实例介绍
【实例简介】
An ideal first text on communication systems in electrical engineering, Modern Digital and Analog Communication Systems is now in its fourth edition. Retaining the superb pedagogical style of the first three editions, the authors first introduce the fundamentals of signals and systems and core commu
Oxford University PrEss In memory of M.E. Van Valkenbi g Calcutta Madra: Madrid Melbut 1921-1997 Mexico City Nairobi Paris poe Taipei Toky o Torcuato Warsay eht 1998 by Oxford 198 Madison Aveuue. New York. New York 10016 All rights reserved. No part of this publication may be reproduced, stored in a retrieval rstem. or transmitted, in any form or by any means, clcctronie. Mechanical, photocopy ing, rwise, witht the. prior permission of Oxford Univeesity Press Library of Congress Cataloging- irl-publicntion Data Lathi, B P(Bhaewandas pannalal and analog comunication systems /B P. athi p. c-(The Oxford series in electrical and computcr cal references (p 3. Statistical communication theoxy. L litic I Series TK51013331998 6213s2^c21 321 i-free pap CONTENTS PREFACE X1 INTRODUCTION 7 on syste Analog and Digital Signal-to-Noisc Ratio, Channel Bandwidth, and the Rate of Communication 8 Modulation 10 B 2 INTRODUCTION TO SIGNALS ]4 2. 1 Size of a signal 2. 2 Classification of Signals 2.3 Some Useful Signal Operalions 24 2.4 Unit Impulse functio 28 2.5 Signals and Vectors 30 2.6 Signal Camparison: Correlation 35 2.7 Signal Representation by Orthogonal Signal Set 40 2. B Trigonometric Fourier Series 44 9 Exponential Fourier Series 5 2. 10 Numerical Computation of Dn 60 3 ANALYSIS AND TRANSMISSION OF SIGNALS 77 3. 1 Aperiodic Signal Representation by fourier Integral. 7T Transforms of Some Useful Functions 8 3.3 Some Properties of the Fourier Transform 84 3.4 Signal Tra through a lincar syster 3.5 Ideal and Practical filters 10 3.6 Signal Distortion aver a Communication Channel 110 vii CONTENTS Contents ix 3.7 Signal Energy and Energy Spectral Denisily 115 8.4 Digital Switc hing Technologics ?383 3.8 Signal Power and Power Spectral Density 123 8.5 Broadband Services for Entertainment and Home Office Applications 392 3. Numerical Computation of Fourier Iransform: The DFT 1.30 8.6 Video Compression 7 High-Definition Television(HDTV 400 X4 AMPLITUDE (LINEAR)MODULATION 757 9 SOME RECENT DEVELOPMENTS AND 1. 1 Baseband and Carrier Communication 157 4.2 Amplitude Modulation: Double Sideband (DSB) 152 MISCELLANEOUS TOPICS. 404 4.3 Amplitude Modulation (AM) 162 9.1 Cellular Telephone(Mobile Radio)System 40-4 4.4 Quadrature Amplitude Modulation(QAM 9. 2 Spread Spectrum Systems 406 4.5 Amplitude Modulation: Single Sideband (SSB) 177 3 ransmission Media 416 4.6 Amplitude Modulalion: Vestigial Sideband (VSB 9. 4 Hybrid nvers 4.7 Carrier Acquisition 16 9.5 Public Switched Telephone Network4 4.8 Superheterodyne AM Receiver 7 85 4.9 Television 197 10 INTRODUCTION TO THEORY OF PROBABILITY 434 5 ANGLE(EXPONENTIAL)MODULATION 208 10. 1 Concept of Probability 434 Y0. 2 Random Variables 44.5 5.1 Concept of Instantaneous Frequency 208 10.3 Statistical Averages(Means) 46 2 Bandwidth of Anglc-Modulated Waves 215 10.4 Centr al-Limit Theorem 472 5.3 Generation of FM 10.5C 47.3 4 Demodulation of FM 23 10.6 Linear Mean Square Estimation 476 5.5 Interference in Angle-Modulated Systems 241 11 RANDOM PROCESSES 487 X6 SAMPLING AND PULSE CODE MODULATION 251 11.1 From Random Variable to Random Process 487 11.2 Powcr Spectral Density of a Random Process.496 6. 1 Sampling Theore 251 11.3 Multiple Random Processes 509 6.2 Pulse-Code Modulation (PCM) 262 11.4 Transmission of Random Processes through Linear Systcms. 510 6. 3 Differential Pulse Code modulation(DPCM) 278 11.5 Bandpass random Processes 514 5. 4 Delta Modulation 281 11.6 Optimum Filtering: Wiener-Hopf Filter 522 ES7 PRINCIPLES OF DIGITAL DATA TRANSMISSION 294 12 BEHAVIOR OF ANALOG SYSTEMS IN THE 7. 1 A Digital Communication System 294 PRESENCE OF NOISE 532 7. 2 Line Coding 297 12. 1 Baseband Systems.5.3 3 Pulse Sh 12.2 Amiplilude-Modulated Systems 5.34 4 Scrambling 319 2.3 Angle-Modulated Systems 54 Regenerative Repeater 322 2. 4 Pulse-Modulated Systems 557 7.6 Detection-Error Probability 329 12.5 Optimum Preemphasis-Deemphasis Systems 567 7 M-ary Communication 334 7. 8 Digital Carrier Systems 337 7. 9 Digital Multiplexing 34 13 BEHAVIOR OF DIGITAL COMMUNICATION SYSTEMS II THE PRESENCE OF NOISE 577 8 EMERGING DIGITAL COMMUNICATIONS TECHNOLOGIES 354 13. I Optimum Threshold Detection 577 8.1 The North American Hierarchy 354 13.2 General Analysis: Optimum Binary Receiver 582 8.2 Digital Services 368 13,3 Carrier Systems: ASK, FSK, PSK, and DPSK 590 3 Broadband Digital Communication: SONEI 377 13. 4 Performance oi Spread Spcctrum Systems 601 CONTENTS 13.5 M-ary Communication 608 13. 6 Synchronization 622 14 OPTIMUM SIGNAL DETECTION 626 14. 1 Geomctrical Representation of Signals: Signal Space PREFACE 14.2 Gaussian Random Proces 14.3 Optimum RcCC 14.4 Equivalent Signal Sets 662 14.5 Nonwhite(Colored)Channel Noise 669 14.6 Other Useful Performance Criteria 670 15 INTRODUCTION TO INFORMATION THEORY 679 .f2 15. 