CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics Communication Basics: Signals: Communication happens in the form of signals. Signals are transmission of energy (mechanical, electrical or light) through appropriate media. A signal that is constant and changed once conveys single information. The more changes in the signal, the more information that the signal can convey. For example, a push can mean one thing and removing it can mean another thing. But how do we send more information than just these two? We can do that by varying the amplitude, i.e., a strong push or a light push could have two different meaning. Or, a rate of change of push, i.e. 10 pushes per minute or 1 push per minute could have different meaning too. Or, even phase, i.e., pushing at a different angle could have different meaning too. Amplitude, frequency and phase are the attributes of a signal that changes with time. This pushing, transfer of mechanical energy has a limit. How many different amplitude, rate and phase of pushing can we transmit and distinguish (receive)? God gave us organs like vocal cord which can create higher rate of pushing and ears to sense that. Higher the rate of pushing the more information it can convey and even the mixing of these different rate could mean different information. And our vocal cord is able to do that as well. We have even media (air) which will carry that signal far, so we don't have to stay close to communicate. But that has a limit too. Then we came out with a solution of converting this pressure wave to electrical signals and then transmitting over long distances. Signals can exists in different forms and transmit over different media. For example, acoustic (pressure waves), electrical, electromagnatic and light signals. Transducers: Different signals and media have their own limitations. So according to need we change signals to different forms. The devices that convert signals from one form to another are called transducers. In general, human do not generate electrical signals, nor do they respond to that or any other form of signals except acoustic signals. Human generate acoustic signals (speech) for communication. But to send that signal far we need to convert that signal to the electrical form. Lecture 13.doc Page 1 (9) CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics Transducers that convert acoustic signals into electrical signals are called microphones. Transducers that convert electric signals into acoustic (sound) signals are called speakers. Microphones: Carbon microphone - used in telephones Moving coil microphones - public address systems Moving magnet microphones - public address systems Piezoeletric microphones - Capacitor microphones - Newer telephones, home audio systems Speakers: Moving coil speakers - public address systems Piezoeletric speakers - Newer telephones, toys Lecture 13.doc Page 2 (9) CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics Transducers converting electrical signals to light lignals: Infrared diode - generates infrared light signals from electrical light signals, used in infrered transmitters (remote control uinit). Photo diode - generates electrical signals from infrared light signals, used in infrered receivers (controled uinit, e.g., TV). We also use these two in a pair to isolate two electrical circuits to reduce noise, and they are called couplers. Similar devices are laser diodes and detectors. The Electromagnetic signals: Information (voice, data, image, video) can be represented by electrical or electromagnetic signals and transmitted over a suitable transmission medium. Information can be transmitted on wires by varying some physical properties such as voltage or current. 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22 1.2 Potential Applications of Blind and Semi-Blind Signal Processing 23 1.2.1 Biomedical Signal Processing 24 1.2.2 Blind Separation of Electrocardiographic Signals of Fetus and Mother 25 1.2.3 Enhancement and Decomposition of EMG Signals 27 v vi CONTENTS 1.2.4 EEG and Data MEG Processing 27 1.2.5 Application of ICA/BSS for Noise and Interference Cancellation in Multi-sensory Biomedical Signals 29 1.2.6 Cocktail Party Problem 34 1.2.7 Digital Communication Systems 35 1.2.7.1 Why Blind? 