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CHAPTER 1

EKT 231COMMUNICATION SYSTEM

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LECTURERS

1. Cik Aini Syuhada Md Zain

ainisyuhada@unimap.edu.my

2. Soh Ping Jack

04-9798873pjsoh@unimap.edu.my

mailto:ainisyuhada@unimap.edu.mymailto:pjsoh@unimap.edu.mymailto:pjsoh@unimap.edu.mymailto:ainisyuhada@unimap.edu.my

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SYNOPSIS

The aim of this subject is :to introduce the students with the basic principles and components ofcommunications system.

This subject will cover various topics such as:

Introduction to Communication System,

Analogue Modulation and Demodulation (e.g. Amplitude Modulation),

Angle Modulation (Frequency Modulation and Phase Modulation),

Digital Modulation,

Noise in Communication System, Transmission System and TransmissionLines.

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Course Outcome (CO)PO1

PO2

PO3

PO4

PO5

PO6

PO7

PO8

PO9

P

O10

P

O11

P

O12

Delivery Mode PossibleAssessment

CO1:

Understand basic principles

of communication systems,

and the essential of

communication system in

real world.

3 1 1 3 1

Lecture;

Laboratory work;

Tutorial;

visiting lecturers

Exams and/ortests;

Lab report

CO2:Ability to analyze noise and

types of analog modulation

and digital modulation and

calculate SNR.

2 2 3 3

Lecture; Laboratorywork;

Tutorial

Exams and/ortests;

CO3:Ability to properly use the

laboratory equipments and

instruments to measure and

analyze output signals and

performsome

troubleshooting

2 3 2 3 3

Laboratory work Lab. Work;

Lab. Report;

CO4:Ability to apply related

software tool in

understanding principle of

communication system.

2 1 3 3

Lecture;

Lab Work;

Discussion

Lab. Work;

Lab Report

CO5:

Ability to think logically,

creatively and innovative,

work in team and

communicate effectively.

3 2 2 3 2

Laboratory work;

Assignments

Discussion;

Oral discussion

COURSE OUTCOMES (OBE)

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REFERENCES

Wayne Tomasi, Electronic CommunicationSystems Fundamentals Through Advanced 5th Ed,Prentice Hall, 2004.

Paul Young, Electronics CommunicationsTechniques, 5thEdition, Prentice Hall, 2004.

Mullet , Basic Telecommunications:The PhysicalLayer, Thomson Learning, 2003.

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ASSESSMENT

Final Exam = 50 %

Coursework = 50 %

Test x 2 = 15 %

Lab Session = 20 %

Lab Test = 10%

Assignments/Quizzes = 5%

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Signals and Systems Defined

A signalis any physical phenomenon which

conveys information

Systemsrespond to signalsand produce new

signals

Excitationsignalsare applied at system

inputsand responsesignalsare produced at

systemoutputs

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A Communication System as a

System Example

A communication systemhas an information

signalplus noise signals

This is an example of a systemthat consists of an

interconnection of smaller systems

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Signal Types

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Conversions Between Signal Types

Sampling

Quantizing

Encoding

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Sound Recording System

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Recorded Sound as a Signal Example

s ign al

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CHAPTER 1INTRODUCTION TO

COMMUNICATION SYSTEM

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Definitions

Communications: Transfer of Information from one place to another.

Should be efficient, reliable, and secured.

Communication system: components/subsystems act together to accomplish

information transfer/exchange

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Definitions (Contd)

Electronic communication system

transmission, reception and processing ofinformation between two or more locations using

electronic circuits. Information source

analog/digital form

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Think!

Have you ever pictured yourself living

in a world without any communication

system?

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Need For Communication

Importance of communication:

exchange of information between two partiesseparated in distances in a more faster andreliable way.

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Information, message and signals

InformationThe commodity produced by the source for transfer

to some user at the destination.

MessageThe physical manifestation of information as

produced by the information source.

SignalsA physical embodiment of informationvoltage

signal or current signal

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Brief History in Communication

Year Events1844 Telegraph

1876 Telephone

1904 AM Radio

1923 Television1936 FM Radio

1962 Satellite

1966 Optical links using laser and

fiber optics1972 Cellular Telephone

1989 Internet

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Development and progress

Communications between human beings

Form of hand gestures and facial expressions

Verbal grunts and groans

Long distance communications

Smoke signals

Telegraph

Telephone

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Contd

Wireless radio signals

Triode vacuum tube

Commercial radio broadcasting

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Analog vs. Digital

Analog

Continuous Variation

Assume the total range of frequencies/time

All information is transmitted

Digital

Takes samples:

non continuous stream of on/off pulses

Translates to 1s and 0s

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Analog vs. Digital

Digital CSAdvantages:-Inexpensive-Privacy preserved(data

encrypted)-Can merge different data-error correction

Disadvantages:-Larger bandwidth-synchronization problem is

relatively difficult

Analog Cs

Disadvantages:

-expensive

-No privacy preserved

-Cannot merge different data

-No error correction capability

Advantages:

-smaller bandwidth

-synchronization problem isrelatively easier.

