Telecommunications demystified: a streamlined course in digital communications PDF
Preview Telecommunications demystified: a streamlined course in digital communications
Telecommunications Demystified A Streamlined Course in Digital Communications (and some Analog) for EE Students and Practicing Engineers by Carl Nassar Eagle Rock, Virginia www.LLH-Publishing.com Library of Congress Cataloging-in-Publication Data Nassar, Carl, 1968 Telecommunications demystified / by Carl Nassar. p. c.m. -- (Demystifying technology series) Includes bibliographical references and index. ISBN 1-878707-55-8 (alk. paper) 1. Telecommunication. I. Title. II. Series. TK5101 .N257 2000 621.382--dc21 00-062902 Copyright © 2001 by LLH Technology Publishing. All rights reser ved. No part of this book may be reproduced, in any form or means whatsoever, without written permission from the publisher. While ever y precaution has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 Cover design: Jim Johnson Developmental editing: Carol Lewis Production: Kelly Johnson Visit us on the web: www.LLH-Publishing.com For revisions and updates, check www.telecommunicationsdemystified.com 1 Introducing Telecommunications............................................ 1 Communication Systems .............................................................................. 1 Definition ............................................................................................................. 1 The Parts of a Communication System .............................................................. 2 An Example of a Communication System .......................................................... 2 The Transmitter .................................................................................................. 3 The Channel ....................................................................................................... 3 The Receiver ...................................................................................................... 3 Telecommunication Systems........................................................................ 3 Definition ............................................................................................................. 3 Four Examples and an Erratic History Lesson ................................................... 4 Analog and Digital Communication Systems ................................................ 6 Some Introductory Definitions............................................................................. 6 Definitions ........................................................................................................... 7 And Digital Became the Favorite ........................................................................ 8 Making It Digital .................................................................................................. 9 Congrats and Conclusion ............................................................................. 10 Problems....................................................................................................... 11 2 Telecommunication Networks.................................................. 2 Telecommunication Network Basics ............................................................. 2 Connecting People with Telephones .................................................................. 2 Connecting More People, Farther Apart ............................................................. 14 Multiplexing�An Alternative to a Lot of Wire ........................................................ 16 First There Was FDM ......................................................................................... 16 Along Came TDM ............................................................................................... 18 POTS: Plain Old Telephone System ............................................................ 19 Local Calls .......................................................................................................... 19 Long Distance Calls............................................................................................ 20 Connecting the Call ............................................................................................ 20 The Signals Sent from Switching Center to Switching Center............................ 21 Class 5 to Class 4 ............................................................................................... 22 Other Signals between Switching Centers ......................................................... 24 Communication Channels............................................................................. 24 Transmission Lines (Wires) ................................................................................ 24 Terrestrial Microwave ......................................................................................... 26 Satellite Connections .......................................................................................... 28 Fiber-optic Links ................................................................................................. 29 Data Communication Networks .................................................................... 31 Mobile Communications ............................................................................... 33 Local Area Networks (LANs) ........................................................................ 35 Conclusion .................................................................................................... 37 Problems....................................................................................................... 38 3 A Review of Some Important Math, Stats, and Systems ....... 3 Random Variables ........................................................................................ 3 Definitions ........................................................................................................... 3 The Distribution Function: One Way to Describe x ............................................. 3 The Density Function: A Second Way to Describe x .......................................... 40 The Mean and the Variance ............................................................................... 41 Example 3.1........................................................................................................ 43 Multiple Random Variables ................................................................................. 44 Random Processes ...................................................................................... 45 A Definition......................................................................................................... 45 Expressing Yourself, or a Complete Statistical Description................................ 47 Expressing Some of Yourself, or a Partial Description ....................................... 47 And in Telecommunications � .............................................................................. 48 Example 3.2........................................................................................................ 48 Signals and Systems: A Quick Peek ............................................................ 50 A Few Signals..................................................................................................... 50 Another Way to Represent a Signal: The Fourier Transform ............................. 51 Example 3.3........................................................................................................ 52 Bandwidth ........................................................................................................... 53 A Linear Time Invariant (LTI) System................................................................. 55 Some Special Linear Time Invariant (LTI) Systems ........................................... 56 Onward ......................................................................................................... 58 Problems....................................................................................................... x 4 Source Coding and Decoding:................................................. 4 Sampling....................................................................................................... 4 Ideal Sampling .................................................................................................... 4 The Sampling...................................................................................................... 4 The Information in the Samples.......................................................................... 62 Getting Back All the Information from the Samples ............................................ 64 Some Commonly Used Words ........................................................................... 