Grami Introduction to Digital Communications

1. Auflage 2015
ISBN: 978-0-12-407658-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 604 Seiten

Introduction to Digital Communications explores the basic principles in the analysis and design of digital communication systems, including design objectives, constraints and trade-offs. After portraying the big picture and laying the background material, this book lucidly progresses to a comprehensive and detailed discussion of all critical elements and key functions in digital communications. - The first undergraduate-level textbook exclusively on digital communications, with a complete coverage of source and channel coding, modulation, and synchronization. - Discusses major aspects of communication networks and multiuser communications - Provides insightful descriptions and intuitive explanations of all complex concepts - Focuses on practical applications and illustrative examples. - A companion Web site includes solutions to end-of-chapter problems and computer exercises, lecture slides, and figures and tables from the text

Dr. Grami received his PhD in Electrical Engineering from the University of Toronto. He has worked for Nortel Networks, where he was involved in the research, design, and development of North America's first digital cellular wireless system.He later joined Telesat Canada, where he was the lead researcher and principal designer of Canada's Anik-F2 Ka-band system, the world's first broadband access satellite system. Dr. Grami is currently an associate professor in the Faculty of Engineering and Applied Science at the University of Ontario Institute of Technology (UOIT), where as a founding faculty member he has led the development of various programs, including the BEng, MEng, and PhD programs in ECE.

Autoren/Hrsg.

