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Southern Methodist University Lyle School of Engineering EETS 7320 Digital Telecommunications Technology. 1. Overview & Introduction 2010 Spring. Class Offering. SMU will offer this course only if there are 12 or more students enrolled by the date of the second session.
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Southern Methodist UniversityLyle School of EngineeringEETS 7320Digital Telecommunications Technology 1. Overview & Introduction 2010 Spring
Class Offering • SMU will offer this course only if there are 12 or more students enrolled by the date of the second session. • Class sessions are Tuesday evening from6:30 to 9:20 with two 10 minute intermissions. Class lectures are available on Power Point files (some with the lecture audio) from web site http://engr.smu.edu/ee/7320
Instructor • Richard Levine (Sc.D., P.E.), Adjunct Professor of Electrical Engineering • 50 years experience in telecom and defense electronics. Recognized expert on digital cellular technology, GSM wireless, etc. • Contact: richard.levine@gmail.com • Contact: +1 972 233 4552, call 8 AM-5 PM central time. Please speak slowly and clearly if leaving a voice message
Student Responsibilities • 13 weeks of class sessions – mostly pre-recorded in form of power point slides with audio. Attendance is not graded, but please read the notes and slides! • Grade based on two items: Item 1 Term Paper • Written by student (not plagiarized) based in research of the literature. Due May 7 or before. • Approximately 15 to 20 pages. Submit on paper. • Topic must be pre-approved before xxxx based on outline or abstract submitted via e-mail to instructor.
Grading Method • Grade based on two items: • Item 2 = One hour mid-term quiz • Multiple choice • Quiz taken in class March xx (first hour) • Non-local students take same quiz proctored by SMU-approved distance education representative before seeing solution lecture. • Final letter grade is equal to term paper grade for student having mid-term quiz grade below section average. Example: paper B+; section average 90; midterm grade 88 gives course grade B+ • Student having mid-term quiz grade equal to or above section average gets one step increase in course letter grade. Example: paper B+; section average 90; midterm grade 90 or more gives course grade A-.
Term Paper Rewrite Permitted • Term paper will be returned with editing and comments to help student to understand how the letter grade was determined. • If invited by the instructor, a student has the option to rewrite the paper for an improved revised grade.
Overview and Introduction • Learn Science and Technology as used for Telecommunications • Semi-technical explanations • Primarily for people working in the telecomm industry who do not have an undergraduate degree in math, physics or engineering • Useful review of related technology for those with a science/technology undergraduate degree.
What is Included in the Course • Object is to explain science and technology issues so students can understand jargon and basic science well enough to make intelligent decisions. • Careful: Ordinary words having vague meanings are assigned very specific meanings in science jargon • Example: Force, power, energy, momentum etc. are approximate synonyms in everyday speech, but each has a very distinct meaning in science. Mass and weight are not the same thing, etc. • Our object is not necessarily to make each student into a physicist or electrical engineer. • Sometimes , when an absolutely complete explanation would take too long, instructor will make statements without proof or without derivation from more fundamental information.
Static Electricity and Current • When a positively charged object and a negatively charged object are connected via a conductor (e.g. a metal wire) electric charge flows from one object to another until the charge difference is neutralized. • In early 19th century Leclanche and others found that they could produce long term current by using two different metal electrodes (e.g. copper and zinc) in a dilute acid solution (e.g. H2SO4) • Samuel FB Morse learned about this from his scientific friends at New York University.
Electrical Telecommunication • Started with the telegraph invented ca. 1837 by Samuel F.B. Morse, an artist. • Theoretical basis of electricity and magnetism not fully understood then. • Morse had help from some of the best American scientists of his day: Joseph Henry, etc. • Telegraph evolved in several ways, including TELEX/TWX (teletypewriter networks) in mid 20th century, and indirectly into the Internet.
Original Telegraph • Original telegraph used a set of pre-manufactured metal characters each having a distinct long and short bump pattern along an edge, for each letter of the alphabet. Metal characters were first arranged in proper order in a metal holder to compose a message, like setting a line of hand-set moveable metal type for printing. • To send the message, a “Clockwork” mechanism moved a metal contact over the bumps, momentarily producing long or short electric current pulses from an electric cell/battery. • At the receiver, current pulses flowing through an electromagnet (coil of wire) tapped a pen to make inked dots or dashes on a moving strip of paper.
