1 / 78

Chapter 3

Chapter 3. Signals and Encoding/Modulating. BY Mr.Sukchatri Prasomsuk. Contents :. 3.1 Analog and Digital 3.2 Periodic and Aperiodic Signals 3.3 Analog Signals 3.4 Time and Frequency Domains 3.5 Composite Signals 3.6 Digital Signals

alvin-riley
Télécharger la présentation

Chapter 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 3 Signals and Encoding/Modulating BY Mr.Sukchatri Prasomsuk

  2. Contents : • 3.1 Analog and Digital • 3.2 Periodic and Aperiodic Signals • 3.3 Analog Signals • 3.4 Time and Frequency Domains • 3.5 Composite Signals • 3.6 Digital Signals • 3.7 Digital-to-Digital Conversion • 3.8 Analog-to-Digital Conversion • 3.9 Digital-to-Analog Conversion • 3.10 Analog-to-Analog Conversion

  3. Introduction : • Information can be in the form of data, voice, picture, image, numeric data, characters, or code. • You cannot roll up a photograph, insert it into a wire and transmit it across network. • must encoded description of the data. • You can use an encoder to create a stream of 1 and 0 that tells the receiving device. • To be transmitted, information must be transformed into electromagnetic signals.

  4. 3.1 Analog and Digital • Analogrefers to something that is continuous : a set of specific points of data and all possible points between. • Ex : Analog data - voice, sound, light, wave,... • Source: Sun, bulb, lamp, microphone, speaker, …. Value Time

  5. 3.1 Analog and Digital • Digital refers to something that is discrete : a set of specific points of data with no other points in between. • Ex. Digital data - is data stored in the memory of a computer in the form of 0s and 1s. • Transfer from one position to another inside or outside the computer. Such as : computer to Printer, CPU to RAM, …. Time Value

  6. 3.1 Analog and Digital • Conclusion : • Signals can be analog or digital. • Analog signals can have any value in a range. • Digital signals can have only a limited number of values.

  7. 3.2 Periodic and APeriodic Signals • Both analog and digital signals can be of two forms: periodic and aperiodic (nonperiodic).

  8. 3.2 Periodic and APeriodic Signals • Periodic Signals : is a signal that it completes a pattern within a measurable time frame, called a period, and repeats that pattern over identical subsequent periods. • The completion of one full pattern is called a cycle. • A period is defined as amount of time(sec.) required to complete one full cycle. • The duration of a period represented by T.

  9. 3.2 Periodic and APeriodic Signals Value • Analog • Digital Time Value Time

  10. 3.2 Periodic and APeriodic Signals • A Periodic or nonperiodic Signals, signal changes constantly without exhibiting a pattern or cycle that repeats over time. • Analog Time Value

  11. 3.2 Periodic and APeriodic Signals • An aperiodic signals can be decomposed into an infinite number of periodic signal. • A sine wave is the simplest periodic signal. • Digital Time Value

  12. 3.3 Analog Signals • Analog signal can be classified as simple or composite. • A simple analog signal, or a sine wave, cannot be decomposed into simpler signals. • A composite analog signal is composed of multiple sine waves.

  13. 3.3 Analog Signals • Simple Analog signals : the sine wave is the most fundamental form of a periodic analog signal. • Visualized as a simple oscillating curve, Its change over the course of a cycle is smooth and consistent, a continuous, rolling flow. • Amplitude : refers to the height of the signal. The unit for amplitude depends on the type of the signal. For electrical signals, the unit is normally volts, amperes, or watts.

  14. 3.3 Analog Signals • Amplitude : Value Time

  15. 3.3 Analog Signals • Period and Frequency : Value Time

  16. 3.3 Analog Signal

  17. 3.3 Analog Signals • Unit of Period : Period is expressed in seconds (s). • The communications industry uses five unit to measure period: • Second (s) • millisecond (ms = 10-3) • microsecond (us = 10-6) • nanosecond (ns = 10-9) • Picosecond (ps = 10-12)

  18. 3.3 Analog Signals • Unit of Frequency : Frequency is expressed in hertz (Hz) . • The communications industry uses five unit to measure frequency: • Hertz (Hz) • Kilohertz (KHz = 103 Hz) • Megahertz (MHz = 106 Hz) • Ginanosecond (GHz = 109 Hz) • Terahertz (THz = 1012 Hz)

  19. 3.3 Analog Signals • Period is the amount of time it takes a signal to complete one cycle; • Frequency is the number of cycles per second. • Frequency and period are inverse of each other: • Frequency (f ) = 1/T • Or • Period (T) = 1/f

  20. 3.3 Analog Signals • Ex.: A sine wave has a frequency of 8 KHz. What is its period? • Solution : • Period (T) = 1/f • = 1/8000 • = 0.000125 sec. • = 125 x 10-6 sec. • Or = 125 us #

  21. 3.3 Analog Signals Change in a short span of time High Frequency Change in a long span of time Low Frequency Note : If a signaldoesnotchangeatall, itsfrequencyiszero(0 Hz). If a signalchangesinstantaneously, itsfrequencyisinfinity.