Grami, Ali

Inhaltsverzeichnis

1;Front Cover;1
2;Introduction to Digital Communications;4
3;Copyright;5
4;Dedication;6
5;Contents;8
6;Preface;14
7;Acknowledgements;16
8;Chapter 1: Introduction;18
8.1;1.1. Historical Review of Communications;18
8.2;1.2. Block Diagram of a Digital Communication System;22
8.3;1.3. Organization of the Book;25
8.4;References;27
9;Chapter 2: Fundamental Aspects of Digital Communications;28
9.1;Introduction;28
9.2;Contents;28
9.3;2.1. Why Digital?;29
9.3.1;2.1.1. Advantages of Digital;30
9.3.2;2.1.2. Disadvantages of Digital;31
9.4;2.2. Communications modalities;32
9.4.1;2.2.1. Text;32
9.4.2;2.2.2. Audio;33
9.4.3;2.2.3. Visual;34
9.5;2.3. Communication network models;35
9.5.1;2.3.1. Layered Architectures;36
9.5.2;2.3.2. OSI Model;36
9.5.3;2.3.3. TCP/IP Protocol Suite;39
9.6;2.4. Guided-Transmission Media;40
9.6.1;2.4.1. Twisted-Pair Cable;40
9.6.2;2.4.2. Coaxial Cable;42
9.6.3;2.4.3. Fiber-Optic Cable;42
9.7;2.5. Radio transmission;43
9.7.1;2.5.1. Advantages of Radio;43
9.7.2;2.5.2. Disadvantages of Radio;43
9.7.3;2.5.3. Radio Spectrum;44
9.7.4;2.5.4. Wave Propagation;45
9.8;2.6. Transmission impairments;48
9.8.1;2.6.1. Attenuation;48
9.8.2;2.6.2. Distortion;48
9.8.3;2.6.3. Interference;50
9.8.4;2.6.4. Noise;51
9.9;2.7. Modulation process;51
9.10;2.8. Fundamental limits in digital transmission;54
9.11;2.9. Digital communication design aspects;54
9.12;Summary and Sources;56
10;Chapter 3: Signals, Systems, and Spectral Analysis;58
10.1;Introduction;58
10.2;3.1. Basic operations on signals;59
10.2.1;3.1.1. Operations Performed on Dependent Variable;59
10.2.2;3.1.2. Operations Performed on Independent Variable;63
10.3;3.2. Classification of signals;66
10.3.1;3.2.1. Continuous-Value and Discrete-Value Signals;66
10.3.2;3.2.2. Continuous-Time and Discrete-Time Signals;66
10.3.3;3.2.3. Analog and Digital Signals;67
10.3.4;3.2.4. Deterministic and Random Signals;68
10.3.5;3.2.5. Real and Complex Signals;68
10.3.6;3.2.6. Periodic and Nonperiodic Signals;69
10.3.7;3.2.7. Even and Odd Signals;70
10.3.8;3.2.8. Energy and Power Signals;71
10.3.9;3.2.9. Causal and Noncausal Signals;73
10.3.10;3.2.10. Time-Limited and Band-Limited Signals;73
10.3.11;3.2.11. Baseband and Bandpass Signals;74
10.4;3.3. Classification of systems;74
10.4.1;3.3.1. Baseband and Passband Systems;75
10.4.2;3.3.2. Invertible and Noninvertible Systems;75
10.4.3;3.3.3. Lumped and Distributed Systems;75
10.4.4;3.3.4. Adaptive and Fixed Systems;76
10.4.5;3.3.5. Systems with or without Feedback;76
10.4.6;3.3.6. Systems with or without Memory;77
10.4.7;3.3.7. Systems with Single/Multiple Inputs and Single/Multiple Outputs;77
10.4.8;3.3.8. Passive and Active Systems;78
10.4.9;3.3.9. Causal and Noncausal Systems;78
10.4.10;3.3.10. Stable and Unstable Systems;78
10.4.11;3.3.11. Continuous-Time and Discrete-Time Systems;78
10.4.12;3.3.12. Power-Limited and Band-Limited Systems;78
10.4.13;3.3.13. Linear and Nonlinear Systems;79
10.4.14;3.3.14. Time-Invariant and Time-Varying Systems;80
10.4.15;3.3.15. Linear Time-Invariant (LTI) Systems;81
10.5;3.4. Sinsuoidal signals;82
10.5.1;3.4.1. Characteristics of Sinusoidal Signals;82
10.5.2;3.4.2. Benefits and Applications of Sinusoidal Signals;85
10.5.3;3.4.3. Relation between Sinusoidal and Complex Exponential Signals;86
10.6;3.5. Elementary signals;88
10.6.1;3.5.1. DC Signal;88
10.6.2;3.5.2. Unit Step Function;88
