PRINCIPLES OF

COMMUNICATION SYSTEMS

Lecture 1- Introduction Elements, Modulation,

Demodulation, Frequency Spectrum

Topic covered

• Introduction to subject

• Elements of Communication system

• Modulation

• General term used in communication

• Frequency spectrum and bandwidth

GENERAL INFORMATION

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INTRODUCTION

What is communication?

Communication is the process of exchanging information.

INTRODUCTION

Methods of communication Face to face Signals Written word (letters) Electrical innovations: Telegraph Telephone Radio Television Internet (computer)

ELEMENTS OF A COMMUNICATION SYSTEM

• Basic components: • Transmitter • Channel or medium • Receiver

Noise degrades or interferes with transmitted information

ELEMENTS OF A COMMUNICATION SYSTEM

COMMUNICATION SYSTEM

Transmitter

• The transmitter is a collection of electronic components and circuits that converts the electrical signal into a signal suitable for transmission over a given medium.

• Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

Communication Channel

• The communication channel is the medium by which the electronic signal is sent from one place to another.

• Types of media include

• Electrical conductors

• Optical media

• Free space

• System-specific media (e.g., water for sonar).

COMMUNICATION SYSTEM

Receivers

• A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back into a form understandable by humans.

• Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.

COMMUNICATION SYSTEM

Attenuation

• Signal attenuation, or degradation, exists in all media of wireless transmission. It is proportional to the square of the distance between the transmitter and receiver.

COMMUNICATION SYSTEM

Transceivers • A transceiver is an electronic unit that

incorporates circuits that both send and receive signals.

• Examples are: • Telephones • Fax machines • Handheld CB radios • Cell phones • Computer modems

COMMUNICATION SYSTEM

Noise

• Noise is random, undesirable electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message.

We will study in more detail

COMMUNICATION SYSTEM

COMMUNICATION SYSTEMS

Digital

Analog

BASEBAND

Baseband Transmission • Baseband information can be sent directly and

unmodified over the medium or can be used to modulate a carrier for transmission over the medium.

• In telephone or intercom systems, the voice is placed on the wires and transmitted.

• In some computer networks, the digital signals are applied

directly to coaxial or twisted-pair cables for transmission.

MODULATION AND MULTIPLEXING

• Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another.

• Modulation makes the information signal more compatible with the medium.

• Multiplexing allows more than one signal to be transmitted concurrently over a single medium.

MODULATION

Broadband Transmission • A carrier is a high frequency signal that is

modulated by audio, video, or data. • A radio-frequency (RF) wave is an electromagnetic

signal that is able to travel long distances through space.

Modulation • It is the process of changing one or more

properties of the analog carrier in proportion with the information signal.

MODULATION

Modulation at the transmitter.

WHY MODULATION IS NECESSARY?

• It is extremely difficult to radiate low frequency signals form an antenna in the form of electromagnetic energy.

• Information signals often occupy the same frequency band and if signals from two or more sources are transmitted at the same time, they would interfere with each other.

• Reduction in noise

ANALOG SIGNAL

3 Basic Parameters of analog signal 1. Amplitude 2. Frequency 3. Phase

TWO SIGNALS WITH THE SAME PHASE AND FREQUENCY, BUT DIFFERENT AMPLITUDES

FREQUENCY

• Frequency is the rate of change of cycle (Positive and Negative) with respect to time.

•Change in a short span of time means high frequency.

•Change over a long span of time means low frequency.

3 SINE WAVES WITH FREQUENCIES 0, 8 & 16

PHASE

Phase describes the position of the

waveform relative to time 0.

THREE SINE WAVES WITH THE SAME AMPLITUDE AND FREQUENCY, BUT

DIFFERENT PHASES

MODULATION AND MULTIPLEXING

Types of modulation. (a) Amplitude modulation. (b) Frequency modulation.

MULTIPLEXING

Multiplexing

• Multiplexing is the process of allowing two or more signals to share the same medium or channel.

• The three basic types of multiplexing are: • Frequency division

• Time division

• Code division

MULTIPLEXING

Multiplexing at the transmitter.

• Electronic communications are classified according to whether they are

1. One-way (Simplex) or two-way (Half duplex or Full duplex) transmissions.

2. Analog or digital signals.

TYPE OF COMMUNICATION

SIMPLEX

• The simplest method of electronic communication is referred to as simplex.

• This type of communication is one-way. Examples are:

• Radio

• TV broadcasting

HALF DUPLEX

• The form of two-way communication in which only one party transmits at a time is known as half duplex.

• Examples are:

• Police, military, etc. radio transmissions

• Walky Talky

• HAM radio

• Morse Code

FULL DUPLEX

• Most electronic communication is two-way and is referred to as duplex.

• When people can talk and listen simultaneously, it is called full duplex.

• Telephone

ANALOG COMMUNICATION

DIGITAL COMMUNICATION

DATA

• Data can be analog or digital.

• The term analog data refers to information that is

continuous.

• Digital data refers to information that has discrete

states.

• Analog data take on continuous values.

• Digital data take on discrete values.

FREQUENCY SPECTRUM

• Available range of frequencies for communication

• Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication

• The spectrum spans the entire bandwidth of communicable frequencies

THE ELECTROMAGNETIC SPECTRUM

• The range of electromagnetic signals encompassing all frequencies is referred to as the electromagnetic spectrum.

