C1 INTRODUCTION TO COMMUNICATION SYSTEMS.pptx

7/29/2019 C1 INTRODUCTION TO COMMUNICATION SYSTEMS.pptx

1/64

CHAPTER 1:

INTRODUCTION TO

COMMUNICATIONSYSTEMS

Prepared by:

DR KHAIRUN NIDZAM B. RAMLI

DEPARTMENT OF COMMUNICATION ENGINEERING

FACULTY OF ELECTRICAL AND ELECTRONICS ENGINEERING


2/64

OVERVIEW ON COMMUNICATION

SYSTEMSTRANSMISSION

IMPAIRMENTS

Figure 1.1 : (a) Basic block diagram for communication (b) example


3/64

Transmitter

Receiver

Signal source Base band

converter

Modulation and

power

amplification

Transmission

(Electromagn

etic Field)

Subsystem

synchronization

Amplification and

demodulation

Base band

inverter

Synchronization

system

Base band

processing

Electromagnetic

field

Figure 1.2 : (a) Basic transmitter block diagram (b) basic receiver.


4/64

Terminology

Electronic communication : transmission, receptionand processing of information between 2 or more

locations using electronic circuit.

Information : analog or digital signal that had been

converted to electromagnetic energy Transmitter: collection of one or more electronic

devices or circuits. That convert the original source into a

signal that is more suitable for transmission over a given

transmission medium Receiver: collection of electronic devices and circuits

that accepts the transmitted signal from the transmission

medium and converts them back to their original form


5/64

Base band converter: to convert the signal source intobase band waveform for the carrier signal before

transmission. Can be either analog or digital system.

Subsystem synchronization: synchronizing connection

between the TX and RX for recovery processes. Transmission medium: provides a means of

transporting signal from the TX to the RX.

eg : copper wire (signal as electrical current flow), optical fiber

cable (signal in e/magnetic light wave), free space (signal in

e/magnetic radio wave)


6/64

Transmission impairments : any undesired effect onthe signals while traveling from the transmitter to thereceiver, such as noise, attenuation, interference andother losses caused by the atmosphere or the mediumitself.

Noise: random, undesired electrical energy that entersthe communication system via the communication media(i.e. inserted between TX and RX) and interferes with thetransmitted message.

Attenuation : drop in signal power due to distance travelby the signal.

Interference : noise signal that has the same frequencyas the information signal.


7/64

Types of Signalsanalog signal : a continuously varying

voltage or currente.g. sound, video

digital signal : binary pulses

or codes

Figure 1.3 : Examples of signals (a) analog (b) digital.


8/64

Analog Signals Components of Speech

Frequency range (of hearing) 20 Hz-20 kHz

Speech 100Hz-7kHz

Easily converted into electromagnetic signal for transmission

Sound frequencies with varying volume converted intoelectromagnetic frequencies with varying voltage

Limit frequency range for voice channel ~ 300-3400Hz


9/64

Digital Signal From computer terminals etc.

Bandwidth depends on data rate


10/64

Electromagnetic Wave

E: Electric fields B: Magnetic fields

Figure 3 : Electromagnetic wave
http://localhost/var/www/apps/conversion/tmp/scratch_5//upload.wikimedia.org/wikipedia/commons/4/4c/Electromagneticwave3D.gif


11/64

ELECTROMAGNETIC SPECTRUM

Electromagnetic wave is a signal where its electricaland magnetic field change at fixed rate.

Frequency range for communication start roughly from200kHz until few giga Hertz (GHz).

Frequency (f)

no. of times a periodic motion occurs in a given period of time Hertz (Hz) or cycles per second Period = time for one repetition (T) T = 1/f

cycle one complete alternation of a waveform

wavelength () distance traveled by an electromagnetic wave during one period= cT f = c

c = 3 x 108 ms-1 (speed of light in free space)


12/64

Designation Freq. Range (Hz) range (m)

ELF 30

300 107

106VF 3003 k 106105

VLF 3 k30 k 105104

LF 30 k300 k 104103

MF 300 k3 M 103102

HF 3 M

30 M 102

101VHF 30 M300 M 101100

UHF 300 M3 G 10010-1

SHF 3 G30 G 10-110-2

EHF 30 G300 G 10-210-3

Table 1: Frequency range (a) designation (b) applications


13/64


14/64


15/64

Figure 4 : Electromagnetic spectrum


16/64

Extremely Low Frequency (ELF) ac power line distribution (50 and 60 Hz) low freq telemetry signal

