Ep301

Learning Outcomes

Upon completion of this chapter, students should be able
to :-

•Understand the element in communication system.
•Understand the information , messages and signal.
•Understand the modulation process and its needs.
•Learn noise, interference and distortion.
•Know the frequency spectrum.
•Understand various types of communication system.

1

INTRODUCTION

The word TELECOMMUNICATION is a combination of two words...
TELE + COMMUNICATION

The word TELE in Latin means DISTANCE.

Hence Telecommunication is DISTANCE COMMUNICATION

2

DEFINATION
Telecommunication is the transmission of messages, over
significant distances, for the purpose of communication.

In earlier times, telecommunications involved the use of
visual signals, such as smoke, semaphore telegraphs, signal
flags, and optical heliographs, or audio messages via coded
drumbeats, lung-blown horns, or sent by loud whistles, for
example.

In the modern age of electricity and electronics, telecommunications has typically
involved the use of electric means such as the telegraph, the telephone, and the
teletype, the use of microwave communications, the use of fiber optics and their
associated electronics, and/or the use of the Internet.

3

CLASSIFICATION OF COMMUNICATION SYSTEMS

Radio
Telephony
Mobile
Comm.
Radio Aids to
Navigations

Broadcasting

Radio
telemetry

Radar

Point to
point

Telegraphy Computer
Comm.

4

INTRODUCTION TO
COMMUNICATION SYSTEM

5

Answers
1.1 What is communication system
System noise
and
interference

Transmission medium
TRANSMITTER OR RECEIVER
Receiver
Communication channel informetion

Information source
( intelligence)
Pysical facility(metalic or optical fiber cable)
or free space( earth atmosphere)

BASIC BLOCK DIAGRAM OF AN ELECTRONIC COMMUNICATION
SYSTEM

6

Components of the Communication System

A) INFORMATION SOURCE

 The message is the information source.
 Example : Text, voice, pictures or video signal
 Information can electrical and non-electrical. Non-electrical information
source must be converted into electrical form before it is transmitted.

B) TRANSMITTER

 A collection of one or more electronic devices or circuits that convert the
original information source into a signal suitable for information.
 A complex processes ( Encoding and modulation ) must be done to the
information signal before transmission.

7

Component of the Communication system

c) Transmission medium
A transmission medium (plural transmission media) is a material substance
(solid, liquid, gas or plasma) that can propagate energy waves. For
example, the transmission medium for sound received by the ears is usually
air, but solids and liquids may also act as transmission media for sound.
The absence of a material medium (the vacuum of empty space) can also be
thought of as a transmission medium for electromagnetic waves such
as light and radio waves. While material substance is not required for
electromagnetic waves to propagate, such waves are usually affected by the
transmission media they pass through, for instance by absorption or
by reflection or refraction at the interfaces between media.

8

d) Channel

 The path provided by a transmission medium can take the form of physical
separation, such as by multipare cable or electrical separation such as by
frequency or time division multiplexing.

 An example is the MIXFM which has its channel allocated at a frequency of
94.5 Mhz.

e) Noise

 Noise is unwanted energy which is usually random in nature that is present in
any point of a commnication system.

 Noise may be due to various causes such atmospheric noise, thermal
agitation noise, shot noise and industrial noise.

9

f) Receiver
A receiver is a collection of one or more electronic devices and
circuits that accept the transmitter signals from the transmission
medium and convert them back into their original form.

-A band pass filter rejects all frequencies above or below its designed
frequency. Most receivers utilize an LC resonant circuit as a band pass
filter. The band pass filter is tuned to the carrier frequency signal of
the transmitting station.
In other words the receiver SELECTs the appropriate station.

The last stage of the communication system is

g) destination equipment which converts these electrical signals into its
original form for the data broadcasting so that it can be easily understand
by the end user or receiver and then this same sort of communication
process is used for the acknowledgment of signals to sender machine.
10

What is information, messages and signal.

