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SCITECHCommunication Theory

Sixth Edition

Dr. T. R. Ganesh Babu

Professor,

Department of Electronics and Communication Engineering,

Muthayammal Engineering College,

Rasipuram - 637 408,

Namakkal District.

SCITECH PUBLICATIONS (INDIA) PVT. LTD.www.scitechpublications.com

ISBN: 9789385983702

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SCITECHCopyright 2019 Scitech Publications (India) Pvt. Ltd.

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978 93 85983 70 2

Published by M. R. Purushothaman for Scitech Publications (India) Pvt. Ltd., OldNo: 3, New No: 5, Bakthavachalam Street, Tambaram West, Chennai - 600 045.Printed at Professional Printers, Chennai - 600 014.

ISBN: 9789385983702


SCITECHPreface to Sixth Edition

The main objective of this book is to provide an introduction to the basicprinciples in Analog Communications for the undergraduates in Electronic, Elec-trical and Computer Engineering. It will also be very useful to students preparingfor professional courses like AMIE and AMIETE. Each chapter contains ShortAnswer Questions, Review Questions and Multiple Choice Questions withAnswers that provide a better understanding of the subject. This book containsmany solved problems and also those problems taken and solved from theUniversity Examinations Question Papers.

Prerequisites to the understanding of the course in Communication Theoryand Systems are Mathematics, Basic electronics and Electronic circuits. Thisbook is divided into Five Chapters.

Chapter 1 begins with the theoretical description of signals and proceeds withthe Fourier Transform Analysis, and also deals with the Amplitude ModulationTechniques, and includes different forms of Amplitude Modulation, Generationand Detection, Times domain representation and spectral characteristics of thesemodulated waves.

Chapter 2 involves Angle Modulation Techniques, which themselves can assumeone of the two interrelated forms (i.e., frequency modulation and phasemodulation).

Chapter 3 provides a basic knowledge of probability and random process and alsodifferent types of Noises and their representation, which is a prerequisite for thenext chapter.

Chapter 4 deals with the Noises in Amplitude and Angle Modulation, and in-cludes derivation of signals to Noise Ratio for different Types of Continuous WaveModulation.

Chapter 5 includes the sampling and quantization, pulse modulation techniques.

We would be glad to receive any comments and suggestions for theimprovement of this book.

December, 2018 Dr. T. R. Ganesh Babu

ISBN: 9789385983702


SCITECHContents

Chapter 1 Amplitude Modulation 1.1 - 1.129

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11.1.1 Basic communication system . . . . . . . . . . . . . . . . 1.11.1.2 Types of communication system . . . . . . . . . . . . . . 1.31.1.3 Classification of communication . . . . . . . . . . . . . . 1.41.1.4 Frequency Range in Communication Systems . . . . . . . 1.41.1.5 Review of Spectral Characteristics of Periodic and Non

Periodic Signals . . . . . . . . . . . . . . . . . . . . . . 1.51.1.6 Fourier Series . . . . . . . . . . . . . . . . . . . . . . . . 1.91.1.7 Fourier Transform . . . . . . . . . . . . . . . . . . . . . 1.131.1.8 Properties of Fourier Transform . . . . . . . . . . . . . . 1.151.1.9 Parseval’s theorem (Energy Density Spectrum) . . . . . . 1.16

1.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.171.3 Need for Modulation . . . . . . . . . . . . . . . . . . . . . . . . 1.171.4 Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . 1.191.5 Power content in AM wave . . . . . . . . . . . . . . . . . . . . . 1.221.6 Power Content in Multiple-Tone Amplitude Modulation . . . . . . 1.301.7 Generation of Amplitude Modulation . . . . . . . . . . . . . . . 1.33

1.7.1 Non-linear Modulator or Small signal modulator . . . . . 1.331.8 Non-Linear Modulation . . . . . . . . . . . . . . . . . . . . . . . 1.34

1.8.1 Square law modulator . . . . . . . . . . . . . . . . . . . 1.341.8.2 Square law diode modulator . . . . . . . . . . . . . . . . 1.351.8.3 Balanced modulator . . . . . . . . . . . . . . . . . . . . 1.36

