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Mobile Communication System (MCS) Overview of Mobile Communication

EETP/ BSNL Platinum Certification Course Version 1.0 June 2014 Page 1of 34

For Restricted Circulation

1 OVERVIEW OF MOBILE COMMUNICATION- HANDSET,

SIM

STRUCTURE

1.1 INTRODUCTION

1.2 LEARNING OBJECTIVES

1.3 WIRELESS COMMUNICATIONS: INCEPTION AND OVERVIEW

1.4 HANDOVER

1.5 LOCATION UPDATE

1.6

MOBILE HANDSET

1.7 SIM (SUBSCRIBER IDENTITY MODULE)

1.8 IDENTIFIERS

1.9 SUMMARY

1.10 SELF ASSESSMENT QUESTIONS

1.11 REFERENCES AND SUGGESTED FURTHER READINGS

1.1 INTRODUCTION

We see that today that Mobile telephones has become an essential part of daily life. In the last

one decade, our country has witnessed tremendous growth in mobile communication area.

Currently number of mobile telephone connections are many a times more than that of fixed(wire line) telephone connections. About 7- 8 million mobile subscribers are added every

month in our country.

In mobile communications the connectivity of the user (Mobile Subscriber) with Mobile

Network is through radio signals and there are no wires from the network to user equipment.

The objective of mobile communications is to provide a truly Anytime, Anywhere

communication. Today mobile is providing Voice, messaging and a number of data services

to users like real time TV, on line payments of utility bills, m-commerce, news,

entertainments etc.

Although mobile telephony can be seen in broad sense as the wireless communication and

wireless services can be offered through various technologies like GSM, CDMA, Cor-DECT,

etc. but here we will talk about GSM (Global System for Mobile Communication) as a

wireless communication technology.


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Comparison of Wire Line &

Wireless TelephonyFeature Wire-Line Wire-Less

UserTerminal

TelephoneSet

MobileHandset

Portability Fixed Portable

Connectivity Wired Wireless

Servicesoffered

Limited Many

the impression, that they can speak (transmit) and hear (receive) simultaneously. This type of

transmission solution is regarded as full duplex transmission.

Figure 1: Comparison of Wire-line and wireless systems.

A limited amount of mobility along with duplex transmission resulted in the Mobile

Telephony. The first commercial wireless car phone telephone service started in the late 1940

in St. Louise, Missouri (USA). It was a car phone service, because at this time, the mobile

phone equipment was bulky and heavy. Actually, in the start-up, it occupied the whole back

of the car. But it was a real full duplex transmission solution. In the 1950s, several vehicle

radio systems were installed in Europe also. These systems are called single cell systems. The

user data transmission takes place between the mobile phone and the base station (BS). A

base station transmits and receives user data. While a mobile phone is only responsible for its

users data transmission and reception, a base station is capable to handle the calls of several

subscribers simultaneously. The transmission of user data from the base station to the mobilephone is called downlink (DL), the transmission from the mobile phone to the base station

uplink (UL) direction. The area, where the wireless transmission between mobile phones and

the base station can take place, is the base stations supply area, called cell.

Figure 2: Cell Coverage Area.

Cell = su l area

Uplink

UL

Base station

Downlink (DL)


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1.4 HANDOVER

Single cell systems are quite limited. The more and more distant the subscriber is from the

base station, the lower the quality of the radio link. If the subscriber is leaving the supply area

of the cell, the communication is not possible any more. In other words, the mobile

communication service was only available within the cell. In order to overcome thislimitation, Multi-cellular systems were introduced. A cellular mobile communication system

consists of several cells, which can overlap. By doing so, a whole geographical area can be

supported with the mobile communication service.

But what happens, when a subscriber moves during a call from one cell to another cell? It

would be very annoying, if the call is dropped. If the subscriber is leaving a cell, and in

parallel is entering a new cell, then the system makes new radio resource available in the

neighboring cell, and then the call is handed over from on cell to the next one. By doing so,

service continuation is guaranteed, even when the subscriber is moving. This process is called

handover (HO).

A handover takes place during a call, i.e. when the mobile phone is in active (dedicated)

mode. A mobile phone can also be in idle mode. In this case, the mobile phone is switched

on, but no resources are allocated to it to allow transmission of user data. In this mode, the

mobile phone is still listening to information, broadcasted by the base station. Why? Imagine,

there is an incoming call to this mobile. The mobile phone is then paged in the cell. This

means the phone receives information that there is a mobile terminated call. A cellular system

may consist of hundreds of cells. If the mobile network does not know, in which cell the

mobile phone is located, it must be paged in all of them. To reduce load on networks, paging

is done in small parts rather to a group of cells of a mobile network. The group of cells in

administrative units in operation is called location area (LA). A mobile phone is paged in

only one location area at a time. The LA is used by the GSM system to search for asubscriber in an active state.