Information
Defined as knowledge or inteligence that communicate between two or more
points, Information in its most restricted technical sense is an
ordered sequence of symbols that record or transmit a message. It can be
recorded as signs, or conveyed as signals by waves

Messages
A telephone circuit is comprised of two or more facilities interconnected in
tandem to provide a transmission path between a source and a destination.
The interconnected facilities maybe temporary as in standard telephone call or
permanent as in a dedicated private carrier system. The information is called
messages.

.
11

Signal

Signals can be defined as measurable quantities which may be either time-
varying or spatial-varying. A signal may be expressed as a function of time and
frequency.
When a signal is expressed as a function of time, it can be either
discrete (discrete-time signal) or continuous (continuous-time signal).
In a more practical sense, there are two basic types of signals:

1)Digital signal
2)Analogue signal

Digital signal
Digital signal can be defined as a discrete signal or discrete-time signal that
generates and process data in form of zeroes and ones (0s and 1s). This implies
that digital signals can take on only a discrete set of values. Digital signal is
quantized (has finite set of values). The value of a Digital signal may be described in
terms of voltage pulses that can be sent over data transmission medium. As
described above, the signal sent is either off (o) or on (1) pluses, representing a
binary digit. For example, computers use digital signals.
12

Analogue signal
Analogue signal (unlike digital signal) is not discrete and quantized.
Analogue signal is continuous in nature and generates continuous values,
leading
to continuous wave pattern.Analogue signals can be used over a variety of
transmission media. For example, telephone lines use analogue protocols.

What Does Signals Do?
•Signals carry information, in form of data, image, sound or pictures.
•Computers depend on digital signals for data transmission.
•The computer stores data in form of zeros and ones, which are called binary
digits.
•A single binary digit is referred to a bit and a set of 8 bits is called a byte.
1024 byte is equal to 1 kilobyte.

13

WHAT IS BAND PASS AND BASE BAND
A bandpass filter is a device that passes frequencies within a certain range
and rejects (attenuates) frequencies outside that range. An example of
an analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–
capacitor circuit. These filters can also be created by cobining a low-pass
filter with a high-pass filter.

14

What is baseband

In telecommunications and signal
processing baseband is an adjective that
describes signals and systems whose range
of frequencies is measured from close to 0
hertz to a cut-off frequency a maximum
bandwidth or highest signal frequency; it is
sometimes used as a noun for a band of
frequencies starting close to zero..

Baseband can often be considered as a synonym to lowpass or non-
modulated, and antonym to passband, bandpass, carrier-
modulated or radio frequency (RF) s

15

1.3 MODULATION AND DEMODULATION

MODULATION is an important step of communication system
In modulation, a message signal, which contains the information is used to control the
parameters of a carrier signal, so as to impress the information onto the carrier.
The Messages
The message or modulating signal may be either:
analogue – denoted by m(t)
digital – denoted by d(t) – i.e. sequences of 1's and 0's
The message signal could also be a multilevel signal, rather than binary; this is not
considered further at this stage.
OR
Modulation is a process in which the characteristics of a
signal circuit is caried in accordance with the information
signal which is to be transmitted.
The modulation signal,which is to be transmitted is known
as Modulating signal.

16

MODULATION……
In electronics modulation is the process of varying one or more properties of a
high-frequency periodic waveform, called the carrier signal, with a modulating
signal which typically contains information to be transmitted. At the
destination, a process of demodulation extracts the modulation signal from the
modulated carrier. The three key parameters of a periodic waveform are
its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"). Any
of these properties can be modified in accordance with a low frequency signal
to obtain the modulated signal. Typically a high-frequency sinusoid waveform is
used as carrier signal, but a square wave pulse train may also be used.
In telecommunications, modulation is the process of conveying a message
signal, for example a digital bit stream or an analog audio signal, inside
another signal that can be physically transmitted. Modulation of a sine
waveform is used to transform a baseband message signal into
a passband signal, for example low-frequency audio signal into a radio-
frequency signal (RF signal).

17

MODULATION…..

