Antenna System in Cellular Mobile Communication

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Department of Electrical & Electronics Engineering

School of Engineering

KATHMANDU UNIVERSITY

ANTENNA SYSTEM IN CELLULAR MOBILE

COMMUNICATION

Project report submitted in partial fulfillmentof the requirement for the degree of

Bachelor of Engineering(Electrical & Electronics Engineering)

By:

SANJAYA GURUNG

NILAB PRADHAN

July 2004


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ANTENNA SYSTEM IN CELLULAR MOBILE

COMMUNICATION

Project report submitted in partial fulfillment

of the requirements for the degree ofBachelor of Engineering

(Electrical & Electronics Engineering)

Department of Electrical & Electronics Engineering

School of Engineering

KATHMANDU UNIVERSITY

July 2004

Approved by:

1. Project Supervisors

______________________ ________________________ _____________

(Signature) (Name) (Date)

______________________ ________________________ _____________


2. Head/In-Charge of the Department _______________________ ________________________ _____________



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Abstract

Antenna System in Cellular Mobile Communication is the project which reveals

the general antenna system for mobile communication in Nepal in front of all theindividuals. Those people who are working in antenna system for Cellular Mobile

Communication (CMC) or who are directly and indirectly relevant to this field will takemuch benefit from our project.

In this project report, general description of various types of antenna used in CMC

system are described. Antenna plays an indispensable role in CMC system. The general block diagram of cellular mobile communication system is also given. Various

calculations regarding the channel capacity, antenna gain, transmitted power versus

distance etc. are also included in this report. You can also know how to design theantenna viz; omni-directional and sectorized antenna by going through this report. As all

the communication system undergoes through various types of degradations, noise and

interferences, it is necessary to have a general concept about these factors. These are alsoincluded. The various schemes for the significant improvement in the quality andquantity aspects of reception of mobile is mentioned here in this report. Here, in this

report, an experimental observation for the measurement of intensity of received power

of MS is also affixed. For the various calculations, the C-programming language codesare also included in this report.


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Acknowledgement:

During our project Antenna System in Cellular Mobile Communication, we faced

many problems and without the co-operation of the people mentioned below, we wouldnot have completed this project. So, we would like to pour our great gratitude towardsthose who gave their hands in our hands during this year. We know that two heads are

better than one and sure and certainly the involvement of several minds and hands in any

project can lead it to much more culmination than only one hand can. So in order theproject to be successful, each and every project should have proper design focusing the

needs of the customers. Those who assisted us in this semester, we admired them a lot for

their friendly behaviour and their precious ideas and views for our project. First of all,

wed like to express our sincere gratitude to our project advisors Mr.Bhupendra BimalChhetri for his great support to our project and the brilliant views and ideas that he gave

for our project and to Mr.Anand Raj Khanal for his kind dealing and guidances which

helped us a lot in choosing and following the right track.We would like to give special thanks to our teacher Mr. Anand Sharma for helping

us in solving our various kinds of problems we faced during our project.

Also we would like to express our gratitude towards Mr. Praveen Bajracharya(Sr.engineer in Base Station section of NTC) for his assistance in understanding the

antenna system in mobile communication and GSM technology of Nepal. We would

also like to thank our senior brother Mr. Sixit Bhatta (engineer in BTS section in UTL)

for his kind and precious assistance he showered on us in understanding the CDMAtechnology in communication system and general antenna system for CDMA telephone

system that is currently being installed in Kathmandu. We also like to thank our senior

brother Mr. Summit Raj Tuladhar for his kind help and co-operation. Last but not the

least, we would like to pour our special gratitude upon our senior brother Mr. Dil KumarGurung for assisting us in different critical situations during our projects and especially in

Auto CAD drawing during our project report preparation.


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2. Some Important Definitions

1. AntennaThe simple dictionary meaning of an antenna is that it is usually metallic device (as

a rod or wire) for radiating or receiving radio waves. The IEEE Standard Definitions ofTerms for Antennas (IEEE Std. 145-1983) defines the antenna as a means for radiatingor receiving radio waves. In other words, the antenna is the transitional structure

between free space and a guiding device. The antenna is also referred to as aerial.

Combining all these definitions, we can extract an excellent definition of antenna as a

metallic (usually) device used for radiating or receiving electromagnetic waves which

acts as the transition region between free space and guiding structure like a transmission

line in order to communicate even in a longer distance.

1.1 Isotropic antenna An isotropic antenna is a hypothetical lossless antenna having equal radiation in

all directions. It radiates its power equally in all the direction in space co-ordinatesystem.

1.2 Directional antenna

Directional antenna receives or radiates electromagnetic waves moreeffectively in one particular direction than in other directions.

1.3 Omni directional antennaThis type of antenna radiates or receives electromagnetic waves in all direction

except in azimuth plane. This type of antenna is non-directional in azimuth plane anddirectional in any orthogonal plane.

2. DirectivityDirectivity of the antenna describes how well it concentrates, or bunches, radio

waves in a given direction. Mathematically, directivity can be defined as the ratio ofmaximum radiation intensity of an antenna to the radiation intensity of the isotropic

antenna.

3. Radiation patternIt is the mathematical function or graphical representation of radiation properties

of the antenna as a function of space co-ordinate. Radiation properties include radiationintensity, power flux density, field strength, directivity phase or polarization.

3.1 Power patternIt is the graphical diagram of received power at a constant radius.


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3.2 Field patternIt is a graph of spatial variation of the electric or magnetic field along a constant

radius.

4.1 Line Of Sight signal (LOS)LOS signal is the signal traveling directly following the straight path from

transmitting antenna to the receiving antenna without any obstacle in its path. LOS signal

is also referred to as direct signalordirect wave.

4.2 Out Of Sight signal (OOS)The signals other than the LOS signal are referred to as OOS signals. These

signals reach to the receiving antenna from transmitting antenna not directly but

following different paths. Other waves are ground reflected wave, sky wave andsurfacewave. The ground reflected waves are highly affected by fading due to the presence of

various scatterers. The sky waves will not return to the earth since the frequencies ofthese waves are greater than that of the critical frequency. The surface waves are always

diffracted around the surface of the earth and are highly attenuated with distance.

5. Reflection

It is the change in the direction of a signal without penetrating the object. It occurs

when the path of a signal is obstructed.

6. Scattering

Scattering can be defined as the deflection of a wave or beam of particles caused by

the collisions with other particles. It occurs when the dimensions of the particles arecomparable to the wavelength of the signal.

7. Interference

A process in which two or more waves are super-imposed in such a way that theyproduce higher peaks, lower troughs, or a new wave pattern. In other word, it is the effect

when the tow or more waves overlap or intersect with each other and the amplitude of the

resulting wave depends upon the frequencies and phases of the individual waves.

7.1 Co-channel Interference

The interference between the signals form the co-channel cells is called the co-channelinterference.

7.2 Adjacent channel InterferenceThe interference between the signals from the adjacent channel cell is called the

adjacent channel interference.


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8. CellCell, in mobile communication system, can be defined as the range area covered by

one of the transmitters in a mobile telephone system that automatically switches a

traveling user between short-range base stations.9. Handoff / Hand Over

It is the process of transferring of mobile station from one channel or base station

to another base station. When a mobile station (subscriber carrying mobile) moves fromone cell to the different cell while a conversation is in progress, the MSC automatically

transfers the call to a new channel belonging to the new base station. This process is

known as handoff.