37 1.2.8 Image Restoration and Understanding 37 2 Solving a System of Algebraic Equations and Related Problems 43 2.1 Formulation of the Problem for Systems of Linear Equations 44 2.2 Least-Squares Problems 45 2.2.1 Basic Features of the Least-Squares Solution 45 2.2.2 Weighted Least-Squares and Best Linear Unbiased Estimation 47 2.2.3 Basic Network Structure-Least-Squares Criteria 49 2.2.4 Iterative Parallel Algorithms for Large and Sparse Systems 49 2.2.5 Iterative Algorithms with Non-negativity Constraints 51 2.2.6 Robust Circuit Structure by Using the Interactively Reweighted Least-Squares Criteria 54 2.2.7 Tikhonov Regularization and SVD 57 2.3 Least Absolute Deviation (1-norm) Solution of Systems of Linear Equations 61 2.3.1 Neural Network Architectures Using a Smooth Approximation and Regularization 62 2.3.2 Neural Network Model for LAD Problem Exploiting Inhibition Principles 64 2.4 Total Least-Squares and Data Least-Squares Problems 67 2.4.1 Problems Formulation 67 2.4.1.1 A Historical Overview of the TLS Problem 67 2.4.2 Total Least-Squares Estimation 69 2.4.3 Adaptive Generalized Total Least-Squares 73 2.4.4 Extended TLS for Correlated Noise Statistics 75 2.4.4.1 Choice of ¯ R NN in Some Practical Situations 77 2.4.5 Adaptive Extended Total Least-Squares 77 2.4.6 An Illustrative Example - Fitting a Straight Line to a Set of Points 78 2.5 Sparse Signal Representation and Minimum Fuel Consumption Problem 79 CONTENTS vii 2.5.1 Approximate Solution of Minimum Fuel Problem Using Iterative LS Approach 81 2.5.2 FOCUSS Algorithms 83 3 Principal/Minor Component Analysis and Related Problems 87 3.1 Introduction 87 3.2 Basic Properties of PCA 88 3.2.1 Eigenvalue Decomposition 88 3.2.2 Estimation of Sample Covariance Matrices 90 3.2.3 Signal and Noise Subspaces - AIC and MDL Criteria for their Estimation 91 3.2.4 Basic Properties of PCA 93 3.3 Extraction of Principal Components 94 3.4 Basic Cost Functions and Adaptive Algorithms for PCA 98 3.4.1 The Rayleigh Quotient – Basic Properties 98 3.4.2 Basic Cost Functions for Computing Principal and Minor Components 99 3.4.3 Fast PCA Algorithm Based on the Power Method 101 3.4.4 Inverse Power Iteration Method 104 3.5 Robust PCA 104 3.6 Adaptive Learning Algorithms for MCA 107 3.7 Unified Parallel Algorithms for PCA/MCA and PSA/MSA 110 3.7.1 Cost Function for Parallel Processing 111 3.7.2 Gradient of J(W) 112 3.7.3 Stability Analysis 113 3.7.4 Unified Stable Algorithms HACKING INTO COMPUTER SYSTEMS A Beginners Guide Guides of the Beginner's Series: So you want to be a harmless hacker? Hacking Windows 95! Hacking into Windows 95 (and a little bit of NT lore)! Hacking from Windows 3.x, 95 and NT How to Get a *Good* Shell Account, Part 1 How to Get a *Good* Shell Account, Part 2 How to use the Web to look up information on hacking. Computer hacking. Where did it begin and how did it grow? GUIDE TO (mostly) HARMLESS HACKING Beginners' Series #1 So you want to be a harmless hacker? "You mean you can hack without breaking the law?" That was the voice of a high school freshman. He had me on the phone because his father had just taken away his computer. His offense? Cracking into my Internet account. The boy had hoped to impress me with how "kewl" he was. But before I realized he had gotten in, a sysadmin at my ISP had spotted the kid's harmless explorations and had alerted the parents. Now the boy wanted my help in getting back on line. I told the kid that I sympathized with his father. What if the sysadmin and I had been major grouches? This kid could have wound up in juvenile detention. Now I don't agree with putting harmless hackers in jail, and I would never have testified against him. But that's what some people do to folks who go snooping in other people's computer accounts -- even when the culprit does no harm. This boy needs to learn how to keep out of trouble! Hacking is the most exhilarating game on the planet. But it stops being fun when you end up in a cell with a roommate named "Spike." But hacking doesn't have to mean breaking laws. In this series of Guides we teach safe hacking so that you don't have to keep looking back over your shoulders for narcs and cops. What we're talking about is hacking as a healthy recreation, and as a free education that can qualify you to get a high paying job. In fact, many network systems administrators, computer scientists and computer security experts first learned their professions, not in some college program, but from the hacker culture. And you may be surprised to discover that ultimately the Internet is safeguarded not by law enforcement agencies, not by giant corporations, but by a worldwide network of, yes, hackers. You, too, can become one of us. And -- hacking can be surprisingly easy. Heck, if I can do it, anyone can! Regardless of why you want to be a hacker, it is definitely a way to have fun, impress your friends, and get dates. If you are a female hacker you become totally irresistible to men. Take my word for it!;^D These Guides to (mostly) Harmless Hacking can be your gateway into this world. After reading just a few of these Guides you will be able to pull off stunts that will be legal, phun, and will impress the heck out of your friends. These Guides can equip you to become one of the vigilantes that keeps the Internet from being destroyed by bad guys. Especially spammers. Heh, heh, heh. You