BLOCK DIAGRAM THE PROCESS OF
MODULATION

18

DEMODULATION
Is the reverse process (to modulation) to recover the message signal m(t) or
d(t) at the receiver.
DEMODULATION is the act of extracting the original information-bearing signal
from a modulated carrier wave. A demodulator is an electronic
circuit (or computer program in a software defined radio) that is used to
recover the information content from the modulated carrier wave.[1]
These terms are traditionally used in connection with radio receivers, but many
other systems use many kinds of demodulators. Another common one is in
amodem, which is a contraction of the terms modulator/demodulator .

19

THE NEEDS OF MODULATION AND
NEEDS OF MODULATON
DEMODULATION
To transfer the message signal from one site another site without any loss for
that we are using modulation.
Modulation classified in two types.

1.Analog modulation.
2.DigitalModulation.

Modulation is need basically to:

i)To increase the bandwidth of the signal

ii)To multiplex more number of signal

20

iii)To reduce the interference( noise and distortion) made when we transmit
the signals with nearly same frequency in the audio frequency range (20-20k)
Hz.

iv) To reduce the antenna height.
For efficient transmission the transmitting antennas should have length at
least equal to a quarter of the wavelength of the signal to be transmitted.

For an electromagnetic wave of frequency 15 kHz, the wavelength λ is 20 km
and one-quarter of this will be equal to 5 km. Obviously, a vertical antenna of
this size is impractible. On the other hand, for a frequency of 1 MHz, this
height is reduced to 75m.

21

Also, the power radiated by an antenna of length l is proportional to (l/λ)2.
This shows that for the same antenna length, power radiated is large for
shorter wavelength. Thus, our signal which is of low frequency must be
translated to the high frequency spectrum of the electromagnetic wave. This
is achieved by the process of modulation.

v) To narrow banding system.

vi) To reduce equipment complexity.

vii)To favors the complexity of the transmission system

Audio frequencies are within the range of 20 Hz to 20 kHz. Without
modulation all signals at same frequencies from different transmitters would
be mixed up. There by giving impossible situation to tune to any one of them.
In order to separate the various signals, radio stations must broadcast at
different frequencies.

22

1.4 NOISE, INTERFERENCE AND DISTORTION
Electrical noise is defined as any undesirable electrical energy
that’s falls within the passband of the signal.

It can be divided into two general categories

i) correlated- its implies a relationship between the signal and
the noise.

ii) uncorrelated-exists only when a signal is present on the
otherhand is present at the time wheather there is a signal or
not.

23

Uncorrelated noise
Uncorrelated noise is present regardless of wheather there is a
signal or not.
Devide into two categories: external and internal.

External Noise
Noise that generated outside the device or circuit. The three primary
sources of external noise are atmospheric, extraterrestrial and man-
made. Refer to notes to explain …( italic)

Internal noise
Is electrical interference generated within a device or circuit. There are
three kinds of internally generated noise shot, transit time and
thermal.
Refer to notes to explain..(italic)

24

Interference is a form of external noise and as the name
implies. Means to disturb or detract from. Electrical interference
is when information signals from one source produce
frequencies that fall outside their allocated bandwidth and
interfere with information signals from another source.

Distortion
A distortion is the alteration of the original shape (or other
characteristic) of an object, image, sound, waveform or other
form of information or representation. Distortion is usually
unwanted, and often many methods are employed to minimize it
in practice. In some fields, however, distortion may be desirable;
such is the case with electric guitar distortion .

25

Continue distortion……………..

This diagram below shows the behaviour
of a signal (made up of a square
wave followed by a sine wave) as it is
passed through various distorting
functions.

1.The first trace (in black) shows the input.
It also shows the output from a non-
distorting transfer function (straight line).

2. A high-pass filter (green trace) will distort the shape of a square wave by
reducing its low frequency components. This is the cause of the "droop" seen
on the top of the pulses. This "pulse distortion" can be very significant when a
train of pulses must pass through an AC-coupled (high-pass filtered) amplifier.
As the sine wave contains only one frequency, its shape is unaltered.

26

3. A low-pass filter (blue trace) will round the pulses by removing the high
frequency components. All systems are low pass to some extent. Note that
the phase of the sine wave is different for the lowpass and the highpass
cases, due to the phase distortion of the filters.

