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The Digital Deluge Lecture 2

The Digital Deluge Lecture 2. Learning in Retirement David Coll Professor Emeritus Department of Systems and Computer Engineering Winter 2009. Digital means discrete (like whole numbers) and Analog means continuous (like physical properties such as temperature, volume, etc.).

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The Digital Deluge Lecture 2

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  1. The Digital DelugeLecture 2 Learning in Retirement David Coll Professor Emeritus Department of Systems and Computer Engineering Winter 2009

  2. Digital means discrete (like whole numbers) and Analog means continuous (like physical properties such as temperature, volume, etc.). • The term analog comes from early computers (circa WWII) used to solve differential equations with continuous variables, • as contrasted with discrete state machines (like an elevator controller) built from open-or-closed switches or on-off digital circuits

  3. Definitions(from whatis.com) Analog • Using physical representation • Relating to a system, device that represents data variation by a measurable physical quality such as temperature, volume, distance, weight, pressure … • Which is continuous in time or space and value

  4. Definitions Digital • Representing data as numbers • Processing • Operating on • Storing • Transmitting • Displaying • Data in the form of numerical digits, as in a digital computer

  5. Representing a physical quantity • such as sound, light, or electricity • by means of samples • taken at discrete times (or places) • and given numerical values • usually in the binary system • as in a digital audio recording • or in digital television • or in digital photography

  6. In Communications • Analog is used to refer to systems with signals that are continuous in value and time • such as AM and FM, where the electrical signals are representations of the information signals.

  7. Amplitude Modulation (AM) ANALOG

  8. Phase or Frequency Modulation (FM)

  9. In Communications • Digital is used to refer to discrete-state, discrete-time signals that can take on only specific values at specific times; • such as • sampled/quantized signals, • pulse modulated signals, • and to data communication signals in general.

  10. Digital Modulation: Discrete in Time and Value

  11. Parameters of Information Sources & Systems • Analog (continuous functions of time, space, weight, …) • voice, audio, image, video, temperature • Bandwidth – frequency (harmonics) range • Statistics – amplitude distribution, power, spectrum (frequency content, harmonics) • Digital (sets of numbers): • ASCII characters, computer words, … • Bit Rate – bps, kbps, Mbps, Gbps, Tbps, Ebps, …

  12. How does Information Become “Digital”?

  13. Digital Representation • Information that is naturally discrete, such as state of a light switch (on-off), integers, or text can be represented by binary numbers in obvious ways. • Text (as generated on a keyboard) is often represented by 8-bit binary numbers. • Speech may be represented by a pressure wave, which is continuous – in time and value – and has to be sampled and quantized to be represented digitally.

  14. Discrete Information • Some information, such as numerals and characters is discrete and can be represented “digitally” easily • Take characters of the English Language for example • The American Standard Code for Information Interchange (ASCII) is the binary representation used in teletype messaging and adopted as a universal computer character representation.

  15. “A” = 11000001 “a” = 11100001 “%” = 10100101 Formatting 10001101 = CR 10001010 = LF Messaging 10000001 = SOH 10000010 = STX 10000011 = ETX 10000100 = EOT

  16. Serendipity • Early minicomputers such as Digital Equipment Corporation (DEC) PDP machines used teletypewriters as terminals • They had • keyboards that generated ASCII code words • printers that accepted ASCIII code words and • punched paper tape I/O that could be used to save and replay messages.

  17. The ASCII code set including • text formatting • CR and LF • and message formatting • SOH, STX ETX, EOT • Became the way computer communications over leased and dial-up telephone lines started • Except for a bunch of computer geeks who used Sun Microsystems workstations which had a different communications scheme built-in.