Voice Frequency (VF) human speech (most intelligent sound)

Very Low Frequency (VLF) upper end of human hearing range

musical instrument government and military (eg. submarine)

Low Frequency (LF) marine and aeronautical navigation as subcarriers

Medium Frequency (MF)

AM radio broadcasting marine and aeronautical comm application High Frequency (HF)

Also known as short wave (SW)

2-way radio communication SW radio broadcast amateur radio and citizen band (CB)


17/64

Very High Frequency (VHF) mobile radio marine and aeronautical communication FM broadcast TV amateur radio

Ultra High Frequency (UHF)

* freq > 1GHz is known as microwave TV land mobile communication cellular phone military certain radar and navigation system

microwave and satellite radio system amateur radio Super High Frequency (SHF)

microwave and satellite radio system radar specialized form of 2-way radio


18/64

Extremely High Frequency (EHF) seldom used in radio communication except in very sophisticated,expensive and specialized application

satellite communication Radar

* freq > 300 GHz are not referred as radio wave

Infrared refers to electromagnetic radiation generally associated with heat

anything that produced heat generate infrared signal

eg : light bulb, human body

astronomy (to detect stars)

electronic photography

heat-seeking guidance system (weapon)

TV remote control

visible light

optical communication


19/64

Bandwidth Portion of the electromagnetic

spectrum occupied by the signal

Frequency range over which a

receiver or other electronic circuits

operate.

Difference between the upper and

lower limit frequency, limits of the

signal, or equipment operation range

Channel bandwidth

Range of frequencies required to

transmit the desired information

i.e. an audio signal (3kHz) being

modulated by a 1000kHz carrier

signal using AM modulation


20/64

TRANSMISSION MEDIUM

Guided coaxial cable, twisted pair, fiber optic,waveguide.

Unguided wireless (terrestrial, spacewave, free space,

earth wave).

Characteristics and quality determined by medium and

signal.

For guided, the medium is more important.

For unguided, the bandwidth produced by the antenna is

more important.

Key concerns are data rate and distance.


21/64

Characteristics of Guided Media

FrequencyRange

TypicalAttenuation

TypicalDelay

RepeaterSpacing

Twisted pair 0 to 3.5 kHz 0.2 dB/km @1 kHz

50 s/km 2 km

Twisted pairs(multi-paircables)

0 to 1 MHz 0.7 dB/km @1 kHz

5 s/km 2 km

Coaxial cable 0 to 500 MHz 7 dB/km @10 MHz

4 s/km 1 to 9 km

Optical fiber 186 to 370THz

0.2 to 0.5dB/km

5 s/km 40 km


22/64

Characteristics of Wireless Propagation Signal travels along three routes

Ground wave

Follows contour of earth

Up to 2MHz

AM radio Sky wave

2 MHz < f < 30 MHz

Amateur radio, BBC world service, Voice of America

Signal refracted from ionosphere layer of upper

atmosphere Line of sight

Above 30MHz

cellular phone


23/64

TRANSMISSION IMPAIRMENTS

Signal received may differ from signal transmitted Analog - degradation of signal quality

Digital - bit errors

Caused by

Attenuation and attenuation distortion

Delay distortion

Noise


24/64

Attenuation Signal strength falls off with distance

Depends on medium

Received signal strength:

must be enough to be detected must be sufficiently higher than noise to be received without

error

Attenuation is an increasing function of frequency

Delay Distortion

Propagation velocity varies with frequency

Noise

Will be discuss later


25/64

TYPES OF ELECTRONIC

COMMUNICATION

Can be classified in three ways Transmission mode (one-way, two-way)

Analog or digital system

Baseband or broadband transmission


26/64

Transmission Mode

One-way (Simplex) info travels in 1 direction only

receive-only, transmit-only

eg. Radio and TV broadcasting, telemetry system

Two-way (duplex)

a) half duplex both direction, but only one way at a time

2-way-alternate, either-way, over-and-out

e.g. police radio

b) Full duplex Both directions at the same time

2-way-simultaneous, both-way

e.g. telephone


27/64

Analog Or Digital System

Analog system energy is transmitted and received in analog form

both info and carrier are analog signals

Digital system Digital transmission

a true digital system where digital pulses are transferredbetween 2 or more points

no analog carrier

original source info may be in digital or analog signal

if analog signal convert to digital pulses prior to

transmission and converted back to analog signal at the RX require a physical medium between TX-RX


28/64


29/64

Advantages of Digital Transmission Digital technology

Low cost LSI/VLSI technology

Data integrity

Longer distances over lower quality lines

Capacity utilization

High bandwidth links economical

High degree of multiplexing easier with digital techniques

Security & Privacy

Encryption

Integration

Can treat analog and digital data similarly


30/64

Baseband Or Broadband Transmission

Baseband transmission putting the original signal directly into the medium

Baseband:

Digital signals are used, but it can also be used with analog

technologies.

