Telecommunications Demystified

375 Pages·2000·2.37 MB·English

by  Carl Nassar

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
Copyright © 2001 by LLH Technology Publishing
All rights reserved. No part of this book may be reproduced, in any
form or means whatsoever, without written permission of the pub-
lisher. While every 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 information contained herein.
Printed in the United States of America.
ISBN 1-878707-77-9 (eBook)
LLH Technology Publishing and HighText Publications are trademarks
of Lewis Lewis & Helms LLC, 3578 Old Rail Road, Eagle Rock, VA,
24085
Contents
Foreword xv
What’s on the CD-ROM? xvii
CHAPTER 1
Introducing Telecommunications ........................................................1
1.1 Communication Systems ...................................................................1
1.1.1 Definition...................................................................................1
1.1.2 The Parts of a Communication System .................................2
1.1.3 An Example of a Communication System .............................2
1.2 Telecommunication Systems.............................................................3
1.2.1 Definition...................................................................................3
1.2.2 Four Examples and an Erratic History Lesson ....................4
1.3 Analog and Digital Communication Systems ..................................6
1.3.1 Some Introductory Definitions ...............................................6
1.3.2 Definitions.................................................................................7
1.3.3 And Digital Became the Favorite ...........................................8
1.3.4 Making It Digital ......................................................................9
1.4 Congrats and Conclusions...............................................................10
CHAPTER 2
Telecommunication Networks..........................................................13
2.1 Telecommunication Network Basics..............................................13
2.1.1 Connecting People with Telephones....................................13
2.1.2 Connecting More People, Farther Apart.............................14
2.1.3 Multiplexing—An Alternative to a Lot of Wire...................16
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Telecommunications Demystified
2.2 POTS: Plain Old Telephone System...............................................19
2.2.1 Local Calls...............................................................................19
2.2.2 Long Distance Calls...............................................................20
2.2.3 The Signals Sent from Switching Center to
Switching Center...................................................................21
2.3 Communication Channels................................................................24
2.3.1 Transmission Lines (Wires) .................................................24
2.3.2 Terrestrial Microwave ...........................................................26
2.3.3 Satellite Connections..............................................................28
2.3.4 Fiber-optic Links.....................................................................29
2.4 Data Communication Networks......................................................31
2.5 Mobile Communications..................................................................33
2.6 Local Area Networks (LANs)..........................................................35
2.7 Conclusion.........................................................................................37
CHAPTER 3
A Review of Some Important Math, Stats, and Systems.......................39
3.1 Random Variables.............................................................................39
3.1.1 Definitions................................................................................39
3.1.2 The Distribution Function: One Way to Describe x...........39
3.1.3 The Density Function: A Second Way to Describe x ..........40
3.1.4 The Mean and the Variance..................................................41
3.1.5 Multiple Random Variables ...................................................44
3.2 Random Processes ...........................................................................45
3.2.1 A Definition .............................................................................45
3.2.2 Expressing Yourself, or a Complete Statistical Description..47
3.2.3 Expressing Some of Yourself, or a Partial Description......47
3.2.4 And in Telecommunications ….............................................48
3.3 Signals and Systems: A Quick Peek ...............................................50
3.3.1 A Few Signals..........................................................................50
3.3.2 Another Way to Represent a Signal:
The Fourier Transform ..........................................................51
3.3.3 Bandwidth...............................................................................53
3.3.4 A Linear Time Invariant (LTI) System ................................55
3.3.5 Some Special Linear Time Invariant (LTI) Systems ..........56
3.4 Onward...............................................................................................58
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Telecommunications Demystified
CHAPTER 4
Source Coding and Decoding: Making it Digital.................................61
4.1 Sampling ............................................................................................61
4.1.1 Ideal Sampling ........................................................................61
4.1.2 Zero-order Hold Sampling.....................................................67
4.1.3 Natural Sampling....................................................................69
4.2 Quantization ......................................................................................71
4.2.1 Meet the Quantizer ................................................................71
4.2.2 The Good Quantizer...............................................................77
4.2.3 The Quantizer and the Telephone........................................88
4.3 Source Coding: Pulse Code Modulator (PCM).............................92
4.3.1 Introducing the PCM.............................................................92
4.3.2 PCM Talk ................................................................................93
4.3.3 The “Good” PCM....................................................................94
4.3.4 Source Decoder: PCM Decoder...........................................95
4.4 Predictive Coding .............................................................................96
4.4.1 The Idea Behind Predictive Coding.....................................97
4.4.2 Why? ........................................................................................97
4.4.3 The Predicted Value and the Predictive Decoder...............98
4.4.4 The Delta Modulator (DM)...................................................99
4.4.5 The Signals in the DM.........................................................101
4.4.6 Overload and Granular Noise .............................................105
4.4.7 Differential PCM (DPCM)..................................................107
4.5 Congrats and Conclusion...............................................................110
CHAPTER 5
Getting It from Here to There: Modulators and Demodulators..........115
5.1 An Introduction...............................................................................115
5.2 Modulators ......................................................................................116
5.2.1 Baseband Modulators..........................................................116
5.2.2 Bandpass Modulators..........................................................124
5.3 Just-in-Time Math, or How to Make a Modulator Signal
Look Funny .....................................................................................133
5.3.1 The Idea.................................................................................134
5.3.2 Representing Modulated Signals........................................138
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5.4 Bring it Home, Baby, or Demodulators........................................146
5.4.1 What Demodulators Do........................................................146
5.4.2 The Channel and Its Noise..................................................147
5.4.3 Building a Demodulator,
Part I—the Receiver Front End..........................................148
5.4.4 The Rest of the Demodulator,
Part II—The Decision Makers...........................................152
5.4.5 How to Build It......................................................................156
5.5 How Good Is It Anyway (Performance Measures) ....................161