But how does the cellular system know, in which location area the mobile phone is

located? And how does the mobile phone know? In every cell, system information is

continuously transmitted. The system information includes the location area information. In

the idle mode, the mobile phone is listening to this system information. If the user moves

from one cell to the next cell, and the new cell belongs to the same location area, the mobile

stays idle. If the new cell belongs to a new location area, then the mobile phone has to

become active. It starts a communication with the network; information is send to the mobile

network. This is stored in databases within the mobile network, and if there is a mobile

terminated call, the network knows where to page the subscriber.

1.5 LOCATION UPDATE

The process, where the mobile phone informs the network about its new location is called

Location Update Procedure (LUP). The registration of the Mobile is done at the VLR (Visitor

Location Register) associated with the Mobile Switching Network.


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Associated terms: 3.2/5/8/12/41 Megapixels, Auto Focus, Shooting Modes, HD

video, LED/Xenon flash.

Battery: The battery (with a capacity expressed in mAh or milli ampere hour)

determines how long your phone keeps working on a single charge.

Associated terms: Li-ion, mAh, removable, non-removable.

Device Connectivity: There are various wired and wireless technologies embedded

today on mobile devices to connect them with other phones, tablets, televisions or

various accessories.

Associated terms: USB On-The-Go, HDMI, Bluetooth 2.0/2.1/3.0, Wi-Fi.

Mobile Internet Connectivity: Phones are no longer used to just make calls andswap texts. Almost every Smartphone now comes with some sort of Internet connectivity via

the operator's data services.

Associated terms:GPRS/EDGE , 3G, 3.5G , HSPA, HSDPA, 4G.

Figure 4: Components of a Mobile Phone.

OS/Platform: The operating system of a phone is the software that makes the phone

work, handling basic tasks like calling, texting as well as more complex ones like mail and

Web browsing. It works in a similar way like Windows and Mac OS do, on a computer.


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Mobile Communication System (MCS) Mobile Antenna System

EETP/Platinum Certification Course Page 10of 34


2 MOBILE ANTENNA SYSTEM

STRUCTURE

2.1 INTRODUCTION

2.2 OBJECTIVES

2.3 ANTENNA

2.4 POLARIZATION

2.5 PROPAGATION PATTERN/RADIATION PATTERN:

2.6 GAIN

2.7 IMPEDANCE

2.8 VSWR

2.9 MECHANICAL FEATURES OF ANTENNA:

2.10 ANTENNA SYSTEMS

2.11 DIVERSITY

2.12 ANTENNA TILT

2.13

SELF ASSESSMENT QUESTIONS

2.1 INTRODUCTION

The transmission and reception of information using Electro Magnetic (EM) waves is known

as Radio or Wireless communication. An EM wave, consists of an Electrical component and

a Magnetic component. The directions of the Electric component, the Magnetic component

and Propagation are mutually perpendicular to each other.

Figure 1: Electro Magnetic Spectrum


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2.2 OBJECTIVES

After completion of this module you will be able to know

Electromagnetic wave

Antenna

Properties of antenna

Antennas used in Mobile

Polarization

2.3 ANTENNA

Antennas transform wire-propagated waves into space-propagated waves. They receive

electromagnetic waves and pass them onto a receiver or they transmit electromagnetic waves,

which have been produced by a transmitter. All the features of passive antennas can be

applied for reception and transmission alike (reciprocality). On one side RF cable is

connected and the other side it is the environment, therefore the surroundings of the antenna

have a strong influence on the antennas electrical features.

2.3.1 THE PRINCIPLE OF AN ANTENNA:

A transmitter sends a high frequency wave into a co-axial cable. A pulsing electrical field is

created between the wires, which cannot free itself from the cable

The end of the cable is bent open. The field lines become longer and are orthogonal to the

wires.

The cable is bent open at right angles. The field lines have now reached a length, which

allows the wave to free itself from the cable. The apparatus radiates an electromagnetic wave,

whereby the length of the two bent pieces of wire corresponds to half of the wavelength. This

is the basic principle of lamda/2-dipole antenna.An electrical field (E) is created due to the voltage potential (U) but also a magnetic field (H)

which is based on the current (I) The amplitude distribution of both fields corresponds to the

voltage and current distribution on the dipole.