  22. 3.3 Analog Signals • Phase : describes the position of the waveform relative to time zero. • Phase is measured in degrees or radians (360 degrees is 2 Pi radians). • A complete period => a phase shift of 360o • half a period => a phase shift of 180o • A quarter period => a phase shift of 90o

  23. 3.3 Analog Signals

  24. 3.3 Analog Signals • Ex : A sine wave is offset 1/6 of a cycle with respect to time zero. What is its phase? Solution we know that one complete cycle is 360 degrees. Therefore, 1/6 of a cycle is 1/6 x 360 = 60 degree #

  25. 3.3 Analog Signals

  26. 3.3 Analog Signals

  27. 3.4 Time and Frequency Domains

  28. 3.4 Time and Frequency Domains

  29. 3.4 Time and Frequency Domains • A low-frequency signal in the frequency domain corresponds to a signal with a long period in the time domain and vice versa. • A signal that changes rapidly in the time domain corresponds to high frequencies in the frequency domain.

  30. 3.5 Composite Signals • Composite Signals : a signal composed of more than one sine wave. • The frequency spectrum of a signal is the combination of all sine wave signal that make up that signal. • Bandwidth : The difference between the highest and the lowest frequencies of a composite signal. It also measures the information-carrying capacity of a line or a network.

  31. 3.5 Composite Signals

  32. 3.5 Composite Signals The frequency spectrum

  33. 3.6 Digital Signals • Digital signal : A discrete signal with a limited number of values. • O is zero voltage (0 V.) • 1 is a positive voltage (5V.)

  34. 3.6 Digital Signals

  35. 3.6 Digital Signals

  36. 3.6 Digital Signals • Ex. A digital signal has a bit rate of 2000 bps. What is the duration of each bit (bit interval)? • Solution The bit interval is the inverse of the bit rate. Bit interval = 1/(bit rate) = 1/2000 = 0.0005 sec. = 500x10-6 sec. = 500 us #

  37. Basics of Encoding Networking Signals

  38. Binary Encoding Schemes

  39. Binary Encoding Schemes

  40. Type of Modulation

  41. Encoding Signals as Voltages

  42. Encoding Singnals as Electromagnatics waves

  43. Encoding and Modulating • We must transform data into signals to send them one place to another. • Different conversion schemes : Conversionmethods Digital-Digital Analog-Digital Digital-Analog Analog-Analog

  44. 3.7 Digital-to-Digital Conversion • Digital-to-Digital encoding : conversion is the representation of digital information by a digital signal.

  45. 3.7 Digital-to-Digital Conversion • Type of digital-to-digital encoding Digital-Digitalencoding Unipolar Polar Bipolar

  46. 3.7 Digital-to-Digital Conversion Polar NRZ RZ Biphase Manchester Differential Manchester NRZ-L NRZ-I

  47. 3.7 Digital-to-Digital Conversion • Unipolar encoding uses only one level of value. • Polar encoding used two levels (positive and negative) of amplitude. • NRZ (Nonreturn to Zero) : NRZ-L, NRZ-I • In NRZ-L the level of the signal is dependent upon the state of the bit. • In NRZ-I the is inverted if a 1 is encountered. • RZ (Return to Zero) : anytime the original data contain strings of consecutive 1s or 0s. • A good encoded digital signal must contain a provision for synchronization.

  48. 3.7 Digital-to-Digital Conversion • Biphase encoding is implemented in two different ways : Manchester and differential Manchester. • In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation. • In differential Manchester encoding, the transition at the middle of the bit is used only for synchronization. Thebit representation is shown by the inversion or noninversion at the beginning of the bit.

  49. 3.7 Digital-to-Digital Conversion

  50. 3.7 Digital-to-Digital Conversion • Bipolar encoding : we use three levels : positive, zero, and negative. Bipolar AMI B8ZS HDB3

More Related