10. Channel capacity It is the maximum number of subscribers in a channel sharing the same frequency

within the cell.

11. Grade Of Service (GOS) It is the measure of ability of a user to access a trunked system during the busiesthour (peak calling time). It is a measure of congestion which is specified as the

probability of a call being blocked or the probability of a call being delayed beyond a

certain amount of time.

12. Trunking efficiency

It is the measure of the number of users which can be offered a particular GOS

(Grade Of Service) with a particular configuration of fixed channels.

13. Blocked call

The call which can not be completed at the time of request, due to congestionespecially in peak calling time is called blocked call. It is also refereed to as a lost call.

14. Traffic intensity

It is the measure of channel time utilization. It is also known as the average channeloccupancy measured in Erlang.

15. Cell splittingCell splitting is the process of sub-dividing a congested cell into smaller cells, each

with its own base station and reduction in antenna height and transmitter power in order

to get the improvement on the cell coverage area and the capacity in cellular system.

16. SectorizationThe technique of replacing single omni directional antenna by several directional

antennas for decreasing co-channel interference as well as adjacent channel interferenceand thus increasing the system performance is called sectoring


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TABLE OF CONTENTS

Contents Page No.

Chapter 1: Introduction ................................................................................1Chapter 2: Overview of the Report................................................................2

Chapter 3: Block Diagram of Antenna System

for telephone and mobile communication ...3Chapter4: Classification of antenna ...4

4.1 General Classification 4

4.2 Antennas used in cellular mobile communication system .6

4.3 Types of Mobile antenna Vs cell site 11Chapter 5: Design of Antenna...12

5.1 Design of omni-directional antenna system ..125.2 Design of directional antenna system ...14

Chapter6: Cell site antenna height ....17

6.1 Visualization of the effective antenna height .18

6.2 Lowering the antenna height ..18Chapter 7: Antenna pattern in free space and in mobile environment ......20

7.1 Theoretical analysis ...21

7.2 Antenna pattern ..23Chapter 8: Performance of mobile communication system ..24

8.1 Scheme for significant improvement of mobile in quality aspect ..24

8.2 Scheme for significant improvement of mobile in reliability aspect ..25

8.3 Scheme for significant improvement of mobile in quality aspect ..258.4 Scheme for significant improvement

of mobile in quality as quantity aspect ...26

Chapter 9:Some Calculations ...279.1 Capacity of a system ...27

9.2 Channel of a cell .....28

9.3 Loss between Tx and Rx in mobile communication ..28

9.4 Friis transmission formula ..299.5 Received Power versus different parameters ..29

Chapter 10:Simulation using Matlab 30

Chapter 11:Analysis of received power intensity of mobile station .32

Chapter 12:Antenna Layout ..33Chapter 13:Informations obtained from NTC about CMC system of Nepal ....35

Chapter 14:Calculations with the use of C-Programming language .36Chapter 15: Gantt Chart 40

Chapter 16: Conclusion 41

Reference ..42


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1. Introduction

A general mobile system and designing of antenna for mobile communication are

the gist in the report of our project titled Antenna System in Cellular MobileCommunication. In order to know the antenna system and designing, first of all, we

should know well the behaviour of antenna. An antenna is a a metallic (usually) deviceused for radiating or receiving electromagnetic waves which acts as the transition region

between free space and guiding structure like a transmission line in order to communicate

even in a longer distance. Without antenna communication is not possible in longerdistance. Here the longer distance means the distance which cant be covered by the

length of the transmission channel (cable). It is not practically realizable to deploy the

cable as the communication channel for the longer distance. For example, forcommunication between USA and Nepal (air distance = about 12,000 km), it is not

possible to assign the cable or any physical transmission channel of length about 12,000

km.An antenna consists of two parts; Transmitter and Receiver. The antenna at the

time of transmitting electromagnetic waves is called transmitting antenna and the same

antenna in the time of receiving electromagnetic waves is called receiving antenna. A

transmitting antenna takes waves that are generated by electrical signals inside a devicesuch as a radio and converts them to waves that can travel in an open space. The waves

that travel in an open space are known as free-space waves. The receiving antenna takes

free-space waves and convert them into guided waves (electrical signals) that arecompatible for cables or wires. So, for the communication between USA and Nepal (say

a call from Nepal to USA), the transmitting antenna located in Nepal transmits the

electromagnetic waves which are received by the receiving antenna located in USA and

hence the communication between them is possible.


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2. Overview of the reportAntenna pattern, antenna tilting, gain, antenna tilting, and antenna height all affect the

cellular system design. The antenna pattern can be omni directional, directional, or any

shape in both the vertical and the horizon planes. Antenna gain compensates for thetransmitted power. Different antenna patterns and antenna gains at the cell site and at the

mobile units would affect the system performance and so must be considered in thesystem design. Here we have considered about cell splitting, Sectorization, umbrella

pattern of antenna system, and different types of mobile antenna for reducing

interference.

Here we have also given a short overview of the design of the directional andomni directional antenna for mobile communication.

The antenna patterns seen in cellular systems are different from the patterns seen

in free space. If a mobile unit travels around a cell site in areas with many buildings, theomni directional antenna will not duplicate the omni pattern. In addition, if the front-to-

back ratio of a directional antenna is found to be 20 dB in free space, it will be only 10

dB at the cell site.Antenna tilting can reduce the interference to the neighboring cells and enhance the weak

spots in the cell. Also the height of the cell-site antenna can affect the area and shape of

the coverage in the system.


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3. Block Diagram of

Antenna System for telephone and mobile communication

Electrical signals

produced by dialing a

number generate guided

waves which travel

through cables or wires

The uplink radio waves

or free space waves arereceived by the satellite

from the satellite dish

antenna kept on Earth

The guided waves

are taken and

converted into spacewaves by the

transmitting antenna

Dialing a number ofany internationalcall from one place

( Tx )

Free space waves are

received andconverted into guided

waves with the down

link frequency by the

receiving antenna

Call received in

another place

( Rx )


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4. Classification of antenna4.1 General classification Antenna can be classified on various bases such as its geometrical shape and size,

its directivity, its radiation pattern, its application and its frequency and wavelength.Antennas are so classified in order to have the proper selection of different type ofantennas for various applications to meet the requirement. Here are some brief details

about different types of antenna.

Antenna can be classified on the basis of:

i) Geometrical shape & size

ii) Directivity

iii) Radiation patterniv) Application

i) Geometrical shape & sizeWe can classify antenna on the basis of its physical shape & size or its

orientation. There are various kinds of antennas falling in this category of

classification.a) Linear wire antennas

- Half-wavelength dipole (mono-pole) antenna, dipole antenna

b) Aperture antennas

c) Array antennasd) Microstrip antennas

e) Reflector antennas

f) Lens antennas

ii) Directivity Antenna can also be classified on the basis of their effective direction, i.e. the

direction in which the antenna can show its effect (radiation or reception). There are

two types of antennas available falling in this category:

a) Directional antennab) Omni directional antenna

a) Directional antennaThis type of antenna receives or radiates electromagnetic waves more effectively

in one particular direction than in other directions.

b) Omni directional antenna This type of antenna radiates or receives electromagnetic waves in all direction

except in azimuth plane. This type of antenna is non-directional in azimuth plane anddirectional in any orthogonal plane or elevated plane. That means this antenna does


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not point only in one direction or it has not the specific direction to radiate or receiveelectro-magnetic wave in any of orthogonal plane.

iii) Radiation patternBasically, there are three types of radiation pattern directional, omni

directionaland isotropicpattern. Among these, an isotropic antenna is a hypotheticallossless antenna having equal radiation in all directions.

iv) Application

On this basis, different antennas can be deployed into different application to

meet our requirement. That is we have to choose the best antenna for the specific

purpose. We can choose antennas for mobile communication, for FM & AM broadcasting, for television broadcasting, for satellite communication, RADAR

communication etc.


