Analog and digital communication prepared according to r 2017

Unit I - Introduce the basic concepts of communication, need of modulation and different types of analog modulation Amplitude lation, Frequency modulation and Phase modulation.. Theory

ANALOG AND DIGITAL

COMMUNICATION

Prepared according to Anna university syllabus R-2017

(Common to III semester-CSE/IT )

Panimalar Engineering College

Chennai.

SREE KAMALAMANI PUBLICATIONS

CHENNAI

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1ST EdiTioN 2014

2Nd REViSEd EdiTioN 2016

Copyright © 2014, by Sree Kamalamani Publications.

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About the Author

G.Elumalai M.E., is working as an Assistant Professor (Grade – I)

in the Department of Electronics and Communication Engineering, Panimalar Engineering College, Chennai He obtained his B.E in Electronics and Communication Engineering; M.E in Applied Electronics and Ph.D pursing in Wireless Sensor Network His areas

of interests are Communication System, Digital communication, Digital signal processing and Wireless Sensor Network He has more than 13 years of experience

M.Jaiganesh M.E., is working as an Assistant Professor in the

Department of Electronics and Communication Engineering, Panimalar Engineering College, Chennai He obtained his B.E in Electronics and Communication Engineering; M.E in Computer and Communication His areas of interests are Communication System, Digital communication, Optical Communication and Embedded system He has more than 4 years of experience

Dear Students,

We are extremely happy to present the book “Analog and Digital Communication” for you This book has been written strictly as per the revised syllabus (R2013) of Anna University We have divided the subject into five units so that the topics can be arranged and understood proper-

ly The topics within the units have been arranged in a proper sequence

to ensure smooth flow of the subject

Unit I - Introduce the basic concepts of communication, need of

modulation and different types of analog modulation (Amplitude lation, Frequency modulation and Phase modulation)

modu-Unit II - Deals with basic concepts of digital communication

which includes ASK, FSK, PSK, QPSK and QAM

Unit III - Discuss about concept of data communication and

various pulse modulation technique

Unit IV - Concentrate on various techniques for error control

cod-ing

Unit V – Describe about multiuser radio communication.

A large number of solved university examples and university questions have been included in each unit, so we are sure that this book will cater all your needs for this subject

We have made every possible effort to eliminate all the errors in this book However if you find any, please let we know, because that will help for us to improve further

G.Elumalai

UNIT I ANALOG COMMUNICATION

Noise: Source of Noise - External Noise- Internal Noise- Noise Calculation Introduction to Communication Systems: Modulation – Types - Need for Modulation Theory of Amplitude Modulation - Evolution and Description of SSB Techniques - Theory

of Frequency and Phase Modulation – Comparison of various Analog Communication System (AM – FM – PM).

UNIT II DIGITAL COMMUNICATION

Amplitude Shift Keying (ASK) – Frequency Shift Keying (FSK) Minimum Shift Keying (MSK) –Phase Shift Keying (PSK) – BPSK – QPSK – 8 PSK – 16 PSK - Quadrature Amplitude Modulation (QAM) – 8 QAM – 16 QAM – Bandwidth Efficiency– Comparison of various Digital Communication System (ASK– FSK – PSK – QAM).

UNIT III DATA AND PULSE COMMUNICATION

Data Communication: History of Data Communication - Standards tions for Data Communication- Data Communication Circuits - Data Communication Codes - Error Detection and Correction Techniques - Data communication Hardware - serial and parallel interfaces Pulse Communication: Pulse Amplitude Modulation (PAM) – Pulse Time Modulation (PTM) – Pulse code Modulation (PCM) - Comparison of various Pulse Communication System (PAM – PTM – PCM).

Organiza-UNIT IV SOURCE AND ERROR CONTROL CODING

Entropy, Source encoding theorem, Shannon fano coding, Huffman coding, mutual information, channel capacity, channel coding theorem, Error Control Coding, linear block codes, cyclic codes,

convolution codes, viterbi decoding algorithm.