The free propagation of the wave from the dipole is achieved by the permanent

transformation from electrical into magnetic energy and vice versa. The thereby resulting

electrical and magnetic fields are at right angles to the direction of propagation


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Figure 2: Field distribution on a Dipole


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2.4 POLARIZATION

Polarization can be defined as the direction of oscillation of the electrical field vector. In

Plane polarization, the direction of the 'E' component does NOT change whereas in Circular

polarization, the direction of the 'E' component changes. Thepolarization of an antenna is the

orientation of the electric field (E-plane)of the radio wave with respect to the Earth's surface

and is determined by the physical structure of the antenna and by its orientation. It has

nothing in common with antenna directionality terms: "horizontal", "vertical", and "circular".

Thus, a simple straight wire antenna will have one polarization when mounted vertically, and

a different polarization when mounted horizontally. "Electromagnetic wave polarization

filters are structures which can be employed to act directly on the electromagnetic wave to

filter out wave energy of an undesired polarization and to pass wave energy of a desired

polarization.

Plane polarization is generally used in terrestrial radio systems and Circular in Satellite

communications. Nowadays, dual polarized antennae are a common sight. Polarization helps

in discrimination and augmenting the capacity of a radio system as well.

Figure 3: Polaization

For Mobile communications generally vertical polarization is used.

For Broadcast systems horizontal polarization is used.

2.5 PROPAGATION PATTERN/RADIATION PATTERN:

In most cases the propagation characteristic of an antenna can be described via elevations

through the horizontal and vertical radiation diagrams Very often a 3-dimensional description

is chosen to describe a complex antenna. The radiation pattern diagram leads to Major and

Minor Lobes of the antenna. Major Lobes of the antenna are those radiation patterns in which

the intensity or strength of the signal is maximum. Minor Lobes are those in which the

intensity is less.

Half-Power-Beam-Width:This term defines the aperture of the antenna. The HPBW is defined by the points in the

horizontal and vertical diagram, which show where the radiated power has reached half the

amplitude of the main radiation direction. These points are also called 3 dB points. Normally

only the major lobe is considered for this. .
http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/E-planehttp://en.wikipedia.org/wiki/E-planehttp://en.wikipedia.org/wiki/Polarization_(waves)


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2.6 GAIN

An antenna without gain radiates energy in every direction. An antenna with gain

concentrates the energy in a defined angle segment of 3-dimensional space. The l/2-dipole is

used as a reference for defining gain. At higher frequencies the gain is often defined with

reference to the isotropic radiator. The isotropic radiator is a non-existent ideal antenna,

which has also an omni directional radiation characteristic in the E-plane and H-plane.

2.7 IMPEDANCE

The impedance of the antenna is simply equal to the voltage applied to its input terminals

divided by the current flow. The frequency dependant impedance of a dipole or antenna is

often adjusted via a symmetry or transformation circuit to meet the 50-Ohm criterion.

Adjustment across a wider frequency range is achieved using compensation circuits.

2.8 VSWR

An impedance of exactly 50 Ohm can only be practically achieved at one frequency. The

VSWR defines how far the impedance differs from 50 Ohm with a wide-band antenna. The

power delivered from the transmitter can no longer be radiated without loss because of this

incorrect compensation. Part of this power is reflected at the antenna and is returned to the

transmitter The forward and return power forms a standing wave with corresponding voltage

minima and maxima. This wave ratio (Voltage Standing Wave Ratio) defines the level of

compensation of the antenna and was previously measured by interval sensor measurements.

A VSWR of 1.5 is standard within mobile communications. In this case the real componentof the complex impedance may vary between the following values:

Maximum Value: 50 Ohms x 1.5 = 75 Ohms

Minimum Value: 50 Ohms / 1.5 = 33 Ohms

2.9 MECHANICAL FEATURES OF ANTENNA

Antennas are always mounted at exposed sites. As a result the antenna must be designed to

withstand the required mechanical loading.

1.Vehicle antennas, for example, must withstand a high wind velocity, vibrations, saloon

washing and still fulfill a limited wind noise requirement

2.Antennas for portable radio equipment are often exposed to ill handling and sometimes

even played with by the user.


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3.Base station antennas are exposed to high wind speed, vibrations, ice, snow, a corrosive

environment and of course also extreme electrostatic loading via lightning

2.9.1 OMNI DIRECTIONAL ANTENNAS:

The horizontal radiation pattern covers 360 degrees and vertical half power beam width is 78

degrees. Hence there will be lot of waste of energy both upwards and downwards in thedesired horizontal plane.

2.9.2 OMNI DIRECTIONAL ANTENNAS WITH GAIN:

By connecting single, and vertically stacked dipoles at a middle distance of one wavelength

the half power beam width can be reduced. As a result the radiated power in the horizontal

plane is increased. This increase is called gain, which is nothing other than binding the

radiated power in a defined direction. A doubling of the number of dipoles results in a gain

increase of 3 dB (double the power).