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4.2 Antennas used in cellular mobile communication system

1) Mobile antenna The requirement of mobile (motor vehicle mounted) antenna is an omni directional

antenna, which can be located as high as possible from the point of reception. Howeverthe physical limitation of antenna height on the vehicle restricts this requirement.

Generally the antenna should at least clear the top of the vehicle.

a. Roof mounted antennaThe antenna pattern of a roof mounted antenna is more or less uniformly

distributed around the mobile unit when measured at an antenna range in the 3 dB high

gain antenna shows a 3 dB gain over the quarter wave antenna. However the gain of theantenna used at the mobile unit must be limited to 3 dB because the cell site antenna is

rarely as high as the broadcasting antenna and out of site conditions often prevail. Themobile antenna with a gain of more than 3 dB can receive only a limited portion of totalmultipath signal in the elevation as measured under the out of site condition.

b. Glass mounted antennaThere are many kinds of glass-mounted antennas. Energy is coupled through the

glass: therefore there is no need to drill a hole. However, some energy is dissipated on

passage through the glass. The antenna gain range is 1 to 3 dB depending on theoperating frequency. The position of the glass-mounted antenna is always lower than that

of the roof-mounted antenna; generally there is a 3 dB difference between these two types

of antenna. Also glass-mounted antennas cannot be installed on the shaded glass found in

some motor vehicles because this type of glass has a high metal content.

c. Mobile high gain antennas

A high gain antenna used on a mobile unit has been studied. This type of high gainantenna should be distinguished from the directional antenna. In the directional antenna,

the antenna beam pattern is suppressed horizontally; in the high gain antenna, the pattern

is suppressed vertically. To apply either a directional antenna or high gain antenna forreception in a radio environment, we must know the origin of the signal. If we point the

directional antenna opposite to the transmitter site, we would in theory receive nothing.

In a mobile radio environment, the scattered signals arrived at mobile unit from

every direction with equal probability. That is why an omni directional antenna is used

the scattered signals also arrived from different elevation angles. Lee and Brandt usedtwo types of antenna, one /4 whip antenna with an elevation coverage of 39o and one of4 dB gain antenna (4 dB gain with respect to the gain of a dipole) with an elevationcoverage of 16

o, and measured the angle of signal arrival ion the sub urban Keyport-

Matawan area of new jersey. There are two type of test: a line of sight(LOS) condition

and an out of sight (OOS) condition. In Lee and Brandt's study the transmitter was


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located at an elevation of approximately of 100 m (300 ft) above sea level. The measuredarea were about 12 m (40 ft) above sea level and the path length about 3mi.The received

signal from the 4 dB gain antenna was 4 dB stronger than that from the whip antenna

under line of sight conditions. This is what we would expect. However, the receivedsignal from the 4 dB gain antenna was only about 2 dB stronger than that from the whip

antenna under OOS conditions.

This is surprising. The region for the latter observation is that the scattered signalsarriving under OOS conditions are spread over a wide elevation angle. A large portion of

the signal outside the elevation angle of 16o

cannot be received by high gain antenna we

may calculate the portion being received by the high gain antenna from the measuredbeam width (the beam width can be roughly obtained from the equation:

0

6.114

D

where,

D is the directivity

and o is beam-widthFor instance, suppose that a 4:1 gain (6 dBi) is expected from the high gain antenna, but

only 2.5:1 is received therefore, 63% of the signal is received by the 4 dB gain antenna

(i.e. 6 dBi) and 37% is felt in the region between 16o

and 39o

generally 2 to 3 db gainantenna (4 to 5 dBi) should be adequate for general use. An antenna gains higher than 2

to 3 dB don't serve the purpose of enhancing level. Moreover, measurements reveal that

the elevation angle for scattered signals received in urban areas is greater than that in suburban areas.

d. Horizontally oriented space diversity antenna

A two-branch space diversity receiver mounted on a motor vehicle has the advantage

of reducing fading and thus can operate at a lower reception level. We must consider the

following factor. The two antennas can be mounted either in line with or perpendicular tothe motion of the vehicle. Theoretical analysis and measured data indicate that the inline

arrangement of the two antennas produces fewer level crossings that is less fading that

the perpendicular arrangement does.

e. Vertically oriented space diversity antenna

The vertical separation between the two space diversity antennas can be determined fromthe correlation between their received signals. A set of measured data was obtained by

using two antennas vertically separated by 1.5 wavelengths.


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2) Microwave antenna

Microwave antenna locationSometimes the reception is poor after the microwave antenna has been mounted

on the antenna tower. A quick way to check the installation before making any other

changes is to move the microwave antenna around within a 2 to 4 ft radius of the

previous position and check the reception level. Surprisingly favorable results can be

obtained immediately because multipart cancellation is avoided as a result ofchanging reflected paths at the receiving antenna.

Also, at any fixed microwave antenna location, the received signal level over a 24-hr

time period varies.

Characteristics of microwave antennas:

Microwave antennas can afford to concentrate their radiated power in a narrow

beam because of the size of the antenna in comparison to the wavelength of the

operating frequency; thus. High antenna gain is obviously desirable. Some of themore significant characteristics are discussed in the following paragraphs.

Beamwidth:The greater the size of the antenna, the narrower the beamwith. Usually the

beamwidth is specified by a half-poer (3 dB) beamwidth and is less than 100 at higher

microwave frequenceies. The beamwidth sometimes can be less than 1.0 The

narrowbeam can reduce the chances of interference from adjacent sources or objects

such as adjacent antennas. However, a narrowbeam antenna requires a fair amount ofmechanical stability for the beam to be aimed at a particular direction.

Side lobes:The side lobes of an antenna pattern would be the potential source of interference

to other microwave paths or would reder the antenna vulnerable to receiveing

interferehce from other microwave paths.

Front-to back ratio: This is defined as the ratio of the maximum gain in the

forward direction to the maximum gain in the backward direction. The front-to-backratio is usually in the range of 20 to 30 dB because of the requirement for isolating or

protecting the main transmission beam from interference.

Repeater requirement:The front-to-back ratio is very critical in repeaters because the same signal

frequencies are used in both directions at one site. An improper design can cause a


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pung-pong ringing type of oscillation from allow front-to-back ratio or from poorisolation between the transmitting port and receiving port of the repeater.

Site-side coupling loss:The coupling loss, in decibels, should be designed to be high as a result of the

transmitting antenna carrying only the output signal and the receiving antenna

receiving only the

If the transmitting and receiving antennas are installed side by side, the typicaltransmitter outputs are usually 60 dB higher than the receiver, input level. Longer link

distance results in increased values. Therefore, the coupling losses must be high in

order to avoid internal system interference. The space separation between to avoidinternal system interference. The space separation between two antennas and the filter

characteristics in the receiver can be combined with a given antenna pattern toachieve the high coupling loss.