1 Measurc of Information 679 15.2 Source Encoding 684 15.3 Error-Free Communication over a Noisy Channel 690 15.4 Channel Capacity of a Discrete Memoriless Channel 693 15.5 Channel Capacity of a Continuous Channel 15.6 Practical Communication Systems in Light of Shannons Equation 717 T he study of communication systems can be divided into two distinct arcas 1. How communication systems work. 2. How they perform in the presence of noise 16 ERROR CORRECTING CODES 728 16. 1 introducti 728 The study of each of these two areas, in turn, requires specific tools. To study the first area, the 16.2 Linear Block Codes 731 students must be farmiliar with signal analysis( Fourier techniques), and to study the second area, 16.3 Cyclic Codcs 737 a basic understanding of probability theoryand random processes is essential For ameaningful 16.4 Burst-Error Detecting and Correcting Codes 745 comparison of various communication systems, it is necessary lo have some understanding of 16.5 Interlaced Codes for Bursl-and Random-Error Correcti 746 the second area. For this reason many instructors feel that the study of communication systcm 16.6 Convolutional Codes 74 Is not complete unless both of the areas are covered reasonably well. Ilowever, it poses one 16.7 Comparison of Coded and Uncoded Systems 755 rious problem: the material to be covered is enormous. The .wo areas along with their tool re overwhelming; it is difficult to cove al in depth in one cou APPENDIXES 764 The curent trend in teaching communication systems is lo study the tools in early prc Signal Sets spent in the beginning in studying the tools( ion) the B. Schwarz Inequality 766 C. Gram-Schmidt Orthogonalization of a Vcctor Set 768 is lille limc left to study the two proper areas of communication. Consequently, teaching a D. Miscellaneous course in communication systems poses a real dilemma. The second area (statistical aspects)of communication theory is a degree harder than the first area, and it can be properly understood only if the first area is wol] assimilated. One of the reasons for the dilemma mentioned earlier INDEX 775 as our attempt to cover both areas at the same time. Tbe students are forced to grapple with the statistical aspects while also trying to become familiar with how communication systcms work, This practice is nost unsound pedagogically because it violates the basic fact that one nust learn io walk before one can run. The ideal solution would be to offer two courses in course dealing with statistical aspects and noise. But in the present curriculum, with so many s as a prerequisite. In this case, it is possible to cover both areas reasonably well in a one-semester course This book, PREFACE Acknowledgments xii I hope, can be adopted to cither case. It can be uscd as a one-semester survey coursc in which analysis. It is shown in Chapter 12 that PM is, in fact, superior to FM for all practical cases the deterministic aspects of communicalion systems are emphasized. It can also be used for a course that deals with deterministic and probabilistic aspects of communication systems. The One of the aims in writing this book has been to make learning a pleasant or at least a le PI ind in probabilities and random processcs. However, intimidating experience for the student by presenting thc subject in a clear, understandable, and as stated earlicr, it is highly desirable for students to have a good background in probabilities logically organized manner. Every effort has heen made to give an insight--rather than just if the course is to be covered in one semester. an understandings well as heuristic explanations of theoretical results wherever possible. Many examples are provided for further clarification of abstract results. Even a partial success in achieving my stated goal would make all my toils worthwhile systems that is within the reach of an avcrage undergraduate and that can be taught in a one semester course(about 40 to 45 hours However, if the students have an adequate background in Fourier analysis and probabilities, it should be possible to cover the first 13 chapters ACKNOWLEDGMENTS Chapter 1 introduces the students to a panoramic view of communication systems. All the important concepts of communication theory are explained qualitatively in a hcuristic It is a pleasure to acknowledge the assistance received from several individuals during the way. This gets the students deeply interested so that thcy are encouraged to study the subject. preparation of this book. I arm greatly indebted to Mr. Maynard Wright, who is a member of Because of this momentum, they are motivated to st udy the tool of signal analysis in Chapters 2 everal standards committees, for his valuable help in several areas of data transmission. He and 3, where a student is encouraged to scc a signal as a vector and to think of the Fourier also contributed Secs.9.4, 9.5, and part of Sec. 93. I greatly appreciate the help of Professor spectrum as a way of representing a signal in terms ofils vector components. Chapters 4 and william Jameson from Montana State University, who conTributed Chapter8 (Emerging Digital 5 discuss amplitude (linear)and angle(nonlinear), modulation, respectively. Many instructor Communication Technologics). I am much obliged to Prof. Brian Woerner and R. M. Buehrer feel that in this digital age, modulation should be deemphasized with a minimal presence. from Virginia Polytechnic Institute for their contribution. The analysis of spread spectru feel that modulation is nol so. much a method of commnunication as a basic tool of signal systcms in Scction 13. 