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2.9.3 DIRECTIONAL ANTENNAS

Directional antennas are provided with reflectors behind the radiating element. This focuses

the energy in a desired direction avoiding transmission in the rear side of the antenna. The

directional antennas are classified into the following types:1.Grid Parabolic Reflector antennas

2. Parabolic Reflector antennas.

3.Cassegrain antennas.

4. Array antennas.

The first two types of antennas are mainly used in fixed point-to-point radio links and the grid

types are employed up to 2GHz whereas the solid parabolic reflector antennas are used for

higher frequencies.

The connectivity between the antennas to the equipments is by coaxial cable up to 2GHz and

for higher frequencies it is by hollow copper tube called wave-guide. The beam width of

these antennas depends on the diameter of the antenna and frequency of operation. They

produce very narrow beams.


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Cassegrain antennas are associated with Satellite communication are comparatively larger

which makes them to be fixed on the ground or roof tops and orient themselves towards the

satellite by operating gear arrangement either manually or using motors.

Array antennas are more predominantly used in broadcasting and mobile communications.

There are two types

(i)End Fire Arrays,

(ii)Panel Antennas

2.9.4 END-FIRE ARRAYS

Directional antennas whose mechanical features are parallel to the main radiation beam are

called "End-fire Arrays". Examples:

Yagi antennas

Logarithmic periodic (log-per) antennasYagi antennas are very common due to their simple and cheap method of construction. The

gain and bandwidth of Yagi antennas are electrically coupled with one other which is anelectrical disadvantage, ie. one criterion is weighed off the other. The mechanical concept is

not suitable for extreme climatic conditions.

A log-periodic antenna is abroadband,multi-element,directional,narrow-beamantenna that

has impedance and radiation characteristics that are regularly repetitive as a logarithmic

function of the excitationfrequency.

2.9.5 PANEL ANTENNAS-BROADSIDE ARRAYS

Panel antennas are made up of several dipoles mounted in front of a reflector so that gain can

be achieved from both the horizontal and vertical plane. This type of antenna is very wellsuited for antenna combinations.
http://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/Directional_antennahttp://en.wikipedia.org/wiki/Beamwidthhttp://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Radiationhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Radiationhttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Beamwidthhttp://en.wikipedia.org/wiki/Directional_antennahttp://en.wikipedia.org/wiki/Broadband


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2.11.1 SPACE DIVERSITY

This system consists of two reception antennas spaced a distance apart. One antenna has a

certain field strength profile with maxima and minima from its coverage area, the other

antenna has a completely different field strength profile although only spaced a few meters

away. Ideally the minima of one antenna will be completely compensated by the maxima of

the other The improvement in the average signal level achieved with this method is called

diversity-gain.

2.11.2 POLARIZATION DIVERSITY

The reflections, which take place within urban areas, are not all of the same polarization, ie.

Horizontal components also exist. Furthermore a mobile telephone is never held exactly

upright which means that all polarizations between vertical and horizontal are possible. It istherefore logical that these signals be also used. Space diversity uses 2 vertically polarized

antennas as reception antennas and compares the signal level. Polarization diversity uses 2

orthogonally polarized antennas and compares the resulting signals.

Figure 4: Horizontal and Vertical Polarization

The dipoles of both antenna systems are horizontally and vertically polarized respectively. A

spatial separation is not necessary which means that the differently polarized dipoles can be

mounted in a common housing. Sufficient isolation can be achieved even if the dipoles are

interlocked into one unit so that the dimensions of a dual-polarized antenna are not greater

than that of a normal polarized antenna.


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A minimum horizontal spacing is only required between the antennas, the antennas can also

be mounted one above the other on the same mast. This makes the complete sector very

compact, thereby easing permission procedures.

Figure 5: Polarization +45/-45

It is also possible to use dipoles at +45/-45 instead of horizontally and vertically (0/90)

placed. One now has two identical systems, which are able to handle both horizontally and

vertically polarized components.

2.12 ANTENNA TILT

Generally two types of tilts

Mechanical

Electrical


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2.12.1 MECHANICAL

Often the base station antenna provides over coverage. That is there is large overlap between

two adjacent cells, which causes increase in handover between the base stations. This puts a

strain on the system. This may also cause disturbances in a neighboring cell which has the

same frequency. For the coverage of the sector, the only that energy which is radiated below

the horizon can be used. Down tilting the antenna limits the range by reducing the field

strength in the horizon and increases the radiated power in the cell that is actually to be

covered. Different methods of down tilting are used. The simplest method of down tilting the

vertical diagram of a directional antenna is the mechanical method to achieve a certain angle

while using an adjustable joint. (Figure below) But the required down tilt is only valid for the

main direction of the horizontal radiation pattern. In the tilt axis direction (+/-90 from main

beam) there is no down tilt at all. Between the angles of 0 and 90 the down tilt angle varies

according to the azimuth direction. These results in a horizontal half-power beam width,

which gets bigger with increasing down tilt angles. The resulting gain reduction depends on

the azimuth direction. Practically upto 6 degree is advisably further reduce the antenna

height.