Back-to back coupling:

The back-to-back coupling loss also should be high (e.g., 60dB) between two

antennas. Two antennas are installed back to back, one transmitting and onereceiving. However, it is much easier to reach a high back-to-back coupling loss than

a side-to- side coupling loss.

Polarization and space diversity in microwave antennas

Polarization:To reduce adjacent channel interference, microwave relay systems can interleave

alternate radio-channel frequencies from a horizontal polarized wave to a verticalpolarized wave.

The same approach can be applied to the left-and right-handed circularly

polarized waves, but the beam widths of antennas for this loss is defined as the ratio

of the poor received in the desired polarization to the poor coupling into otherpolarization. The cross coupling required for one hop.

Space diversity:The two antennas separated vertically or horizontally can be used for a two-

branch space-diversity arrangement. In a space-diversity receiver, the requiredreception level is relatively low so that the transmitted power on the end of the linkcan be reduced. This is also an effective method for increasing the coupling loss

between the transmitting antenna and receiving antenna.


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Types of microwave-link antenna:

Two kinds of antenna are used for microwave links

1. A parabolic dish, used for short-haul systems. Antennas sizes range form 1.5 m

(5fg) to 3 m (10ft) in diameter.2. A horn-reflector antenna, to trap the energy outward from the focala. Good matchreturn loss 40-50 dB.

Installation of microwave antennas:

A microwave antenna cannot be installed at any arbitrary location. Selection of anoptimum position is very important. In many situations if we cannot move horizontally,

we can move vertically. In a microwave-link setup, there are two fixed effective antenna

heights, one at each end based on each reflection plane where the reflection point is

incident on it. The gain of the received signal also relates to the two effective antenna

heights if they are low. The antenna location can be move around to find the bestreception level. Sometimes it is worthwhile to take time to search for the location that

gives the best reception.

Types of antenna used in BS and MS in cellular mobile communication

In MS (Mobile Station)

Omni-directional (monopole antenna)

It is used due to its broadband characteristics and simple construction, monopole

antenna is used in the hand held unit (Mobile Station).A4

monopole is very popular in

mobile communication. Other alternatives of monopole antenna are loop antenna, micro-strip antenna, spiral antenna etc.

In BS (Base Station)Panel antenna

i) Omni-directional

ii) SectoralPanel antenna = dipole array inside it and is covered with radome

Frequency range of population --- 1420 to 1530 MHzSectoral antenna operates in polarization diversity


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4.3 Types of Mobile Antenna Vs cell site

Traffic congestion criteria

i) Congested traffic in some particular areasThe sectorized antennas must be installed in the tower. Generally the three

sectorization is the most popular one. The three sectorization means using three

separate antennas in 120o

We may direct each antenna to those directions where the

subscribers are located. We use these types of antennas in the towers of highlycongested city and where the omni-directional antenna cant accomplishes the need of

the very large traffic.

ii) Congested traffic in a particular areaIn this case, we use directional antenna which is directed only in a fixed

particular area. We use directional antenna instead of omni-directional antenna to

avoid waste of power of omni-directional antenna in undesired directions (areas).Generally the directional antenna is used in the towers of highway where there are

people (subscriber) residing only in a particular area.

iii) Equally distributed Traffic (subscribers) within a particular area

In this case, we use omni-directionalantenna. No need of sectorization in this

case. The power radiated by the omni-directional antenna is equally showered in all

direction within a particular region within the limit of its power. Generally the

omni-directional antennas are used in the towers of small city where there are few butequally distributed in all directions.


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5. Design of antenna5.1 Design of an omni directional antenna system

K = 7 cell pattern doesnt provide a sufficient frequency reuse distance separation

even when an ideal condition of flat terrain is assumed. The worst case is at the locationwhere the mobile unit would receive the weakest signal from its own cell site but stronginterference from all interfering cell sites.

Fig.(1) Illustration of 1st

tier co-channel cells for a cluster size of N = 7.

M

D-R

D-R

D

D

D+R

D+R

R


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In the worst case the mobile unit is at the cell boundary (point X), as shown in thefigure (1).the distances from all six co channel interfering sites are also shown in the

figure: two distances of D-R, two distances of D, and two distances of D + R. following

the mobile propagation rule of 40 dB/decade, we obtain C R-4

, I D-4

,Then the carrier to interference ratio is:

444

4

)(22)(2

RDDRD

R

I

C

444 )1(22)1(2

1

qqq----------------------------------------------------------- (1)

whereR

Dq = co-channel reuse factor.

We may use the shortest distance D-R for all six interferer as a worst case then the aboveequation can be written as

4

4

)(6

RD

R

I

C-------------------------------------------------------------------- (2)

here for K = 7, we have q = KR

D3 = 73 = 4.6

I

C= 17 dB from equation (1) and for the worst case from equation (2),

I

C= 14.47 dB

In reality because of the imperfect site location and the rolling nature of the terrain

configuration, the C/I received is always worse than 17 dB or could be 14 dB and lower.

Such an instance can easily occur in a heavy traffic situation. Therefore the system mustbe designed around C/I of worst case. In that case the co channel interference factor of q

= 4.6 is in-sufficient (i.e. reuse factor = K = 7)

Therefore in the omni-directional cell system, K = 9 or K =12 would be a correctchoice. Then the value of q is:

R

Dq = 3K

At K = 9, q = 5.196

At K = 12, q = 6.0

Substituting this value in equation (1) we obtainC/I = 84.5 = 19.25 dB ----------- for K = 9C/ I = 179.33 = 22.54 dB -------- for K = 12

Substituting this value in equation (2) we obtain

C/I = 51.67 = 17.133 dB -------- for K = 9

C/ I = 104.167 = 20.177 dB ---- for K = 12


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The K = 9 and K = 12 cell pattern are used when the traffic is light. Each cell covers an

adequate area with adequate numbers of channel to handle traffic. These patterns are not

valid for the case when there is a huge traffic.

5.2 Design of a directional antenna system

When the cell traffic begins to increase, we need to use the frequency spectrum

efficiently and avoid increasing the number of cells K in a 7-cell frequency reuse pattern.

When K increases the number of frequency channels assigned in a cell must becomesmaller (assuming a total allocated channel divided by K) and the efficiency of applying

the frequency reuse scheme decreases.

Instead of increasing the number K in a set of cells, let us keep K = 7 and introduce a

directional antenna arrangement. The co-channel interference can be reduced by using

directional antennas. This means that each cell is divided into 3 or 6 sectors and uses 3 or6 directional antennas at a base station. Each sector is assigned a set of frequencies

(channels). The interference between two co-channel cells decreases as shown below:

i) For K=7 (i.e. q = 4.6)

a) Three sector case D+0.7R

MS

D

Fig. 3-sector case for K = 7

The three-sector case is shown in fig. To illustrate the worst-case situation, two co-channel cells are shown in fig.. The mobile unit at position E will experience grater

interference in the lower shaded cell sector site. This is because the mobile receiver

receives the weakest signal from its own cell but fairly strong interference from the

4

3

4

7

5

5

4

3

2

2

6

1

2

5

1

3

1

6

6


23/50

interfering cell. In a three sector case, the interference is effective only in one directionbecause the front to back ratio of a cell site directional antenna is at least 10 dB or more

in a mobile radio environment. The worst-case co-channel interference in a directional

antenna sectors in which interference occurs may be calculated. Because of the use ofdirectional antennas, the number of principal interferers is reduced from 6 to 2. The worst

case of C/I occurs when the mobile unit is at position E, at which point the distance

between the mobile unit and the two interfering antennas is roughly D +2

R; however, C/I

can be calculated more precisely as follows. The value of C/I can be obtained by the

following expression (assuming that the worst case is at position E at which the distancefrom the two interferers are D + 0.7 and D).