Telegraph Product Evolution • Within a year, operators recognized that the receiver could be simplified by omitting the pen, ink supply and moving paper. • The telegrapher could send a message by manually pressing on an electric switch contact (“telegraph key”). • A skilled human telegrapher could send or recognize the distinct character sounds by ear and write them in conventional text, at 30 words per minute or more. • This was an era of relatively low labor/staff costs, and high equipment costs. • The skilled telegrapher was a necessary person at each end of the chain between the end customer sender and receiver, along with the “Western Union messenger,” typically a boy on a bicycle, who carried the message on paper in ordinary text to/from the end customer.
Telephone Missed by Western Union • Within a few years almost all the regional telegraph companies united into one nationwide telegraph firm named Western Union (WU) • In 1876 Alexander G. Bell, a teacher of deaf children, invented the telephone. Historians say the transmission of voice was a last minute afterthought, since his original purpose was to send multiple telegraph messages simultaneously over the same wire, using a different audio frequency “carrier” signal for each message, instead of turning the loop current on and off. • Bell offered his patent to WUfor $100 000. They rejected the offer, believing that then-existing deficiencies in voice quality could not be corrected, and failing to recognize the importance of lower costs and immediate conversation without need for a skilled telegrapher. • Approximately 10 years later WU recognized they had lost significant market share to the telephone. They hired Thomas Edison to design a greatly improved microphone and with it they negotiated a deal that was not very clever and would be illegal today under anti-trust laws. They agreed to not compete with Bell in exchange for a yearly “payoff.”
Western Union Constricted • In 1890 Bell (then American Telephone & Telegraph – AT&T) bought up Western Union, but was forced to sell it again in 1914 due to antitrust laws. Under the antitrust settlement (the “Kingsbury commitment”) they also stopped buying up independent suburban telephone companies. • After World War 2, Western Union and the Canadian railroad companies set up TELEX, a circuit-switched electro-mechanical teletypewriter network in North America patterned after a similar system in Europe. • In the 1960s AT&T established a competitive service called TWX (both names are abbreviations for TELetypeWriter EXchange), but sold it to Western Union just as data communication and Internet technology supplanted both systems. • TELEX/TWX required end subscribers to buy a relatively expensive keyboard and printer, but no skill beyond the ability to type was needed. For messages in foreign languages, the written form allowed translation with the aid of some knowledge and a bilingual dictionary. • Western Union still exists and handles telegrams, but its major business now is international money orders.
Further Telephone Developments • During 1880-1920 AT&T bought up its major manufacturing supplier (Western Electric Co. - WECo) and, thanks to the Bell patents, owned the local telephone wires in most major US cities. AT&T was also a significant part owner of Bell Canada and Northern Electric Co., a Canadian near-monopoly on service and manufacturing similar to that in the US. Also owned the Bell Telephone Manufacturing Co. factories in many countries, ultimately mostly sold to ITT due to further antitrust settlements in 1930s. • WECo set up a research and development group that evolved into Bell Telephone Laboratories (Bell Labs). Some of its accomplishments: • Replacement of earth conductors (a method used for telegraph) with copper 2-wire “loops” having less electrical resistance, better audio quality (1890). • Analog long distance network, ultimately using frequency division multiplexing (FDM) to carry up to 12 conversations on two loops between central offices by 1930s. • Invention of the transistor (1948). • Digital “T-1” long distance networks (1961), and some of its outgrowths. • Analog cellular telephone system (1975) • Several Nobel prizes awarded to Bell Labs scientists for fundamental research
Subscriber Dialing • Early telephone networks required a human operator to establish connections. Labor intensive and costly • Almon B. Strowger, a mortician, built the first successful “dial” telephone system in 1895 (actually a push button subscriber interface) • Electromechanical switching systems reached a high level of development in 1940s • Switching systems today are mostly computer controlled
Digital Transmission and Switching • Digital technology first appeared in the telephone network as an improvement in the quality and capacity of long distance circuit switching (T1 digital multiplexer, ca. 1961) • Use of more sophisticated digital voice coding allowed use of packet switching, a more cost effective way of transmitting both voice and data over the same packet switched digital network (e.g. Voice over Internet Protocol)
Benefits of Digital Technology • For systems in which the end signals are analog (audio, video, etc.) the quality of the final result has a degree of imperfection set by the designer, and it does not degrade due to longer transmission distance, more generations of copies, etc. • Both computers and digital telecom systems use the same or similar hardware • Economy of scale due to larger production runs of the same devices in both markets and shared use of the same digital switching and transmission
Telecom Competition • Until 1968 most US telephone companies connected only their own rented equipment to their customers. Tom Carter, a Texas “maverick” radio engineer from Kaufman County (just east of Dallas) fought this restriction through the US federal court system. • The Carterfone decision of the US supreme court allowed subscribers to own their own telephone sets, then to eventually own/buy their own long distance services, etc. • This open competitive marketplace spurred the development of many sophisticated telecom services.