4) A slightly non-linear transfer function (purple), this one is gently
compressing as may be typical of a tube audio amplifier, will compress the
peaks of the sine wave. This will cause small amounts of low order harmonics
to be generated.

5)A hard-clipping transfer function (red) will generate high order harmonics.
Parts of the transfer function are flat, which indicates that all information
about the input signal has been lost in this region.

27

Signal to noise(S/N) power ratio
Refer to notes…..

1. Formula
2. Solve S/N power ratio
3. Distinguish between noise factor and noise figure.

28

1.5 Electromagnetic and Radio Waves
The transmission of energy through free space (vacuum) is done by
electromagnetic waves.

Electromagnetic waves are caused by oscillations of electric and magnetic
fields. These waves moves at a constant velocity of 3 x 10 8 m/s.

Electromagnetic waves are used to transmit :

a)Long or short wave radio signals
b)FM wavelength radio signals
c)Wireless communication signals

They are also responsible for transmitting energy in the form of :

a)Microwave, infrared radiation (IR)
b)Ultraviolet light (UV), X-rays, Gamma rays

λ=c/f
29

Electromagnetic Spectrum
The electromagnetic spectrum extends from below frequencies used for modern radio
to gamma radiation at the short-wavelength end, covering wavelengths from thousands of
kilometers down to a fraction of the size of an atom.

30

Radio Frequency (RF) Spectrum
Audio Frequency (AF) is any frequency that human can hear, ( 20 Hz – 20 Khz)

Radio Frequency (RF) is any frequency above the range of human perception
which is greater than 20 Khz.

Frequency Band Frequency  Application
Very Low 3 - 30 KHz > 10000m Telegraphy, human range frequency
Frequency (VLF)
Low Frequency 30-300 KHz 10000-1000m Point to point, navigation
(LF)
Medium 300K-3 MHz 1000-100m AM radio broadcast,
Frequency (MF) maritime/aeronautical mobile
High 3 - 30 MHz 100 - 10 m Shortwave Broadcast Radio
Frequency(HF)
Very high 30 - 300 10 - 1 m Low band: TV Band1- Channel 2-6, Mid
Frequency(VHF) MHz band: FM radio, High Band: TV Band 2-
Channel 7-13
Ultra High 300M - 1 m - 10 cm Mobile phone, Channel 14 - 70
frequency (UHF) 1GHz
Super high 3-30 GHz 0.01-0.001 m satellite communucation, C-band, x-
frequency (SHF) band,Ku-band, Ka-band.
Extremely High 30 - 300 GHz  0.01m Satellite, radar system, IR, UV, X-rays,
Frekuensi (EHF) Gamma Rays.

31

Analog or Digital Communication
Communications signals can be either by analog signals or digital signals. These
are analog communication systems and digital communication systems.

• For an analog signal, the signal is varied continuously with respect to the
information.

• In a digital signal, the information is encoded as a set of discrete values (for
example, a set of ones and zeros).

Fact – Optical Fiber provides cheaper
bandwidth for long distance
communication

32

Frequency(f),wavelength(λ) and velocity(V)

V = f λ,
F = 1/ T
From the graph :
Ampl/V.
Time = 10s

Amplitude = 10V
frequency = 1/T = 1/10 = 0.1Hz
10

0
5 10 time/s

ONE CYCLE

WAVE AMPLITUDE vs TIME

33

Ampl/V
.

1
0
0
5 10 distance/ m

wavelength, 

WAVE AMPLITUDE vs DISTANCE

Example : Given f = 300Mhz and V = 3 x 108 m/s, find the wavelength.

Answer : wavelength, λ = v / f = 3 x 108/ 300 x 106

= 1 meter

34


Ampl/V.

10

0

360 Angle(o)
180

WAVE AMPLITUDE vs ANGLE

35

Frequency(f),wavelength(λ) and speed(V)

Ampl/V. 

10

0 180 360 sudut (o)

From the graph,  = 180o - 90o = 90o

Method to calculate angle from analog wave

Two oscillators that have the same frequency and different
phases have a phase difference, and the oscillators are said to
be out of phase with each other. The amount by which such
oscillators are out of step with each other can be expressed in
degrees from 0° to 360°, or in radians from 0 to 2π.