4 and some parts of Sec. 9.2 are based solely on their contribution. I processing; it will always be nceded not only in the area of communication(digital or analog), appreciate the enthusiastic help of Jerry Olup in preparation of the solutions manual. Thanks but also in many other areas of electrical engincering. Hence, neglecting modulation may prove i are also due to several reviewers, especially Profs. w. Green, James Kang, Dan Murphy, w Jameson, Jeff Reed, R. vaz, S. Bibyk, C. Alexander and S. Mousavinczhad I aIn obliged lo th sampling, pulse DPCM) and delta modulation. Chapter 7 discusses transmission of digital data. Sorne emerging Berkeley-Cambridge Pruss for- thcir purmission to use the material( Chapters 2 and 3) from digitai Technologies in digital data transmission are the subject of Chapter 8. Chapter 9 their forthcoming publication Signal Processing and Linear Systems by B. P. Lathi. Finally, I discusscs some recent developments(such as cellular lobal owc a dcbt of gratitude to my wife Rajani for her patience and understanding positioning systems), along withi miscellaneous topics such as communication media, optical communication, satellite communication, and hybrid circuits. Chapter 10 and 11 provic B. P LATHE reasonably thorough treatment of the theory of probability and random processes. This is the second tool required for the study of communication systems. Every attempt is made to motivate students and sustain their interest through these chapters by providing applications to communications problems wherever possiblc. Chapters 12 and 13 discuss the hehavior of mmunication systems in the presence of noise. Optimum signal detection is presented in Chapter 14, and information theory is the subject uf Chapter 15. Finally, error-contrul coing is introduced in Chapter 16. Analog pulse modulation systems such as PAM, PPM, and PWM are deemphasized in comparison to digital schemes (PCM, DPCM, and DM) because the applications of the former in communications are hard to find. In the trcatment of angle modulation, rather than compartmentalizing FM and PM, we have provided a generalized treatment of angle modulation, where FM and PM arc merely two(of the infinite)special cases. 'Tone-moduliale FM is deemphasized for a sound reason. Since angle modulation is nonlinear, the conchusion derived from tone modulation cannot be blindly applied to modulation by other basehand signals. in fact, these conclusions arc misleading in many instances. For cxample, in the Aloticr Ieasun given for the alleged inferiority of PM is that the phase deviation has to he restricted to a value less literature PM gets short shrift as being inferior to FM, a conclusion based on tone -modulation than It has bcen shown in Chapter 5 that this is simply not true of band-limited analog signals CEE CODE OF ETHICS MODERN DIGITAL AND ANALOG We, Lhe members of the IEEE, in rccognition of the importance of our technologies in affecting the COMMUNICATION quality of life throughout the world, and in accepting a personal obligation to our profession, its members SYSTEMS and the communities we serve, do hcrcbv commit ourselves to conduct of the highest cthical and professional manner and agree 1. to accept responsibility in making engineering decisions consistent with the safety, health, ann welfare of the public, and to disclose promptly factors that might endanger the public or thc emvironment id real eived conflicts of interest whenever possible. and to disclose them to affected parties when they do exist 3. to be honest and realistic in stating claims or estimates based on available data; 4. to reject bribery in all of iLs forms; 5. to improve understanding of lechnology; its appropriate application, and potenLial consequences 6. to maintain and improve our technical competence and to undertake technological tasks for others only if qualified by training or experience, or after full disclosure of pertinent limitations 7. to seek, accept, and offer honest criticism of technical work to acknowledge and correct errors, and to craiL properly the contributions of others 8. to treat fairly all persons regardless of such factors as race. religion, gender, disability, age,or 9. to avoid injuring others, their property, reputation, or employment by false or malicious action following this code of ethics Approved by IEEE Board of Directors, August 1ggo For further informalion please cousult the IEEB Ethics Committee www page INTRODUCTION I his book examines communication by electrical signals. In the past, messages have been carTied by runners, carier pigeons, drun beals, and torches. These schemes were adequate for the distances and"data rates"of the age. Tn most parts of the world, these uperseded by cicatrical can transmiT signals over much longer distances(even to distant planets and galaxies) and at Electrical communication is reliable and economical; communication technology is alleviating the energy crisis by trading information processing for a more rational use of energy resources. Some examples: Important discussions now mostly communicated face to face in meetings or conferences, often requiring travel, are increasingly using tcleconferring Similarly, teleshopping and Telebanking will provide services by electronic communication, and newspapers may be replaced by electronic news services COMMUNICATION SYSTEM Figure l 1 shows three examples of communication systems. A typical communication system can be modeled as shown in Fig. 1. 