Figure 6: Mechanically down tilt of Panel

2.12.2 ELECTRICAL TILT

The other method used is electrical down tilt. In this method, the altering the phases of thesignal being fed to dipoles of an antenna. By altering the phases, the main direction of the

vertical radiation pattern can be adjusted. Figure (next page), shows dipoles that are fed from

top to bottom with a rising phase of 70. The different phases are achieved by using feeder

cables of different lengths for each dipole. The electrical down tilt has the advantage, that the

adjusted down tilt angle is constant over the whole azimuth range. The horizontal half-power

beam width remains unaltered. However, the down tilt angle is fixed and cannot be changed.

Practically upto 6 degree is advisably further reduce the antenna height.


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radiated power in the horizontal plane is ___________. This increase is called

____________________, which is nothing other than binding the radiated power in a

defined direction.

10. A doubling of the number of dipoles results in a gain increase of ________________


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Mobile Communication System (MCS) Feeder Cable & VSWR



3 FEEDER CABLE & VSWR

STRUCTURE

3.1 INTRODUCTION

3.2 OBJECTIVE

3.3 RF FEEDER CABLE BASICS

3.4 HOW RF FEEDER CABLE WORKS

3.5 RF JUMPER CABLE

3.6 VSWR AND ITS MEASUREMENTS

3.7

SUMMARY



3.1 INTRODUCTION

RF feeder cable is used to feed antennas and deliver radio frequency power from onepoint to another. The most common type of antenna feeder used today is undoubtedly coaxial

feeder or coax cable. Coax cable, often referred to as RF cable, offers advantages ofconvenience of use while being able to provide a good level of performance. In view of this

vast amount of coax cable, coax feeder are manufactured each year, and it is also available in

a wide variety of forms for different applications.

3.2 OBJECTIVE

After reading this unit, you should be able to understand:

RF Feeder Cable Basics of Mobile communication.

How Feeder Cable works.

RF Jumpers Cable of Mobile communication.

VSWR and its Measurements.

3.3 RF FEEDER CABLE BASICS

RF feeder cable is normally seen as a thick electrical cable. The cable is made from a

number of different elements that when together enable the coax cable to carry the radio

frequency signals with a low level of loss from one location to another. The main elements

within a feeder cable are:

1. Centre conductor2. Insulating dielectric

3. Outer conductor4. Outer protecting jacket or sheath


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The overall construction of the RF feeder cable can be seen in the diagram below and from

this it can be seen that it is built up from a number of concentric layers. Although there are

many varieties of coax cable, the basic overall construction remains the same.

Cross section though RF feeder cable

1. Centr e conductorThe centre conductor of the RF feeder is almost universally madeof copper. Sometimes it may be a single conductor whilst in other RF cables it may

consist of several strands.

2. I nsulating dielectri cBetween the two conductors of the feeder cable there is aninsulating dielectric. This holds the two conductors apart and in an ideal world would

not introduce any loss, although it is one of the chief causes of loss in reality. This

feeder cable dielectric may be solid or as in the case of many low loss cables it may

be semi-airspace because it is the dielectric that introduces most of the loss. This maybe in the form of long "tubes" in the dielectric, or a "foam" construction where air

forms a major part of the material.

3. Outer conductorThe outer conductor of the RF cable is normally made from a copperbraid. This enables the feeder cable to be flexible which would not be the case if the

outer conductor was solid, although in some varieties made for particular applications

it is. To improve the screening double or even triple screened feeder cables are

sometimes used. Normally this is accomplished by placing one braid directly over

another although in some instances a copper foil or tape outer may be used. By using

additional layers of screening, the levels of stray pick-up and radiation areconsiderably reduced. The loss is marginally lower.

4. Outer protecting jacket or sheathFinally there is a final cover or outer sheath to thefeeder cable. This serves little electrical function, but can prevent earth loops forming.

It also gives a vital protection needed to prevent dirt and moisture attacking the cable,

and prevent the feeder cable from being damaged by other mechanical means.


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3.4 HOW RF FEEDER CABLE WORKS

A feeder cable carries current in both the inner and the outer conductors. These

current are equal and opposite and as a result all the fields are confined within the cable and it

neither radiates nor picks up signals.