can also learn how to keep the bad guys from messing with your Internet account, email, and personal computer. You'll learn not to be frightened by silly hoaxes that pranksters use to keep the average Internet user in a tizzy. If you hang in with us through a year or so, you can learn enough and meet the people on our email list and IRC channel who can help you to become truly elite. However, before you plunge into the hacker subculture, be prepared for that hacker attitude. You have been warned. So .welcome to the adventure of hacking! WHAT DO I NEED IN ORDER TO HACK? You may wonder whether hackers need expensive computer equipment and a shelf full of technical manuals. The answer is NO! Hacking can be surprisingly easy! Better yet, if you know how to search the Web, you can find almost any Reading 1 Learning English Every year students in many (1) ……………………………. learn English. (2) ……………………………. of these students are young children. Others are teenagers. Many are adults. Some learn at school, others study (3) ………………………… themselves. A few learn English just by (4) ……………………………. the language in films, (5) …………………………………. television, in the office, or among their friends. But not many are lucky to do that. Most people must work (6) ……………………………. to learn another language. Learning another language! Learning English! Why do all these people want to learn English? It is (7) …………………………….to answer that question. Many boys and girls learn English at school because it is one of their subjects. Many adults learn English because it is (8) ……………………………. for their work. Teenagers often learn English (9) ……………………………. their higher studies, because some of their book are in English at the college or University. Other people learn English because they want to read newspapers or magazines (10) …………………… English. 1 2 3 4 5 6 7 8 9 10 a. countries a. None a. for a. hear a. on a. hardly a. horrible a. use a. for a. for b. homes b. Some b. with b. heard b. at b. hard b. cold b. used b. with b. with c. house c. Any c. by c. to hear c. in c. easy c. difficult c. useful c. to c. to d. families d. All d. on d. hearing d. to d. easily d. careful d. useless d. of d. in Reading 2 Learning a second language Some people learn a second language (1) …………………………….Other people have trouble learning a new language. How can you help (2) ……………………………. learn a new language, such as English? There are several ways to make learning English a little (3) ……………………………. and more interesting. The first step is to feel positive about learning English. If you believe that you can learn, you will learn. (4) ……………………………. patient. You do not to have to understand (5) ……………………………. all at once. It’s natural to make mistakes when you learn something new. We can learn from our mistakes. The second step is to practice your English. For example, write in a journal, or diary, everyday. You will get used to (6) …………………………….in English, and you will feel comfortable expressing your ideas in English. After several weeks, you will see that your writing is improving. (7) ……………………………. you must speak English every day. You can practice with your classmates (8) ……………………………. class. The third step is to keep a record of your language learning. You can write this in your journal. After (9) ……………………………. class, think about what you can did. Did you answer a question (10) …………………………….? Did you understand something the teacher explained? Perhaps the lesson was difficult, but you tried to understand it. It is important to practice every day and make a record of your achievements. 1 2 3 4 5 6 7 8 9 10 a. ease a. itself a. ease a. be a. anything a. write a. In addition a. of side a. some a. correct b. easy b. yourself b. easy b. being b. nothing b. writing b. Addition b. outside b. each b. correction c. easily c. himself c. easily c. to be c. everything c. to write c. Additional c. beside c. all c. correctly d. all a, b, c d. herself d. easier d. been d. something d. written d. By addition d. by side d. few d. corrective Reading 3 Every year many people in the world learn English. Some of them are young children. (1)………………are teenagers. Many are adults. Some learn at school, and some learn in evening classes. A few learn English by (2) ……………………….or just by (3) ………………………. to the language on television or among their friends. Most people must work hard to learn English. (4) ………………………. do all these people want to learn English? It is difficult to answer that question. Young children learn English at school to study better at their subject. Many adults learn English because (5) ………………………. useful for their work. Teenagers often learn English for their (6) …………………… studies, because some of their books are written (7) ……………………….English at their college or university. 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