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Comprehensive Guide: Digital Encoding Techniques

Explore digital encoding methods including unipolar, polar, NRZ, RZ, biphase, and bipolar AMI, B8ZS, HDB3 encoding schemes. Learn analog-to-digital encoding with PAM and PCM techniques.

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Comprehensive Guide: Digital Encoding Techniques

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  1. Encoding Prof. Choong Seon HONG

  2. 5 장 부호화(Encoding) 5.1 Digital-to-Digital 5.2 Analog-to-Digital 5.3 Digital-to-Analog 5.4 Analog-to-Analog

  3. 부호화(cont’d) • Information must be encoded into signals before it can be transported across communication media. • Different encoding schemes

  4. 5.1 Digital-to-Digital 부호화 ~ is the representation of digital information by a digital signal. • Digital-to-Digital encoding

  5. Digital-to-Digital 부호화(cont’d) • Types of digital-to-digital encoding

  6. Digital-to-Digital 부호화(cont’d) • Unipolar • uses only one level of value(1: positive value, 0: idle ) • Simple and inexpensive • Unipolar encoding

  7. Digital-to-Digital 부호화(cont’d) • Unipolar encoding problems • almost obsolete today • Having DC(Direct Current)Component : 직류성분 (a component with zero frequency) • cannot travel through media that cannot handle DC components , such as microwave. • Synchronization(동기) • The receiver has to rely on a timer.

  8. Digital-to-Digital 부호화(cont’d) • Polar ~ uses two levels (positive and negative) of amplitude. • Types of polar encoding

  9. Digital-to-Digital 부호화(cont’d) • NRZ(Non-Return to Zero) • NRZ-L : the level of the signal is dependent upon the state of the bit • NRZ-I : the signal is inverted if a 1 is encountered

  10. Digital-to-Digital 부호화(cont’d) • NRZ-L and NRZ-I encoding

  11. Digital-to-Digital 부호화(cont’d) • RZ(Return to Zero) • using three values (positive, negative, zero) 1 : positive-to-zero 0 : negative-to-zero • The signal changes not between bits but during each bit

  12. Digital-to-Digital 부호화(cont’d) • RZ encoding

  13. Digital-to-Digital 부호화(cont’d) • The main disadvantages of RZ encoding • requiring two signal changes to encode one bit and therefore occupies more bandwidth

  14. Digital-to-Digital 부호화(cont’d) • Biphase • provides probably the best existing solution to the problem of synchronization • is implemented in two different ways. • Manchester : used by Ethernet LANs • Differential Manchester : used by Token Ring LANs

  15. Digital-to-Digital 부호화(cont’d) • Manchester and Differential Manchester encoding

  16. Digital-to-Digital 부호화(cont’d) • In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation • In Differential Manchester, the transition at the middle of the bit is used only for synchronization.

  17. Digital-to-Digital 부호화(cont’d) • Bipolar • uses three voltage levels(positive, negative,zero) • zero level : binary 0 • positive and negative voltage : 1(alternate)

  18. Digital-to-Digital 부호화(cont’d) • Type of bipolar encoding

  19. Digital-to-Digital 부호화(cont’d) • Bipolar AMI(Alternate Mark Inversion) ~ is the simplest type of bipolar encoding • Bipolar AMI changes poles with every 1 it encounters • These changes provide the synchronization needed by the receiver • But, there is no mechanism to ensure the synchronization of a long string of 0s

  20. Digital-to-Digital 부호화(cont’d) • Bipolar AMI encoding

  21. Digital-to-Digital 부호화(cont’d) • B8ZS(Bipolar 8-Zero Substitution) • is the convention adopted in North America to provide synchronization of long strings of 0s.

  22. Digital-to-Digital 부호화(cont’d) • B8ZS encoding

  23. Digital-to-Digital 부호화(cont’d) • HDB3(High-Density Bipolar 3) • is the convention adopted in Europe and Japan.

  24. Digital-to-Digital 부호화(cont’d) • HDB3 encoding

  25. Digital-to-Digital 부호화(cont’d) • Example 5.1 • Using B8ZS, encode the bit stream 10000000000100. Assume that the polarity of the first 1 is positive. • Solution

  26. Digital-to-Digital 부호화(cont’d) • Example 5.2 • using HDB3, encoded the bit stream 10000000000100. Assume that the number of 1s so far is odd and the first 1 is positive. • Solution

  27. Digital-to-Digital 부호화(cont’d) • Exercise Amplitude 1 1 0 0 0 0 0 0 0 0 0 1 0 1 0 Time AMI Time B8ZS Time HDB3

  28. 5.2 Analog-to-Digital 부호화 • is the representation of analog information by a digital signal. (recording singer’s voice onto a compact disc) • Analog-to-Digital Encoding

  29. Analog-to-Digital 부호화(cont’d) • PAM(Pulse Amplitude Modulation) • This technique takes analog information, samples it, and generates a series of pulses based on the results of the sampling. * Term sampling means measuring the amplitude of the signal at equal intervals.