Telecom Competitive Boom & Bust • From about 1970-2000 the telecom industry grew rapidly, then “crashed” • Highly competitive sourcing of long distance services (MCI, etc.), fiber optics and switching hardware lowered the cost radically. Only cellular systems grew rapidly enough to truly prosper in this market. • Some hardware vendors and service firms (sadly, MCI and Nortel in particular) mendaciously hid their true losses and eventually were forced into bankruptcy. • Many other honest vendors suffered as well, and many were merged into competitive firms. • Full disclosure: The instructor worked for AT&T Bell Labs 1963-1969, MCI 1982-1984, Nortel 1984-1990.
Brief Review of Electronic Hardware • Electronic hardware can be categorized based on signal processes • Linear devices (audio and radio waveform power amplifiers, etc.) • Improvements of linearity and reduction of noise via feedback or feed-forward • Non-linear devices • Analog-Digital Convertors • Basics of digital logic • Combinatorial logic • Memory • Basics of Computers, electronic switching, digital signal processing, etc.
Transmission Channels, Ideal and Imperfect • Electromagnetic signal transmission via wire, wireless and optical fiber • Fourier series represents signal as a sum of sine waves • Radio spectrum • Bandwidth limitations • Power “loss” • Additive random noise • All “resistors” have thermal noise • Fading • Interference (signals from other sources)
Related Technologies • Improved digital telecom systems include • Data “compression”: encoding of information at a low bit rate. Best done by understanding the underlying statistics and physics of the data or messages and the reception mechanisms of the ear or eye • Lossless coding (example: facsimile) • Lossy coding (example: LPC audio, JPEG, HDTV, etc.) • Error protection: accurate transmission and reconstruction of data or message via an imperfect channel. Requires transmission of redundant information. • encryption: prevents unauthorized persons from understanding signal content.
Encryption and Authentication • Cellular radio systems have stimulated application and development of new encryption and authentication technologies. • Transmission channels are accessible to unauthorized eavesdroppers. • Running key bit-stream is theoretically ideal, but real problems relate to synchronization and generation of a pseudo-random key.
Product Success or Failure • In some cases new products do not succeed because they don’t or can’t meet technical requirements. • Example 1: About 1990 many telephone companies and cable TV companies were seriously engaged in merger negotiations for about a year, based on misunderstandings. • At that time the technology to connect telephone calls via cable TV or to deliver TV via telephone wires was not available. • Satisfactory technology is available today. • An objective of this course is to help avoid wrong decisions of this type
Some Planned Products Don’t Meet End User’s Desires • Most unsuccessful products in the telecom industry meet all technical requirements but are not perceived by many potential customers to have good price/performance ratio • We do not directly address these customer satisfaction issues in this course. Economists and product planners use focus groups and other methods to try to avoid unsatisfactory pricing. • Example 2: XM-Sirius subscriber satellite radio broadcasting recurring subscriber fee rejected by majority of potential customers. Very few pay for continuing service after a 1 year free trial.
Product 3: Scheduled Airline Telephone Service • Airfone, Aircell and similar telephone calls from scheduled airline flights cost approximately $3 per minute. Handsets are installed on seat backs in the aircraft. • Full disclosure: The instructor is a co-inventor on some Aircell patents. • Incidental note: Jack Goeken founded both Airfone and MCI. • So far, many technological designs have been tried but none are profitable. • Focus groups and extensive marketing tests indicate that air travelers perceive about $ 0.10 per minute as reasonable. • Numerous technology methods have been studied but none can meet the perceived price target so far.
