BEJ30103 ELECTRONICS COMMUNICATION SYSTEMS CHAPTER …

CHAPTER 1: Introduction to

Communication Systems

BEJ30103 – ELECTRONICS

COMMUNICATION SYSTEMS

BEB31803 ELECTRONIC COMMUNICATION SYSTEM

Dept of Communication Engineering, FKEE

Topics Covered in Chapter 1

1. Introduction to Communication Systems

2. Terminology

3. The Electromagnetic Spectrum

4. Bandwidth

5. Types of Electronic Communication

6. Modulation and Multiplexing

7. Decibel and Power



Introduction to Communication System

Communication is the process of exchanging

information from one point to another.

Main barriers are language and distance

Contemporary society’s emphasis is now on the

accumulation, packaging and exchange of

information.

Should be efficient, reliable, and secure.

Requires transmitter, channel or medium and

receiver.

During the communication process, noise degrades

or interferes with the transmitted information.



Transmitter

Receiver

Signal source Base band

converter

Modulation and

power amplification

Transmission

(Electromagnetic

Field)

Subsystem

synchronization

Amplification and

demodulation

Base band

inverter

Synchronization

system

Base band

processing

Electromagnetic

field



TERMINOLOGY

Electronic communication

transmission, reception and processing of information

between 2 or more locations using electronic circuit.

Information

The commodity produced by the source for transfer to

some user at the destination.

Message

The physical manifestation of information as produced by

the information source.

Signals

A physical embodiment of information – voltage signal or current signal



TYPES OF SIGNALS

analog signal : a continuously varying

voltage or current

e.g. sound, video

digital signal : binary pulses

or codes

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



TERMINOLOGY

Transmitter (Tx)

collection of one or more electronic devices or circuits that converts the original source into a signal that is more suitable for transmission over a given transmission medium, e.g. modulation, coding, mixing, translate

Other functions performed - Amplification, filtering, radiation (antenna)

Message converted into electrical signals by transducers

Receiver (Rx)

collection of electronic devices and circuits that accepts the transmitted signal from the transmission medium and converts them back to their original form, e.g.. mixing, demodulation, decoding

Other functions performed: Amplification, filtering.

Transducer converts the electrical signal at its input into a form desired by the system used



Modulation

a process of changing one or more properties of the

analog carrier in proportion to the information signal.

Mixing

A process of combining two or more signals.

Filtering

A process of removing some unwanted components or

features from a signal.

Most often, this means removing some frequencies and

not others in order to suppress interfering signals and

reduce background noise.



Base band converter

to convert the signal source into base 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.

e.g. : copper wire (signal as electrical current flow),

optical fiber cable (signal in electromagnetic light wave),

free space (signal in electromagnetic radio wave)



ELECTROMAGNETIC SPECTRUM

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

Frequency range for communication start roughly from 200kHz until few giga Hertz (GHz).

E: Electric fields B: Magnetic fields

Figure 3 : Electromagnetic wave

//upload.wikimedia.org/wikipedia/commons/4/4c/Electromagneticwave3D.gif

//upload.wikimedia.org/wikipedia/commons/4/4c/Electromagneticwave3D.gif



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)



Designation Freq. Range (Hz) range (m)

ELF 30 – 300 107 – 106

VF 300 – 3 k 106 – 105

VLF 3 k – 30 k 105 – 104

LF 30 k – 300 k 104 – 103

MF 300 k – 3 M 103 – 102

HF 3 M – 30 M 102 – 101

VHF 30 M – 300 M 101 – 100

UHF 300 M – 3 G 100 – 10-1

SHF 3 G – 30 G 10-1 – 10-2

EHF 30 G – 300 G 10-2 – 10-3

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



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 (e.g.. 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)

Very High Frequency (VHF)

mobile radio

marine and aeronautical communication

FM broadcast, TV, amateur radio



Ultra High Frequency (UHF)

* frequency > 1GHz is known as microwave

TV, amateur radio

land mobile communication, cellular phone

Military, certain radar and navigation system

microwave and satellite radio system

Super High Frequency (SHF)

microwave and satellite radio system, radar

specialized form of 2-way radio

Extremely High Frequency (EHF)

seldom used in radio communication except in very sophisticated, expensive and specialized application

satellite communication, Radar



Infrared*

refers to electromagnetic radiation generally associated with heat

anything that produced heat generate infrared signal e.g. : light bulb, human body

astronomy (to detect stars), electronic photography

heat-seeking guidance system (weapon)

TV remote control

visible light

optical communication

* freq > 300 GHz are not referred as radio wave



BANDWIDTH

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

e.g. an audio signal (3kHz) being modulated by a 1000kHz carrier signal using AM modulation



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.



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



TRANSMISSION IMPAIRMENTS

any undesired effect on the signals while traveling

from the transmitter to the receiver, such as noise,

attenuation, interference and other losses caused

by the atmosphere or the medium itself

Analog - degradation of signal quality

Digital - bit errors

Caused by

Attenuation

Noise

Interference



Noise

random, undesired electrical energy that enters the

communication system via the circuits/devices or

communication media (i.e. inserted between Tx and

Rx) and interferes with the transmitted message.

Attenuation

drop in signal power due to distance travel by the

signal.

Interference

noise signal that has the same frequency as the

information signal.