UNIT V MULTI-USER RADIO COMMUNICATION

Advanced Mobile Phone System (AMPS) - Global System for Mobile tions (GSM) - Code division multiple access (CDMA) – Cellular Concept and Frequency Reuse - Channel Assignment and Hand - Overview of Multiple Access Schemes - Satellite Communication - Bluetooth

1.14 Comparison of various analog communication

2.8 Amplitude shift keying (or) Digital Amplitude

2.10 Minimum shift keying (or) continuous phase

2.20 Comparison of various digital

3.11 Introduction to error detection and

3.14 Data communication hardware 3.51

3.25 Comparison of various pulse communication system 3.115

UNIT – IV SOURCE AND ERROR CONTROL CODING 4.1-4.138

Solved two mark questions 4.130

UNIT – V MULTI-USER RADIO COMMUNICATION 5.1-5.78

Noise: Source of Noise - External Noise- Internal Noise- Noise Calculation Introduction to Communication Systems: Modulation – Types - Need for Modulation Theory of Amplitude Modulation - Evo-lution and Description of SSB Techniques - Theory of Frequency and Phase Modulation – Comparison of various Analog Communication System (AM – FM – PM).

Unit 1

ANALOG COMMUNICATION

1.1 INTRODUCTION

link) between two points for information exchange

‰ The science of communication involving long distances is called telecommunication ,the word tele stands for long distance

‰ The information can be of different type such as sound, picture, music computer data etc.,

t A receiver

1.1.1 Elements of communication system:

The block diagram of elements of communication system is as shown in figure 1.1

Information

Source Transmitter Channel Receiver Destination

Noise and Distortion

Figure 1.1 Block diagram of simple communication system

The elements of basic communication system are as follows

1 Information or input signal

Information or input signal

• The communication system has been developing for communicating useful information from one place to the other

• This information can be in the form of a sound signal like speech or music, or it can be in the form of pictures or it can be data informa-tion coming from a computer

equivalent of the information to a suitable form corresponding to communicate through communication medium (or) channel

‰ The transmitter consists of the electronic circuits such as modulator, amplifier, mixer, oscillator and power amplifier

‰ In addition to that it increases the power level of the signal The power level should be increased in order to cover a large range.

Communication channel

The communication channel is the medium used for mission of electronic signal from one place to the other The communication medium can be conducting wires, cables, optical fibre or free space Depending on the type of communication medium, two types

trans-of communication systems will exist They are:

• Wire communication (or) line communication

• Wireless communication (or) radio communication

The output transducer converts the electrical signal at the output

of the receiver back to the original form (i.e) Sound, picture and data signals

The typical examples of output transducer are loud speakers, picture tube computer monitor etc

1.2 NOISE

‰ Noise is an unwanted signal that interferes with the desired message signal

interference is called as noise

External Noise may be classified as

‰ This noise is also called as atmospheric noise (or) static noise

appliances, such as motors, automobiles and aircraft ignition etc.,

the noise This noise is effective in frequency range of 1 MHz -

‰ In semi-conductor devices, it is caused due to random diffusion

of minority carriers (or) random generation of recombination of electron hole

‰ Shot noise is not normally observed during measurement of direct noise current, because it is small compared to the DC-value

‰ Shot noise has a flat response spectrum The mean squared noise component is proportional to the DC-flowing and for most

of the devices the mean square shot noise current is given by,

Where

1.2.3.2 Thermal noise

a conducting medium such as a resistor, and this motion in turn is randomized through collisions caused by imperfection

in the structure of conductors The net effect of motion of all electrons constitutes an electric current flowing through the resistor, causing the noise

This noise is also known as resistor noise (or) Johnson noise

thermal noise is given by

ωα

Where,

T- Ambient temperature in degree kelvin

G- Conductance of the resistor in mhos

K - Boltzman constant

a - average number of collisions per sec per electron

1.2.3.3 Partition noise

? This noise is generated whenever a current has to divide between two (or) more electrodes and results from random fluctuation in the division