Product 4: Iridium Satellite Cell Phones • The iridium system supports direct radio communication between handsets and one of 66 low orbit satellites. Service is available even over oceans and completely unpopulated regions with no base stations. Charges are about $15 or more per minute. Handsets cost approx. $3000 • Iridium satellite cellular network is presently in bankruptcy. It’s small ongoing customer list is comprised mainly of certain government agencies. • Several other planned competitive low-orbit satellite systems were abandoned when the lack of customers became widely known.
Product 5 OnStar, ATX GPS/cellular locating system • Example: OnStar cell phone and Global Satellite Positioning (GPS) receiver are factory installed in most GM vehicles, with the first year of service included gratis. Like XM-Sirius, the majority of drivers reject paying for ongoing service. • Consumers perceive about $5 per month as reasonable, in contrast to the current price of $60 per month. • OnStar automatically connects to support desk in case of an accident, and can be used to track stolen cars, etc. • Full disclosure: The instructor has testified as an expert witness in several patent litigation cases involving these technologies.
Southern Methodist UniversityLyle School of EngineeringEETS 7320Digital Telecommunications Technology 2. Scientific Background 2010 Spring
Some Scientific Background • Matter and energy • Elements and elementary “particles” • Described as particles or waves • In some cases, Einstein’s relativity analysis is also necessary • Pre-eminent importance of electrons • Hold together nuclei to make molecules, solids, etc. • Generate or receive electromagnetic waves when moving. • In an isolated system where the energy of all items is relatively “low,” the total mass of all the objects is “conserved,” meaning the total mass cannot decrease or increase. • When the energy of items in a reaction is sufficiently high, mass m can be converted to/from energy T according to the formula T=m·c2. These circumstances are seldom relevant to telecom. (T is energy in joules, c is speed of light, 300 000 000 meters/second.)
Ancient Mythology • Until the 19th century most “science” was based on myths. • Even today many newspapers and magazines print an astrology column (based on assumed vague influence in our lives of star positions in the sky). • Most natural phenomena (weather, earthquakes, stars and planets, etc.) were “explained” in terms of social interactions (jealousy, revenge, etc.) of mythical gods on Mount Olympus, etc. • Today we still use names of mythical gods as basis of the names of the 7 days of the week.
Ancient Theory of Elements • Ancient Greek philosophers theorized vaguely that all materials were made up of combinations of elements, but they were not able to clearly distinguish between mixtures (like rock) vs. compounds (like iron oxide “rust”) • They wrongly guessed that there were only 4 “earthly” elements (essences): namely, earth (dirt), air, fire and water. They also postulated a fifth element (the “quintessential” element) which make up stars, planets and other heavenly bodies that had different behavior than earthly objects: • Heavenly (quintessential) objects stayed in motion indefinitely, while earthly objects eventually stopped moving. • Ancient philosophers didn’t recognize some intrinsically pure substances (like gold) to be elements.
Philosophers and Scientists • Although very intelligent and inquiring, Aristotle and his contemporaries assumed that velocity of moving bodies was proportional to force. • They did not adequately understand the meaning of acceleration. • Most importantly, they did not perform many quantitative measurements or experiments. • Isaac Newton invented the method of calculus to analyze motion of non-constant velocity. • Using measurements from Galileo and Copernicus, he was able to analyze motion of planets. • Newton and Christian Huygens (18th century)were aware that light could be analyzed based on wave or particle models • Erwin Schrödinger, Einstein and other 20th century scientists analyzed the electron via wave methods
Chemical Elements • In 18th-19th century, chemists (Dalton, Lavoisier) identified some relatively simple chemical compounds, and discovered that each one was always formed in a fixed ratio of the atomic weight of the elements involved • Elements were identified as substances which could not be further subdivided into other materials (using “ordinary” amounts of energy). • If cyclotrons (“atom smashers”) existed in the 19th century, chemists would probably have been very confused! • In some cases it is easier to understand science when you know only approximate data than when you have massive amounts of accurate data. • Example: water (H2O) is made up of fixed portions of hydrogen and oxygen • These reactions were the first examples of quantum theory, although seldom identified as such.