C/I (worst case) =44

4

)7.0(

DRD

R=

44)7.0(

1 qq

Let, q = 4.6, then

C/I (worst case) = 285 = 24.5 dB ----------------- (1)

The C/I received by a mobile unit from the 120o

directional antennas sector system

expressed in equation (1) greatly exceeds 18 dB in a worst case equation (1) shows that

using directional antenna sectors can improve the signal to interference ratio. That isreusing the co-channel interference. However in reality the C/I could be 6 dB weaker

than in equation (1) in a heavily traffic area as a result of irregular terrain contour and

imperfect site locations. The remaining 18.5 dB is still adequate.

b) Six sector case

We may also divide a cell into 6 sectors by using six 60o

beam directional antenna. In

this case only one instance of interference can occur in each sector. Therefore C/I ratio in

this case is

4

4

)7.0(

RD

R

I

C= (q + 0.7)

4---------------------- (2)

For q = 4.6, equation (2) can be given as

C/I = 794 = 29 dB


24/50

Which shows a further reduction of co-channel interference. If we use the sameargument as we did for equation (1) and subtract 6 dB from the result of equation (2) the

remaining 23 dB is still more than adequate. When heavy traffic occurs, the 60o

sector

configuration can be used to reduce co-channel interference. However as fewer channelsare generally allowed in a 60

osector and the trunking efficiency decreases. In certain

cases more available channel could be assigned in a 60o

sector.

ii) K=4 (i.e. q = 3.46)

a) Three sector case

Fig. 3-sector case for K = 4

I

C(worst case) = dB

qq2097

)7.0(

1

44

But after subtracting 6 dB for the same reason, we get only 14 dB which is within an

unacceptable range.

3

1

3

4

1

2

4

3

1

4

2

4

3

3

2

1

2

3

3


25/50

b) Six sector case

I

C(worst case) = dB

q

275.359

)1(

1

4

and after subtracting 6 dB, we get 21 dB which is still within the acceptable range.

6. Cell site antenna height

There are several points, which need to be clarified concerning cell site antenna heighteffects.

Antenna height unchanged

If the power of the cell site transmitter changes the whole signal strength can be linearlyupdated according to the change in power. If the transmitted power increased by 3dB to

each grid in the signal strength map. The relative difference in power among the grids

remains the same.

Antenna height changedIf the antenna height changes, then signal strength map obtained from the old antennaheight cannot be updated. With the simple antenna height antenna formula as

1

1'log20

hhg

Where h1 is the old actual antenna height and h1'is the new actual antenna height.

However we can we can still use the same terrain contour data along the radio path (from

the cell site antenna to each grid)to figure out the difference in gain resulting from the

different effective antenna heights in each grid

e

e

h

hg

'' log20

where he is the old effective antenna height and he' is the new effective antennaheight. The additional gain (increase or decrease) will be added to the signal strength grid

based on the old antenna height.


26/50


27/50

2. In a Valley

The effective antenna height he1 which is less than actual antenna height h1 if

113

2hhe and the antenna is lowered to 1

2

1h then the new effective antenna height will be

111116

1)

3

2(

2

1hhhhhe

Then the antenna gain is reduced by

1

1

3

2

6

1

log20

h

h

G

= -12 dB

This simply proves that the lowered antenna height in a valley is very effective inreducing the radiated power in the distant high elevation area. However, in the area

adjacent to the cell site antenna, the effective antenna height is same as the actual antenna

height. The power reduction caused by decreasing antenna height by half is only

62

1

log201

1

h

h

dB

3. In a forested areaIn forested area the antenna should clear the tops of any tree in vicinityH,

especially when they are very close to the antenna. In this case decreasing the

height of the antenna would not be the proper procedure for reducing co channelinterference because excessive attenuation of the desired signal would occur in

the vicinity of the antenna and in its cell boundary if antenna were below the

treetop level.


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7. Antenna pattern in free space and in mobile environment

The antenna pattern we normally use is the one we measured from the antenna range

(open, non-urban area) or an antenna dark room. However when the antenna is placed onthe urban or suburban environment and the mobile antenna is lower than the height of the

surroundings, the cell site antennas pattern as a mobile unit received in a circleequidistant around the cell site is quite different from the free space antenna pattern.

Consider the following facts in the mobile radio environment.

1. The strongest reception still coincides with the strongest signal strength of thedirectional antenna.

2. The pattern is distorted in urban and suburban environment'

3. For a 120o

directional antenna the back lobe (or front to back ratio) is about 10dBless than the front lobe, regardless of whether a weak side lobe pattern or a no

side lobe pattern is designed in a free space condition. This condition exists

because the strong signal radiates in front bouncing back from the surrounding sothat the energy can be received from the back of the antenna.

4. A design specification of the front to back ratio of the directional antenna (from

the manufacturers catalogue) is different from the actual front to back ratio in the

mobile radio environment. Therefore the environment and the antenna beamwidth determines how the antenna would be used in the mobile radio

environment. For example if a 60o

directional antenna is used in the mobile radio

environment, the actual front to back ratio can vary depending on the givenenvironment. If the close in man made structure in front of an antenna is highly

reflect able to the signal then the front to back ratio of low master directional

antenna can be as low as 6 dB in some circumstances. In this case the directional

antenna beam width pattern has no correlation between it measured in the freespace and it measured in the mobile radio environment. If all the building are far

away from the directional antenna, then front to back ratio measured in the field

will be close to the specified antenna pattern, usually 20 dB.

Regular check of the cell site antenna

Air pressurized cable is often used in cell antenna to prevent moisture from

entering the cable and causing excessive attenuation. One method to check the cell site

antenna is to measure the power delivered to the antenna terminal; however few systemshave this capability. The other method is to measure the VSWR at the bottom of the

tower In this case the loss or reflected power due to cable under normal conditions should

be considered. For the high tower VSWR may not be accurate.If each cable connector has 1 dB loss due to energy leakage and two midsection 1 dB loss

connectors are used in the transmitted system the reflected power Pb indicated in the

VSWR would be 4 dB less than the real reflected power.


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Choosing the antenna site

When a site is chosen on the map there is 50% chance that the site location cannot

be acquired written rule state that an antenna location can be found within quarter of the

size of cell R/4.If the site is an 8 miles cell, the antenna can be located within a2 milesradius. The hypothesis is based on the simulation result that the change in site within the

2 miles radius would not at the coverage pattern at the distance 8 miles away. If the site is

2 miles cell the antenna can be located within 0.5 miles radius. The quarter radius rulecan be applied only relatively flat terrain, not in a hilly area. To determine whether this

rule can be applied in a general area one can use the point-to-point prediction method to

plot the coverage at different site locations and compare the differences.