? It would be expected therefore that a diode would be less noisy than a transistor, if third electrode draws current

? For this reason, the input stage of microwave receiver is often a diode circuit The spectrum of the partition is flat

1.2.3.4 Flicker noise (or) low frequency noise

Flicker noise occurs due to imperfection in cathode surface of electron tubes and surface around the junctions of semiconductor devices In the semiconductor, flicker noise arise from fluctuation in the carrier density, which in turn give rise to fluctuation in the conductivity

of the material The power density of the flicker noise is inversely

proportional to frequency (ie) S (w) a 1

f

Hence, this noise becomes significant at very low frequencies (below a few KHz)

1.2.4 Calculation of noise

i Signal to noise Ratio (SNR)

It is defined as the ratio of signal power to noise power either input side (or) at output side of the circuit (or) device

Noise power at the input

Output Signal powerOutput Noise power

ii Noise Figure

Noise figure is defined as, the ratio of the signal to noise power ratio supplied to the input terminals of a receiver (SNRi) to the signal

to noise power ratio supplied to the output terminal (or) load resistor (SNR0)

Amplifier (receiver) Generator (Antenna)

Figure 1.1 (a) Block Diagram of calculation of noise figure

Calculate noise figure consider a network shown in figure 1.1(a) The network has the following

1 Input impedance Rt

3 An Overall voltage gain

It is led from a source that is antenna of internal resistance Ra The internal resistance Ra, may or may not be equal to Rt The figure 1.1(a) shows the block diagram of such 4 terminals network

The calculation procedures are as follows

From the figure 1.1(a), we can obtain signal input voltage Vsi and

Similarly the noise input voltage Vni and power Pni can be calculated

Step 3 Calculation of input SNR

PniUsing equation (3) and (5), we get

2Rt/(Ra + Rt)2)4KTB (Ra/ Ra + Rt)

2.Rt

The output signal power will be given as,

The noise output power may be quite difficult to calculate for instance, it can be simply written as,

Step 6 Calculation of the output SNR

The output signal to noise (SNR0) will be found as,

Step 7 Calculation of Noise figure (F)

The general expression for noise figure is

This is the necessary equation

1.3 INTRODUCTION TO COMMUNICATION SYSTEMS

Electronics communication system can be classified into various categories based on the following parameters

1 Whether the system is unidirectional (or) bidirectional

2 Whether it uses an analog (or) digital information signal

3 Whether the system uses baseband transmission (or) uses some kind of modulation

Electronics communication systems

Unidirectional/

Bidirectional

communication

Nature of Information signal

Technique of transmission

Simplex

system

Half duplex

Analog Digital Baseband

transmission

Communication using modulation

Full Duplex

Figure 1.2 Classification of communication system

1.3.1 Classifications based on directions of Communication

Based on whether the system communicates only in one direction (or) otherwise, the communication systems are classified as,

1 Simplex system

2 Half duplex systems

3 Full duplex systems Communication System

Unidirectional

(Simplex)

Bidirectional (Duplex)

Simplex system

In these systems the information is communicated

in only one direction , they cannot receive

For example, the radio, TV-broadcasting and telemetry System of

a satellite to earth

Half duplex system

These systems are bidirectional they can transmit as well as receive but not simultaneously

At a time these systems can either transmit (or) receive, for example a trans-receiver (or)walky talky set

Full duplex System

These are truly bidirectional systems as they allow the communication to take place in both the direction simultaneously

These systems can transmit as well as receive simultaneously , for example the telephone Systems

Transmitter + Receiver 1

Transmitter + Receiver 2

Bidirectional flow

of information

Communication link

Figure 1.3 Basic Block diagram of full duplex system

1.3.2 Classifications based on the nature of Information signal

Based on nature of information signal, Communication system classified into two categories namely,