65 Example 4.1........................................................................................................ 66 Zero-order Hold Sampling .................................................................................. 67 The Information in the Samples.......................................................................... 67 Example 4.2........................................................................................................ 68 Natural Sampling ................................................................................................ 69 The Information in the Samples.......................................................................... 70 Quantization.................................................................................................. 71 Meet the Quantizer ............................................................................................. 71 Example 4.3........................................................................................................ 73 Who wants it? ..................................................................................................... 73 Quantizer Terms ................................................................................................. 74 Types of Quantizers............................................................................................ 75 Example 4.4........................................................................................................ 76 The Good Quantizer ........................................................................................... 77 What Is a Good Quantizer? ................................................................................ 77 Measures of Performance .................................................................................. 77 A �Classic� ........................................................................................................... 78 Creating the Good Quantizer.............................................................................. 81 Example 4.5........................................................................................................ 86 The Quantizer and the Telephone ...................................................................... 88 The Idea.............................................................................................................. 88 Source Coding: Pulse Code Modulator (PCM) ............................................. 92 Introducing the PCM ........................................................................................... 92 PCM Talk ............................................................................................................ 93 The �Good� PCM ................................................................................................. 94 Source Decoder: PCM Decoder ......................................................................... 95 Predictive Coding.......................................................................................... 96 The Idea Behind Predictive Coding .................................................................... 97 Why?................................................................................................................... 97 The Predicted Value and the Predictive Decoder ............................................... 98 The Delta Modulator (DM) .................................................................................. 99 How the DM creates an ...................................................................................... 99 The Block Diagram of the DM............................................................................. 100 The Sampler and the Quantizer in the DM ......................................................... 100 The Signals in the DM ........................................................................................ 2 Example 4.6........................................................................................................ 104 Overload and Granular Noise ............................................................................. 105 Differential PCM (DPCM).................................................................................... 107 The Predicted Value ........................................................................................... 107 Example 4.7........................................................................................................ 109 The Block Diagram ............................................................................................. 109 Congrats and Conclusion ............................................................................. 110 Problems....................................................................................................... 111 5 Getting It from Here to There: .................................................. 5.1 An Introduction.............................................................................................. 5.1 Modulators .................................................................................................... 116 Baseband Modulators ......................................................................................... 116 NRZ Modulators.................................................................................................. 117 RZ Modulators .................................................................................................... 118 Phase-encoded Modulators................................................................................ 120 Which Modulator to Use? ................................................................................... 122 Example 5.1........................................................................................................ 124 Bandpass Modulators ......................................................................................... 124 ASK..................................................................................................................... 125 PSK..................................................................................................................... 127 FSK ..................................................................................................................... 129 QAM.................................................................................................................... 130 Example 5.2........................................................................................................ 131 Choosing a Modulation Method .......................................................................... 131 Just-in- Time Math, or How to Make a Modulator Signal Look Funny .......... 133 The Idea.............................................................................................................. 134 Example 5.3........................................................................................................ 136 Representing Modulated Signals........................................................................ 138 BPSK .................................................................................................................. 139 PSK..................................................................................................................... 140 ASK..................................................................................................................... 143 QAM.................................................................................................................... 145 Bring it Home, Baby, or Demodulators ......................................................... 146 What Demodulators Do ...................................................................................... 146 The Channel and Its Noise ................................................................................. 147 Building a Demodulator, Part I�the Receiver Front End ...................................... 148 What it does........................................................................................................ 148 An orthonormal basis for r(t) ............................................................................... 148 Representing r(t) as a vector using the orthonormal basis ................................. 149 Building the Receiver Front End ......................................................................... 151 Example 5.4........................................................................................................ 152 The Rest of the Demodulator, Part II�The Decision Makers ............................... 152 What It Does ....................................................................................................... 