36

1.5.3 Bandwidth
The two most significant limitations on the performance of a communications
system are noise and bandwidth. The bandwidth of an information signal is
simply the difference between the highest and the lowest frequencies
contained the information, and the bandwidth of a communication channel is
the difference between the highest and lowest frequencies that the channel will
allow to pass through it

Bandwidth has several related meanings:
Bandwidth (signal processing) or analog bandwidth, frequency
bandwidth or radio bandwidth: a measure of the width of a range of
frequencies, measured in hertz
Bandwidth (computing) or digital bandwidth: a rate of data transfer, bit rate or
throughput, measured in bits per second (bps)
Spectral linewidth: the width of an atomic or molecular spectral line, measured
in hertz

37

Bandwidth…..
The bandwidth of a communications channel must be large enough to pass
all significant information frequencies.In other words the bandwidth of the
communications channel must be equal to or greater than the bandwidth of
the information.

Bandwidth(BW) = f2- f1

Give some example from the formula …….
38

1.6 Types of communication system

39

1.Broadcast communication system
Broadcasting is the distribution of audio and video content to a dispersed
audience via radio, television, or other.
Receiving parties may include the general public or a relatively large
subset of thereof.
Historically, there have been several different types of electronic
broadcasting media:
Example…..

Block diagram of broadcast receiver using AGC

40

1. Telephone broadcasting (1881–1932): the earliest form of electronic
broadcasting (not counting data services offered by stock telegraph
companies from 1867, if ticker-tapes are excluded from the definition).
Telephone broadcasting began with the advent of Théâtrophone ("Theatre
Phone") systems, which were telephone-based distribution systems allowing
subscribers to listen to live operaand theatre performances over telephone
lines, created by French inventor Clément Ader in 1881. Telephone
broadcasting also grew to include telephone newspaper services for news
and entertainment programming which were introduced in the
1890s, primarily located in large European cities. These telephone-
based subscription services were the first examples of electrical/electronic
broadcasting and offered a wide variety of programming .
2. Radio broadcasting (experimentally from 1906, commercially from 1920):
radio broadcasting is an audio (sound) broadcasting service, broadcast
through the air as radio waves from a transmitter to an antenna and, thus,
to a receiving device. Stations can be linked in radio networks to broadcast
common programming, either in syndication or simulcast or both.

41

Continue….
3.Television broadcasting (telecast), experimentally from 1925, commercially
from the 1930s: this video-programming medium was long-awaited by the
general public and rapidly rose to compete with its older radio-broadcasting
sibling.
4.Cable radio (also called "cable FM", from 1928) and cable television (from
1932): both via coaxial cable, serving principally as transmission mediums for
programming produced at either radio or television stations, with limited
production of cable-dedicated programming.
5.Satellite television (from circa 1974) and satellite radio (from circa 1990): meant
for direct-to-home broadcast programming (as opposed to studio network
uplinks and downlinks), provides a mix of traditional radio or television broadcast
programming, or both, with satellite-dedicated programming.
6.Webcasting of video/television (from circa 1993) and audio/radio (from circa
1994) streams: offers a mix of traditional radio and television station broadcast
programming with internet-dedicated webcast programming.

42

2. Mobile communication system
A mobile phone, cell phone or hand phone is an electronic device used to
make mobile telephone calls across a wide geographic area, served by many
public cells, allowing the user to be mobile. By contrast, a cordless
telephone is used only within the range of a single, private base station, for
example within a home or an office.A mobile phone can make and receive
telephone calls to and from the public telephone network which includes
other mobiles and fixed-line phones across the world. It does this by
connecting to a cellular network provided by a mobile network operator.In
addition to telephony, modern mobile phones also support a wide variety of
other services such as text messaging, MMS, email, Internet access, short-
range wireless communications (infrared, Bluetooth), business
applications, gaming and photography. Mobile phones that offer these more
general computing capabilities are referred to as smartphones.