This means that the cable operates by propagating an electromagnetic wave inside the

cable. As there are no fields outside the feeder cable it is not affected by nearby objects.

Accordingly it is ideal for applications where the RF cable has to be routed through or around

buildings or close to many other objects. This is a particular advantage of coaxial feeder

when compared with other forms of feeder such as two wire (open wire, or twin) feeders

refers to the technique of transmitting information over microwave frequencies, using various

integrated technologies. The portion of the microwave spectrum called millimeter wave is

highly susceptible to attenuation by the atmosphere (especially during wet weather). The term

SHF corresponds to "MICROWAVE" Cent metric waves. As a convention frequencies,

above 1 GHz and up to 40 GHz are termed as Microwave. However, most of the m/w

systems available are in the range of 1 to 18 GHz.

3.5 RF JUMPER CABLE

RF Jumper cables serve its varied purposes as a connector between main feeders and

antennas. Also, these jumpers can be connected in between main feeders and RF equipment,

such as telecom tower, BTS, antenna feeder system.

1.5.1 Application: Used for connection between Antenna and Feeder Cable, connecting

between Cabinet and Feeder Cable

1.5.2 Features: a. Excellent VSWR Performanceb.Flexibility and small bending diameters

c. Complete weatherproof

d. Available in any cable length with a large variety of connector

combination

3.6 VSWR AND ITS MEASUREMENTS

Standing-wave ratio (SWR) is a mathematical expression of the non-uniformity of an

electromagnetic field (EM field)on a transmission line such ascoaxial cable.Usually, SWR

is defined as the ratio of the maximum radio-frequency (RF) voltage to the minimum RFvoltage along the line. This is also known as the voltage standing-wave ratio (VSWR). Under

ideal conditions, the RF voltage on asignal transmission line is the same at all points on the

line. The ideal VSWR is therefore 1:1. (Often the SWR value is written simply in terms of

the first number, or numerator, of the ratio because the second number, or denominator, is

always 1.) When the line and loadimpedancesare identical and the SWR is 1, all of the RF

power that reaches a load from a transmission line is utilized by that load. If the impedance of

the load is not identical to the impedance of the transmission line, the load does not absorb all

the RF power that reaches it. Instead, some of the RF power is sent back toward the signal

source when the signal reaches the point where the line is connected to the load. This is

known as reflected power or reverse power.
http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci212055,00.htmlhttp://searchdatacenter.techtarget.com/sDefinition/0,,sid80_gci211806,00.htmlhttp://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214263,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci213320,00.htmlhttp://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212986,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci212333,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci212333,00.htmlhttp://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212986,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci213320,00.htmlhttp://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214263,00.htmlhttp://searchdatacenter.techtarget.com/sDefinition/0,,sid80_gci211806,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci212055,00.html


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The VSWR on a transmission line is mathematically related to the ratio of reflected power to

forward power. In general, the higher the ratio of reflected power to forward power, the

greater is the VSWR. The converse is also true. When the SWR on a transmission line is

high, the power loss in the line is greater than the loss that occurs when the VSWR is 1. For

this reason, RF engineers strive to minimize the VSWR on communications transmission

lines. A high VSWR can have other undesirable effects, too, such as transmission-lineoverheating or breakdown of the dielectric material separating the line conductors. The

permissible value of the VSWR is 1.3 maximum.

3.6.1 VSWR MEASUREMENTS

Regardless of the calibration method used, the frequency range for the desired

measurements must be set before calibrating the site Master. The following procedure selects

the frequency range for the calibration.

Step 1. Press the FREQ/DISTkey.

Step 2. Press the F1 soft key.

Step 3. Enter the desired start frequency using the key pad or the Up/Down arrow key.

Step 4. Press ENTER to set F1 to the desired frequency.

Step 5.Press the F2 soft key.

Step 6.Enter the desired stop frequency using the keypad or the Up/Down arrow key.

Step 7. Press ENTER to set F2 to the desired frequency.

3.6.2 CALIBRATION

For accurate results, the Site Master must be calibrated before making any

measurements. The Site Master must be re-calibrated whenever the setup frequency changes

or when the test port extension cable is removed or replaced.

Step 1. Select the appropriate frequency range, as described in the procedure above.

Step 2. Press the START CAL key. The massage CONNECT OPEN or InstaCal to RF out

Port will appear in the display.

Step 3. Connect the InstaCal module to the RF Out port.

Step 4. Press the ENTER key. The Site Master senses the InstalCal module and

automatically calibrates the unit using the OSL (Open, Short & Load) procedure. The

calibration should take about 45 seconds.