152 How It Works ...................................................................................................... 153 How to Build It..................................................................................................... 156 The Correlator Receiver ..................................................................................... 156 Example 5.5........................................................................................................ 157 The Matched Filter Receiver�Version 1 .............................................................. 158 The Matched Filter Receiver �Version 2 ............................................................. 159 How Good Is It Anyway (Performance Measures)........................................ 161 A Performance Measure..................................................................................... 161 Evaluation of ....................................................................................................... 162 for Simple Cases ................................................................................................ 162 The BPSK Modulator Remembered ................................................................... 162 The BPSK Demodulator: A Summary................................................................. 162 Evaluating the P( ................................................................................................ 163 Some Well-known P( .......................................................................................... 166 s .......................................................................................................................... 166 What We Just Did ......................................................................................... 166 Problems....................................................................................................... 167 6 Channel Coding and Decoding:............................................... 0 Simple Block Coding..................................................................................... 172 The Single Parity Check Bit Coder ..................................................................... 172 Example 6.1........................................................................................................ 174 Some Terminology.............................................................................................. 175 Rectangular Codes ............................................................................................. 175 Channel Coders for Rectangular Codes ............................................................. 175 Channel Decoders for Rectangular Codes ......................................................... 176 Example 6.2........................................................................................................ 176 Linear block codes ........................................................................................ 177 Introduction ......................................................................................................... 177 Example 6.3........................................................................................................ 178 Understanding Why ............................................................................................ 179 Systematic Linear Block Codes .......................................................................... 181 Example 6.4........................................................................................................ 181 The Decoding ..................................................................................................... 182 Example 6.5........................................................................................................ 184 Example 6.6........................................................................................................ 186 Performance of the Block Coders ................................................................. 188 Performances of Single Parity Check Bit Coders/Decoders ............................... 188 The Performance of Rectangular Codes ............................................................ 189 The Performance of Linear Block Codes............................................................ 189 Example 6.7........................................................................................................ 190 Benefits and Costs of Block Coders ............................................................. 192 Conclusion .................................................................................................... 193 Problems....................................................................................................... 194 7 Channel Coding and Decoding:............................................... 1 Convolutional Coders ................................................................................... 1 Our Example ....................................................................................................... 1 Making Sure We� .....v..e.. .G...o..t. .I.t................................................................. 199 Polynomial Representation ................................................................................. 200 The Trellis Diagram ............................................................................................ 201 Example 7.1........................................................................................................ 202 Channel Decoding ........................................................................................ 203 Using a Trellis Diagram ...................................................................................... 204 Example 7.2........................................................................................................ 206 The Viterbi Algorithm .......................................................................................... 206 Example 7.3........................................................................................................ 212 Performance of the Convolutional Coder...................................................... 213 Catastrophic Codes ...................................................................................... 214 Building Your Own ........................................................................................ 216 Problems....................................................................................................... 217 8 Trellis-Coded Modulation (TCM).............................................. 8 The Idea........................................................................................................ 222 Improving on the Idea ................................................................................... 225 Example 8.1........................................................................................................ 229 The Receiver End of Things ......................................................................... 230 The Input............................................................................................................. 231 The TCM Decoder Front End ............................................................................. 233 The Rest of the TCM Decoder............................................................................ 234 Example 8.2........................................................................................................ 236 Searching for the Best Path................................................................................ 237 Problems....................................................................................................... 242 9 Channel Filtering and Equalizers............................................. i Modulators and Pulse Shaping ..................................................................... i Example 9.1........................................................................................................ 248 The Channel That Thought It Was a Filter.................................................... 249 Example 9.2........................................................................................................ 250 Receivers: A First Try ................................................................................... 251 The Proposed Receiver ...................................................................................... 251 Making the Receiver a Good One ...................................................................... 254 The Proposed Receiver: Problems and Usefulness ........................................... 256 Example 9.3........................................................................................................ 