10.6.3;3.5.3. Exponential Signal;89
10.6.4;3.5.4. Sinc Function;89
10.6.5;3.5.5. Gaussian Pulse;90
10.6.6;3.5.6. Unit Ramp Function;90
10.6.7;3.5.7. Signum Function;91
10.6.8;3.5.8. Rectangular Pulse;92
10.6.9;3.5.9. Dirac Delta or Unit Impulse Function;93
10.6.10;3.5.10. Periodic Pulse and Impulse Trains;94
10.7;3.6. Fourier series;95
10.7.1;3.6.1. Orthogonal Functions;95
10.7.2;3.6.2. Dirichlets Conditions;96
10.7.3;3.6.3. Quadrature Fourier Series;97
10.7.4;3.6.4. Polar Fourier Series;100
10.7.5;3.6.5. Complex Exponential Fourier Series;101
10.7.6;3.6.6. Spectrum of Periodic Signals;101
10.7.7;3.6.7. Power of Periodic Signals;104
10.8;3.7. Fourier transform;105
10.8.1;3.7.1. Fourier Transform Pair;106
10.8.2;3.7.2. Fourier Spectra;107
10.8.3;3.7.3. Fourier Transform for Periodic Signals;111
10.8.4;3.7.4. Properties of Fourier Transform;114
10.8.5;3.7.5. Numerical Computation of Fourier Transform: Discrete Fourier Transform;130
10.9;3.8. Time and frequency relations;133
10.9.1;3.8.1. Bandwidth Definitions;133
10.9.2;3.8.2. Time-Bandwidth Product;135
10.10;3.9. Signal Transmission through systems;137
10.10.1;3.9.1. Signal Transmission through LTI Systems;137
10.10.2;3.9.2. Time Response and Convolution in LTI Systems;140
10.10.3;3.9.3. Frequency Response and Transfer Function in LTI Systems;141
10.10.4;3.9.4. Application of Periodic Signals to LTI Systems;143
10.10.5;3.9.5. Distortionless Transmission;144
10.10.6;3.9.6. Nonlinear Distortion;146
10.11;3.10. Communication filters;148
10.11.1;3.10.1. Ideal Filters;148
10.11.2;3.10.2. Filter Types;151
10.11.3;3.10.3. Filter Design;152
10.12;3.11. Spectral density and autocorrelation functions;153
10.12.1;3.11.1. Energy Spectral Density;154
10.12.2;3.11.2. Autocorrelation of Energy Signals;154
10.12.3;3.11.3. Power Spectral Density;155
10.12.4;3.11.4. Autocorrelation of Power Signals;156
10.13;3.12. Lowpass and bandpass signals;157
10.13.1;3.12.1. Lowpass Representation of Bandpass Signals;158
10.13.2;3.12.2. Quadrature Amplitude Modulation;158
10.13.3;3.12.3. Phase and Group Delay;159
10.14;Summary and Sources;161
10.15;Problems;162
10.16;Computer Exercises;166
11;Chapter 4: Probability, Random Variables, and Random Processes;168
11.1;Introduction;168
11.2;4.1. Probability;169
11.2.1;4.1.1. Basic Definitions;169
11.2.2;4.1.2. Axioms of Probability;170
11.2.3;4.1.3. Conditional Probability and Bayes Rule;171
11.3;4.2. Random variables;177
11.3.1;4.2.1. Single Random Variable;177
11.3.2;4.2.2. Important Single Random Variables;181
11.3.3;4.2.3. Expected Value;186
11.3.4;4.2.4. Conditional cdf and pdf of a Random Variable;188
11.3.5;4.2.5. Functions of a Single Random Variable;189
11.3.6;4.2.6. Chebyshev Inequality;191
11.3.7;4.2.7. Pair of Random Variables;192
11.3.8;4.2.8. Independent, Uncorrelated, and Orthogonal Random Variables;195
11.3.9;4.2.9. Jointly Gaussian Random Variables;198
11.3.10;4.2.10. Sum of Random Variables;198
11.4;4.3. Random processes;201
11.4.1;4.3.1. Basic Concepts;201
11.4.2;4.3.2. Statistical Averages;203
11.4.3;4.3.3. Stationary Processes;204
11.4.4;4.3.4. Ergodic Processes;207
11.4.5;4.3.5. Power Spectral Density;209
11.4.6;4.3.6. Response of Linear Time-Invariant Systems to Random Processes;212
11.4.7;4.3.7. Gaussian Random Process;214
11.4.8;4.3.8. Noise;216
11.4.9;4.3.9. Narrowband Bandpass Noise;218
11.4.10;4.3.10. Sampling Theorem of Random Signals;220