Electrostatic Charge • Amber (“electron” in Greek) is a fossilized hard-dried tree resin. • 18th century French scientist Charles François de Cisternay DuFay discovered that there are two kinds of static electricity, • one produced by rubbing fur with glass (vitreous, positive) • the other by rubbing silk on resin (resinous, negative). • terms positive and negative were coined independently by William Watson and Benjamin Franklin (American scientist and statesman). Incidentally, it would have been more convenient to use the opposite names. • Scientists ultimately recognized that an electrically neutral object had equal amounts of both types of static electricity, but exhibited an attractive or repulsive force to another charged object when some “electricity” was added or removed. • Negative electricity (electrons) can also be emitted from some metals by shining a light wave onto them, leaving a net positive charge on the metal • Flowing or current electricity is not static (stationary).
Some Physical Units • The meter (m), a length equal to 1/299792458 of the distance that light travels in a vacuum in one second. • Originally historically intended to be 1/40 000 000 of the circumference of the earth. Old definition of meter as 39.37 inches is obsolete. • Note: one inch is exactly 25.4 millimeters. • The kilogram (kg), a platinum-iridium unit of mass stored at the International Bureau of Weights and Measures in Sèvres (Parisian suburb) France. • Originally historically the kg was the mass of a 0.1 meter (edge length) cube of pure water (approx one liter of water). The pound mass is now defined as equal to 0.45359237 kg, exactly. • A second (s) is the time duration of 9 192 631 770 periods of the electromagnetic radiation (light wave) corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[, originally historically defined as 1⁄86 400 of a day (a day is the average time required for the earth to complete one rotation around its axis). For more explanation see: • See http://physics.nist.gov/Pubs/SP330/sp330.pdf and • http://www.nrc-cnrc.gc.ca/eng/projects/inms/fountain-clock.html • These 3 units are sufficient for the basis of mechanical physics. To also analyze electrical physics, an electrical unit, the ampere of current, is the 4th base unit used in the Système International (SI, mksA or Giorgi units) or practical set of physics units.
Expressing Big and Small Numbers • Scientific notation: We write a large number like 45 678 000 000 in the form 4.5678·10+10 • We write a very small number like 0.000 000 098 76 in the form 9.876·10-8 • Blanks separating groups of 3 digits avoid the confusion due to use of commas (North America) vs. periods (full stops, dots) in most other countries. • Examples above are both positive numbers. Negative number example: -1.6·10-19
Atomic Theory • About 1900 physicists recognized from experiments that an atom (the smallest item of a chemical element) had a positive nucleus of very small diameter in relation to the spacing of atoms in a molecule. Experiments showed that so-called alpha particles (chunks of proton and neutron material) emitted from naturally radioactive atoms mostly passed through thin gold foils, but an occasional alpha particle bounced back! • Alpha particles are naturally emitted from some radioactive materials (for example, uranium, actinium, etc.). An alpha particle comprises 2 protons and two neutrons, total atomic weight ~4.
Discovery of the Nucleus • When Ernest Rutherford discovered that some of the alpha particles bounced back he wrote… “It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch [artillery] shell at a piece of tissue paper and it came back and hit you.” For more background regarding alpha particles see: http://rspa.royalsocietypublishing.org/content/82/557/495 • Most of the mass (and therefore the weight) of each atom is due to the mass of the nucleus
The Photoelectric Effect • In 1905 after studying the experimental relationship between the frequency f of a light wave that illuminates a piece of “light” metal (sodium, potassium, etc.) and the energy of the negative charge particles (electrons) emitted from the metal surface, Albert Einstein theorized that the energy was not related to the brightness (amplitude) of the light wave, but was transferred in chunks (quanta) of energy equal to hf, less a correction factor (so-called “work function”) which was the same for all samples of each particular metal. • Incidentally, Philipp Lenard, the physicist who did the experiment, later in 1930s became a Nazi sympathizer and attacked Einstein in his writings. Lenard was an outcast from most of the scientific community due to his political affiliations. • Einstein later received the Nobel prize specifically for this theory.
