAverage speed 110 Km/h

r

C) Building – Handheld (CLASS 1)

Human body attenuation 3 dBPenetration attenuation 12 dBAverage speed 2.5 Km/h

r

Coverage Area to be considered:

In this project we are asked to provide a good coverage area with

minimum interference and the area given was shown in the figure below

which is named as area 3 and 4:

Latitudes: 33 00’00” N Longitudes:93 20’00” W

32 50’50” N 93 40’00” W

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The geographical area shown above is the area in which the cellular

network to be designed and the topography and morphology for the area

is shown in the figure below, also it can be seen that is mostly forest area

and a very small portion of the area is urban where the traffic intensity will

be high.

Topography:

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Morphology:

2.2 Choice of Cell Radius:

For the prediction of the base station coverage under the different terrain

conditions we must define the cell radius of that base station and this

thing can be done by considering about the threshold level of the mobile

receiver. In general the threshold level is 102dBm for the mobile means

that the signal level above threshold is not acceptable, but if the terrain

conditions are taken into account then the signal level will vary and it will

not create a perfect circle so as to predict cell radius, thus in the project

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the cell radius is taken as 3km uniformly for each base station and thus

forming a grid pattern of 3 sectors which makes easy to place base station

in the given area. In other words cell radius can be defined as, measuring

the signal level from base station and noting the minimum distance point

away from base station which gives us the acceptable signal level that will

be the cell radius for that base station.

2.3 Antenna Selection Criteria:

This is the most important part of the project as coverage area of a

particular base station depends on the antenna which is installed and if

the antenna is not selected correctly then the whole system will suffer and

the system cost may also increase. Thus the selection of antenna should

be done in such a way that it is well suited for a given area and provides

sufficient coverage with large gain also.

Moreover in this project each base station sectoring is done and 3 sectors

for each base station is present, so the antenna should be directional not

Omni directional because if Omni directional antenna are chosen then it

will cause interference in its neighbouring sectors as sectoring is done so

in each sector the frequency will b different and the frequency reuse

concept cannot be achieved. All in all we can say that when sectoring is

done use of directional antenna with high gain is worth full as Omni

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directional antennas are mostly used in rural areas where the traffic

intensity is very less. For designing a cellular system there are several

things which should be kept in mind which area as described below-

Coverage

The first and foremost thing which be kept in mind that where the

antenna is to be placed and how much area it has to cover. Thus an

antenna which can cover large enough area to with all the other

parameters unaffected described below should be chosen and this

thing can be done by analysing the terrain data of that area as the

coverage area of an antenna largely depend on the place where it is

situated.

Interference

After the coverage area is achieved then interference level is to be

checked and if the interference is high then it has to be minimised in

order to provide good service, while minimising the interference

level coverage area must be looked out whether it is affected or not.

The best way to achieve this is to allot frequency to each sector of a

base station properly moreover the antenna specification such as

antenna height, power and tilting should be adjusted so far to

minimise interference

Traffic carrying capacity

The antenna selected should also carry the traffic in that area

effectively and the traffic is distributed according to morphology.

Overall the system can handle traffic easily with less blocking

probability and a good GoS which is 2% in this project.

Gain

Gain of the antenna is directly related to its directivity, the more the

gain of an antenna more directional it will be. While sectoring is

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done the antenna should be good enough directional with high gain

so as to provide strongest signal for its sector. And in case if the

antenna is to be tilted to minimise the interference it can be done as

tilting is done only to high gain direction antenna because tilting an

Omni directional antenna is of no use.

Front to back ratio

Front to back ratio of an antenna can be measured by its radiation

pattern and this ratio should be high enough so that it does not

cause interference with other sectors. In other words it is the ratio of

power gain between the front and the rear of a directional antenna.

Null fill

Null is the area present in between the side lobes which means the

area where signal level is nearly equal to zero. These null may be in

order of 30 or more dB which is less than one thousand of the total

energy. Null fill is done to prevent the signal overshooting the

nearest part of the intended coverage area for the antennas located

on mountains or tall towers.

Prone to atmospheric conditions

Antenna structure should be strong enough to handle wind pressure,

rain, storms etc, thus the signal level should not be so much affected

that the system tends to fail.

Cost

Although the base station antenna contribute very less part of the

overall cost of the system, this thing should be kept in mind as in

case of failure the system engineer should have a spare antenna for

its replacement. As we know in a communication system each of its

part has its own importance on the system performance and also the

total cost.

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There are two ways by which the teletraffic can be carried out easily i.e.

installing another base station near a pre installed site working on

different frequency or to increase the number of traffic channels.

2.5 Grade of Service and Blocking Probability:

For a cellular system the grade of service should be good enough so that

the customers are well satisfied by the service. The grade of service

depends on the call quality which includes voice quality, call drop etc. In

other words the amount of traffic not handled by the network helps to

determine the quality of service. Mathematically it is the ratio of lost traffic

to the offered traffic.