2. The components of a communication system are as awS The source originates a message, such as a human voice, a television picture, a lelclypu message,or data. If the data is nonelectrical(human voice, teletype message, television picture), it must be converted by an input transducer into an clectrical wavcform referred to as the baseband signal or message signal The transmitter modifies the baseband signal for efficient transmission f The channel is a medium-such as wire, coaxial cable, a waveguide an optical fibe r a radio link through which the transmitter output is set With che exception of the postal servi t The transmitter consists of one or more of the following subsystems: a preemphasizer, a sampler, a quantizer, a coder, and a modulator. Similarly, the 2 NTRODUCTION Analog and Digilal Messages 3 signal nes sa Transfilter Che Figure 1.2 Communicat on systcm The signal is not only distorted by thc channel, but it is also contaminated along the path by undesirable signals lumped under the broad term noise, which are random and unpredictable signals Irom causes external and internal. Extermal noise includes interference from signals transmitted on nearby channels, human-made noise generated by Faulty contact switches for electrical equipment, automobile ignition radiaLion, Auurcscent lights or natural noise from 好 lighting, as wcll as electrical storms and solar and intergalactic radiation. With proper care external noise can be minimized or even climinated Internal noise results from thermal notion of electrons in conductors, Tandom emission, and diffusion or recombination of charged carriers in eleclronic devices. Proper care can reduce the effect ofinternal noise but can never eliminate It Noise is onc of the hasic factors that set limits on the rate of communication signal-to-noise ratio(SNR) is defil The channel distorts the signal, and noise accumulates along the path. Worse yet, une signal strength decreases while the noise level increases with distance from the transmitter. Thus the SnR is continuously decrcasing along the length of the channel. Amplification of the received signal Lo make up for the attenuation is of no avail because the noise will be amplified in the same proportion, and the snr remains, at best, unchanged Figure 1.1 Same examples of communications system ANALOG AND DIGITAL MESSAGES The receiver reprocesses the signal received from the channel by undoing the sig Messages are digital or analog. Digital messages are constructed with a finite number of modificaTions made at the transmitter and the channel. The receiver output is fed to the output symbols. For example, printed language consists of 26 letters: 10 numbers, a space, and several ransducer, which converts the electrical signal to its original form-the message punctuation marks. Thus, a text is a digilalIIessagc constructed from about 50 symbols. Human The destination is the unit to which the message is communicated. speech is also a digital message, because it is made up from a finite vocabulary in a language a channel acts partly as a filter to attenuate the signal and distort its waveform. The Similarly, a Morse-coded telegraph mcssage is a digital message constructed from a set of only signal attenuation increases with the length of the channel, varying from a few percent for two symbols-mark and space. It is therefore a binary message implying only two symbols short distances to orders of magnitude for interplanetary communication. The waveform js a digital message constructed with M symbols is called an M-ary message distorted because of different amounts of attenuation and phasc shift suffered by different Analog messages, on the other hand, are characterized by data whose values vary over frequency components of the signal. For example, a square pulse is rounded or"spread out a continuous range. For example, the temperature or the atmospheric pressure of a certain during the transmission. This type of distortion, called linear distortion, can be partiy corrected at the receiver by an equalizer with gain and phase characteristics complementary to thosc of Acually, amplification. further deteriorates the SNR because of the amplifier noise the channel. The channel may also cause nonlinear distortion through attenuation that vanes Here we imply the printed cxl of the speech rather than its derails snch as the promuncision uf words und varying with the signal amplitude. Such distortion can also be partly corrected by a complementary ch, emphasis, and nd so on." Ihe speech signal from a microphone contains all these delails. This signal is an analog signal, und its information content is more than a thousand times the information in the writen equalizer at the receiver the saint spccch 【实例截图】
【核心代码】
An ideal first text on communication systems in electrical engineering, Modern Digital and Analog Communication Systems is now in its fourth edition. Retaining the superb pedagogical style of the first three editions, the authors first introduce the fundamentals of signals and systems and core commu