1 Analog Communication system

2 Digital communication system

Analog Communication

In this communication technique, the transmitted signal is in the form of analog (or) continuous in nature through the communication channel (or) media

Digital communication

In this communication technique, the transmitted signal is in the form of digital pulses of constant amplitude, frequency and phase

1.3.3 Classification based on the technique of transmission

Based on the technique used for the signal transmission we can categories into two namely,

1 Base band transmission

2 Communication systems using modulation

Another example of baseband transmission is computer data transmission over a Co-axial Cables in the computer networks (eg RS

232 cables)

Thus , the base band transmission is the transmission of the original information signal as it is

Limitations of Baseband transmission

The baseband transmission cannot be used with certain medium (eg) it cannot be used for the radio transmission where the medium is

Drawbacks of baseband transmission (without modulation)

1 Excessively large antenna heights

2 Signals get mixed up

3 Short range of communication

4 Multiplexing is not possible and

5 Poor quality of reception

Why modulation

overcome using modulation

In radio communication, signals from various sources are transmitted through a common medium that is in open (free) space This causes interference among various signals, and no useful message is received by the receiver

The problem of interference is solved by translating the message signals to different radio frequency spectra This is done by the transmitter by a process known as ”Modulation”

1.4 MODULATION

Define: In the modulation process, two signals are used namely

the modulating signal and the carrier signal

Modulating signal Baseband signal Low frequency signal

Carrier signal High frequency signal

(or) (or)

In simple, modulation is the process of mixing of modulating signal and carrier signal together

In the process of modulation , the baseband signal is translated (i.e) shifted from low frequency to high frequency

1.5 NEED FOR MODULATION (OR) ADVANTAGES OF MODULATION

The advantages of modulation are,

1.5.1 Easy of radiation

As the signals are translated to higher frequencies,

it becomes relatively easier to design amplifier circuits as well as

antenna systems at these increased frequencies.

1.5.2 Adjustment of bandwidth

Bandwidth of a modulated signal may be made smaller (or) larger than the original signal

Signal to noise ratio (SNR) in the receiver which is a function

of the signal Bandwidth can thus be improved by proper control of bandwidth at the modulating stage

1.5.3 Reduction in antenna height

When free space is used as a communication media, messages are transmitted with the help of antennas

If the signals are transmitted without modulation, the size of antenna needed for an effective radiation would be of the order of the half of the wavelength, given as,

Antenna height is = λ

2

c2f

1.5.4 Avoid mixing of signals

Each modulating signal (message signal) is modulated with different carrier then they will occupy different slot in the frequency domain (different channels).Thus modulation avoids mixing of signals

1.5.5 Increases the range of communication

The modulation process increases the frequency

of the signal to be transmitted Hence, increases the range of communication

1.5.6 Multiplexing

If different message signals are transmitted without modulation through a single channel may causes interference with one another (i.e) overlap with one another

To overcome this interference means, we need n-number of channels for n-message signals separately

But different message signals can be transmitted over a same channel (single channel) without interference using the techniques

1.5.7 Improves quality of reception

Due to modulation, the effect of noise is reduced to great extent This improves quality of reception

The two basic types of communications systems are analog and digital

Carrier - continuous signalMessage - Digital (or) analog signalCarrier - continuous signal (analog)

Digital communication

Continuous

modulation

Analog pulse modulation DPCM DM ADM PCM

Phase modulation (PM)

Frequency modulation (FM)

Figire 1.4 Classifications of Modulation

Where,

Linear modulation

The modulation system following the superposition

theorem of spectra is known as linear modulation system.

Frequency is simply the number of times a periodic motion, such

as a sine wave of voltage (or) current, occurs in a given period of time

electromagnetic wave during the time of one cycle.

The International Telecommunication Union (ITU) is an international agency is control of allocating frequencies and services within the overall frequency spectrum

Frequency (UHF) 300MHZ -3GHZ 10cm - 1m

Very High frequency

(VHF) 30 - 300MHZ 1 -10mHigh frequency(HF) 3 - 30MHZ 10-100m

It consists of the amplitude and phase spectrums of the signal The frequency spectrum indicates the amplitude and phase of various frequency components present in the given signal.