1.9 Linear Modulator . . . . . . . . . . . . . . . . . . . . . . . . . . 1.381.9.1 Collector modulation method . . . . . . . . . . . . . . . 1.381.9.2 Switching modulator using diode . . . . . . . . . . . . . 1.401.9.3 AM modulation . . . . . . . . . . . . . . . . . . . . . . . 1.41

1.10 Double Sideband Suppressed Carrier AM . . . . . . . . . . . . . 1.451.11 Generation of DSB-SC-AM . . . . . . . . . . . . . . . . . . . . 1.48

1.11.1 Balanced modulator . . . . . . . . . . . . . . . . . . . . 1.481.11.2 Ring modulator . . . . . . . . . . . . . . . . . . . . . . . 1.49

1.12 Hilbert Transform . . . . . . . . . . . . . . . . . . . . . . . . . . 1.531.13 Pre Envelope and Complex Envelope . . . . . . . . . . . . . . . . 1.57

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SCITECH1.13.1 Pre envelope or analytic signal . . . . . . . . . . . . . . . 1.571.13.2 Complex envelope . . . . . . . . . . . . . . . . . . . . . 1.57

1.14 Single Side Band Suppresed Carrier Modulation (SSB-SC) . . . . 1.571.14.1 Generation of SSB-SC AM . . . . . . . . . . . . . . . . . 1.601.14.2 Filter method . . . . . . . . . . . . . . . . . . . . . . . . 1.601.14.3 Phase shift method . . . . . . . . . . . . . . . . . . . . . 1.611.14.4 Modified phase shift method or Weavers method . . . . . 1.62

1.15 Comparison of Three Methods of Generation of SSB . . . . . . . 1.641.16 Advantages and Disadvantages of SSB-SC-AM . . . . . . . . . . 1.651.17 Demodulation of AM Wave . . . . . . . . . . . . . . . . . . . . . 1.66

1.17.1 Square-law detector . . . . . . . . . . . . . . . . . . . . 1.671.17.2 Linear diode or Envelope detector . . . . . . . . . . . . . 1.69

1.18 Demodulation of DSB-SC Signal . . . . . . . . . . . . . . . . . . 1.751.18.1 Linear detectors . . . . . . . . . . . . . . . . . . . . . . . 1.751.18.2 Envelope detection after suitable carrier re-insertion . . . 1.78

1.19 Demodulation of SSB-SC signal . . . . . . . . . . . . . . . . . . 1.801.19.1 Phasor diagram and waveform of SSB-SC signal . . . . . 1.811.19.2 Waveform of SSB-SC with large carrier signal . . . . . . 1.821.19.3 Detection of the SSB-SC signal having large carrier . . . . 1.82

1.20 Vestigial Side Band (VSB) Modulation System . . . . . . . . . . 1.841.21 Comparison of AM System . . . . . . . . . . . . . . . . . . . . . 1.901.22 Superheterodyne Receiver . . . . . . . . . . . . . . . . . . . . . 1.921.23 FM Superheterodyne Receiver . . . . . . . . . . . . . . . . . . . 1.941.24 Performance Parameters of Receivers . . . . . . . . . . . . . . . 1.95

Questions with Short Answers . . . . . . . . . . . . . . . . . . . 1.114Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . 1.122Multiple Choice Questions with Answers . . . . . . . . . . . . . 1.122

Chapter 2 Angle Modulation 2.1 - 2.69

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12.2 Frequency Modulation . . . . . . . . . . . . . . . . . . . . . . . 2.2

2.2.1 Mathematical Representation of FM Signal . . . . . . . . 2.32.2.2 Narrow Band Frequency Modulation (NBFM) . . . . . . 2.52.2.3 Wide Band Frequency Modulation (WBFM) . . . . . . . 2.8

2.3 Transmission Bandwidth of an FM Signal . . . . . . . . . . . . . 2.16

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SCITECH2.4 Phase Modulation (PM) . . . . . . . . . . . . . . . . . . . . . . . 2.182.5 Generation of FM Signals . . . . . . . . . . . . . . . . . . . . . . 2.24

2.5.1 Direct Method of FM Generation . . . . . . . . . . . . . 2.242.5.2 Indirect Method (Armstrong method) . . . . . . . . . . . 2.28