11.5;Summary and Sources;221
11.6;Problems;222
11.7;Computer Exercises;233
12;Chapter 5: Analog-to-Digital Conversion;234
12.1;Introduction;234
12.2;5.1. Sampling process;235
12.2.1;5.1.1. Sampling Theorem;236
12.2.2;5.1.2. Undersampling and Aliasing Effect;241
12.2.3;5.1.3. Natural Sampling and Flat-Top Sampling;245
12.2.4;5.1.4. Upsampling and Oversampling;249
12.2.5;5.1.5. Sampling of Bandpass Signals and Random Signals;250
12.3;5.2. Quantization process;253
12.3.1;5.2.1. Uniform Quantization;254
12.3.2;5.2.2. Nonuniform Quantization;257
12.3.3;5.2.3. Vector Quantization;261
12.4;5.3. Digital pulse modulation;263
12.4.1;5.3.1. Pulse-Code Modulation (PCM);264
12.4.2;5.3.2. Differential PCM (DPCM) and Adaptive DPCM (ADPCM);269
12.4.3;5.3.3. Delta Modulation (DM) and Adaptive DM (ADM);271
12.5;5.4. Line codes;273
12.5.1;5.4.1. Line Coding Schemes and Selection Criteria;273
12.5.2;5.4.2. Power Spectral Density of Line Codes;275
12.6;Summary and Sources;277
12.7;Problems;278
12.8;Computer Exercises;281
13;Chapter 6: Baseband Digital Transmission;282
13.1;Introduction;282
13.2;6.1. Baseband binary PAM transmission system model;283
13.3;6.2. Intersymbol interference;285
13.3.1;6.2.1. Nyquist Criterion for Distortionless (Zero-ISI) Transmission;285
13.3.2;6.2.2. Raised-Cosine Pulse Spectrum;290
13.3.3;6.2.3. Eye Diagrams;290
13.4;6.3. Optimum system design for noise immunity;294
13.4.1;6.3.1. Bit Error Rate Derivation;295
13.4.2;6.3.2. Optimum Transmitting and Receiving Filters;296
13.4.3;6.3.3. Design Procedure and Example;297
13.5;6.4. Baseband M-ary signaling schemes;299
13.5.1;6.4.1. Bandwidth and Bit Rate;299
13.5.2;6.4.2. Power and Bit Error Rate;300
13.5.3;6.4.3. Binary vs. M-ary Signaling Schemes;302
13.6;6.5. Equalization;303
13.6.1;6.5.1. Viterbi Equalizers;303
13.6.2;6.5.2. Linear Equalizers;305
13.6.3;6.5.3. Decision-Feedback Equalizers;307
13.6.4;6.5.4. Adaptive Equalization;308
13.7;Summary and Sources;310
13.8;Problems;311
13.9;Computer Exercises;314
14;Chapter 7: Passband Digital Transmission;316
14.1;Introduction;316
14.2;7.1. Optimum receiver principles;317
14.2.1;7.1.1. System Model;317
14.2.2;7.1.2. Gram-Schmidt Orthogonalization Procedure;319
14.2.3;7.1.3. Geometric Representation and Interpretation of Signals;322
14.2.4;7.1.4. Receiver Implementation;323
14.2.5;7.1.5. Probability of Error;327
14.2.6;7.1.6. Nonwhite Noise and Noncoherent Detection;331
14.3;7.2. Binary digital modulation schemes;333
14.3.1;7.2.1. Binary Amplitude-Shift Keying;334
14.3.2;7.2.2. Binary Frequency-Shift Keying;336
14.3.3;7.2.3. Binary Phase-Shift Keying;339
14.3.4;7.2.4. Comparison of Binary Digital Modulation Schemes;343
14.4;7.3. Coherent quaternary signaling schemes;345
14.4.1;7.3.1. Quadrature Phase-Shift Keying;345
14.4.2;7.3.2. Offset Quadrature Phase-Shift Keying;350
14.4.3;7.3.3. Minimum-Shift Keying;350
14.5;7.4. M-ary coherent modulation techniques;354
14.5.1;7.4.1. M-ary Amplitude-Shift Keying;355
14.5.2;7.4.2. M-ary Phase-Shift Keying;357
14.5.3;7.4.3. M-ary Quadrature Amplitude Modulation;359
14.5.4;7.4.4. M-ary Frequency-Shift Keying;363
14.5.5;7.4.5. Comparison of M-ary Modulation Schemes;365
14.6;7.5. Orthogonal Frequency-Division Multiplexing;367
14.7;Summary and Sources;369
14.8;Problems;370
14.9;Computer Exercises;372
15;Chapter 8: Synchronization;374
15.1;Introduction;374
15.2;8.1. Synchronization levels;375