5.5.1 A Performance Measure .....................................................161
5.5.2 Evaluation of P(ε) for Simple Cases.................................162
5.5.3 Some well-known P(ε)’s.....................................................166
5.6 What We Just Did ...........................................................................166
CHAPTER 6
Channel Coding and Decoding: Part 1–Block Coding and Decoding...171
6.1 Simple Block Coding.....................................................................172
6.1.1 The Single Parity Check Bit Coder....................................172
6.1.2 Some Terminology...............................................................175
6.1.3 Rectangular Codes ...............................................................175
6.2 Linear block codes..........................................................................177
6.2.1 Introduction...........................................................................177
6.2.2 Understanding Why.............................................................179
6.2.3 Systematic Linear Block Codes..........................................181
6.2.4 The Decoding .......................................................................182
6.3 Performance of the Block Coders ................................................188
6.3.1 Performances of Single Parity Check Bit
Coders/Decoders ................................................................188
6.3.2 The Performance of Rectangular Codes............................189
6.3.3 The Performance of Linear Block Codes..........................189
6.4 Benefits and Costs of Block Coders.............................................192
6.5 Conclusion.......................................................................................193
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CHAPTER 7
Channel Coding and Decoding:
Part 2–Convolutional Coding and Decoding....................................197
7.1 Convolutional Coders.....................................................................197
7.1.1 Our Example.........................................................................197
7.1.2 Making Sure We’ve Got It ...................................................199
7.1.3 Polynomial Representation..................................................200
7.1.4 The Trellis Diagram.............................................................201
7.2 Channel Decoding..........................................................................203
7.2.1 Using a Trellis Diagram ......................................................204
7.2.2 The Viterbi Algorithm...........................................................206
7.3 Performance of the Convolutional Coder ....................................213
7.4 Catastrophic Codes ........................................................................214
7.5 Building Your Own .........................................................................216
CHAPTER 8
Trellis-Coded Modulation (TCM)
The Wisdom of Modulator and Coder Togetherness.........................221
8.1 The Idea...........................................................................................222
8.2 Improving on the Idea....................................................................225
8.3 The Receiver End of Things..........................................................230
8.3.1 The Input...............................................................................231
8.3.2 The TCM Decoder Front End ............................................233
8.3.3 The Rest of the TCM Decoder............................................234
8.3.4 Searching for the Best Path ................................................237
CHAPTER 9
Channel Filtering and Equalizers ...................................................245
9.1 Modulators and Pulse Shaping .....................................................245
9.2 The Channel That Thought It Was a Filter .................................249
9.3 Receivers: A First Try....................................................................251
9.3.1 The Proposed Receiver........................................................251
9.3.2 Making the Receiver a Good One ......................................254
9.3.3 The Proposed Receiver: Problems and Usefulness..........256
9.4 Optimal Receiver Front End..........................................................258
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9.5 Optimal Rest-of-the-Receiver .........................................................262
9.5.1 The Input................................................................................262
9.5.2 A Problem with the Input, and a Solution..........................264
9.5.3 The Final Part of the Optimal Receiver.............................265
9.5.4 An Issue with Using the Whitening Filter and MLSE......271
9.6 Linear Equalizers............................................................................271
9.6.1 Zero Forcing Linear Equalizer............................................272
9.6.2 MMSE (Minimum Mean Squared Error) Equalizer........273
9.7 Other Equalizers: the FSE and the DFE......................................274
9.8 Conclusion.......................................................................................275
CHAPTER 10
Estimation and Synchronization.....................................................279
10.1 Introduction...................................................................................279
10.2 Estimation......................................................................................280
10.2.1 Our Goal ............................................................................280
10.2.2 What We Need to Get an Estimate of a Given r............281
10.2.3 Estimating a Given r, the First Way................................281
10.2.4 Estimating a Given r, the Second Way...........................282
10.2.5 Estimating a Given r, the Third Way..............................283
10.3 Evaluating Channel Phase: A Practical Example......................285
10.3.1 Our Example and Its Theoretically Computed Estimate..285
10.3.2 The Practical Estimator: the PLL ...................................290
10.3.3 Updates to the Practical Estimator in MPSK ................292
10.4 Conclusion.....................................................................................294
CHAPTER 11
Multiple Access Schemes:
Teaching Telecommunications Systems to Share...............................299
11.1 What It Is.......................................................................................299
11.2 The Underlying Ideas...................................................................300
11.3 TDMA ............................................................................................303
11.4 FDMA ............................................................................................305
11.5 CDMA............................................................................................306
11.5.1 Introduction.......................................................................306
11.5.2 DS-CDMA..........................................................................310
viii
11.5.3 FH-CDMA .........................................................................312
11.5.4 MC-CDMA ........................................................................313
11.6 CIMA..............................................................................................315
11.7 Conclusion.....................................................................................318
CHAPTER 12
Analog Communications...............................................................321
12.1 Modulation—An Overview..........................................................321
12.2 Amplitude Modulation (AM).......................................................322
12.2.1 AM Modulators—in Time ...............................................323
12.2.2 AM Modulation—in Frequency......................................326
12.2.3 Demodulation of AM Signals—Noise-Free Case..........328
12.2.4 An Alternative to AM—DSB-SC......................................330
12.3 Frequency Modulation (FM).......................................................334
12.3.1 The Modulator in FM ......................................................335
12.3.2 The Demodulator in FM..................................................339
12.4 The Superheterodyne Receiver...................................................339
12.5 Summary .......................................................................................341
Annotated References and Bibliography .........................................345
Index..........................................................................................349
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