Oxford University PrEss In memory of M.E. Van Valkenbi g Calcutta Madra: Madrid Melbut 1921-1997 Mexico City Nairobi Paris poe Taipei Toky o Torcuato Warsay eht 1998 by Oxford 198 Madison Aveuue. New York. New York 10016 All rights reserved. No part of this publication may be reproduced, stored in a retrieval rstem. or transmitted, in any form or by any means, clcctronie. Mechanical, photocopy ing, rwise, witht the. prior permission of Oxford Univeesity Press Library of Congress Cataloging- irl-publicntion Data Lathi, B P(Bhaewandas pannalal and analog comunication systems /B P. athi p. c-(The Oxford series in electrical and computcr cal references (p 3. Statistical communication theoxy. L litic I Series TK51013331998 6213s2^c21 321 i-free pap CONTENTS PREFACE X1 INTRODUCTION 7 on syste Analog and Digital Signal-to-Noisc Ratio, Channel Bandwidth, and the Rate of Communication 8 Modulation 10 B 2 INTRODUCTION TO SIGNALS ]4 2. 1 Size of a signal 2. 2 Classification of Signals 2.3 Some Useful Signal Operalions 24 2.4 Unit Impulse functio 28 2.5 Signals and Vectors 30 2.6 Signal Camparison: Correlation 35 2.7 Signal Representation by Orthogonal Signal Set 40 2. B Trigonometric Fourier Series 44 9 Exponential Fourier Series 5 2. 10 Numerical Computation of Dn 60 3 ANALYSIS AND TRANSMISSION OF SIGNALS 77 3. 1 Aperiodic Signal Representation by fourier Integral. 7T Transforms of Some Useful Functions 8 3.3 Some Properties of the Fourier Transform 84 3.4 Signal Tra through a lincar syster 3.5 Ideal and Practical filters 10 3.6 Signal Distortion aver a Communication Channel 110 vii CONTENTS Contents ix 3.7 Signal Energy and Energy Spectral Denisily 115 8.4 Digital Switc hing Technologics ?383 3.8 Signal Power and Power Spectral Density 123 8.5 Broadband Services for Entertainment and Home Office Applications 392 3. Numerical Computation of Fourier Iransform: The DFT 1.30 8.6 Video Compression 7 High-Definition Television(HDTV 400 X4 AMPLITUDE (LINEAR)MODULATION 757 9 SOME RECENT DEVELOPMENTS AND 1. 1 Baseband and Carrier Communication 157 4.2 Amplitude Modulation: Double Sideband (DSB) 152 MISCELLANEOUS TOPICS. 404 4.3 Amplitude Modulation (AM) 162 9.1 Cellular Telephone(Mobile Radio)System 40-4 4.4 Quadrature Amplitude Modulation(QAM 9. 2 Spread Spectrum Systems 406 4.5 Amplitude Modulation: Single Sideband (SSB) 177 3 ransmission Media 416 4.6 Amplitude Modulalion: Vestigial Sideband (VSB 9. 4 Hybrid nvers 4.7 Carrier Acquisition 16 9.5 Public Switched Telephone Network4 4.8 Superheterodyne AM Receiver 7 85 4.9 Television 197 10 INTRODUCTION TO THEORY OF PROBABILITY 434 5 ANGLE(EXPONENTIAL)MODULATION 208 10. 1 Concept of Probability 434 Y0. 2 Random Variables 44.5 5.1 Concept of Instantaneous Frequency 208 10.3 Statistical Averages(Means) 46 2 Bandwidth of Anglc-Modulated Waves 215 10.4 Centr al-Limit Theorem 472 5.3 Generation of FM 10.5C 47.3 4 Demodulation of FM 23 10.6 Linear Mean Square Estimation 476 5.5 Interference in Angle-Modulated Systems 241 11 RANDOM PROCESSES 487 X6 SAMPLING AND PULSE CODE MODULATION 251 11.1 From Random Variable to Random Process 487 11.2 Powcr Spectral Density of a Random Process.496 6. 1 Sampling Theore 251 11.3 Multiple Random Processes 509 6.2 Pulse-Code Modulation (PCM) 262 11.4 Transmission of Random Processes through Linear Systcms. 510 6. 3 Differential Pulse Code modulation(DPCM) 278 11.5 Bandpass random Processes 514 5. 4 Delta Modulation 281 11.6 Optimum Filtering: Wiener-Hopf Filter 522 ES7 PRINCIPLES OF DIGITAL DATA TRANSMISSION 294 12 BEHAVIOR OF ANALOG SYSTEMS IN THE 7. 1 A Digital Communication System 294 PRESENCE OF NOISE 532 7. 2 Line Coding 297 12. 1 Baseband Systems.5.3 3 Pulse Sh 12.2 Amiplilude-Modulated Systems 5.34 4 Scrambling 319 2.3 Angle-Modulated Systems 54 Regenerative Repeater 322 2. 4 Pulse-Modulated Systems 557 7.6 Detection-Error Probability 329 12.5 Optimum Preemphasis-Deemphasis Systems 567 7 M-ary Communication 334 7. 8 Digital Carrier Systems 337 7. 9 Digital Multiplexing 34 13 BEHAVIOR OF DIGITAL COMMUNICATION SYSTEMS II THE PRESENCE OF NOISE 577 8 EMERGING DIGITAL COMMUNICATIONS TECHNOLOGIES 354 13. I Optimum Threshold Detection 577 8.1 The North American Hierarchy 354 13.2 General Analysis: Optimum Binary Receiver 582 8.2 Digital Services 368 13,3 Carrier Systems: ASK, FSK, PSK, and DPSK 590 3 Broadband Digital Communication: SONEI 377 13. 4 Performance oi Spread Spcctrum Systems 601 CONTENTS 13.5 M-ary Communication 608 13. 6 Synchronization 622 14 OPTIMUM SIGNAL DETECTION 626 14. 1 Geomctrical Representation of Signals: Signal Space PREFACE 14.2 Gaussian Random Proces 14.3 Optimum RcCC 14.4 Equivalent Signal Sets 662 14.5 Nonwhite(Colored)Channel Noise 669 14.6 Other Useful Performance Criteria 670 15 INTRODUCTION TO INFORMATION THEORY 679 .f2 15. 1 Measurc of Information 679 15.2 Source Encoding 684 15.3 Error-Free Communication over a Noisy Channel 690 15.4 Channel Capacity of a Discrete Memoriless Channel 693 15.5 Channel Capacity of a Continuous Channel 15.6 Practical Communication Systems in Light of Shannons Equation 717 T he study of communication systems can be divided into two distinct arcas 1. How communication systems work. 2. How they perform in the presence of noise 16 ERROR CORRECTING CODES 728 16. 