15.3;8.2. Scrambling;376
15.3.1;8.2.1. Pseudorandom Scrambler;377
15.3.2;8.2.2. Self-Synchronizing Scrambler;379
15.4;8.3. Phase-Locked Loop (PLL);380
15.4.1;8.3.1. Basic Operation;381
15.4.2;8.3.2. Linear Model of PLL;383
15.5;8.4. Carrier Recovery;385
15.5.1;8.4.1. The Mth-Power Loop;385
15.5.2;8.4.2. The Costas Loop;386
15.6;8.5. Symbol Synchronization;387
15.6.1;8.5.1. Nonlinear-Filter Synchronizer;388
15.6.2;8.5.2. Early-Late Gate Synchronizer;389
15.7;Summary and Sources;391
15.8;Problems;391
15.9;Computer Exercises;392
16;Chapter 9: Information Theory;394
16.1;Introduction;394
16.2;9.1. Measure of information;395
16.2.1;9.1.1. Information Content;395
16.2.2;9.1.2. Average Information Content;397
16.2.3;9.1.3. Extended DMS;399
16.3;9.2. Classification of source codes;401
16.3.1;9.2.1. Block Codes;401
16.3.2;9.2.2. Fixed-Length Codes;401
16.3.3;9.2.3. Variable-Length Codes;402
16.3.4;9.2.4. Distinct Codes;402
16.3.5;9.2.5. Prefix-Free (Instantaneous) Codes;402
16.3.6;9.2.6. Uniquely Decodable Codes;402
16.3.7;9.2.7. Kraft Inequality;403
16.3.8;9.2.8. Extension Codes;404
16.4;9.3. Source Coding theorem;405
16.5;9.4. Lossless data compression;408
16.5.1;9.4.1. Huffman Source Coding Algorithm;408
16.5.2;9.4.2. Lempel-Ziv Source Coding Algorithm;412
16.6;9.5. Discrete Memoryless channels;414
16.6.1;9.5.1. Channel Transition Probabilities;414
16.6.2;9.5.2. Mutual Information;415
16.6.3;9.5.3. Capacity of Discrete Memory Channel;416
16.7;9.6. Channel coding theorem;417
16.8;9.7. Gaussian Channel Capacity Theorem;418
16.9;Summary and Sources;421
16.10;Problems;422
16.11;Computer Exercises;425
17;Chapter 10: Error-Control Coding;426
17.1;Introduction;426
17.2;10.1. Errors;427
17.2.1;10.1.1. Types of Errors;427
17.2.2;10.1.2. Methods of Controlling Errors;428
17.2.3;10.1.3. Classes of Codes;429
17.2.4;10.1.4. Decoding Methods;430
17.3;10.2. Error-detection methods;431
17.3.1;10.2.1. Parity-Check Codes;431
17.3.2;10.2.2. Checksum;434
17.3.3;10.2.3. Cyclic Redundancy Check;435
17.4;10.3. Automatic Repeat Request (ARQ);438
17.4.1;10.3.1. Stop-and-Wait, Go-Back-N, and Selective-Repeat ARQ Techniques;439
17.4.2;10.3.2. Performance of ARQ Systems;441
17.5;10.4. Block codes;443
17.5.1;10.4.1. Description and Capabilities of Linear Block Codes;443
17.5.2;10.4.2. Syndrome-Based Decoding;447
17.5.3;10.4.3. Well-Known Codes;450
17.6;10.5. Convolutional codes;452
17.6.1;10.5.1. Representations of Convolutional Codes;453
17.6.2;10.5.2. Maximum-Likelihood Decoding: The Viterbi Algorithm;457
17.6.3;10.5.3. Trellis-Coded Modulation;459
17.7;10.6. Compound codes;461
17.7.1;10.6.1. Interleavering;462
17.7.2;10.6.2. Simple Combining Codes;465
17.7.3;10.6.3. Turbo Codes;467
17.7.4;10.6.4. Low-Density Parity-Check Codes;470
17.8;Summary and Sources;470
17.9;Problems;471
17.10;Computer Exercises;472
18;Chapter 11: Communication Networks;474
18.1;Introduction;474
18.2;11.1. Multiplexing;475
18.2.1;11.1.1. Frequency-Division Multiplexing;475
18.2.2;11.1.2. Time-Division Multiplexing;477
18.2.3;11.1.3. Wavelength-Division Multiplexing;477
18.3;11.2. Duplexing;478
18.3.1;11.2.1. Frequency-Division Duplexing;479
18.3.2;11.2.2. Time-Division Duplexing;481
18.4;11.3. Multiple Access;481
18.4.1;11.3.1. Frequency-Division Multiple Access;482
18.4.2;11.3.2. Time-Division Multiple Access;482
18.4.3;11.3.3. Code-Division Multiple Access;484