The frequency spectrum enables us to analyze and synthesize a signal

1.7.6 Demodulation (or) Detection

The process of extracting a modulating (or) baseband signal from the modulated signal is called “demodulation”

In other words , Demodulation (or) detection is the process by which the message signal is recovered from the modulated signal at receiver

Definition

Amplitude modulation (AM) is the process by which amplitude of the carrier signal is varied in accordance with the instantaneous value (amplitude) of the modulating signal, but frequency and phase remains constant

1.8.1 Mathematical Representation of an AM wave

Let us consider,

The Carrier signal Vc(t) = Vcsinω ct (2)

Where,

V c Amplitude of the carrier signal (volts)

V m _ Amplitude of the modulating signal (volts)

ωm _ Frequency of the modulating signal (HZ)

ωc _ Frequency of the carrier signal (HZ)

According to the definition of amplitude modulation, the amplitude of the carrier signal is changed after modulation with respect

V AM (t) = V c [1+m a sin (2f m )t] sin (2f c )t (4)a

The equation (4)a represents the time domain representation of

sin A sin B = cos(A-B) - cos(A+B)

2Equation (2) becomes,

VAM(t) = Vcsinωc t + m 2 cos (ωa V c c -ωm)t- m 2 cos(ωa V c c+ ωm)t (3)

In equation (3),

• First term represents carrier signal (volts)

• Second term represents lower side band signal (volts)

• Third term represents upper sideband signal (volts)

The Figure 1.7 shows the voltage spectrum for an AM – DSBFC wave (or) AM – signal

maVc 2

maVc 2

The (-) sign associated with the USB – represents a phase shift of

180 The figure 1.8 shows the frequency domain representation

Figure 1.8 Frequency domain representation of AM-wave.

The equation (2) shows the frequency domain representation of AM- signal

• First term represents the unmodulated carrier signal with the

BW = Bandwidth = fUSB - fLSB

= ( f c + f m ) - ( f c - f m )

= f c + f m - f c +f m

Where, BW = Bandwidth is hertz.

Thus, the Bandwidth of the AM-signal is the twice that of the maximum frequency of modulating signal

1.8.5 AM- Envelope (or) Graphical representation of AM-wave

AM- DSBFC is sometimes called conventional AM (or) simply AM

AM is simply called as Double sideband Full carrier (DSBFC) is probably the most commonly used The figure 1.9 shows the graphical representation of AM – signal

• The shape of the modulated wave (AM) is called AM –envelope which contains all the frequencies and is used to transfer the information through the systems

• An increase in the modulating signal amplitude causes the amplitude of the carrier to increase

• Without signal, the AM output waveform is simply the carrier signal

• The repetition rate of the envelope is equal to the frequency of the modulating signal

1.8.6 Phasor Representation of an AM-wave

The amplitude variation in an AM-system can be explained with the help of a phasor diagram as shown in figure 1.10

o

maVc 2

Figure 1.10 Phasor representation of AM-wave

• The phasor for the upper sideband rotate anticlockwise at an angular frequency of wm, faster than the carrier frequency ωc (i.e) (ωm>ωc)

• The phasor for the lower sideband rotates clockwise at an angular frequency of wm, slower than the carrier frequency (ωc) (i.e)(ωm<ωc)

• The resulting amplitude of the modulated wave at any instant is the vector sum of the two- sideband phasors

• Vc is carrier wave phasor, taken as reference phasor and the resulting phasor is VAM (t)

• The phasors for carrier and the upper and lower side frequencies combine, sometimes in phase (adding) and sometimes out of phase (subtracting)

1.8.7 Modulation index and percentage modulation

Modulation index

In AM wave, the modulation index (ma) is defined as the ratio

of maximum amplitude of modulating signal to maximum amplitude of carrier signal