Reduction of co-channel interference by means of Notch in the tilted

antenna pattern

Reduction of co-channel interference in a cellular mobile system is always a challengingproblem. A number of methods can be considered such as

1. Increasing the separation between two co channel cell

2. Using directional antenna in the base station, or

3. Lowering the antenna height at the base station.

Method 1 is not advisable because as the number of frequency-reuse cell increases,

the system efficiency, which is directly proportional to the number of channels per cell,decreases. Method 3 is not recommended because such an arrangement also weakens the

reception level at the mobile unit. However, method 2 is good approach. Especially whenthe number of frequency-reuse cells is fixed. The use of directional antennas in each cellcan serve two purposes:

1. For the further reduction of co channel interference if the interference canbe eliminated by a fixed separation if co channel cells and

2. Increasing the channel capacity when the traffic increases. Here we try to

further reduce the co channel interference by intelligently setting up the

directional antenna

7.1 Theoretical analysisUnder normal circumstances radiation from a co channel-serving site can easily

interfere with another channel cell .Directional antenna can reduce the interference in thesystem by eliminating the radiation to the rest of its 240

osector. However, co-channel

interference can exist even when a directional antenna is used, as the serving site can


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interfere with the co channel cell that is directly a head. Let us assume that a seven cellcellular system (K = 7) is used. The co channel interference reduction factor q becomes

Q = (3N)

0.5

= 4.6

And the co channel cell separation D can be found if the cell radius is known

D = qR = 4.6RWith a separation of 4.6R, the area of interference are the interference receiving

cell is illuminated by the central 19o

sector of the entire (120o) transmitting antenna

pattern at the serving cell. If three identical directional antenna are implemented in everycell, with each antenna covering a 120

osector, then every sector receives interference in

the central 19o

sector of the entire 120o

angle at the interfering cell. Therefore, attempt

should be made to reduce the signal strength of the interference in this 19o

sector.

To achieve the significant gain of C/I in the interference- receiving cell, we should

consider using a notch in the central of the antenna pattern at the interfering cell. Anantenna pattern with a notch in the center can be obtained in a number of ways. One

relatively simple way is to tilt the high-gain directional antenna downward.

Cautions in tilting antennas

When a base station antenna is tilted down by 10o, the strength of the received

signal in the horizontal direction is decreased by 4 dB. But the strength of the received

signal 1o

below the horizontal is decreased by 3.5 dB only 0.5 dB stronger than in the 0o

case. This is very important observation. For e.g., the elevation angel at the boundary of a

2-miles serving cell with a 100ft antenna mast is about 0.5o.this means that the serving

cell and the interfering cell are separated by only 0.5o

at most then by tilting three

antenna down by 10o

, the interference by the interfering cell is reduced by an additional0.25 dB. This is an insignificant improvement the total power received is 4 dB less than

in the no-tilt case. If the tilt is increased to 20o, the received power drops by 16 dB and

the reduction in interference due to tilting the antenna is only 1 dB at the interferencecell. Therefore the antenna vertical pattern and the antenna height play a major role in

justifying antenna tilting. Sometimes, tilting the antenna upward may increase signal

coverage if interference is not a problem

Umbrella pattern effect

Umbrella pattern can be achieved by the discone antenna .the umbrella pattern

can be applied to reduce co channel interference just as the downward tilted directionalantenna pattern is .the umbrella pattern can be used for an omni directional pattern for adirectional antenna pattern. The tilted directional pattern can create notch after tilting 20o

more in front of the beam, but the umbrella pattern cannot. There fore the umbrella

pattern might be recommended for every cell site where the interference prevails. Theumbrella pattern, in which energy is confined to the immediate area of the antenna, is


31/50

effective in reducing both co-channel and long distance interference. Also in a hillyterrain areas there are many holes (weak signal spots). With a normal antenna pattern, we

cannot raise the antenna high enough to cover these holes and decrease co channel

interference at the same time. However the advantage of the umbrella pattern is that wecan increase the antenna height and still decrease co-channel interference.

Antenna height decreases

When antenna height decreased, the reception power is also decreased. Howeverthe formula is based in the difference between the old and new effective height and not

on the antenna actual height. Therefore the effective antenna height is the same as the

actual antenna height only when the mobile unit is traveling in flat ground. it is easy to

decrease antenna height to control coverage in the flat terrain area. For decreasingantenna height in a hilly area, it is difficult task. Therefore a decrease in antenna height

would affect the coverage, thus antenna height become very difficult to control in anoverall plan. Some area within the cell may have a high attenuation while another maynot

7.2 Antenna pattern

The design of different antenna pattern should be according to the terrain contour,

the population and other condition within the given area. Of course this is the difficulttask For instance implementation of antenna tilting or use of an antenna pattern might be

necessary in certain area in order to reduce interference.Side lobe control (i.e. control of secondary lobe formation in an antenna radiation

pattern) is also very critical in the implementation of a directional antenna. Coverage can

be control by means of following method

1. When the entire antenna is facing outward the resultant pattern is verydifficult to control because ripples and deep nulls frequently form.

2. With skewed direction antenna the resultant pattern becomes smoother.

Therefore, this configuration is more attractive.


32/50

8. Performance of mobile communication system

8.1 Scheme for significant improvement of mobile in quality aspect

Sectorization

The total number of available channels can be divided into sets (subgroups)

depending on the sectorization of the cell configuration: the 1200-sector system, the 60

0-

sector system, and the 450-sector system. A seven-cell system usually uses three 120

0

sectors per cell, with the total number of channel sets being 21. In certain locations and

special situations, the sector angle can be reduced (narrowed) in order to assign morechannels in one sector without increasing neighboring-channel interference.

Sectorization serves the same purpose as the channel-borrowing scheme in delaying cell

splitting. In addition, channel co-ordination to avoid co-channel interference is much

easier in sectorization than in cell splitting. Given the same number of channels, trucking

efficiency decreases in sectorization.

Comparison of omni cells (non sectorized cells) and sectorized cells

Omni cells. If a K + 7 frequency-reuse pattern is used, the frequency sets assigned

in each cell can be followed by the frequency-management. However, terrain is seldom

flat; therefore, K= 12 is sometimes needed for reducing co channel interference. ForK=12, the channel-reuse distance is D = 6R, or the co channel reduction factor q=6.

Sectorized cells.

There are three basic types:1. The 120

0-sector cell is used for both transmitting and receiving sectorization.

Each sector has an assigned a number of frequencies. Changing sectors duringa call requires handoffs.

2. The 600-sector cell is used for both transmitting and receiving sectorization.

Changing sectors during a call requires handoffs. More handoffs are expected

for a 60 sector than a 120 sector in areas close to cell sites (close-in areas).3. The 120

oor 60

osector cell is used for receiving sectorization only. In this

case, the transmitting antenna is omni directional. The number of channels in

this cell is not subdivided for each sect. Therefore, no handoffs are requiredwhen changing sectors. This receiving sectorization-only configuration does

not decrease interference or increase the D/R ratio; it only allows for a more

accurate decision regarding handing off the calls to neighboring cells.