1 introducti 728 The study of each of these two areas, in turn, requires specific tools. To study the first area, the 16.2 Linear Block Codes 731 students must be farmiliar with signal analysis( Fourier techniques), and to study the second area, 16.3 Cyclic Codcs 737 a basic understanding of probability theoryand random processes is essential For ameaningful 16.4 Burst-Error Detecting and Correcting Codes 745 comparison of various communication systems, it is necessary lo have some understanding of 16.5 Interlaced Codes for Bursl-and Random-Error Correcti 746 the second area. For this reason many instructors feel that the study of communication systcm 16.6 Convolutional Codes 74 Is not complete unless both of the areas are covered reasonably well. Ilowever, it poses one 16.7 Comparison of Coded and Uncoded Systems 755 rious problem: the material to be covered is enormous. The .wo areas along with their tool re overwhelming; it is difficult to cove al in depth in one cou APPENDIXES 764 The curent trend in teaching communication systems is lo study the tools in early prc Signal Sets spent in the beginning in studying the tools( ion) the B. Schwarz Inequality 766 C. Gram-Schmidt Orthogonalization of a Vcctor Set 768 is lille limc left to study the two proper areas of communication. Consequently, teaching a D. Miscellaneous course in communication systems poses a real dilemma. The second area (statistical aspects)of communication theory is a degree harder than the first area, and it can be properly understood only if the first area is wol] assimilated. One of the reasons for the dilemma mentioned earlier INDEX 775 as our attempt to cover both areas at the same time. Tbe students are forced to grapple with the statistical aspects while also trying to become familiar with how communication systcms work, This practice is nost unsound pedagogically because it violates the basic fact that one nust learn io walk before one can run. The ideal solution would be to offer two courses in course dealing with statistical aspects and noise. But in the present curriculum, with so many s as a prerequisite. In this case, it is possible to cover both areas reasonably well in a one-semester course This book, PREFACE Acknowledgments xii I hope, can be adopted to cither case. It can be uscd as a one-semester survey coursc in which analysis. It is shown in Chapter 12 that PM is, in fact, superior to FM for all practical cases the deterministic aspects of communicalion systems are emphasized. It can also be used for a course that deals with deterministic and probabilistic aspects of communication systems. The One of the aims in writing this book has been to make learning a pleasant or at least a le PI ind in probabilities and random processcs. However, intimidating experience for the student by presenting thc subject in a clear, understandable, and as stated earlicr, it is highly desirable for students to have a good background in probabilities logically organized manner. Every effort has heen made to give an insight--rather than just if the course is to be covered in one semester. an understandings well as heuristic explanations of theoretical results wherever possible. Many examples are provided for further clarification of abstract results. Even a partial success in achieving my stated goal would make all my toils worthwhile systems that is within the reach of an avcrage undergraduate and that can be taught in a one semester course(about 40 to 45 hours However, if the students have an adequate background in Fourier analysis and probabilities, it should be possible to cover the first 13 chapters ACKNOWLEDGMENTS Chapter 1 introduces the students to a panoramic view of communication systems. All the important concepts of communication theory are explained qualitatively in a hcuristic It is a pleasure to acknowledge the assistance received from several individuals during the way. This gets the students deeply interested so that thcy are encouraged to study the subject. preparation of this book. I arm greatly indebted to Mr. Maynard Wright, who is a member of Because of this momentum, they are motivated to st udy the tool of signal analysis in Chapters 2 everal standards committees, for his valuable help in several areas of data transmission. He and 3, where a student is encouraged to scc a signal as a vector and to think of the Fourier also contributed Secs.9.4, 9.5, and part of Sec. 93. I greatly appreciate the help of Professor spectrum as a way of representing a signal in terms ofils vector components. Chapters 4 and william Jameson from Montana State University, who conTributed Chapter8 (Emerging Digital 5 discuss amplitude (linear)and angle(nonlinear), modulation, respectively. Many instructor Communication Technologics). I am much obliged to Prof. Brian Woerner and R. M. Buehrer feel that in this digital age, modulation should be deemphasized with a minimal presence. from Virginia Polytechnic Institute for their contribution. The analysis of spread spectru feel that modulation is nol so. much a method of commnunication as a basic tool of signal systcms in Scction 13. 