THE ELECTROMAGNETIC SPECTRUM

Figure 1-13: The electromagnetic spectrum.

THE ELECTROMAGNETIC SPECTRUM

Frequency Ranges from 30 Hz to 300 GHz

• The electromagnetic spectrum is divided into segments:

Extremely Low Frequencies (ELF) 30–300 Hz.

Voice Frequencies (VF) 300–3000 Hz.

Very Low Frequencies (VLF) include the higher end of the

human hearing range up to

about 20 kHz.

Low Frequencies (LF) 30–300 kHz.

Medium Frequencies (MF)

300–3000 kHz

AM radio 535–1605 kHz.

ELECTROMAGNETIC SPECTRUM

Frequency Ranges from 30 Hz to 300 GHz

High Frequencies (HF)

(short waves; VOA, BBC

broadcasts; government and

military two-way communication;

amateur radio, CB.

3–30 MHz

Very High Frequencies (VHF)

FM radio broadcasting (88–108

MHz), television channels 2–13.

30–300 MHz

Ultra High Frequencies (UHF)

TV channels 14–67, cellular

phones, military communication.

300–3000 MHz

ELECTROMAGNETIC SPECTRUM

Frequency Ranges from 30 Hz to 300 GHz

Microwaves and Super High

Frequencies (SHF)

Satellite communication, radar,

wireless LANs, microwave ovens

1–30 GHz

Extremely High Frequencies (EHF)

Satellite communication, computer

data, radar

30–300 GHz

BA

N

D

Frequen

cy

range

Designations applications

2 30 Hz-

300 Hz ELF (

Extremely

low

frequencies)

Include AC power distribution signals (60Hz) and low telemetry

signals.

3 0.3 KHz –

3 KHz VF ( Voice

frequencies) Include frequencies generally associated with human speech.

Standard Telephone channels have a 300 Hz to 3000 Hz bandwidth

and are often called Voice Frequency of Voice band frequencies.

4 3 KHz –

30 KHz VLF( Very

low

frequencies)

Includes upper end of the hearing range. Used for Specialized

government and military systems like submarine communications

5 30 KHZ –

300 KHz LF (low

frequencies) Used for marine and aeronautical navigation

6 0.3 MHz

– 3 MHz Mf( MEDIUM

FREQUECNIE

S)

Used for commercial AM radio broadcasting (535 KHZ to 1605 KHz)

7 3 MHZ –

30 MHz HF ( high

frequencies) Referred as SHORT waves. Used in two way radio communications

, Voice of America and Radio Free Europe broadcast within the HF

band.

Amateur radio and citizens band (CB) radio are also use signals in

this range.

8 30 MHz -

300 MHz VHF( Very

high

frequency)

Used for mobile radio, marine and aeronautical communications,

commercial FM broadcasting ( 88 MHz to 108 MHz) and

commercial TV broadcasting of channels 2 to 13 ( 54 MHz to 216

MHz)

9 300 MHz

– 3 GHz UHF ( Ultra high

frequency) Used by commercial TV broadcasting of channels 14 to

83 , land mobile communications services, cellular

telephones, certain radar and navigation systems, and

microwave and satellite Radio systems. Frequencies

above 1 GHz are considered microwave frequencies,

which include the upper end of the UHF range.

10 3 GHz –

30 GHZ SHF( Super high

frequency) Used for microwave and satellite radio communications

systems.

11 30 GHz –

300 GHz EHF ( Extremely

high frequency) Seldom used for radio communication except in very

sophisticated expensive and specialized applications.

12 0.3 THz –

3 THz Infrared Light Not referred as radio waves. It refers to Electromagnetic

radiation generally associated with heat. Used in heat

seeking guidance systems, electronic photography , and

astronomy.

13 3 THz –

30 Thz Infra red light

14 30 THz –

300 THz Infra red light

15 0.3 PHz-

3 PHZ Visible light Includes electromagnetic frequencies that fall within the

visible range of humans . Light wave communications is

used with optical fiber systems.

16 3 PHz- 30

PHz Ultraviolet light Ultraviolet rays, X rays, Gamma Rays and cosmic rays

have little application to electronic communication.

ELECTROMAGNETIC FREQUENCY SPECTRUM

17 30 PHz – 300 PHz

X rays

18 0.3 EHz- 3 EHz

Gamma rays

19 3 EHz – 30 EHz

Cosmic rays

WAVELENGTH

• It is the length that one cycle of an electromagnetic wave occupies in space i.e. the distance between similar points in a repetitive wave.

• It is inversely proportional to the velocity of propagation.

WAVELENGTH

BANDWIDTH

• Bandwidth (BW) is that portion of the electromagnetic spectrum occupied by a signal.

• Channel bandwidth refers to the range of frequencies required to transmit the desired information.

BANDWIDTH

More Room at the Top

• Today, virtually the entire frequency spectrum between approximately 30 kHz and 300 MHz has been spoken for.

• There is tremendous competition for these frequencies, between companies, individuals, and government services in individual carriers and between the different nations of the world.

• The electromagnetic spectrum is one of our most precious natural resources.

BANDWIDTH

More Room at the Top • Communication engineering is devoted to making

the best use of that finite spectrum.

• Great effort goes into developing communication techniques that minimize the bandwidth required to transmit given information and thus conserve spectrum space.

• This provides more room for additional communication channels and gives other services or users an opportunity to take advantage of it.