  18. Common Sense Digitization of Analog Information • All continuous signals can be represented by a collection of numbers to any degree of accuracy by • sampling often enough and • using enough quantization levels* to represent the signal value at the sampling instants. • * determined by the number of digits in the representation

  19. Analog-to-Digital Conversion • Two stage process • Sample • Sampling Theorem • Nyquist Rate • Quantize • Precision, SNR (% average error) • Note: a digital representation of an analog value always has error

  20. The Sampling Theorem • Shannon’s Sampling Theorem states that • any bandlimited signal may be represented by samples taken at a rate of twice its highest frequency*, and • may be reconstructed without errorif the appropriate interpolation functions are used**. * Twice the highest frequency is called the Nyquist Rate. ** Physically unrealizable sinx/x or (sinc) functions. Nerd Alert

  21. Impulse Sampling

  22. Reconstruction

  23. Summary • All signals can be represented by a collection of numbers to any degree of accuracy by sampling often enough and using enough quantization levels to represent the signal value at the sampling instant.

  24. Summary (for irrepressible nerds only) • Shannon’s Sampling Theorem states that any strictly bandlimited function may be presented by sampling at a rate that is at least twice as fast as the highest frequency in the signal, and that it may be recovered without distortion by passing the (impulse) samples through an ideal low-pass filter with a bandwidth equal to that of the signal.

  25. Quantization • For processing, storage or communication, samples with infinite precision must be quantized • Such that a range, or interval, of values is represented by a single, finite precision, number • For example, by a finite binary number.

  26. Quantization 7 7 7 7 7 6 5 5 4 3 3 2 2 1 1 1 time -2 -2 -3 -3 -3 -4

  27. Reconstitution 7 7 7 7 7 6 5 5 4 3 3 2 2 1 1 1 time -2 -2 -3 -3 -3 -4 -2 Quantum Boundary Actual Value ERROR Reconstruction Value -3 -3 Quantum Boundary -4

  28. Quantization Error (for nerds and audiophiles) • The quantization error depends on the number of distinct quantization intervals used. • If N binary digits are used, the number of distinct intervals is 2N. • The signal-to-quantization-error ratio is about (6N + 1.8) dB.

  29. Binary Representation • Once information is discretized, or sampled, a number can be assigned to represent the value of each sample. • The number can be expressed as a binary number, e.g., 2009 is 1024 + 512 + 256 + 128 +64 + 32 + 8 + 4 + 1 1x 210 + 1x 29 + 1x 28 + 1x 27 + 1x 26 +1x 25 +1x 23 + 1x 22 + 1x 20 11111101101

  30. Summary The basis of the Digital Deluge is the universal adoption of a technology that can create, process, and communicate information that is represented in digital form.

  31. So much for Digital Representation • Now, let’s look at Digital Information Technologies • But, first • Let us pause for a short break ….

  32. Let us look at the Digital Technologies • Communications • Computing

  33. Digital Communications • We have • Sources of Information • That create information • Destinations for Information • That use information • and we have • Communications Networks • That provide connectivity between them • We also have Terminals • That interface (connect) the Sources and Destinations to the Networks.

  34. A Taxonomy of Telecommunications • Sources • Channels • Destinations Term Dest Channels Source Term Term Dest

  35. What are “Digital” Communications? • Modern Telecommunication Systemsare designed to accept and deliver information made up of sequences of binary signals. • These systems and the connections through them are enabled and controlled by computers.

  36. What is Special About NOW?Why the Deluge NOW? • Realization of the Telecomm Dream • Unified Communications • ubiquitous high speed, multimedia, reliable, standardized networks • The All-IP Multimedia Network • The Internet and the WWW • Ubiquitous Broadband Access • Wired (FTTP) • Wireless(Cellular/WLAN)

  37. More on Communications • We will discuss communications later when we look at delivering digital information.

  38. Computers: Universal Digital Processing Machines • Computers are universal digital machines that can • accept information in digital form • store it • process it in many ways • output it to various devices • display it • communicate it • All under control of a set of pre-determined steps called a program.

  39. The Evolution of the Computer • Intelligent Information Agents • Communications, Processing, Control • Programmable • Powerful Hardware: speed, memory • Handheld/Mobile • Robotic • autonomous tasks • in touch with local environment

  40. Terminals and Switches • Terminal Equipment • the sources and destinations of information, are digital machines, i.e., computers, in the broadest sense. • Network Switches are also computers.

  41. Software Development • Highly evolutionary • Use of complex components • Standardization

  42. Communications A & D I/O Processor Intelligent Agent: Telematics

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