43

GSM (Global System for Mobile Communications, originally Groupe Spécial
Mobile), is a standard set developed by the European Telecommunications
Standards Institute (ETSI) to describe technologies for second generation (or
"2G") digital cellular networks. Developed as a replacement for first generation
analog cellular networks, the GSM standard originally described a digital, circuit
switched network optimized for full duplex voice telephony.

The standard was expanded over time to include first
circuit switched data transport, then packet data transport
via GPRS. Packet data transmission speeds were later
increased via EDGE. The GSM standard is succeeded by
the third generation (or 3G") UMTS standard developed by
the 3GPP.
GSM networks will evolve further as they begin to
incorporate fourth generation (or "4G") LTE
Advanced standards. "GSM" is a trademark owned by
the GSM Association.

44

Mobile phone subscribers worldwide
700000

600000
subscribers (x 1000)

500000 Analog total
GSM total
400000 CDMA total
300000 TDMA total
PDC/PHS total
200000 total
100000

0
1996 1997 1998 1999 2000 2001

Mobile Communications: Wireless 4.1.1
Telecommunication Systems

Block diagram of Mobile communication system

A wireless communication link includes a transmitter, a receiver, and a
channel,as shown in Figure. Most links are full duplex and include a
transmitter and a receiver or a transceiver at each end of the link
46

in Fig. 2-2 (a). In peer-to-peer systems, mobile units communicate directly
with each other. Mobile units sharing a frequency channel can communicate
with one another, and independent conversations can take place on different
channels. Many amateur, and most CB radio contacts fit into this peer-to-peer
model, as shown in Fig. 2-2 (b). In peer-to-peer systems, a mobile can
sometimes hear only one of two other mobiles that are using a channel, when
a total of three users are active.
47

3. Fixed communication system
Technology basically gives us a lot of advantages to really connect
on what we are up to and one of the most important and most commonly used
to us is “Communication”, whereas we basically exchange information from one
another sometimes by the way of Fixed Communication Systems. I think more
surprisingly is that the evolution of this systems that allows us to communicate
even in the hardest possibilities.
With the help of Fixed Communication Systems, we are able to have better
communication through any means of communications there is.
One of the most common means of technology in
our world is the telephone, and with it it’s pretty
much a basic point to have access on a telephone
wherever you may be. In every phone servers there
is Fixed Communication System in which basically
becomes the root in order for a simple
communication by the use of telephone or hand
held phones to another.
48

4. Data communication system
Data Communications is the transfer of data or information between a source
and a receiver. The source transmits the data and the receiver receives it. The
actual generation of the information is not part of Data Communications nor is
the resulting action of the information at the receiver. Data Communication is
interested in the transfer of data, the method of transfer and the preservation of
the data during the transfer process.
In Local Area Networks, we are interested in "connectivity", connecting
computers together to share resources. Even though the computers can have
different disk operating systems, languages, cabling and locations, they still can
communicate to one another and share resources.
The purpose of Data Communications is to provide the rules and regulations that
allow computers with different disk operating systems, languages, cabling and
locations to share resources. The rules and regulations are called protocols and
standards in Data Communications.

49

BASIC BLOCK DIAGRAM OF DATA COMMUNICATION
50

Refer to the block diagram of data communication

There is a source of digital information ( primary station), transmission
medium ( facility) and a destination (secondary station) .

The primary source is usually a main frame computer wth its own set of
local terminals and peripherals equipment.

The digital information is then transferred by using the transmission
medium such as free- space radio transmission ( terrestrial and satellite
microwave), metallic cable facilities ( both digital and analog systems) and
fiber-potic cable( light propogation).

DTE (Data Terminal Equipment)
refers to the interface equipment used at the station between the host and
modem to adapt the digital signals from the computer and terminals to
suitable form for transmission.

51

DCE ( data communication Equipment)

Means the equipment that converts digital signal to analog signals
and interfaces the data terminal equipment to the analog
transmission medium.DCE is nothing but a modem (
modulator/demodulator). It converts binary digital signals to
analog signals such as PSK.FSK and QAM and vice versa.

52

ASSIGNMENT

1. Compare between Broadcast and mobile communication system.

2. Compare between Fixed communication and data communication system.

53

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