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8.2 Scheme for significant improvement of mobile in reliability aspect

Range Extension by the use of Repeater

We use the repeater in cellular mobile communication system for extending therange of the reception of the receiver. Especially we use the repeater when it is hard for

the transmitted signal to reach up to the receiver set. Repeaters are bidirectional in natureand simultaneously send signals to and receive signals from a serving base station. Upon

receiving signals from a base stations in forward link, the repeater amplifies and

reradiates the base station signals to the specific coverage region. Repeaters are beingwidely used to provide coverage into and around buildings, where coverage has been

traditionally weak.

8.3 Scheme for significant improvement of mobile in quantity aspect

Cell Splitting:

Why splitting?

The motivation behind implementing a cellular mobile system is to improve theutilization of spectrum efficiency. The frequency reuse scheme is one concept, and cell

splitting is another concept. When traffic density starts to build up and the frequency

channels in each cell cannot provide enough mobile calls, the original cell can be splitinto smaller cells. Usually the new radius is one-half the original radius cell site is not

use.

New cell radius = old cell radius/2

New cell area = old cell area/4

Let each new cell carry the same maximum traffic load of the old cell; then, in theory,

New traffic load / unit area = 4 traffic load/ Unit area

How splitting?

There are two kinds of cell-splitting techniques:

1. Permanent splitting. The installation of every new split cell has to be plannedahead of time; the number of channels, the transmitted power, the assigned

frequencies, the choosing of the cell-site selection and the traffic load

consideration should all be considered. When ready, the actual service cut-over should be set at the lowest traffic point, usually at midnight on a weaken.

Hopefully, only a few calls will be dropped because of this cut-over,

assuming that the downtime of the system is within 2 h


34/50

2. Dynamic splitting. This scheme is based on utilizing the allocated spectrumefficiency in real time. The algorithm for dynamically splitting cell sites is a

tedious job since we cannot afford to have

Effect of splitting:When the cell splitting is occurring, in order to maintain the frequency-reuse distance

ratio q in a system, there are two considerations.

1. Cells splitting affects the neighboring cells, splitting cells causes anunbalanced situation in power and frequency-reuse distance and makes it

necessary to split small cells in the neighboring cells. This phenomenon is thesame as a ripple effect.

2. Certain channels should be used as barriers. To the same extent, large andsmall cells can be isolated by selecting a group of frequencies, which will beused only in the cells located between the large cells on one side and the small

cells on the other side, in order to eliminate the interference being transmittedfrom the large cells to the small cells.

3. Small Cells (Micro cells)

8.4 Scheme for significant improvement in quality as well as quantity

aspects of mobileMicro-cell Zone Concept

Fig. Microcell Zone concept for 3-microcell

Tx/RxTx/Rx

Tx/Rx

ZoneS

elector

BaseStation

Microwave or fiber-optic link


35/50

By the use of sectorization technique, we can increase the system performance (i.e,quality of the signal) but side by side, there will be a large increment of handoffs which

results the increment of load on the switching and control link elements of the mobile

system. So there must be some technique for the solution of this problem. So a microcellzone conceptis introduced which decreases the co-channel interference (i.e improves the

signal quality) and also leads to an increased capacity without the degradation in trunking

efficiency caused by sectoring.In this scheme, each of the three or more zones (represented as Tx/Rx) in above

figure are connected to a single base station and share the same radio equipment (same

frequency). Generally, the zones are connected by coaxial cable, fiber optic cable, ormicrowave link to the base station. All those multiple zones (3 zones considered here)

and a single base station make up a cell. As a mobile travels within a cell, it served by

the zone with the strongest signal. This approach (i.e micro-cell zone concept) is superior

to sectoring since antennas are placed at the outer edges of the cell, and any base station

channel may be assigned to any zone by the base station.As the mobile travels from one zone to another within the cell, it retains the same

channel. Thus, unlike in sectoring, a handoff is not required at the MSC when the mobiletravels between zones within the cell since all the three zones have the same frequency.

The base station simply switches the channel to a different zones site. In this way, a given

channel is active only in the particular zone in which the mobile is traveling, and hencethe base station radiation is localized and interference is reduced.

9. Some Calculations9.1 Capacity of a system

Let the total number of channel be S, K be the channel allocated for each cell, N be thenumber of cell in a cluster, then the total number of channel S is given by

S = KN

And if C is the capacity of the system, thenC = MS = MKN

where M is the number of times the cluster is replicated

Hence, we see that the capacity of the system increases as the number of cell decreases.


36/50

9.2 Channel in a cell

Suppose,

total Bandwidth = 33 MHzchannel Bandwidth = 50 KHz

total available channel = 33000/50= 660 channels

Now, for N = 4, channel/cell = 660/4 = 165 channels

for N = 7, channel/cell = 660/7 = 94.286 94 channelsfor N = 12, channel/cell = 660/12 = 55 channels

Hence, from above, we see that the number of channel per cell (capacity) increases as N

decreases and vice versa.

Also ,we have

Q =R

D= N3

where

Q is the co-channel reuse ratio or co-channel reuse factorD is the co-channel distance or frequency reuse distance

R is the radius of the cell

N is the number of cell in a cluster

Hence, as we go on decreasing Q by decreasing N, the capacity of the system increases.

But we cant decrease factor N to a larger extent due to the system performance(transmission quality). As we go on decreasing N, obviously the capacity increases but

the cost for that is the degradation of transmission quality due to the co-channel

interference. So there must be a trade-off between system performance and the systemcapacity. In other words, we must decrease the number of cell (N) up to that limit where

the ratio S/I is with in an acceptable range.

9.3 Loss between Tx and Rx in mobile communicationIn every communication system, the loss do occur and so cellular mobile

communication system also incur the loss which is given by the formula

6.147)(log20)(log20log10log10 10101010 dfGGL rtp dB

where

Lp is the path (communication path) lossGt is the gain of transmitting antenna

Gris the gain of receiving antenna


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f is the frequency of signal in MHzd is the distance between transmitting and receiving antenna

9.4 Friis transmission formula

Pr(dBW) = Pt (dBW) + Gt (dBW) + Gr(dBW) FSL (dB)

where FSL is the free space loss and is given by the formula

FSL = 20 log10 (

d4)

Here, d is the distance between the transmitting and receiving antenna

9.5 Received Power versus different parameters

i) Received power Vs distance between Tx and RxWe have, received power is given by

2

2

4 d

GGPP rttr

Pr2

1

dReceived power is inversely proportional to the square of the distance between thetransmitter and the receiver.

From the above equation, we can see that when the distance is doubled then receivedpower decreases by 6 dB and when the distance between Tx and Rx is 10 times greaterthan the original distance, then the received power decreases by 20 dB. In conclusion, the

received power decreases with the distance at the rate of 6 dB/octave and 20 dB/decade.

ii) Received power Vs height of the Base Station (BS)Received power is proportional to the square of the height of the BS antenna. So doubling

the height of the BS antenna corresponds to the reduction of path loss by 6 dB. It means

that increment of the BS height will increases the gain of antenna. Thus the receivedpower increases as the BS antenna height increases.

2

1

2

10log10

b

b

h

h

G

where 1bh = old height of BS

2bh = new height of BS


38/50

iii) Received power Vs height of the Mobile Station (MS)Received power is proportional to the height (not square of the height) of MS antenna.

The increment of the height of MS increases gain and thus power received also increases.