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Basic Requirements of

Communication System Rate of information transfer:

how fast the information can be transferred

Purity of signal received:whether the signal received is the same as the signal

being transmit

Simplicity of the system

the simpler the system, the better Reliability

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Elements of Communication

System(CS)

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Elements of CS(contd)

Information

The communication system exists to convey amessage.

Message comes from information source

Information forms - audio, video, text or data

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contd

Transmitter: Processes input signal to produce a transmitted signal

that suited the characteristic of transmission channel.

E.g. modulation, coding, mixing, translate

Other functions performed - Amplification, filtering,antenna

Message converted to into electrical signals by

transducers E.g. speech waves are converted to voltage variation

by a microphone

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Elements of CS(contd)

Channel (transmission media):

a medium that bridges the distance from source todestination. Eg:Atmosphere (free space), coaxial

cable, fiber optics, waveguide signals undergoes degradation from noise ,

interference and distortion

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Elements of CS(contd)

Receiver:

to recover the message signal contained in thereceived signal from the output of the channel, and

convert it to a form suitable for the outputtransducer.

E.g. mixing, demodulation, decoding

Other functions performed: Amplification, filtering.Transducer converts the electrical signal at its input

into a form desired by the system used

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Modulation

What is modulation? a process of changing one or more properties of the

analog carrier in proportion to the information

signal. One of the characteristics of the carrier signal is

changed according to the variations of themodulating signal.

AMamplitude, E FMfrequency ,

PM - phase ,

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Modulation (contd)

Why modulation is needed?

To generate a modulated signal suited andcompatible to the characteristics of the transmission

channel. For ease radiation and reduction of antenna size

Reduction of noise and interference

Channel assignment Increase transmission speed

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Noise, interference and distortion

Noise

unwanted signals that coincide with the desired signals.

Two type of noise:internal and external noise.

Internal noise Caused by internal devices/components in the circuits.

External noise

noise that is generated outside the circuit.

E.g. atmospheric noise,solar noise, cosmic noise, man madenoise.

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Noise, interference and distortion

(Contd)

Interference

Contamination by extraneous signals from humansources.

E.g. from other transmitters, power lines andmachineries.

Occurs most often in radio systems whose receiving

antennas usually intercept several signals at the sametime

One type of noise.

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Noise, interference and distortion

(Contd)

Distortion

Signals or waves perturbation caused by imperfectresponse of the system to the desired signal itself.

May be corrected or reduced with the help ofequalizers.

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Limitations in communication

systemTechnological problems

Includes equipment availability, economic factors,federal regulations and interaction with existing

systems. Problem solved in theory but perfect solutions may

not be practical.

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Limitations in communication

system (contd)

Physicals limitations

Bandwidth limitation

Measure of speed

The system ability to follow signal variations depends onthe transmission bandwidth.

Available bandwidth determines the maximum signalspeed.

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Limitations in communication

system (contd)

Noise limitation

Unavoidable.

The kinetic theory.

Noise relative to an information signal is measured interms of signal to noise ratio (SNR).

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Communication system design

Compromise within:

Transmission time and power

SNR performance

Cost of equipments

Channel capacity

Bandwidth

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FREQUENCY AND WAVELENGTH

Cycle- One complete occurrence of arepeating wave (periodic signal) such as one

positive and one negative alternation of a sine

wave.Frequency- the number of cycles of a signal

that occur in one second.

Period - the time distance between two similar

points on a periodic wave.Wavelength- the distance traveled by an

electromagnetic (radio) wave during one

period.

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One cycle

time

PERIOD AND FREQUENCY

COMPARED

Frequency = f = 1/T

T = One period

F d l th d

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+

0 time

distance

Frequency and wavelength compared

f = 1/T

T

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CALCULATING WAVELENGTH

AND FREQUENCY

= wavelength in meters

f = frequency in MHz

= 300/f

f = 300/

THE ELECTROMAGNETIC SPECTRUM

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ELF

103m

107m

104m

105m

106m

10m

1m

10-1m

10-2m

10-3m

10-4m

102m

300Hz

30Hz

30kHz

3kHz

300kHz

30MHz

3MHz

300MHz

3GHz

300GHz

30GHz

THE ELECTROMAGNETIC SPECTRUM

FROM 30 HZ TO 300 GHZ

UHFVHFHFMFLFVLFVF SHF EHF

Frequency

Wavelength

Millimeter

waves

( = 300/f)

(f = 300/)

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LOW AND MEDIUM

FREQUENCIES

Extremely Low Frequencies - 30 to 300 Hz

Voice Frequencies - 300 to 3000 Hz

Very Low Frequencies - 3 kHz to 30 kHz

Low Frequencies - 30 kHz to 300 kHz

Medium Frequencies - 300 kHz to 3 MHz

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HIGH FREQUENCIES

High Frequencies- 3 MHz to 30 MHz

Very High Frequencies- 30 MHz to 300 MHz

Ultra High Frequencies

- 300 MHz to 3 GHz

(1 GHz and above = microwaves)