GoS = A-A0/A

Where,

A-actual traffic

A-A0-lost traffic

The blocking probability is the probability of a call not carried out when the

system is busy or the traffic channels are all equipped. This happens due

to traffic overload or lack of traffic channels. When the number of traffic

channels is all busy then the new call originated will be blocked.

3 NETWORK SOLUTION DESCRIPTION

For a cellular network to be designed the main objective of a BTS engineer

is:

To obtain adequate coverage over the entire service area to

ensure that high quality services and data services with less

error rates can be offered to the users.

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To offer the subscriber traffic network capacity with

sufficiently low blocking and call dropping rate.

To enable an economical network implementation when the

service is established and a controlled network expansion

during the lifecycle of the network.

For the network operator good network planning is:

Less amount of money utilized for the infrastructure.

More pleased customers (good service quality).

Less need for adjustments.

For an operator network optimization is:

Better return for investment.

Less need for costly hardware updates.

Less need for new sites (which are very expensive).

3.1 Network Configuration:

A telecommunication network consists of a base station, antenna, mobile

users, MSC’s, PSTN and microwave links connecting the mobile users with

the stations. The base station in this project which forms a cellular network

are placed as shown in the figure below and the table shows their exact

positions:

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Base

Station

Position according to

morphology

Latitude Longitude

BTS001 Deciduous Forest 32°58'43.2

"N

93°38'20.5"

WBTS002 Mixed Forest 32°58'58.1

"N

93°34'39.2"

WBTS003 Deciduous Forest 32°51'34.6

"N

93°35'09.5"


"N

93°38'24.9"

WBTS005 Grasslands 32°58'38.0

"N

93°31'02.1"


"N

93°34'18.7"

WBTS007 Evergreen Forest 32°54'11.1

"N

93°30'44.0"


"N

93°32'21.7"

WBTS009 Deciduous Forest 32°51'04.5 93°38'37.9"

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"N WBTS0010 Grasslands 32°53'30.7

"N

93°38'38.1"

W

BTS0011 Mixed Forest 32°56'24.4"N

93°35'43.2"W

BTS0012 Deciduous Forest 32°51'18.3

"N

93°25'16.8"


"N

93°29'00.7"


"N

93°27'23.2"


"N

93°27'04.1"


"N

93°29'06.7"


"N

93°32'23.2"


"N

93°20'43.3"


"N

93°20'58.7"


"N

93°24'03.3"


"N

93°23'43.4"


"N

93°25'44.0"


"N

93°21'21.8"


"N

93°21'30.3"

W

1.4.1Frequency management

Frequency management is the most important concept to be followed

specifically in order to create a system which has minimum interference.

Each sector of a cell has allotted a different frequency so as to avoid any

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co channel interference. The same frequency is used at the frequency

reuse distance so that they will not interfere. The spacing between the

frequencies should also be proper as well spaced frequency will not cause

adjacent channel interference.

In this project each base station is divided into 3 sectors spaced at 0°,

120° and 240° the spacing done shown in the figure below-

0o

240o 120o

Sector A

Sector BSector C

1.4.2Cell clustering

The figure below shows how the frequency in each sector is assigned for a

3 cell cluster layout and the same frequency is reused by keeping in mind

the frequency reuse distance.

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1

23

1A

2A3A

1B

2B3B

1C

2C3C1

23

1A

2A3A

1B

2B3B

1C

2C3C

1

23

1A

2A3A

1B

2B3B

1C

2C3C

1

23

1A

2A3A

1B

2B3B

1C

2C3C

1.4.3RF channel numbering

Table 2.3 shows the RF channels numbering for cellular cluster size of N = 3

1A

1

GSM-900 uses 890–915 MHz to send information from the mobile station

the base station (uplink) and 935–960 MHz for the reverse direction

(downlink), providing 124 RF channels (channel numbers 1 to 124) spaced

at 200 kHz. Duplex spacing of 45 MHz is used.

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1.5 Base Station Site Configuration

1.5.1 Antenna configuration

This project is designed by selecting the antenna model 7146-38 which is

highly directional with a gain of 14dBd. Although it has many side lobes

which is alright as it does not create any null. The elevation beamwidth is

7.0 which is very small and hence effective in providing a good coverage

area. Also this antenna is well suitable for the 120° sectoring pattern cell.

As this antenna is highly directional, thus giving excellent coverage.

The reason behind the selection of this antenna is that its beamwidth isnot too narrow or too wide as it has to be directional because sectoring is

done and in case to reduce interference if tilting is needed we can do

easily because tilting an antenna whose beamwidth is not narrow will not

make any difference in the coverage and interference. Also at last the

coverage achieved by this antenna under the frequency range is the best

and that is why the antenna model 7146-38 is the best and thus chosen.