Step 5.Verify that the calibration has been properly performed by checking that the CAL

ON! Message is displayed in the upper left corner of the display.3.6.3 DISTANCE TO FAULTVSWR MEASUREMENT

Step 1. Press the FREQ/DIST key. Press the MODE key.

Step 2.Set the D1 and D2 values. The Site Master default for D1 is zero.

Step 3. Select DTF-SWR using the Up/Down arrow key and press ENTER.

Step 4.Connect the Test Port Extension cable to the RF port and calibrate the Site Master.

Step 5. Save the calibration set up.

Step 6. Connect the Device under Test to the Site Master Phase stable Test Port Extension

cable. A trace will be displayed on the screen as long as the Site Master is in sweep

mode.

Step 7. The Value of VSWR & Distance from the site master will be displayed.


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3.7 SUMMARY

RF feeder cable is used to feed antennas and deliver radio frequency power from BTS

to Antenna. RF Jumper cables serve its varied purposes as a connector between main feeders

and antennas. Also, these jumpers can be connected in between main feeders and RF

equipment, such as telecom tower, BTS, antenna feeder system. VSWR is defined as the ratio

of the maximum radio-frequency (RF)voltage to the minimum RF voltage along the line.


Q. 1 The radius of the constant SWR circle is

a) Voltage SWR b) current SWR c) Both d) None

Q.2 In the bench the source is always followed by

a) Attenuator b) Isolator c) Wave meter d) Detector

Q.3 The centre conductor of the RF feeder is almost universally made of

a) Iron b) Copper c) Silver d) Aluminumb)

Q.4 In the bench the source is modulated by a frequency

a) 1 KHz b) 10 KHz c) 100 KHz d) None33.

Q.5 Tunable probe exists over / in

a) VSWR meter b) Slotted section c) Attenuator d) None34.

Q.6 The method used to measure high VSWR is

a) Slotted line method b) Double minimum method c) Both d) None35.

Q.7 Low VSWR method can be used to measure VSWR up to

a) ten b) five c) three d) None

Q.8 What is standard VSWR within mobile communications

a) 1 b) 1.5 c) 2.5 d) None

Q.9 If the RF connector is not terminated properly on the feeder cable, which is

connected to the antenna, then it will result in

a) Power amp will become faulty b) The Radiated power will become low c) Both

d) None.

Q.10 The device which can convert wire-propagated waves into space propagated waves
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214263,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci213320,00.htmlhttp://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci213320,00.htmlhttp://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214263,00.html


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a) Antenna b) Reflector c) Feeder Cable d) None.

Question No. Answer Question No. Answer

1 C 6 B2 B 7 A

3 B 8 B

4 A 9 B

5 B 10 A


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Mobile Communication System (MCS) Cel lu lar Concept



Small, battery-powered handsets

Performance of handovers

4.3 CELLULAR SYSTEM CHARACTERISTICS

4.3.1 GENERAL

Cellular radio systems allow the subscriber to place and receive telephone calls over the

wire-line telephone network where ever cellular coverage is provided. Roaming capabilities

extend service to users traveling outside their outside home service areas.

4.3.2 CHARACTERISTICS OF DIGITAL CELLULAR SYSTEMS

The distinguishing features of digital cellular systems compared to other mobile radio

systems are:

Small cells

A cellular system uses many base stations with relatively small coverage radii (on theorder of a 100 m to 30 km).

Frequency reuse

The spectrum allocated for a cellular network is limited. As a result there is a limit to the

number of channels or frequencies that can be used. For this reason each frequency is

used simultaneously by multiple base-mobile pairs. This frequency reuse allows a much

higher subscriber density per MHz of spectrum than other systems. System capacity can

be further increased by reducing the cell size (the coverage area of a single base station),

down to radii as small as 200 m.

Small, battery-powered handsets In addition to supporting much higher densities thanprevious systems, this approach enables the use of small, battery-powered handsets witha radio frequency that is lower than the large mobile units used in earlier systems.

Performance of handoversIn cellular systems, continuous coverage is achieved by executing a handover (the seamless

transfer of the call from one base station to another) as the mobile unit crosses cell

boundaries. This requires the mobile to change frequencies under control of the cellular

network.

4.4 FREQUENCY REUSE

4.4.1 WHY FREQUENCY REUSE

The spectrum allocated for a cellular network is limited. As a result there is a limit to the

number of frequencies or channels that can be used. A cellular network can only provide

service to a large number of subscribers, if the channels allocated to it can be reused. Channel

reuse is implemented by using the same channels within cells located at different positions in

the cellular network service area.

Radio channels can be reused provided the separation between cells containing the same

channel set is far enough apart so that co-channel interference can be kept below acceptable

levels most of the time. Cells using the same channel set are called co-channel cells.