257 Optimal Receiver Front End ......................................................................... 258 Optimal Rest-of-the-Receiver ....................................................................... 262 The Input............................................................................................................. 262 A Problem with the Input, and a Solution............................................................ 264 The Final Part of the Optimal Receiver............................................................... 265 Example 9.4........................................................................................................ 270 An Issue with Using the Whitening Filter and MLSE .......................................... 271 Linear Equalizers .......................................................................................... 271 Zero Forcing Linear Equalizer ............................................................................ 272 MMSE (Minimum Mean Squared Error) Equalizer ............................................. 273 Example 9.5........................................................................................................ 273 Other Equalizers: the FSE and the DFE ....................................................... 274 Conclusion .................................................................................................... 275 Problems....................................................................................................... 276 10 Estimation and Synchronization ............................................ 10 Introduction ................................................................................................... 10 Estimation: Part 1 ......................................................................................... 280 Our Goal ............................................................................................................. 280 What We Need to Get an Estimate of a Given r ................................................. 281 Estimating a Given r, the First Way .................................................................... 281 Estimating a Given r, the Second Way ............................................................... 282 Estimating a Given r, the Third Way ................................................................... 283 Example 10.1...................................................................................................... 283 Evaluating Channel Phase: A Practical Example ......................................... 285 Our Example and Its Theoretically Computed Estimate ..................................... 285 The Practical Estimator: the PLL ........................................................................ 290 Updates to the Practical Estimator in MPSK ...................................................... 292 Conclusion .................................................................................................... 295 Problems....................................................................................................... 296 11 Multiple Access Schemes....................................................... 11 What It Is....................................................................................................... 11 The Underlying Ideas.................................................................................... 300 Example 11.1...................................................................................................... 302 TDMA............................................................................................................ 303 Example 11.2...................................................................................................... 305 FDMA............................................................................................................ 305 CDMA ........................................................................................................... 306 Introduction ......................................................................................................... 306 DS-CDMA ........................................................................................................... 310 FH-CDMA ........................................................................................................... 312 MC-CDMA .......................................................................................................... 313 CIMA............................................................................................................. 315 Conclusion .................................................................................................... 318 Problems....................................................................................................... 319 12 Analog Communications ........................................................ 12.1 Modulation�An Overview ............................................................................... 12.1 Amplitude Modulation (AM) .......................................................................... 322 AM Modulators�in Time ....................................................................................... 323 Example 12.1...................................................................................................... 325 AM Modulation�in Frequency .............................................................................. 326 Demodulation of AM Signals�Noise-Free Case .................................................. 328 An Alternative to AM�DSB-SC ............................................................................ 330 Example 12.2...................................................................................................... 333 Frequency Modulation (FM).......................................................................... 334 The Modulator in FM........................................................................................... 335 Example 12.3...................................................................................................... 338 The Demodulator in FM ...................................................................................... 339 The Superheterodyne Receiver.................................................................... 339 Summary ...................................................................................................... 341 Problems....................................................................................................... 342 Annotated References and Bibliography ................................... 5. Index .............................................................................................. 175 Acknowledgments In this life of mine, I have been blessed with an abundance of won- derful people. This book would be incomplete without at least a page to say “thank you,” for these are people alive in me and, therefore, alive in the pages of this book. Dr. Reza Soleymani, your careful guidance through the turmoil that surrounded my Ph.D. days was nothing short of a miracle. You showed me, through your example, how to handle even the most difficult of situations with grace and grit, both academically and in all of life. Dr. Derek Lile, Department Head at CSU—a young faculty could not ask for better guidance. Your thoughtfulness, caring, and gentle support have helped nurture the best of who I am. I am grateful. Steve Shattil, Vice President of Idris Communications, you are indeed a genius of a man whose ideas have inspired me to walk down new roads in the wireless world. Arnold Alagar, President of Idris, thank you for sharing the bigger picture with me, helping guide my research out of obscure journals and into a world full of opportunity. To both of you, I am grateful for both our technological partnerships and our friendships. Bala Natarajan and Zhiqiang Wu, my two long-time Ph.D. students, your support for my research efforts, through your commitment and dedication, has not gone unnoticed. Thank you for giving so fully of yourselves. Dr. Maier Blostien, who asked me to change my acknowledgments page in my Ph.D. thesis to something less gushy, let me thank you now for saving the day when my Ph.D. days looked numbered. I appreciate your candor and your daring. Carol Lewis, my publisher at LLH Technology Publishing, thank you for believing in this project and moving it from manuscript to “masterpiece.” Gretchen Brooks Nassar, you hold my hand and invite me to fly off the cliffs and into Oceans of Wonder. Your support in inviting me to pursue my dreams is nothing short of a gift straight from the heavens. I love you. xi
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