4 and some parts of Sec. 9.2 are based solely on their contribution. I processing; it will always be nceded not only in the area of communication(digital or analog), appreciate the enthusiastic help of Jerry Olup in preparation of the solutions manual. Thanks but also in many other areas of electrical engincering. Hence, neglecting modulation may prove i are also due to several reviewers, especially Profs. w. Green, James Kang, Dan Murphy, w Jameson, Jeff Reed, R. vaz, S. Bibyk, C. Alexander and S. Mousavinczhad I aIn obliged lo th sampling, pulse DPCM) and delta modulation. Chapter 7 discusses transmission of digital data. Sorne emerging Berkeley-Cambridge Pruss for- thcir purmission to use the material( Chapters 2 and 3) from digitai Technologies in digital data transmission are the subject of Chapter 8. Chapter 9 their forthcoming publication Signal Processing and Linear Systems by B. P. Lathi. Finally, I discusscs some recent developments(such as cellular lobal owc a dcbt of gratitude to my wife Rajani for her patience and understanding positioning systems), along withi miscellaneous topics such as communication media, optical communication, satellite communication, and hybrid circuits. Chapter 10 and 11 provic B. P LATHE reasonably thorough treatment of the theory of probability and random processes. This is the second tool required for the study of communication systems. Every attempt is made to motivate students and sustain their interest through these chapters by providing applications to communications problems wherever possiblc. Chapters 12 and 13 discuss the hehavior of mmunication systems in the presence of noise. Optimum signal detection is presented in Chapter 14, and information theory is the subject uf Chapter 15. Finally, error-contrul coing is introduced in Chapter 16. Analog pulse modulation systems such as PAM, PPM, and PWM are deemphasized in comparison to digital schemes (PCM, DPCM, and DM) because the applications of the former in communications are hard to find. In the trcatment of angle modulation, rather than compartmentalizing FM and PM, we have provided a generalized treatment of angle modulation, where FM and PM arc merely two(of the infinite)special cases. 'Tone-moduliale FM is deemphasized for a sound reason. Since angle modulation is nonlinear, the conchusion derived from tone modulation cannot be blindly applied to modulation by other basehand signals. in fact, these conclusions arc misleading in many instances. For cxample, in the Aloticr Ieasun given for the alleged inferiority of PM is that the phase deviation has to he restricted to a value less literature PM gets short shrift as being inferior to FM, a conclusion based on tone -modulation than It has bcen shown in Chapter 5 that this is simply not true of band-limited analog signals CEE CODE OF ETHICS MODERN DIGITAL AND ANALOG We, Lhe members of the IEEE, in rccognition of the importance of our technologies in affecting the COMMUNICATION quality of life throughout the world, and in accepting a personal obligation to our profession, its members SYSTEMS and the communities we serve, do hcrcbv commit ourselves to conduct of the highest cthical and professional manner and agree 1. to accept responsibility in making engineering decisions consistent with the safety, health, ann welfare of the public, and to disclose promptly factors that might endanger the public or thc emvironment id real eived conflicts of interest whenever possible. and to disclose them to affected parties when they do exist 3. to be honest and realistic in stating claims or estimates based on available data; 4. to reject bribery in all of iLs forms; 5. to improve understanding of lechnology; its appropriate application, and potenLial consequences 6. to maintain and improve our technical competence and to undertake technological tasks for others only if qualified by training or experience, or after full disclosure of pertinent limitations 7. to seek, accept, and offer honest criticism of technical work to acknowledge and correct errors, and to craiL properly the contributions of others 8. to treat fairly all persons regardless of such factors as race. religion, gender, disability, age,or 9. to avoid injuring others, their property, reputation, or employment by false or malicious action following this code of ethics Approved by IEEE Board of Directors, August 1ggo For further informalion please cousult the IEEB Ethics Committee www page INTRODUCTION I his book examines communication by electrical signals. In the past, messages have been carTied by runners, carier pigeons, drun beals, and torches. These schemes were adequate for the distances and"data rates"of the age. Tn most parts of the world, these uperseded by cicatrical can transmiT signals over much longer distances(even to distant planets and galaxies) and at Electrical communication is reliable and economical; communication technology is alleviating the energy crisis by trading information processing for a more rational use of energy resources. Some examples: Important discussions now mostly communicated face to face in meetings or conferences, often requiring travel, are increasingly using tcleconferring Similarly, teleshopping and Telebanking will provide services by electronic communication, and newspapers may be replaced by electronic news services COMMUNICATION SYSTEM Figure l 1 shows three examples of communication systems. A typical communication system can be modeled as shown in Fig. 1. 