LECTURE 1

INTRODUCTION TO PRINCIPLES OF

COMMUNICATION ENGINEERING

PART 1

WHAT DO YOU UNDERSTAND

ofCOMMUNICATION SYSTEM?

DEFINITIONS OF COMMUNICATIONS Humans exchanging

information Machines exchanging

information Conveying thoughts, feelings,

ideas, and facts Sending and receiving

information by electronic means

BARRIERS TO COMMUNICATIONS

Language: human, computer, or electronic

Distance: space between sending and receiving parties

COMMON FORMS OF COMMUNICATIONS

Human voice: face-to-face conversations, public speakers, actors in plays, etc.

Audio: CDs, tape, records, radio Body language: non-verbal Print: newspapers, magazines,

books, etc. Film: still and movie Video: movies, graphics and

animation Music: personal, concerts

FORMS OF ELECTRONIC COMMUNICATIONS

Radio and TV broadcasting Telephone, wired and wireless Fax Pagers Computer networks: modem,

e-mail, Internet and World Wide Web, wireless

Satellites, radar, radio telescopes

Communication systems

Basic components:

Transmitter Channel or medium Receiver Noise degrades or

interferes with transmitted information.

Communication Systems

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 Systems

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 is the medium

for sonar).

Communication Systems

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 Systems

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 Systems

Noise Noise is random, undesirable

electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message.

TYPES OF COMMUNICATIONS

TX RX

TX

TX

RX

RX

Simplex:One-way

Duplex:Two-wayHalf duplex:Alternate TX/RXFull duplex:SimultaneousTX/RX

Channel

Channel(s)

TYPES OF COMMUNICATIONS SIGNALS

Analog - smooth and continuous voltage variation.

Digital - binary or two voltage levels.

Time

COMMUNICATIONS SIGNAL VARIATIONS Baseband - 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 a frequency much higher than the baseband signal.

Basic analog communications system

Modulator

Demodulator

Transmission Channel

Input transducer

Transmitter

Receiver

Output transducer

Carrier

EM waves (modulated signal)

EM waves (modulated signal)

Baseband signal (electrical signal)

Baseband signal (electrical signal)

19

MODULATION

An electronic technique in which a baseband information signal modifies a carrier signal (usually a sine wave) for the purpose of frequency translation and carrying the information signal via radio.

The common types of modulation are amplitude, frequency and phase.

Why modulation is needed?

To generate a modulated signal suited and compatible to the characteristics of the transmission channel.For ease radiation and reduction of antenna sizeReduction of noise and interferenceChannel assignmentIncrease transmission speed

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Modulation at the transmitter

AMPLITUDE MODULATION

High-frequency carrier, normally muchhigher than the baseband frequency

The modulating (baseband) signal is a sinusoid in this example.

FREQUENCY MODULATION

The baseband signal controls the carrier’s frequency and the carrier’s amplitude remains constant.

Res

tin

g f c

Incr

easi

ng

f c Incr

easi

ng

f c

Dec

reas

ing

f c

Res

tin

g f c

Mod

ula

tin

g si

gnal

Car

rier

FM

MULTIPLEXING

Multiplexing (MUX or MPX) - the process of simultaneously transmitting two or more baseband information signals over a single communications channel.

Demultiplexing (DEMUX or DMPX) - the process of recovering the individual baseband signals from the multiplexed signal.

MULTIPLEXING AND DEMULTIPLEXING

MUX DEMUX

Single communications channel (radio or cable)

Original baseband information signals

Recovered basebandinformation signals

Modulation and Multiplexing

ELECTRONIC COMMUNICATIONS APPLICATIONS

Radio broadcasting (AM & FM) Television broadcasting

(analog & DTV) Cable TV Wireless remote control Paging Navigation and direction

finding Telemetry

ELECTRONIC COMMUNICATIONS APPLICATIONS (Continued)

Radio astronomy Surveillance RF identification (ID) Music services Telephones (wired, cordless,

cellular) Facsimile Two-way radio

ELECTRONIC COMMUNICATIONS APPLICATIONS (Continued)

Radar Sonar Amateur radio Citizens and family radio Data communications Networks Internet and World Wide

Web

FREQUENCY AND WAVELENGTH

Cycle - One complete occurrence of a repeating 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.

One cycle

time

PERIOD AND FREQUENCY COMPARED

Frequency = f = 1/T

T = One period

+

0 time

distance

Frequency and wavelength compared

f = 1/T

T

CALCULATING WAVELENGTH AND FREQUENCY

= wavelength in meters

f = frequency in MHz

= 300/f

f = 300/

ELF

103 m

107 m

104 m

105 m

106 m

10 m

1 m

10-1 m

10-2 m

10-3 m

10-4 m

102 m

300

Hz

30 H

z

30 k

Hz

3 k

Hz

300

kH

z

30 M

Hz

3 M

Hz

300

MH

z

3 G

Hz

300

GH

z

30 G

Hz

THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ

UHFVHFHFMFLFVLFVF SHF EHF

Frequency

Wavelength

Mill

imet

erw

aves

( = 300/f)

(f = 300/)

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

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

10-3 m

10-4 m

300

GH

zM

illi

met

erw

aves

THE ELECTROMAGNETIC SPECTRUM ABOVE 300 GHZ

Wavelength

0.8

x 10

-6 m

0.4

x 10

-6 m

Infr

ared

Vis

ible

Ult

ravi

olet

X-r

ays

Gam

ma

rays

Cos

mic

ray

s

10-5 m

OPTICAL FREQUENCIES

Infrared - 0.7 to 10 micron Visible light - 0.4 to 0.8

micron Ultraviolet - Shorter than

0.4 micronNote: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

Noise, interference and distortion

Noise:unwanted signals that coincide with the desired signals. Noise is random, undesirable electric energy.

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. Eg: atmospheric noise,solar noise, cosmic noise, man made noise.

Interference-one type of external noise Distortion: signal being distorted

Limitations in communication system

Physical constraint -Delay, attenuation, bandwidth

limitation, etc Technological constraint hardware. Expertise- economy, law

Frequency Spectrum &Bandwidth

The frequency spectrum of a waveform consists of all frequencies contained in the waveform and their 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 the lowest frequency from the highest.

Frequency Spectrum &Bandwidth(cont’d)

Bandwidth of the information signal equals to the difference between the highest and lowest frequency contained in the signal.

Similarly, bandwidth of communication channel is the difference between the highest and lowest frequency that the channel allow to pass through it