18.5;11.4. Random access;485
18.5.1;11.4.1. ALOHA;485
18.5.2;11.4.2. CSMA;488
18.6;11.5. Controlled Access;490
18.6.1;11.5.1. Reservation;490
18.6.2;11.5.2. Polling;491
18.7;11.6. Wired Communication Networks;491
18.7.1;11.6.1. Circuit-Switched and Packet-Switched Networks;492
18.7.2;11.6.2. Topology;493
18.7.3;11.6.3. Routing and Flow Control;496
18.7.4;11.6.4. Local Area Networks;497
18.7.5;11.6.5. Telephone and Cable Networks;499
18.8;11.7. Network Security and Cryptography;502
18.8.1;11.7.1. Private-Key Cryptography;503
18.8.2;11.7.2. Public-Key Cryptography;504
18.8.3;11.7.3. Digital Signatures;505
18.9;Summary and Sources;507
18.10;Problems;508
19;Chapter 12: Wireless Communications;510
19.1;Introduction;510
19.2;12.1. Radio-link analysis;511
19.2.1;12.1.1. Sources of Interference, Loss, and Noise;511
19.2.2;12.1.2. Received Signal Power and Path Loss;512
19.2.3;12.1.3. Noise Temperature and Receive Figure of Merit;513
19.2.4;12.1.4. Link Margin and Link Threshold;514
19.3;12.2. Frequency reuse;515
19.3.1;12.2.1. Dual Polarization;516
19.3.2;12.2.2. Spatial Separation;517
19.4;12.3. Mobile-radio propagation characteristics;521
19.4.1;12.3.1. Radio-Propagation Mechanisms;521
19.4.2;12.3.2. Doppler Effect;523
19.4.3;12.3.3. Delay Spread and Coherent Bandwidth;524
19.4.4;12.3.4. Doppler Spread and Coherence Time;525
19.4.5;12.3.5. Large-Scale Fading and Small-Scale Fading;525
19.4.6;12.3.6. Fast Fading and Slow Fading;526
19.4.7;12.3.7. Flat Fading and Frequency-Selective Fading;527
19.5;12.4. Diversity;528
19.5.1;12.4.1. Time Diversity;529
19.5.2;12.4.2. Space Diversity;530
19.5.3;12.4.3. Site Diversity;530
19.5.4;12.4.4. Frequency Diversity;530
19.5.5;12.4.5. Polarization Diversity;531
19.5.6;12.4.6. Angle Diversity;531
19.5.7;12.4.7. Path Diversity;531
19.6;12.5. Diversity-combining methods;532
19.6.1;12.5.1. Selection Combining;532
19.6.2;12.5.2. Maximal-Ratio Combining;533
19.6.3;12.5.3. Equal-Gain Combining;533
19.7;12.6. Emerging wireless communication systems;534
19.7.1;12.6.1. Evolution of Wireless Communication Systems;534
19.7.2;12.6.2. 4G Systems;535
19.7.3;12.6.3. TV White Spaces;540
19.8;Summary and Sources;542
19.9;Problems;543
20;Appendix: Analog Continuous-Wave Modulation;546
20.1;Introduction;546
20.2;A.1. Analog Continuous-Wave (CW) Modulation;547
20.3;A.2. Amplitude moDUlation;549
20.3.1;A.2.1. Conventional Amplitude Modulation;550
20.3.2;A.2.2. Double-Sideband Suppressed-Carrier Amplitude Modulation;556
20.3.3;A.2.3. Single-Sideband Amplitude Modulation;559
20.3.4;A.2.4. Vestigial-Sideband Amplitude Modulation;560
20.4;A.3. Frequency modUlation;567
20.4.1;A.3.1. Representation of FM Signals;567
20.4.2;A.3.2. Spectral Analysis of FM Signals;568
20.4.3;A.3.3. FM Modulation and Demodulation;571
20.5;A.4. Amplitude Nonlinearity in Analog CW Modulation;573
20.5.1;A.4.1. Effect of Amplitude Nonlinearity on AM Systems;573
20.5.2;A.4.2. Effect of Amplitude Nonlinearity on FM Systems;574
20.6;A.5. Noise in analog CW modulation;575
20.6.1;A.5.1. Effect of Noise on AM Systems;576
20.6.2;A.5.2. Effect of Noise on FM Systems;577
20.7;A.6. Commercial radio broadcasting;580
20.7.1;A.6.1. AM Radio Broadcasting and Reception;580
20.7.2;A.6.2. FM Radio Broadcasting and Reception;582
20.8;A.7. Comparison of Analog CW Modulation Schemes;584
20.9;Summary and Sources;585
21;List of Acronyms and Abbreviations;590
22;Index;596