2.6 Demodulators or FM Detectors . . . . . . . . . . . . . . . . . . . 2.292.6.1 Slope Detectors . . . . . . . . . . . . . . . . . . . . . . . 2.302.6.2 Phase difference detector . . . . . . . . . . . . . . . . . . 2.332.6.3 PLL-FM Demodulator . . . . . . . . . . . . . . . . . . . 2.40

2.7 Comparison of FM Demodulator . . . . . . . . . . . . . . . . . . 2.472.8 Comparison between FM and PM . . . . . . . . . . . . . . . . . 2.482.9 Comparison of AM and FM . . . . . . . . . . . . . . . . . . . . 2.48


Chapter 3 Random Process 3.1 - 3.55

3.1 Introduction to Probability Theory . . . . . . . . . . . . . . . . . 3.13.2 Definitions of Probability . . . . . . . . . . . . . . . . . . . . . . 3.4

3.2.1 Mathematical (or) Apriori (or) Classical . . . . . . . . . . 3.43.2.2 Von-Mises’s Statistical (or) empirical definition of proba-

bility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.43.2.3 Axiomatic Approach to probability (Modern Approach) . 3.53.2.4 Addition Law of Probability . . . . . . . . . . . . . . . . 3.53.2.5 Conditional Probability . . . . . . . . . . . . . . . . . . . 3.63.2.6 Multiplication Law of Probability . . . . . . . . . . . . . 3.63.2.7 Bayes Theorem . . . . . . . . . . . . . . . . . . . . . . . 3.7

3.3 Random Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 3.83.3.1 Definition of a Random Variable . . . . . . . . . . . . . . 3.83.3.2 Definition of Distribution Function . . . . . . . . . . . . 3.83.3.3 Discontinuous (or) Discrete Variable . . . . . . . . . . . . 3.93.3.4 Continuous Random Variable . . . . . . . . . . . . . . . 3.103.3.5 Numerical Characteristics . . . . . . . . . . . . . . . . . 3.103.3.6 Distributions . . . . . . . . . . . . . . . . . . . . . . . . 3.12

3.4 Central Limit Theorem . . . . . . . . . . . . . . . . . . . . . . . 3.153.5 Mathematical Definition of a Random Process . . . . . . . . . . . 3.17

ISBN: 9789385983702


SCITECH3.6 Stationary Process . . . . . . . . . . . . . . . . . . . . . . . . . . 3.19

3.7 Mean, Correlation and Covariance Functions . . . . . . . . . . . 3.20

3.7.1 Mean . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.20

3.7.2 Autocorrelation . . . . . . . . . . . . . . . . . . . . . . . 3.20

3.7.3 Cross correlation function . . . . . . . . . . . . . . . . . 3.27

3.8 Transmission of Random Process through a Linear Time Invariantfilter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.33

3.9 Power Spectral density . . . . . . . . . . . . . . . . . . . . . . . 3.34

3.9.1 Properties of power spectral density . . . . . . . . . . . . 3.36

3.9.2 Relation among the power spectral density of the inputand output Random Process . . . . . . . . . . . . . . . . 3.40

3.9.3 Cross Spectral Density . . . . . . . . . . . . . . . . . . . 3.41

3.10 Ergodic Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.43

3.11 Gaussian Process . . . . . . . . . . . . . . . . . . . . . . . . . . 3.48

3.12 Properties of a Gaussian Process . . . . . . . . . . . . . . . . . . 3.49


Chapter 4 Noise Characterization 4.1 - 4.74

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.2 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.3 Shot Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2

4.3.1 Shot noise in semiconductor diode . . . . . . . . . . . . . 4.3

4.4 Thermal Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3

4.5 Addition of Noise due to Several Source in Series . . . . . . . . . 4.6

4.6 Thermal Noise in RC Circuit . . . . . . . . . . . . . . . . . . . . 4.10

4.7 White Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11

4.8 Noise figure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14

4.9 Cascade Connection of two ports Network . . . . . . . . . . . . . 4.16

4.10 Noise Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 4.17

4.11 Narrowband Noise . . . . . . . . . . . . . . . . . . . . . . . . . 4.28

4.11.1 Representation of Narrowband Noise in terms of in-phaseand Quadrature components . . . . . . . . . . . . . . . . 4.28

