Session 2013Lecture # 2

InstructorKashif Shahzad

Course Details Text Book: Electronic Communication System by

Kennedy and Davis

Reference Text: Modern Digital and Analog Communication System by B.P. Lathi

(Soft copy is available on group page)

Course Instructor: Kashif Shahzad Email: kashifshahzad31@yahoo.com Cell: +92 333 5186231

Course homepage: http://groups.yahoo.com/group/prestonadvcommsystems

Course Breakdown

Assignments: 10%Quizzes: 10%Others: 05%Mid Term: 25%Terminal: 50%

Learning Objective Explain the principles of a communication

systems Discuss the nature of information, different types

of signals involved and their characteristics Make the distinction between Analog and Digital

communication systems Determine the need of modulation and

differentiate various type of modulation techniques in time, frequency domain

Important steps in analog to digital conversion, PCM, PAM, PPM etc

“We will deal with almost every important phenomenon at physical layer level”

Review of last week (Lecture 1) Basic concept of Data, Information and Redundancy

Relationship of Data and Signals

Signals and Systems

Different types of Signals (Chp 2 Reference) Analog vs Digital Continuous vs Discrete Periodic vs Aperiodic Energy vs Power Stochastic vs Deterministic

Today’s MenuEssential Parts of Communication System

TransmitterReceiverChannel

Time and frequency domain relationshipConcept of Spectrum & BandwidthConcept of Passband & Baseband SignalsModulation & DemodulationFourier Series (3 types)

COMMUNICATION OVER LONG DISTANCES IS NO LONGER A PROBLEM.

8

Communication : To transfer information from one place to another

Communication System History 1837 – Samuel Morse invented telegraph. 1858 – First telegraph cable across Atlantic (Canada –

Ireland) 1876 – Alexander Graham Bell invented telephone. 1988 – Heinrich Hertz introduce electromagnetic field theory. 1897 – Marconi invented wireless telegraph. 1906 – Radio communication system was invented. 1923 – Television was invented. 1938 – Radar and microwave system was invented for World

War II. 1950 – TDM was invented. 1956 – First telephone cable was installed across Atlantic. 1960 – Laser was invented 1962 – Satellite communication 1969 – Internet DARPA 1970 – Corning Glass invented optical fiber. 1975 – Digital telephone was introduced. 1985 – Facsimile machine. 1988 – Installation of fiber optic cable across Pacific and

Atlantic. 1990 – World Wide Web and Digital Communication. 1998 – Digital Television. 9

10

The Real AimThe Real Aim“If the information that you want to send is your voice, how to make sure that what you are saying is understood by your friend?”

Basic Parts of a Communication System

Basic Communication System

11

Transmitter Transmission Medium Receiver

InputTransducer

Output Transducer

Noise

wired / wirelessmtx(t)

s(t) r(t)

ptx(t)

n(t)

mrx(t)prx(t)

s(t) – Input signal; audio, video, image, data etc.mtx(t) – Modulating signal; input signal that has been converted to electrical

signal.ptx(t) – Modulated signal transmit by the transmitter.n(t) – Noise signal.prx(t) – Modulated signal receive by the receiver.mrx(t) – Modulating signal at the receiver.r(t) – Output signal.

Component Function in Basic Communication System

12

Input Transducer – convert input signal, s(t) in electrical forms. eg: microphone.

Transmitter – involve modulation process – convert modulating signal, mtx(t) to modulated signal, ptx(t). And finally transmit the signal.

Transmission medium – connecting the transmitter and the receiver that enable the modulated signal, ptx(t) propagate through the medium.

Receiver – receive the modulated signal, prx(t) and then convert the signal to modulating signal, mrx(t) through the process called demodulation.

Output Transducer – convert the modulating signal, mrx(t) to its original forms (output signal), r(t) that is useful to the users. eg: loud speaker.

Transmission Medium (Guided)Twisted pairUnshielded Twisted Pair (UTP)Shielded Twisted Pair (STP)

Coaxial

Fiber Optic

Waveguide

14

100 Mbps is how many bits per sec?

Which is bigger: 10,000 Mbps, 0.01Tbps or 10Gbps?

Wireless channel capacity:

Concept of Time Domain and Frequency DomainAll signals exist in real world in time domainOscilloscopes shows signals as a function of timeBut it is yet again the representation of data as a

function of time

We can view the same information as a function of some other variable which may have a useful meaning

In analysis composite signals are hard to analyzeHence we use frequency domain

WHAT IS FREQUENCY SPECTRUM

IT CONSISTS OF ALL FREQUENCIES CONTAINED IN THE WAVEFORM AND THEIR RESPECTIVE AMPLITUDE IN THE FREQUENCY DOMAIN.