Frequency division multiplexing is not possibleBaseband is bi-directional transmission

Short distance signal travelling

Entire bandwidth of the cable is consumed by a single signal in a

baseband transmission.

Eg : (i) Ethernet


31/64

Broadband transmission original signal is used to modulate a carrier for transmission

over the medium

Broadband:

Analog signals are used

Transmission of data is unidirectionalSignal travelling distance is long

Frequency division multiplexing is possible

The signals are sent on multiple frequencies and allow all the

multiple signals are sent simultaneously in broadband

transmission. Eg : (i) Digital Subscriber Line (DSL) and Cable Television

Networks


32/64

Analog Signals Carrying Analog and Digital Data


33/64

Digital Signals Carrying Analog and Digital Data


34/64

Encoding Techniques

Digital data, digital signal Analog data, digital signal

Digital data, analog signal

Analog data, analog signal


35/64

Digital Data, Digital Signal

Need to know Timing of bits - when they start and end

Signal levels

Factors affecting successful interpreting of signals Signal to noise ratio

Data rate

Bandwidth Example

Nonreturn to Zero-Level (NRZ-L)

Nonreturn to Zero Inverted (NRZI)

Bipolar -AMI

Pseudoternary

Manchester Differential Manchester

B8ZS

HDB3


36/64

Digital Data, Analog Signal

Public telephone system 300Hz to 3400Hz

Use modem (modulator

-demodulator)

Example

Amplitude shift keying (ASK)

Frequency shift keying (FSK)

Phase shift keying (PSK)


37/64

Analog Data, Digital Signal

Digitization Conversion of analog data into digital data

Digital data can then be transmitted using digital encoding such as

NRZ-L

Digital data can then be converted to analog signal

Analog to digital conversion done using a codec

Example

Pulse code modulation

Delta modulation


38/64

Analog Data, Analog Signals

modulate analog signals to thehigher frequency

Types of analog modulation

Amplitude

Frequency Phase

Modulation : process of

changing one or more

properties (amplitude,

frequency, phase) of the

carrier in proportion with the

info signal


39/64

MODULATION

Why? It is extremely difficult to radiate low frequency signals from

an antenna in the form of electromagnetic energy

it is possible theoretically but impractical realistically

c= f

f,

antenna length usually 1/2 or 1/4 of

for voice signal (300 - 3000 Hz), require very largeantenna expensive to construct and consume more pore

(arperture).


40/64

Info signal often occupy the same frequency band, and ifsignals from 2 or more sources are transmitted at the same

time, they would interfere with each other

i.e. all commercial FM station broadcast voice and music

signals that occupy the AF from 300 Hz - 15 kHz

to avoid interference, each station converts its into to adifferent frequency band

more space at higher frequency many channels can be

formed to carry many simultaneous communication without

interference


41/64

Modulation Techniques

let v(t) = Vc sin (2ft + ) general expression for a time varying sine wave of voltage as a high

frequency carrier signal

modulating signal modulation performed

analog AM FM PM

l l l

v(t) = Vc sin (2 . f . t + )l l l

digital ASK FSK PSK

QAM


42/64

MULTIPLEXING

Transmission of info from more than one source over thesame transmission medium

increase the no. of communication channel more info

transmitted reduce cost and higher utilization of the

transmission line


43/64

Frequency Division Multiplexing (FDM)

Multiple signals share common BW of a singlecommunication channel

Useful BW of medium exceeds required bandwidth of

channel

each signal occupies a separate portion of the BW

Each signal modulates a different sub-carrier freq

Sub-carriers are linearly mixed to form a composite

signal that is usually used to modulate a final carrier for

transmission

carrier frequencies separated so signals do not overlap(guard bands)

Channel allocated even if no data


44/64

at the RX, the recoveringof the individual signal is

done with a DEMUX

whose main component is

BPF tuned to the individual

sub-carrier freq.