The figure below shows the antenna specification with azimuth andelevation beamwidth

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f 1 f 3f 2 f 124 f 1’ f 3’f 2’ f 124’f 0

Lower Band (25 MHz)

890 – 915 MHz

Upper Band (25 MHz)

935 – 960 MHz

Centre

Gap

45 MHz

200

kHz




Telecommunications

3.2.2Coverage Area

After configuring the cellular network with installing base station sites and

allocating frequency to each sector and adjusting power level and height

of the antenna the coverage area we found was fair enough as more than

85% of the area was under the signal level of -85dBm. This is achieved by

simulating the base station with the parameters are attached at last in the

appendix part and checking the composite forward, performed on the

forward link which means the RBS are transmitting and the mobile are

receiving. The coverage achieved is shown in the figure-

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When the legend is set to -95dBm and we see that 99% of the area is

under the coverage area where the signal strength is more than-95dBm

which is no way close to the threshold level -102dBm. Even if the 5dB fademargin is taken into account then the minimum signal level will be -97dBm

and in this area is seen that at -97dbm the signal strength or the coverage

is 100% which is a sign of a good cellular network. The screenshot of the

signal strength of -95 dBm and -97dBm is shown on next page. In brief the

coverage percentage is:

Signal Level Coverage

-85dBm- 86%

-95dBm 99%

-97dBm 100%

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1.6 Resolving Interference Issues

As long as the frequency channels are assigned correctly the interference

will be very less because the main cause of interference is the wrong

allotment of frequency to the network. Sometimes the power level of the

base station may cause interference even if the frequency is assigned

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Adjacent channel interference caused when the frequency spacing is not done properly, there

should be enough spacing between the two frequencies so as to avoid adjacent channel

interference. In the project sectoring is done and if we look up the frequency table the

frequency assigned to each sector is widely spaced and there is no chance of them to get

interfere and thus there is no adjacent channel interference is seen in the project. Its main

reason is poor frequency control.

1.6.3Composite interference

The software shows the composite interference in the form of C/I ratio.

Basically composite interference is the mixture of all the interference

including adjacent and co channel interference. In this project the

acceptable C/I is set to 12dB which means if the C/I ratio drops below 12dB

then it is not acceptable because this will drop when there is more

interference as compared to the main signal

The other reasons for the composite interference may be include

environmental interference, terrain, human body attenuation, penetration

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attenuation etc. Thus we conclude that the more the C/I ratio is the better

the signal level is.

1.7 Teletraffic Handling Capacity Analysis

In this project the traffic resolving problem was the major part as after

achieving coverage traffic needs to be handled. At first most of the base

station were facing difficulties in controlling traffic for their area. The best

way to control traffic is to shuffle base stations according to traffic and

then minimising the traffic problem. While shuffling the base station

coverage area was affected and it became the vital task to maintain the

coverage and controlling the traffic simultaneously.

After trying really hard on the base station I end up with 24 base station

for the whole area with 6 of the base station in need of an extra

transceiver as the traffic for one or the other sector was high and just two

transceiver could not able to handle the traffic, thus there was a need to

add another transceiver. Another way is to add one more base station to

the place where the traffic is high but if adding one more transceiver

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solves the problem then adding a base station would be wastage of lot of

money as installing another base station is costly in comparison to adding

a transceiver.

In the cell planner software we need to create the traffic for a particular

area and for my area the total traffic was 480 Erlang.. Traffic can be

distributed uniformly or according to morphology database. When the

traffic is set uniform it will create the bins for the work area and assign

same traffic to each bin regardless of the location. Also when the traffic is

distributed according to the morphology database, then the bins created

for the work area have traffic in non uniform manner. The traffic is defined

according to the morphology database which is fed into the system.

In this project the traffic is assigned according to the Erlang B table and an

example of how the traffic bins look like after creating it and its can be

predicted that the bins which are more dark that location has high traffic

comparing to the bins which are light.

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1.8 Best server

In Cell Plan, Best Server is the sector, or site, which supplies the higher

acceptable signal level (forward) for the subscriber of the selected class of

service, receiving also acceptable reverse signal. Besides, for a sector

considered best server, the terminal must not be requiring handoff, and in

case it has required, its request was not attended

Good communication quality in links, forward and reverses can be assured

in the points with best server identification.

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1.9 Bit Error Rate

In the field of communication the quality criterion is expressed in terms of

Bit error rate. BER can be defined as the number of errors that occur in a

string of a stated number of bits. Mathematically it can be stated as:

BER = No. of error/Total bits

The BER depends on the transmission medium, as how much noise is

present which attenuates the signal and causes the transmitted bits to lost

and more than 94% of the transmission was done with a BER of less than

1%.