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4.4.2 CELL CLUSTERING

Within the service area (PLMN), specific channel sets are reused at a different location

(another cell). In the example, there are 7 channel sets: A through G. Neighboring cells are

not allowed to use the same frequencies. For this reason all channel sets are used in a cluster

of neighboring cells. As there are 7 channel sets, the PLMN can be divided into clusters of 7

cells each. The figure shows three clusters.

The number of channel sets is called K. K is also called the reuse factor. In the figure, K=7.

Valid values of K can be found using equation (where i and j are integers):

K=i+j+I*j

4.4.3 OTHER CELL CLUSTERS

The more cells in a cluster, the greater the separation between co-channel cells when Other

clusters are deployed. The idea is to keep co-channel cell separation the same throughout the

system area for cells of the same size. Some valid cluster sizes that allow this are: 1, 3, 4, 7, 9

and 12.

4.4.4 PROCEDURE FOR LOCATING CO-CHANNEL CELLS

It is always possible to find cells using the same channel set, if only the value of K is known.

The following procedure is used.

Step Action

1 Use the integer values i and j from the equation, and start

With the upper left cell. Through this cell, draw the j-axis.

2 Draw the i-axis. To find the starting point for the i-axis, count j cellsdown the j-axis. In the example, one has to count 2 cells down (j=2).

The positive direction of the i-axis is always two cell faces (120degrees) relative to the positive direction of the j-axis.

3 Find the first co-channel cell. It is found by counting i cells in the positivei-axis direction. In the example, i = 3.

4 Find the other co-locating cells by repeating the previous steps. TheStarting point is again at the upper left cell, but now choose another

Direction for the j-axis (e.g. rotate the j-axis with 60 degrees, which isone cell face). As each cell has 6 faces, one will find 6 co-channel cellsaround the starting cells. These are the nearest located co-channelcells.

Signal attenuation With distanceFrequencies can be reused throughout a service area because radio signals typically attenuate

with distance to the base station (or mobile station). When the distance between cells using

the same frequencies becomes too small, co-channel

Interference might occur and lead to service interruption or unacceptable quality of

serviceCapacity/Performance Trade-offs :n If K increases, then performance increasesn If K increases, then call capacity decreases per cellThe number of sites to cover a given area with a given high traffic density, and hence the cost

of the infrastructure, is determined directly by the reuse factor and the number of trafficchannels that can be extracted from the available spectrum. These two factors are


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compounded in what is called spectral efficiency of the system. Not all systems allow the

same performance in this domain: they depend in particular on the robustness of the radio

transmission scheme against interference, but also on the use of a number of technical tricks,

such as reducing transmission during the silences of a speech communication. The spectral

efficiency, together with the constraints on the cell size, determines also the possible

compromises between the capacity and the cost of the infrastructure. All this explains theimportance given to spectral efficiency.

Many technical tricks to improve spectral efficiency were conceived during the system design

and have been introduced in GSM. They increase the complexity, but this is balanced by the

economical advantages of a better efficiency. The major points are the following:

The control of the transmitted power on the radio path aims at minimizing the average power

broadcast by mobile stations as well as by base stations, whilst keeping transmission quality

above a given threshold. This reduces the level of interference caused to the other

communications;

Frequency hopping improves transmission quality at slow speeds through frequency

diversity, and improves spectral efficiency through interferer diversity;

Discontinuous transmission, where by transmission is suppressed when possible, allows areduction in the interference level of other communications. Depending on the type of user

information transmitted, it is possible to derive the need for effective transmission. In the case

of speech, the mechanism called VAD (Voice Activity Detection) allows transmission

requirements to be reduced by an important factor (typically, reduced by half);

The mobile assisted handover, whereby the mobile station provides measurements

concerning neighboring cells, enables efficient handover decision algorithms aimed at

minimizing the interference generated by the cell (whilst keeping the transmission quality

above some threshold).


1. How cellular concepts increase the capacity of the network?

2. The cellular system design was pioneered by during70s by______________________________in the United States, and the initial realization

was known as _____________________________________________.

3. List out the characteristics of digital cellular systems?

4. Why frequency reuse is done.

5. What is co-channel and adjacent channel?

6. What is discontinuous transmission?

7. Explain VAD?

8. Explain cell clustering with a formula.

9. Suggest the ways in which interference can be reduced in mobile network.

10. Explain the trade-off between capacity and coverage.


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4.6 REFERENCES:

1. The GSM system for mobile communication-Michel Mouly & Marie-Bernadette Pautet.

2. GSM system Engineering-Asha Mehrotra (Artech House Publisher).

telecom 1 unit

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