For analog signal, i.e.

radio broadcast


45/64

FDM System


46/64

Time Division Multiplexing (TDM)

Each channel is assigned a timeslot and may transmit for a brief

period using the entire BW of the

medium

Data rate of medium exceeds

data rate of digital signal to betransmitted

signal sources takes times to

transmit

Time slots do not have to be

evenly distributed amongstsources

for both analog and digital signal


47/64

TDM System


48/64

TDM of Analog and Digital Sources


49/64

Wavelength Division Multiplexing

(WDM)

Similar of FDM coupling light at 2 or more discrete wavelengths, into

and out of an optical fiber

Multiple beams of light at different frequency

Each colour of light () carries separate data channel unlike FDM (same time, same transmission path),

different travels at different speed and did not take thesame path, but enter the fiber at the same time and

same transmission medium each arrives at the RX at a slightly different time


50/64

WDM System

Fiber cable

1, 2.. n

1

2

n

1

2

n

Laser optic source

To laseroptical

detector


51/64

Gain

Ratio output to the input Output has greater amplitude than the input

Most amplifiers are power amplifier, the same procedure can beused to calculate power gain, Ap.

Ap = Pout/Pin

FIgure 1.4 Amplifier Gain

in

outV

V

V

input

outputA


52/64

Example 1.1What is the gain of an amplifier that produces an output of 750 mV for

30 V input?

Example 1.2

The power output of an amplifier is 6 W. The power gain is 80. What is

the input power?

Example 1.3

Three cascade amplifier have power gains of 5, 2, and 17. The input

power is 40 mW. What is the output power?


53/64

Attenuation

Refers to loss introduced by a circuit Output is less than input

For cascade circuit, total attenuation is

AT=A1 A2 A3.. Voltage divider network may introduce attenuation

in

out

V

VAnAttenuatio

Figure 1.5 Voltage divider introduces attenuation


54/64

Attenuation can be offset by introducing gain

Figure 1.6 Total attenuation in cascaded network

Figure 1.7 Gain offsets the attenuation


55/64

Figure 1.8 Total gain is the product of the individual stage gains and attenuation


56/64

Example 1.4A voltage divider shown in Figure 1.7 has values of R1 = 10k and R2= 47k.

1. What is the attenuation?

2. What amplifier gain would you need to offset the loss for an

overall gain of 1?


57/64

Example 1.5An amplifier has gain of 45,000, which is too much for the amplification.

With an input voltage of 20 V, what attenuation factor is needed tokeep the output voltage from exceeding 100mV? Let A1= amplifier gain

= 45,000; A2 = attenuation factor; AT = total gain.


58/64

Bit Error Rate

Another significant measure of system performance in term of noise

is bit error rate (BER)

Specify the number of bits that are corrupted or destroy as data are

transmitted from TX to the RX

BER of 10-6 indicate that 1 bit out of 1 million bits is corrupted in the

transmission Several factor contribute to BER is

Bandwidth

Transmission speed

Transmission medium

Environment

Transmission distance

Transmitter and receiver performance


59/64

Decibel (dB) is a log unit that can be used to measure ratios.

Power ratio in communication is usually expressed in dB. Logarithmic nature of dB large range in power ratios is compressed

dB = 10 log10 (P1/P2)

Voltage or current ratios can also be expressed in dB

Gain and attenuation often expressed in decibels, rather than

absolute value

Using decibel, total gain or attenuation can be calculated by simply

adding the gains and the attenuation expressed in decibel.

Power Measurement - Decibel

20log

20log

10 log

out

in

ou t

in

out

in

VFor votage dB V

IFor current dB

I

PFor power dB

P


60/64

Beside performing ratio operation, decibel is also used to expressed

power in communication.

A notation is added after the dB simbol

dBW, dBm, dB etc.

For dBm, reference level 1mW

A larger unit, dBW has reference value of 1W. dBm and dBW are decibel units used for expressing power in

communication.

dB to power ratio


61/64


62/64

dBm and dBW are often used for power measurement in

communication. dB units with respect to some fix reference levels

For dBm, reference level 1mW

dBm = 10 log10 (P/ 1 mW)

A larger unit, dBW has reference value of 1W.

Power in mW dBm

0.01

0.1

0.5

12

10

100

1000

-20

-10

-3

03

10

20

30


63/64

Example 1.6

A microphone has output value of -50dBm, calculate the actual output

power?


64/64

Example 1.7

For a three-stage system with an input power Pin = -20dBm and power gains of the three stages are 13 dB, 16 dB,

and -6 dB, determine the output power:

1. in dBm2. in mW

C1 INTRODUCTION TO COMMUNICATION SYSTEMS.pptx

Documents