1

2

10log10m

m

hhG

where 1mh = old height of MS

2mh = new height of MS

10. Simulation using Matlab10.1 Omindirectional pattern


39/50

10.2 Directional Pattern

10.3 Directional pattern for dipole antenna


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11. Analysis of received power intensity of mobile station

Fig. Block Diagram of Analysis of Received power intensity of mobile station

Principle:When the receiving antenna of mobile station receives the signal from the

transmitting antenna of Base Station, then the A.C. voltage induced can be extracted asan output of receiver antenna. That induced A.C. voltage can be converted into D.C.

voltage by the use of Full wave Rectifier. The obtained voltage is in analog form which

can be converted into digital form by using the electronic chip called Analog to Digital

Converter (ADC). The o/p voltage in analog form is not user friendly (cant read thereading easily). So we have to make that reading very easily readable for all the user. So,

to do that, we introduce ADC for converting analog into digital form. The output of the

ADC is fed into the BCD to Seven Segment Decoder and then into Seven Segment

Display. The output of the seven segment display is now readable for all the user.We, now can place the mobile station in various places within the range of

transmitted power of the transmitting antenna and locate the area where the mobilestation antenna receives the signal with greatest received power (intensity). So, by the

analysis of this experiment, we can find the region where the receiver can detect the

signal and also the extreme power detectable region of the receiver.

BCD to 7-Segment

decoder

Rx Full Wave Rectifier

ADC

Tx

7-Segment Display

Mobile Station Antenna

Induced A.C. voltage

D.C. analog voltage

D.C. digital voltage

electromagnetic wave

output

Base Station Antenna


41/50

12. Antenna Layout

An antenna works best when its physical size corresponds to a quantity known as

the antennas electrical size. The electrical size of an antenna depends on the wavelengthof the radio waves being sent or received. An antenna radiates energy most efficientlywhen its length is a particular fraction of the intended wavelength. When the length of an

antenna is a major fraction of the corresponding wavelength (a quarter-wavelength ( 4

1)

or half-wavelength ( 2

1)is often used), the radio waves oscillating back and forth along

the antenna will encounter each other in such a way that the wave crests do not interferewith one another. The waves will resonate, or be in harmony, and will then radiate from

the antenna with the greatest efficiency.

If an antenna is not long enough or is too long for the intended radio frequency, thewave crests will encounter and interfere with one another as they travel back and forthalong the antenna, thus reducing the efficiency. The antenna then acts like a capacitor or

an inductor (depending on the shape of the antenna) and stores, rather than radiates,

energy. The electrical length of an antenna can be altered by adding a metal loop of wireknown as a loading coil to one end of the antenna, thus increasing the amount of wire in

the antenna. Loading coils are used when the practical length of an antenna would be toolong. Adding a coil to a short antenna increases the antennas electrical length, improves

its resonance at the desired frequency, and increases the antennas efficiency.The radio waves used by AM radio have wavelengths of about 300 m (about 1,000

ft). Most AM transmitter antennas are built to a height of about 75 m (about 250 ft),

which, in this case, is the length of a quarter-wavelength. With a tower of this height, anAM radio antenna will radiate radio waves most efficiently. Since an antenna that is 75

meters tall would be impractical for a portable AM radio receiver, AM radios use a

special coil of wire inside the radio for an antenna. The coil of wire is wrapped around aniron-like magnetic material called a ferrite. When radio waves come into contact with the

coil of wire, they induce an electric charge within the coil. The magnetic ferrite helps

confine and concentrate the electrical energy in the coil and aids in reception.

Television and FM radio use tall broadcast towers as well but use much shorterwavelengths, corresponding to much higher frequencies, than AM radio. Therefore,

television and FM radio waves have wavelengths of only about 3 m (about 10 ft). As a

result, the corresponding antennas are much shorter. Buildings and other obstructionsclose to the ground can block these high-frequency radio waves. Thus the towers are used

to raise the antennas above these obstructions in order to provide a greater broadcasting

range. Receiving antennas for television sets and FM radios are small enough to beinstalled on these devices themselves, but the antennas are often mounted high on

rooftops for better reception.


42/50

Example:If we want to prepare the antenna for GSM mobile communication, then we must

consider the frequency of mobile communication system for GSM.

We have,Frequency for GSM ( f ) = 900 MHz

Wavelength ,6

8

10900

103

f

C m = 333.333 mm = 33.333 cm

Theoretically,

length l of the antenna is related with the wavelength as

4

l for monopole antenna and

2

l for dipole antenna

4

l =

4

10333.333 3= 83.33 mm = 8.333 cm for dipole antenna

2

l =

2

10333.333 3= 41.66 mm = 4.166 cm for monopole antenna


43/50

13. Informations obtained from NTCabout CMC system of

Nepal

Transmitted power of BS = 40 W

BTS = 4 W

MS = 0.02 WReceiver power of MS = -62 dBm to -100 dBm

BS = ..Receiver sensitivity of MS = -102 dBm

BS = .

i) Omni-directional ----------35 km

ii) Directional (sectorized) ----- 8-12 km

BS antenna height = 35 m

BS antenna height in new road = 8 mBS antenna height in outside valley = 70 m

Avg. MS antenna height = 5 m

Antenna gain = 18 dBLife of antenna = 15 years


44/50

14. Calculations with the use of C-Programming language

i) Calculation of Antenna Gain

#include#include#includevoid main(){clrscr();float diameter,frequency,gain_ln,gain_log;cout


45/50

}cout


46/50

iv) Friis Transmission Formula.

b) Analysing transmitted power Vs distance between Tx and Rx

#include#include#includevoid main(){clrscr();float power_tr,power_rc,gain_tr,gain_rc,FSL_ln,FSL_log;float distance,frequency;cout


47/50

float reuse_factor;cout


48/50

15. Gantt Chart

Time schedule

Group division and project

selection

Collection of books and

materials related to antennasystem for mobile comm

n

Introductory presentation

Visit to NTC and prepare a

note about general layout ofantenna system of mobile

communication in Nepal

Visit to UTL and studied

about wireless system with

CDMA technology

Thorough study of the

project consulting variousbooks and websites in net

Work on softwares for

various calculations

Analysis of antenna layout

using lab equipment

Attempts on simulation of

radiation pattern of antenna

using MATLAB

Preparation for project report

and project presentation

2 4 6 10 12 14 16 18 20 22 24 26 28

Week


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16. Conclusion The research study in general system in cellular mobile communication was done.Various patterns of antenna radiation were obtained. Also different calculations regarding

the channel capacity, antenna gain, transmitted power Vs distance were calculated usingthe C-programming language. The presuming analysis about the different schemes such

as improving signal quality and quantity aspects and also the reliability of the mobilesystem were done.


50/50

References:

Rajeswori Chatterjee Antenna Theory and Practice 2nd Edition, New AgeInternational (p) Limited

William C.Y. Lee Mobile Cellular Telecommunications Systems Mc Graw HillBook Company

Theodore S Rappaport Wireless Communications 2nd Edition, PearsonEducation

Constantine A. Balanis Antenna Theory 2nd Edition, John Wiley & Sons, Inc. Microsoft Encarta Reference Library 2003 Microsoft Corporation Private Ltd.

Documents

Antenna System in Cellular Mobile Communication