2. The components of a communication system are as awS The source originates a message, such as a human voice, a television picture, a lelclypu message,or data. If the data is nonelectrical(human voice, teletype message, television picture), it must be converted by an input transducer into an clectrical wavcform referred to as the baseband signal or message signal The transmitter modifies the baseband signal for efficient transmission f The channel is a medium-such as wire, coaxial cable, a waveguide an optical fibe r a radio link through which the transmitter output is set With che exception of the postal servi t The transmitter consists of one or more of the following subsystems: a preemphasizer, a sampler, a quantizer, a coder, and a modulator. Similarly, the 2 NTRODUCTION Analog and Digilal Messages 3 signal nes sa Transfilter Che Figure 1.2 Communicat on systcm The signal is not only distorted by thc channel, but it is also contaminated along the path by undesirable signals lumped under the broad term noise, which are random and unpredictable signals Irom causes external and internal. Extermal noise includes interference from signals transmitted on nearby channels, human-made noise generated by Faulty contact switches for electrical equipment, automobile ignition radiaLion, Auurcscent lights or natural noise from 好 lighting, as wcll as electrical storms and solar and intergalactic radiation. With proper care external noise can be minimized or even climinated Internal noise results from thermal notion of electrons in conductors, Tandom emission, and diffusion or recombination of charged carriers in eleclronic devices. Proper care can reduce the effect ofinternal noise but can never eliminate It Noise is onc of the hasic factors that set limits on the rate of communication signal-to-noise ratio(SNR) is defil The channel distorts the signal, and noise accumulates along the path. Worse yet, une signal strength decreases while the noise level increases with distance from the transmitter. Thus the SnR is continuously decrcasing along the length of the channel. Amplification of the received signal Lo make up for the attenuation is of no avail because the noise will be amplified in the same proportion, and the snr remains, at best, unchanged Figure 1.1 Same examples of communications system ANALOG AND DIGITAL MESSAGES The receiver reprocesses the signal received from the channel by undoing the sig Messages are digital or analog. Digital messages are constructed with a finite number of modificaTions made at the transmitter and the channel. The receiver output is fed to the output symbols. For example, printed language consists of 26 letters: 10 numbers, a space, and several ransducer, which converts the electrical signal to its original form-the message punctuation marks. Thus, a text is a digilalIIessagc constructed from about 50 symbols. Human The destination is the unit to which the message is communicated. speech is also a digital message, because it is made up from a finite vocabulary in a language a channel acts partly as a filter to attenuate the signal and distort its waveform. The Similarly, a Morse-coded telegraph mcssage is a digital message constructed from a set of only signal attenuation increases with the length of the channel, varying from a few percent for two symbols-mark and space. It is therefore a binary message implying only two symbols short distances to orders of magnitude for interplanetary communication. The waveform js a digital message constructed with M symbols is called an M-ary message distorted because of different amounts of attenuation and phasc shift suffered by different Analog messages, on the other hand, are characterized by data whose values vary over frequency components of the signal. For example, a square pulse is rounded or"spread out a continuous range. For example, the temperature or the atmospheric pressure of a certain during the transmission. This type of distortion, called linear distortion, can be partiy corrected at the receiver by an equalizer with gain and phase characteristics complementary to thosc of Acually, amplification. further deteriorates the SNR because of the amplifier noise the channel. The channel may also cause nonlinear distortion through attenuation that vanes Here we imply the printed cxl of the speech rather than its derails snch as the promuncision uf words und varying with the signal amplitude. Such distortion can also be partly corrected by a complementary ch, emphasis, and nd so on." Ihe speech signal from a microphone contains all these delails. This signal is an analog signal, und its information content is more than a thousand times the information in the writen equalizer at the receiver the saint spccch 【实例截图】
【核心代码】
标签：
好例子网口号：伸出你的我的手 — 分享！
小贴士
感谢您为本站写下的评论，您的评论对其它用户来说具有重要的参考价值，所以请认真填写。
- 类似“顶”、“沙发”之类没有营养的文字，对勤劳贡献的楼主来说是令人沮丧的反馈信息。
- 相信您也不想看到一排文字/表情墙，所以请不要反馈意义不大的重复字符，也请尽量不要纯表情的回复。
- 提问之前请再仔细看一遍楼主的说明，或许是您遗漏了。
- 请勿到处挖坑绊人、招贴广告。既占空间让人厌烦，又没人会搭理，于人于己都无利。
关于好例子网
本站旨在为广大IT学习爱好者提供一个非营利性互相学习交流分享平台。本站所有资源都可以被免费获取学习研究。本站资源来自网友分享，对搜索内容的合法性不具有预见性、识别性、控制性，仅供学习研究，请务必在下载后24小时内给予删除，不得用于其他任何用途，否则后果自负。基于互联网的特殊性，平台无法对用户传输的作品、信息、内容的权属或合法性、安全性、合规性、真实性、科学性、完整权、有效性等进行实质审查；无论平台是否已进行审查，用户均应自行承担因其传输的作品、信息、内容而可能或已经产生的侵权或权属纠纷等法律责任。本站所有资源不代表本站的观点或立场，基于网友分享，根据中国法律《信息网络传播权保护条例》第二十二与二十三条之规定，若资源存在侵权或相关问题请联系本站客服人员，点此联系我们。关于更多版权及免责申明参见 版权及免责申明
网友评论
我要评论