Super High Frequencies- 3 GHz to 30 GHz

Extremely High Frequencies

- 30 GHz to 300 GHz

THE ELECTROMAGNETIC

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10-3m

10-4m

300GHz

Millimeter

waves

THE ELECTROMAGNETIC

SPECTRUM ABOVE 300 GHZ

Wavelength

0.8x10-6m

0.4x10-6m

Infrared

V

isible

Ultraviolet

X-rays

Gam

marays

Cos

micrays

10-5m

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OPTICAL FREQUENCIES

Infrared - 0.7 to 10 micron

Visible light - 0.4 to 0.8 micron

Ultraviolet - Shorter than 0.4 micron

Note: A micron is one millionth of a meter.

Light waves are measured and expressed

in wavelength rather than frequency.

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TYPES OF COMMUNICATIONS

TX RX

TX

TX

RX

RX

Simplex:

One-way

Duplex:

Two-way

Half duplex:

Alternate TX/RX

Full duplex:

Simultaneous

TX/RX

Channel

Channel(s)

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COMMUNICATIONS SIGNAL

VARIATIONSBaseband- The original information

signal such as audio, video, or computer

data. Can be analog or digital.

Broadband- The baseband signal

modulates or modifies a carrier signal,

which is usually a sine wave at afrequency much higher than the

baseband signal.

V i f f i ti

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Various forms of communication

system Broadcast: radio and television

Mobile communications

Fixed communication system- land line

Data communication-internet

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Frequency Spectrum &Bandwidth

The frequency spectrum of a waveform consistsof all frequencies contained in the waveform andtheir amplitudes plotted in the frequency

domain.The bandwidth of a frequency spectrum is the

range of of frequencies contained in the

spectrum.It is calculated by subtracting thelowest frequency from the highest.

F S &B d id h

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Frequency Spectrum &Bandwidth

(contd)

Bandwidth of the information signal equals tothe difference between the highest and lowestfrequency contained in the signal.

Similarly, bandwidth of communication channelis the difference between the highest and lowestfrequency that the channel allow to pass through

it

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Power gain

Signal level gain

signal gain

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signal gain

In Engineering Problems, we have known the termsignal gain / mechanical advantage;

Examples are chain pulley block, cantilever, gear,amplifier, transformer.

Voltage amplifier: Av= Vo/Vi.Transistors current gain: = ic/ib,

Chain pulley block: weight lifted/weight applied.

Transformer: secondary voltage/primary voltage gear box: output torque/input torque.

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Power gain

It is the ratio of output power over input power.

Ap= Po/Pi.

If the energy is consumed in doing a work, Power gainis always1.

Example is transformer, chain pulley block, gearboxes etc have power gain less than one.

In amplifiers, the apparent power gain may be more

than one. The signal power is amplified. DC electricpower is transformed into signal power.

In signal gain:

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In signal gain:

The advantage or, signal gain may be >1 though the

power gain is < 1.

At first instance, it appears that there is no apparentrelation between signal gain and power gain.

It is because the friction of the load in which thepower is fed, is not accounted.

P r nd lt in in

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Power and voltage gain in

communication

In communication, due to known characteristicimpedance of the channel, the power andvoltage gains become explicit.

It is designated in terms of decibels, dB.

Power gain in dB = 10 log (Po/Pi) dB.

Voltage gain in dB = 20 log (Vo/Vi) dB.Here if power gain < 1, voltage gain

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power ratio Po/Pi = 10,000 = 40 dB

Voltage ratio Vo/Vi = 100 = 40 dB.

See that Po/Pi = (Vo/Vi)2

(Po/Pi)dB = 2(Vo/Vi)dB

g g ( o i)

Voltage gain in dB = 20 log (Vo/Vi) dB.

are absolute gains

Term is power

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Alternatively:

Power gain = 10(gain in dB/10)

Voltage gain = 10 (gain in dB/20)

Examples:

A 64 dB gain means 106.4= 2.5212x106watts.

An attenuation by 0.01= 10 log(0.01)

= -20 dB

E l

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Examples:

Let there be two amplifiers in cascade. Theirgains are 13 dB and 10 dB respectively.

The overall gain is 13+10 = 23 dB.

In terms of ratio:

23 dB = 10(23/10)= 200

13 dB = 10(13/10)= 20

10 dB = 10(10/10)

= 10Again 20 x 10 = 200.

same

Sum

multiplication

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Relative dB

It is convenient to express signals with somereferencesuch as

1mW power or,

1 V voltage level.

This permits input- and output- signals to beexpressed in terms of relativedB.

When referenced to 1mW, it is written dBm

When referenced to 1 V, it is written as dBV

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Relative dB is not a gain

but is termed as gain wrt a reference.

5 watts signal,

In relative dB; 10 log(5W/1mW) = 36.99 dBm

500 V signal:

In relative dB; 20 log(500 V /1 V ) = 53.98dB

V