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1.10 Interconnection of Base Station Sites to Switching Centre

After installing the base stations and achieving the desired coverage area

and controlling the traffic the next final step to create a cellular network is

to install a MSC through which all the base stations are connected via

microwave links with the microwave antennas. The main function of MSC is that

to processes the call and connects the cell site radio link to the PSTN.

The MSC should be installed to place which is the top most point so as to

get a direct link from the microwave antenna to the base station. The

network formed looks like as shown in the figure. There should not be

more than 10Km microwave link because that much long distance link

might fail. So in order to connect one single MSC to all the station not all

the stations are directly connected, some of them are connected to

another base station which acts as the repeater for the following base

station.

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The microwave antenna used for the setting up the MSC is shown below:

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1.10.1 Backhaul network

Backhaul transmission in GSM networks includes transmission lines

between GSM core network and BSS network elements, the BSC and BTS.

A typical GSM backhaul network is shown in the figure below:

Each radio cell site in a network requires connectivity to a mobile

switching centre (MSC), which can be implemented by metallic cable, fibre

cables, or microwave radio links. The technology, capacity and topology of

the network connecting cell sites to MSC will depend on many factors,

including technical and economical. The task for this part of the project is

to choose a location for the MSC and establish a fixed network based on

technical feasibility and traffic requirements.

1.10.2 Path profile

After setting up the MSC and creating microwave links between the

stations we need to check the path profile link and the cell planner gives

the path profile shown the Fresnel zone and for a perfect path profile the

line of sight should be clear from any obstacles and the first Fresnel zone

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should also be clear. The two example of the path profile shown by the

software is shown below.

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3 DISCUSSION AND CRITIQUE

1.11 Achievements

This project helped me to understand the concept of cellular network

deeply and taught me how to deal with the problems faced by a system

engineer such as co-channel interference, adjacent interference etc. It alsoprovides me the knowledge of each and every work which a network

engineer will have to do while designing the network. This is project is

basically what I really want to do in future.

As the given objective is to design a cellular network for the given

geographical area providing a good coverage area with minimum

interference and also carry the traffic for that area maintaining the qualityof service.

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The overall results achieved in this project are:

Coverage area 86% at signal level of -85dBm and 99% at signal level

of -95dBm

Co-channel interference was found to be negligible

Adjacent channel interference was zero percent

More than 99% was carried out easily

GoS achieved was 0.5%

This project is accomplished after installing 24 base stations withmaximum antenna height of 50m and power 50Watts and adding 6 extra

transceivers to few of the base stations in order to carry the simulated

traffic easily and maintaining the grade of service.

1.12 Difficulties Encountered

Major difficulties faced were:

Minimising the interference level as frequency reuse concept was

followed. So the frequency reuse distance is be maintained which

was a challenge.

The geographical area was uneven so in order to provide coverage

was a big ask and this was achieved by playing with the base station

parameters such as antenna pattern, height and power.

Traffic was the major concern in this project as there were many

areas where the traffic intensity was very high and only single base

station equipped with two transceivers in each sector was not

enough to handle the traffic. This problem was overcome by adding

one more base station or increasing the no. of transceiver.

Achieving a clear line of sight while creating the microwave links and

also the first Fresnel zone should be clear. This was easily carried

out by increasing the microwave antenna height or by creating a link

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from MSC to a base station via another base station acting as a

repeater.

1.13 Points learned and Future Work

This project helped me developing the skills needed to design a

cellular network for a real geographical area and taught me to deal

with various difficulties which a system engineer might face while

doing it practically.

It provides me to understand and work on the software needed forthe designing of the cellular network called Cell Planner very well.

Through this software I learned the concept of terms like frequency

reuse, co-channel interference, handover, BER etc

Moreover it helped me to deal with the traffic in a particular area

and how to allocate each base station so that the traffic in whole

area is carried out efficiently.

Through this software I came to know about the setting up of MSCand how the microwave links can be established.

4 APPENDICES

1.13.1 CelPlanner Output

1.13.2 Traffic Simulation Result

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5 REFERENCES

[1]Parsons, J. D., “The Mobile Radio Channel”, Second Edition, John Wiley

& Sons Ltd, 2000

[2]Garg, V. K., Wilkes, J E, "Wireless and Personal Communications

Systems", Prentice-Hall

[3]Garg, V. K., Wilkes, J E, "Principles and Applications of GSM, 1/e",

Prentice-Hall

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[4]Lee, William C. Y., "Mobile Cellular Telecommunications: Analog and

Digital Systems", second Edition, McGraw-Hill, Inc.

[5]CelPlanner User Guide, CelPlanner Manuals, CelPlan Technologies, Inc.

[6] CelPlan Technologies, Inc. website www.celplan.com

[7]Project Specification

http://www.celplan.com/

http://www.celplan.com/

Documents

Tde Final Report