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



TYPES OF ELECTRONIC COMMUNICATION

Can be classified in three ways

Transmission mode (one-way, two-way)

Analog or digital system

Baseband or broadband transmission



Transmission Mode

One-way (Simplex)

info travels in 1 direction only

receive-only, transmit-only

e.g.. 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



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 transferred

between 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



Digital radio

transmission of digitally modulated analog carriers between

2 or more points

modulating signal and demodulated signals are digital pulses

the digital pulses could originate from a digital transmission

system, from a digital source i.e. computer, or a binary

encoded analog signal

transmission medium may be physical facility or free space



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



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 possible

Baseband 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



Broadband transmission

original signal is used to modulate a carrier for

transmission over the medium

Broadband:

Analog signals are used

Transmission of data is unidirectional

Signal 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



Encoding Techniques

From the previous discussion, it is obvious that we

can have 4 types of transmission system.

Digital data, digital signal

Analog data, digital signal

Digital data, analog signal

Analog data, analog signal



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

Manchester

Differential Manchester



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)



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



Analog Data, Analog Signals

modulate analog signals to the higher

frequency

Types of analog modulation

Amplitude (AM)

Frequency (FM)

Phase (PM)

Modulation : process of changing one or

more properties (amplitude, frequency,

phase) of the carrier in proportion with

the info signal



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

Thus, for voice signal (300 - 3000 Hz), require very large

antenna expensive to construct and consume more

pore (aperture).



Info signal often occupy the same frequency

band, and if signals from 2 or more sources are

transmitted at the same time, they would

interfere with each other

e.g. 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 a

different frequency band

more space at higher frequency many channels can be

formed to carry many simultaneous communication

without interference



MULTIPLEXING

Transmission of info from more than one source

over the same transmission medium

increase the no. of communication channel

more info transmitted reduce cost and higher

utilization of the transmission line



Frequency Division Multiplexing (FDM)

Multiple signals share common BW of a single communication 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



• at the RX, the recovering

of 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



Time Division Multiplexing (TDM)

Each channel is assigned a time slot 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 be transmitted

signal sources takes times to transmit

Time slots do not have to be evenly distributed amongst sources

for both analog and digital signal



Gain

Ratio output to the input

Output has greater amplitude than the input

Most amplifiers are power amplifier, the same

procedure can be used to calculate power gain, Ap.

Ap = Pout/Pin

FIgure 1.4 Amplifier Gain

in

outV

V

V

input

outputA



Example 1.1

What 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?



Attenuation

Refers to loss introduced by a

circuit

Output is less than input

𝐴𝑡𝑡𝑒𝑛𝑢𝑎𝑡𝑖𝑜𝑛, 𝐴 =𝑉𝑜𝑢𝑡𝑉𝑖𝑛

For cascade circuit, total

attenuation is

𝐴𝑇 = 𝐴1 × 𝐴2 × 𝐴3…

Voltage divider network may

introduce attenuation

Figure 1.5 Voltage divider introduces attenuation



Attenuation can be

offset by introducing

gain

Figure 1.6 Total attenuation in cascaded network

Figure 1.7 Gain offsets the attenuation



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



Example 1.4

A 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?



Example 1.5

An 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 to keep the output voltage from exceeding

100mV? Let A1= amplifier gain = 45,000; A2 = attenuation factor;

AT = total gain.



Decibel - Gain

A common way to express power, gain and loss is to use the decibel unit.

The conversion from absolute value to decibel is given by

𝑣𝑎𝑙𝑢𝑒(𝑑𝐵) = 10log10(𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑣𝑎𝑙𝑢𝑒)

dB is not really a unit, it is just a notation to tell the reader that the value is given in dB.

E.g. 2 in dB is 10 log10 2 = 3𝑑𝐵.

E.g. 0.5 in dB is 10 log10 0.5 = −3𝑑𝐵 (Loss)

Logarithmic nature of dB large range in absolute value is compressed

Gain and attenuation (loss) 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



Decibel - Power

Decibel is also used to expressed power in communication.

A notation is added after the dB simbol

dBW, dBm, dB etc.

dBm and dBW are decibel units used for expressing power in

communication.

For dBm, reference level (denominator) 1mW

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

E.g. 1 mW 10 log101𝑚𝑊

1𝑚𝑊= 0 𝑑𝐵𝑚

E.g. 1000mW 10 log101000𝑚𝑊

1𝑚𝑊= 30𝑑𝐵𝑚

E.g 1000 mW = 1W 10 log101𝑊

1𝑊= 0 𝑑𝐵𝑊

Notice that the

notation dBm is

used for power in

mW and dBW for

power in Watt.



Examples

Power in mW dBm dBW

0.01

0.1

0.5

1

2

10

100

1000

-20

-10

-3

0

3

10

20

30



Decibel - Power Ratio

Decibel (dB) is also used to measure ratios, i.e. gain,

attenuation, SNR.

Power ratio in communication is usually expressed in dB.

dB = 10 log10 (P1/P2)

For ratios, there is no unit (just dB to tell the value is in dB)

Voltage or current ratios can also be expressed in dB

20log

20log

10 log

out

in

out

in

out

in

VFor voltage dB

V

IFor current dB

I

PFor power dB

P



Example 1.6

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

output power?

Example 1.7

For a three-stage system with an input power Pin = -20 dBm and power gains

of the three stages are 13 dB, 16 dB, and -6 dB, determine the output power:

1. in dBm

2. in mW

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