Fundamental “Particles” • The most important fundamental particle in the telecom business is the electron, which can be described as a wave and in some cases approximately as a small particle. Electrons have several properties • Electric charge= -1.629·10-19 coulomb (or ampere ·second, to be explained) • Electron mass varies according to velocity, but when the velocity is low compared to speed of light, the so-called rest mass is me= 9.109·10-31 kg • For wave analysis purposes, electron wavelength λ is inversely related to momentum p. That is p=h/λ. • Planck’s constant: h = 6.023·10-34 joule·second • Reciprocal wavelength (1/λ) is measured in units of reciprocal meters (also called “diopter” in optics). The direction of a reciprocal wavelength vector is parallel to the direction of the wave propagation (the “ray” direction of geometrical optics).
Energy, power amps and volts • For simplicity of the explanation, assume that we can buy an accurate voltmeter and ammeter (ampere meter) for making measurements. For now, we do not explain how it works. • A voltmeter has two electrodes (insulated wires) and an indicator dial/display. The dial indicates the difference in electrode voltage. • A voltage difference is the ratio of the energy difference at two end points of a path, to the electric charge moved along that path. One volt = one joule (energy unit) / one coulomb (electric charge unit). • When a constant voltage v is applied to a coil of insulated wire (an inductor), for t seconds, a magnetic “field” having a value v·t (unit volt second or weber) is produced in that coil.
Energy, power amps and volts • An ammeter is a measuring instrument having two electrodes (wires) and a dial/display that indicates the amount of electric current (charge flow) through the ammeter from one electrode to the other. • A coulomb (1 C=1 A·s) of electric charge is the result of a 1 ampere (1 A) electric current flow collected for 1 second. • Typically, electric charge is collected on a “plate” or electrode of a capacitor. A capacitor is typically constructed of two conductive metal plates (electrodes) on opposite sides of an insulator (for example, an insulating plastic film). • In an isolated system, electric charge is conserved.
Power and Energy • A watt (1 W) is the power flow due to 1 A flowing through a voltage difference of 1 volt (1 V). • Energy (measured in joule units) is the product of power with time. • In an isolated system, the total energy of all objects in that system is “conserved,” that is, it does not increase or decrease with time. Very important for physics.
More Units of Measurement • momentum (p) unit is m·kg/second • p is a vector characterized by both a magnitude and a direction in 3-dimensional space. We indicate this by using a bold type character or writing the momentum as a combination of three mutually perpendicular components • A low energy electron analyzed as a particle has a momentum magnitude equal to the product of its apparent (ray) velocity and me. • Total momentum of several objects is computed by adding • In an isolated system, the total momentum of all objects in that system is “conserved,” that is, it does not increase or decrease with time. Very important for physics.
More Units • A joule (1 J) is the energy collected from 1 W flow for 1 second (1 J= 1 W·s). Energy collected for 3600 seconds (an hour) at a 1 W rate is 3600 W·s or 3600 J, a number perhaps more familiar to you from a bill for electric power as a watt hour. (Most electric bills give the energy in kilowatt hours.) • Note that a scientific unit named after a person is written un-abbreviated with lower case letters. When it is abbreviated, the first letter of the abbreviation is capitalized.
Planck’s Constant h • When gasses are heated to a high temperature, they produce electromagnetic radiation (light or x-rays for example) at various discrete frequencies, characteristic of the gas used. • Examples: Neon signs or ultra-violet light produced from mercury vapor inside a fluorescent light tube. • When solids are heated they mostly produce a continuous spectrum of electromagnetic waves over a range of frequencies. • German physicist Max Planck analyzed (ca. 1895) emission from solids. Earlier theories predicted incorrectly that unlimited power would be emitted at higher frequencies (the so-called “ultraviolet catastrophe”). By including an algebra term that reduced the emitted power at high frequencies in accordance with experiments, Planck did away with the “catastrophe.” The formula term was interpreted by Planck as describing transfer of “chunks” (quanta) of energy hf at frequency f, rather than transfer of any arbitrary amount of energy. • Note on symbols: The Greek lower case letter nu (written ν) is another symbol for frequency. Take care, it closely resembles the letter v.
More fundamental particles • Protons (positive charge in nucleus) • Neutrons (in nucleus of some atoms) • Photons (name for blobs of energy transfer to/from electromagnetic waves) • Many others that play only an indirect role in telecom. Examples: positrons, quarks, etc. Very important in theoretical physics, but not for telecom. We don’t need to study these, which simplifies this course significantly.
END • 1. Overview