Leseproben

Chapter 2

Fundamental Aspects of Digital Communications

Abstract

This chapter briefly provides a descriptive overview of major aspects of digital communications with a view to set the stage for what will be covered in the rest of the book. A quantitative discussion and detailed analysis of critical elements of digital communication systems will be provided in the following chapters. To provide a fundamental understanding of digital communication system analysis and design, this chapter begins with the rationale behind digital, vis-à-vis analog. The focus then turns toward network models, transmission media and impairments, and radio transmission and spectrum. Following a brief discussion on the fundamental limits in digital transmission, an array of inter-related, inter-dependent design objectives and a host of interacting and conflicting design constraints are identified.

Keywords

Digital

communication modality

OSI model

TCP/IP model;twisted-pair

coaxial cable

fiber-optic cable

wave propagation mode

radio spectrum

frequency band

transmission impairment

modulation process

design objective

design constraint

Contents

Introduction   11

2.1 Why Digital?   12

2.2 Communications Modalities   15

2.3 Communication Network Models   18

2.4 Guided-Transmission Media   23

2.5 Radio Transmission   26

2.6 Transmission Impairments   31

2.7 Modulation Process   34

2.8 Fundamental Limits in Digital Transmission   37

2.9 Digital Communication Design Aspects   37

Summary and Sources   39

Introduction

In today’s world, communications are essential and pervasive, as the age of communications with anyone, anytime, anywhere has arrived. The theme is multimedia—the confluence of voice, data, image, music, text, graphics, and video warranting simultaneous transmission in an integrated fashion. With the push of advancing digital technology and the pull of public demand for an array of innovative applications, it is highly anticipated that every aspect of digital communications will continue to broaden so as to usher in even more achievements. The emerging trend is toward low-cost, high-speed, high-performance, utterly-secure, highly-personalized, context-aware, location-sensitive, and time-critical multimedia applications. After studying this chapter on the fundamental aspects of digital communications and understanding all relevant concepts, students should be able to do the following:

1. State the numerous merits of digital and its dominance in communications.

2. Know the few drawbacks of digital and how they can be mitigated.

3. Understand how text can be represented.

4. Expand on the audio characteristics and the impact of digitization on speech and music.

5. Explain the attributes of image and video and the impact of compression on them.

6. Identify how computers form packets to send them over communication networks.

7. Distinguish between the various characteristics associated with wired transmission media.

8. Highlight the benefits and shortcomings associated with radio communications.

9. Assess various modes of radio wave propagation.

10. Define the modulation process.

11. Identify the principal reasons signals may need to be modulated.

12. Describe signal attenuation.

13. Differentiate among different types of distortions along with their possible remedies.

14. Discuss various sources of interference and how to mitigate them.

15. Summarize various sources of noise.

16. Grasp the limiting factors of a band-limited Gaussian channel.

17. Appreciate the relationship among power, bandwidth, and capacity.

18. Outline digital communication design objectives.

19. List digital communication design constraints.

20. Connect the fundamental aspects of digital communications.

2.1 Why Digital?

The telegraph, invented in the mid-nineteenth century, was the forerunner of digital communications. However, it is now that we can emphatically say digital is the pervasive technology of the twenty-first century and beyond, as the first generation of cellular phones in the late seventies was the last major analog communication invention. During the past three decades, communication networks, systems, and devices have all moved toward digital. The primary examples are wireless networks, Internet, MP3 players, smartphones, HDTV, GPS, and satellite TV and radio. Digital communication technology will continue to bring about intelligent infrastructures and sophisticated end-user devices, through which a host of applications in entertainment (e.g., wireless video on demand), education (e.g., online interactive multimedia courses), information (e.g., 3-D video streaming), and business (e.g., mobile commerce) will be provided. The burgeoning field of digital communications will thus continue to affect almost all aspects of our contemporary life.

A basic definition of digital is the transmission of a message using binary digits (bits) or symbols from a finite alphabet during a finite time interval (bit or symbol duration). A bit or symbol occurring in each interval is mapped onto a continuous-time waveform that is then sent across the channel. Over any finite interval, the continuous-time waveform at the channel output belongs to a finite set of possible waveforms. This is in contrast to analog communications, where the output can assume any possible waveform. Digital can bring about many significant benefits, of course, at the expense of few shortcomings, for there is no free lunch in digital communications.

2.1.1 Advantages of Digital

Design efficiency: Digital is inherently more efficient than analog in exchanging power for bandwidth, the two premium resources in communications. Since an essentially unlimited range of signal conditioning and processing options are available to the designer, effective trade-offs among power, bandwidth, performance, and complexity can be more readily accommodated. For any required performance, there is a three-way trade-off among power, bandwidth, and complexity (i.e., an increase in one means the other two will be reduced).

Versatile hardware: The processing power of digital integrated circuits continues to approximately double every 18 months to 2 years. These programmable processors easily allow the implementation of improved designs or changed requirements. Digital circuits are generally less sensitive to physical effects, such as vibration, aging components, and external temperature. They also allow a greater dynamic range (the difference between the largest and the smallest signal values). Processing is now less costly than precious bandwidth and power resources. This in turn allows considerable flexibility in designing communication systems.

New and enhanced services: In today’s widely distributed way of life, Internet services, such as web browsing, e-mailing, texting, e-commerce, streaming and interactive multimedia services, have all become feasible and some even indispensable. It is also easier to integrate different services, with various modalities, into the same transmission scheme or to enhance services through transmission of some additional information, such as playing music or receiving a phone call with all relevant details.

Control of quality: A desired distortion level can be initially set and then kept nearly fixed at that value at every step (link) of a digital communication path. This reconstruction of the digital signal is done by appropriately-spaced regenerative repeaters, which do not allow accumulation of noise and interference. On the other hand, once the analog signal is distorted, the distortion cannot be removed and a repeater in an analog system (i.e., an amplifier) regenerates the distortion together with the signal. In a way, in an analog system, the noises add, whereas in a digital system, the bit error rates add. In other words, with many regenerative repeaters along the path, the impact in an analog system is a reduction of many decibels (dBs) in the signal-to-noise ratio (SNR), whereas the effect in a digital system is a reduction of only a few dBs in the SNR.

Improved security: Digital encryption,...