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PART IIPhysical Layer
Position of the physical layer
Services
ChaptersChapter 3   SignalsChapter 4   Digital TransmissionChapter 5   Analog TransmissionChapter 6   MultiplexingChapter ...
Chapter 3             Signals            Lecture 3
Note:    To be transmitted, data must betransformed to electromagnetic signals.
3.1 Analog and Digital Analog and Digital Data Analog and Digital Signals Periodic and Aperiodic Signals
Note:   Signals can be analog or digital.  Analog signals can have an infinite  number of values in a range; digitalsignal...
Figure 3.1   Comparison of analog and digital signals
Note:In data communication, we commonly   use periodic analog signals and       aperiodic digital signals.
3.2 Analog Signals Sine Wave Phase Examples of Sine Waves Time and Frequency Domains Composite Signals Bandwidth
Figure 3.2   A sine wave
Figure 3.3   Amplitude
Note:Frequency and period are inverses of            each other.
Figure 3.4   Period and frequency
Table 3.1 Units of periods and frequencies        Unit        Equivalent            Unit     EquivalentSeconds (s)        ...
Example 1Express a period of 100 ms in microseconds, and expressthe corresponding frequency in kilohertz.SolutionFrom Tabl...
Note:  Frequency is the rate of change withrespect to time. Change in a short span of time means high frequency. Change  o...
Note:  If a signal does not change at all, its  frequency is zero. If a signal changesinstantaneously, its frequency is in...
Note:Phase describes the position of the waveform relative to time zero.
Figure 3.5   Relationships between different phases
Example 2A sine wave is offset one-sixth of a cycle with respect totime zero. What is its phase in degrees and radians?Sol...
Figure 3.6   Sine wave examples
Figure 3.6   Sine wave examples (continued)
Figure 3.6   Sine wave examples (continued)
Note:An analog signal is best represented in       the frequency domain.
Figure 3.7   Time and frequency domains
Figure 3.7   Time and frequency domains (continued)
Figure 3.7   Time and frequency domains (continued)
Note:  A single-frequency sine wave is notuseful in data communications; we need      to change one or more of its    char...
Note:    When we change one or morecharacteristics of a single-frequencysignal, it becomes a composite signal     made of ...
Note:  According to Fourier analysis, anycomposite signal can be represented as  a combination of simple sine waveswith di...
Figure 3.8   Square wave
Figure 3.9   Three harmonics
Figure 3.10   Adding first three harmonics
Figure 3.11   Frequency spectrum comparison
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Transcript of "Data com 3 FUUAST"

  1. 1. PART IIPhysical Layer
  2. 2. Position of the physical layer
  3. 3. Services
  4. 4. ChaptersChapter 3 SignalsChapter 4 Digital TransmissionChapter 5 Analog TransmissionChapter 6 MultiplexingChapter 7 Transmission MediaChapter 8 Circuit Switching and Telephone NetworkChapter 9 High Speed Digital Access
  5. 5. Chapter 3 Signals Lecture 3
  6. 6. Note: To be transmitted, data must betransformed to electromagnetic signals.
  7. 7. 3.1 Analog and Digital Analog and Digital Data Analog and Digital Signals Periodic and Aperiodic Signals
  8. 8. Note: Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digitalsignals can have only a limited number of values.
  9. 9. Figure 3.1 Comparison of analog and digital signals
  10. 10. Note:In data communication, we commonly use periodic analog signals and aperiodic digital signals.
  11. 11. 3.2 Analog Signals Sine Wave Phase Examples of Sine Waves Time and Frequency Domains Composite Signals Bandwidth
  12. 12. Figure 3.2 A sine wave
  13. 13. Figure 3.3 Amplitude
  14. 14. Note:Frequency and period are inverses of each other.
  15. 15. Figure 3.4 Period and frequency
  16. 16. Table 3.1 Units of periods and frequencies Unit Equivalent Unit EquivalentSeconds (s) 1s hertz (Hz) 1 HzMilliseconds (ms) 10–3 s kilohertz (KHz) 103 HzMicroseconds (ms) 10–6 s megahertz (MHz) 106 HzNanoseconds (ns) 10–9 s gigahertz (GHz) 109 HzPicoseconds (ps) 10–12 s terahertz (THz) 1012 Hz
  17. 17. Example 1Express a period of 100 ms in microseconds, and expressthe corresponding frequency in kilohertz.SolutionFrom Table 3.1 we find the equivalent of 1 ms.We makethe following substitutions:100 ms = 100 10-3 s = 100 10-3 10 s = 105 sNow we use the inverse relationship to find thefrequency, changing hertz to kilohertz100 ms = 100 10-3 s = 10-1 sf = 1/10-1 Hz = 10 10-3 KHz = 10-2 KHz
  18. 18. Note: Frequency is the rate of change withrespect to time. Change in a short span of time means high frequency. Change over a long span of time means low frequency.
  19. 19. Note: If a signal does not change at all, its frequency is zero. If a signal changesinstantaneously, its frequency is infinite.
  20. 20. Note:Phase describes the position of the waveform relative to time zero.
  21. 21. Figure 3.5 Relationships between different phases
  22. 22. Example 2A sine wave is offset one-sixth of a cycle with respect totime zero. What is its phase in degrees and radians?SolutionWe know that one complete cycle is 360 degrees.Therefore, 1/6 cycle is (1/6) 360 = 60 degrees = 60 x 2 /360 rad = 1.046 rad
  23. 23. Figure 3.6 Sine wave examples
  24. 24. Figure 3.6 Sine wave examples (continued)
  25. 25. Figure 3.6 Sine wave examples (continued)
  26. 26. Note:An analog signal is best represented in the frequency domain.
  27. 27. Figure 3.7 Time and frequency domains
  28. 28. Figure 3.7 Time and frequency domains (continued)
  29. 29. Figure 3.7 Time and frequency domains (continued)
  30. 30. Note: A single-frequency sine wave is notuseful in data communications; we need to change one or more of its characteristics to make it useful.
  31. 31. Note: When we change one or morecharacteristics of a single-frequencysignal, it becomes a composite signal made of many frequencies.
  32. 32. Note: According to Fourier analysis, anycomposite signal can be represented as a combination of simple sine waveswith different frequencies, phases, and amplitudes.
  33. 33. Figure 3.8 Square wave
  34. 34. Figure 3.9 Three harmonics
  35. 35. Figure 3.10 Adding first three harmonics
  36. 36. Figure 3.11 Frequency spectrum comparison
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