17

Another Look

Time Domain Sine wave viewed as an impulse function in frequency domain

Spectrum Analyzer

Oscilloscope vs Spectrum Analyzer

22

10

0M

Hz

Waveguide

Coaxial Cable

Twisted PairCable

Infra

red V

isibl

e

Ultra

viol

et

Optical Fiber

Extra

H

igh

F

req

uen

cyE

HF

Su

per

Hig

h

Fre

qu

en

cyS

HF

Ultra

H

igh

F

req

uen

cyUH

FV

ery

Hig

h

Fre

qu

en

cyV

HF

Hig

h

Fre

qu

en

cyHF

Med

ium

F

req

uen

cyMF

Low

F

req

uen

cyLF

Very L

ow

Fre

qu

en

cyVL

FAu

di

o

Line-of-sight radio

Skywave radio

Groundwave radio

Wavelength

Frequencydesignations

Transmission media

Propagation modes

Representativeapplications

Frequency

Laser beam

100km 10km 1km 100m 10m 1m 10cm 1cm 10-6m

Tele

ph

on

eT

ele

gra

ph

Mob

il rad

io

VH

F T

V a

nd

FM

Mob

il an

d A

ero

nau

tical

UH

F T

V

CB

rad

ioA

mate

ur ra

dio

AM

bro

ad

castin

g

Aero

nau

tical

Su

bm

arin

e ca

ble

Navig

atio

nT

ran

soce

an

ic rad

io

Bro

ad

ban

d P

CS

Wire

less co

mm

un

icatio

nC

ellu

lar, P

ag

er

Sate

llite-sa

tellite

Micro

wave

rela

yE

arth

-sate

lliteR

ad

ar

Wid

eb

an

d d

ata

1kH

z

10

kH

z

10

0kH

z

1M

Hz

10

MH

z

1G

Hz

10

GH

z

1G

0H

z

10

14H

z

10

15H

z

Concept of Bandwidth IT IS THE DIFFERENCE BETWEEN

THE HIGHEST FREQUENCIES AND THE LOWEST FREQUENCIES OF THE INPUT SIGNAL FREQUENCIES (fB = 2fm ).

The bandwidth of a communication signal bandwidth of the information signal.

23

Data (nonelectrical)

Electrical Waveform

Without any shift in the range of frequencies of the signalThe signal is in its original form, not changed by modulation.

Baseband is the original information that is to be Sent.

It starts from zero and to some specific frequency

WHAT IS BASEBAND SIGNAL ?WHAT IS BASEBAND SIGNAL ?

WHAT IS PASSBAND SIGNAL ?WHAT IS PASSBAND SIGNAL ?

After modulation, the original baseband signal is moved to a range of frequency which far more higher than the baseband signal

So it’s a range of frequency shifted after modulation

What is Modulation MODULATION IS THE PROCESS OF

CHANGING SOME PROPERTYOF THE INFORMATION SOURCES INTO SUITABLE FORM FOR TRANSMISSION THROUGH THE PHISICAL MEDIUM/CHANNEL

“Process of coverting baseband signal into passband signal is called modulation”

It is performed in the Transmitter by a device called Modulator. 26

Transmitter

Carrier

Information to be transmitted

(Baseband signal)

Transmittedsignal

Channel

Receivedsignal

Receiver

Recovery of information

Typical Modulation

Modulation

28

TYPE OF MODULATION

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

29

TYPE OF MODULATION

30

Need for Modulation Channel assignment (various information

sources are not always suitable for direct transmission over a given channel)

Efficient Utilization of bandwidth and multiplexing

Reduce noise &interference

Reduction in antenna size31

What is Demodulation DEMODULATION IS THE REVERSE

PROCESS OF MODULATION BY CONVERTING THE MODULATED INFORMATION SOURCES BACK TO ITS ORIGINAL INFORMATION (IT REMOVES THE INFORMATION FROM THE CARRIER SIGNAL).

It is performed in the Receiver by a device called Demodulator.

32

Example If human voice frequencies contain

signals between 300 Hz and 3000 Hz, a voice frequency channel should have bandwidth equal or greater than 2700 Hz.

a communication channel cannot propagate a signal that contains a frequency that is changing at a rate greater than the Channel Bandwidth.

33

Transmitter Block Diagram

Lecture 27 34

Signal

SourceModulator

Power

Amplifier

Antenna

AM TransmitterBlock diagram

In Modulator the audio modulates the RF amplitude

RFoscillator

ModulatorThe modulator converts the frequency of the

input signal from the audio range (0-5kHz) to the carrier frequency of the station (i.e.. 605kHz-615kHz)

Lecture 27 36

frequency

5kHz

Frequency domain representation of input

Frequency domain representation of output

frequency

610kHz

Receiver Block Diagram

Lecture 27 37

RF

Amplifier

IF

Mixer

IF

Amplifier

Envelope

Detector

Audio

Amplifier

Antenna

Speaker

Trigonometric Fourier SeriesA signal g(t) in the interval

t1 t t1+T0 can be represented by

1

000 )sin()cos()(n

nn tnbtnaatg 011 Tttt

01

1

)(1

00

Tt

t

dttgT

a

01

1

)cos()(2

00

Tt

t

n dttntgT

a

01

1

)sin()(2

00

Tt

t

n dttntgT

b T0 = 2 / 0

Reduced Form of Trigonometric Fourier SeriesOr, in the compact form

If g(t) is even then bn = 0 for all nIf g(t) is odd then an=0 for all n.

1

00 )cos()(n

nn tnCCtg

;22nnn baC

n

nn a

b1tan

011 Tttt

C0 = a0 ;

Remarks on Fourier Series (FS) Representations

The frequency 0= 2/T0 is called the fundamental frequency and the multiple of this frequency n0 is called the nth harmonic.

FS of g(t) is equal to g(t) over the interval t1 t t1+T0 only.

The FS for all t is a periodic function of period T0 in which the segment of g(t) over the interval t1 t t1+T0 repeats periodically.

If the function g(t) itself is periodic with period T0 then the FS represents g(t) for all t.

Exponential Fourier Series

Dn is related to Cn and n as

| Dn | is called the amplitude spectrum of the signal.

Dn is called the phase spectrum of the signal.

They provide a frequency-domain representation of the signal.

011 Tttt

)0(

000)(

nn

tjnn

n

tjnn eDDeDtg

dtetgT

DT

tjnn

0

0)(1

0

nnn CDD2

1|||| nnn DD

NoteMaterial for today was from Chapter 1 text book

This concludes Chapter # 1

Concepts of time, frequency, baseband, passband, bandwidth and spectrum are not exclusively available in chapter 1 but are available in subsequent chapters buried within text.

Questions ????