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SCITECH4.11.2 Representation of Narrowband noise in terms of envelope

and phase components . . . . . . . . . . . . . . . . . . . 4.304.12 Sine Wave plus Narrowband Noise . . . . . . . . . . . . . . . . . 4.324.13 Noise Performance of AM and FM System . . . . . . . . . . . . 4.354.14 Signal to Noise Ratio (SNR) . . . . . . . . . . . . . . . . . . . . 4.354.15 Noise in Amplitude Modulated Systems . . . . . . . . . . . . . . 4.36

4.15.1 Noise in DSB - SC -AM using Coherent Detection . . . . 4.364.15.2 Noise performance in SSBSC AM using coherent

detection . . . . . . . . . . . . . . . . . . . . . . . . . . 4.394.15.3 Noise in AM Receivers using Envelope Detection . . . . 4.41

4.16 Noise in FM Receiver . . . . . . . . . . . . . . . . . . . . . . . . 4.444.17 Capture Effect in FM Receiver . . . . . . . . . . . . . . . . . . . 4.524.18 FM Threshold effect . . . . . . . . . . . . . . . . . . . . . . . . 4.534.19 Pre-Emphasis and De-Emphasis in FM . . . . . . . . . . . . . . . 4.56

4.19.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 4.58Questions with Short Answers . . . . . . . . . . . . . . . . 4.64Review Questions . . . . . . . . . . . . . . . . . . . . . . 4.69Multiple Choice Questions with Answer . . . . . . . . . . . 4.70

Chapter 5 Sampling and Quantization 5.1 - 5.625.1 Sampling Theorem (Low Pass Sampling) . . . . . . . . . . . . . 5.15.2 Signal Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . 5.45.3 Natural Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . 5.75.4 Sampler Implementation . . . . . . . . . . . . . . . . . . . . . . 5.8

5.4.1 Without over sampling . . . . . . . . . . . . . . . . . . . 5.95.4.2 With over sampling . . . . . . . . . . . . . . . . . . . . . 5.9

5.5 Significance of Nyquist Sampling Theorem . . . . . . . . . . . . 5.105.6 Aliasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11

5.6.1 Aliasing distortion . . . . . . . . . . . . . . . . . . . . . 5.125.7 Quantization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.18

5.7.1 Uniform quantization . . . . . . . . . . . . . . . . . . . . 5.205.7.2 Mid tread uniform quantizer . . . . . . . . . . . . . . . . 5.20

5.8 Non-Uniform Quantization (Robust Quantization) . . . . . . . . 5.245.9 Logarithmic Companding of Speech Signals . . . . . . . . . . . 5.26

ISBN: 9789385983702


SCITECH5.10 Quantization Noise (or) Quantization Error . . . . . . . . . . . . 5.315.11 Pulse Amplitude Modulation . . . . . . . . . . . . . . . . . . . . 5.345.12 Pulse Time Modulation . . . . . . . . . . . . . . . . . . . . . . . 5.36

5.12.1 Pulse Position Modulation (PPM) . . . . . . . . . . . . . 5.365.12.2 Pulse Width Modulation (PWM) . . . . . . . . . . . . . . 5.375.12.3 Generation of PWM and PPM . . . . . . . . . . . . . . . 5.375.12.4 Demodulation of PWM signals . . . . . . . . . . . . . . . 5.395.12.5 Demodulation of PPM signal . . . . . . . . . . . . . . . . 5.39

5.13 Pulse Code Modulation (PCM) . . . . . . . . . . . . . . . . . . . 5.425.14 Time Division Multiplexing . . . . . . . . . . . . . . . . . . . . 5.475.15 Frequency Division Multiplexing . . . . . . . . . . . . . . . . . . 5.52

Questions with Short Answer . . . . . . . . . . . . . . . . 5.54Review Questions . . . . . . . . . . . . . . . . . . . . . . 5.59Multiple Choice Questions with Answer . . . . . . . . . . . 5.61Index I.1 - I.3Bibliography

University Question Solved Papers - Download the following linkhttp://scitechpublications.com/shop/electronics-and-communication-engineering/communication-theory-6th-edn/

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