  30. Analog-to-Digital 부호화(cont’d) • PAM

  31. Analog-to-Digital 부호화(cont’d) • PCM(Pulse Code Modulation) • Quantization is a method of assigning integral values in a specific range to sampled instances.

  32. Analog-to-Digital 부호화(cont’d) • Quantized PAM signal

  33. Analog-to-Digital 부호화(cont’d) • Quantized sample  Assign sign and magnitude value (seven-bit binary equivalent) • Quantizing using sign and magnitude

  34. Analog-to-Digital 부호화(cont’d) • The binary digits are then transformed into a digital signal using one of the digital-to-digital encoding techniques(예 : unipolar) • PCM

  35. Analog-to-Digital 부호화(cont’d) • From analog signal to PCM digital code

  36. Analog-to-Digital 부호화(cont’d) • Sampling Rate • How many samples are sufficient ? • According to the Nyquist theorem • The sampling rate must be at least two times the highest frequency

  37. Analog-to-Digital 부호화(cont’d) • Example 5.3 • What sampling rate is needed for a signal with a bandwidth of 10,000Hz (1000 to 11,000Hz) ? If the quantization is eight bits per sample, what is the bit rate ? • Solution • The sampling rate must be twice the highest frequency in the signal : • Sampling rate = 2 (11,000) = 22,000 samples/s • Data rate = (22,000 samples/s) (8 bits/sample) = 176 Kbps

  38. Analog-to-Digital 부호화(cont’d) • Example 5.4 • A signal is sampled. Each sample requires at least 12 levels of operation (+0 to +5 and –0 to –5). How many bits should be sent for each sample ? • Solution • need for 4 bits : one bit for the sign and three bits for the value

  39. Analog-to-Digital 부호화(cont’d) • Example 5.5 • We want to digitize the human voice. What is the bit rate assuming eight bits per sample ? • Solution • Human voice frequencies : 0 to 40000 Hz • Sampling rate : 4000 x 2 = 8,000 samples/second • Bit Rate = sampling rate x Number of bits per sample = 8000 x 8 = 64,000 bits/s = 64 Kbps

  40. 5.3 Digital-to-Analog 부호화 • ASK(Amplitude Shift Keying) • FSK(Frequency Shift Keying) • PSK(Phase Shift Keying) • QAM(Quadrature Amplitude Modulation) : related to Amplitude and Phase Shift Keying = modulation

  41. Digital-to-Analog 부호화(cont’d) • Type of Digital-to-Analog encoding

  42. Digital-to-Analog 부호화(cont’d) • Bit rate : the number of bits per second. • Baud rate : the number of signal units per second. • Baud rate is less than or equal to the bit rate. • Bit rate equals the baud rate x the number of bits represented by each signal unit • 반송신호 또는 주파수 (Carrier Signal or Carrier Frequency) • base signal for the information signal

  43. Digital-to-Analog 부호화(cont’d) • Example 5.6 • An analog signal carries four bits in each signal element. If 1000 signal elements are sent per second, find the baud rate and the bit rate. • Solution • Baud rate = Number of signal elements = 1000 bauds per second • Bit rate = Baud rate x Number of bits per signal element = 1000 x 4 = 4000 bps

  44. Digital-to-Analog 부호화(cont’d) • Example 5.7 • The bit rate of a signal : 3000 • If each signal element carries six bits, what is the baud rate ? • Solution • Baud rate = Bit rate/ number of bits per signal element = 3000/6 = 500 baud per second

  45. Digital-to-Analog 부호화(cont’d) • ASK(Amplitude Shift Keying) • Both frequency and phase remain constant while the amplitude changes. • Highly susceptible to noise interference • Noise usually affects the amplitude.

  46. Digital-to-Analog 부호화(cont’d) • ASK encoding

  47. Digital-to-Analog 부호화(cont’d) • Relationship between baud rate and bandwidth in ASK • BW = (1 + d) x N baud N baud : Baud rate d : factor related to the condition of the line (with a minimum value of 0)

  48. Digital-to-Analog 부호화(cont’d) • Example 5.8 • Find the minimum bandwidth for an ASK signal transmitting at 2000 bps. Transmission mode is half-duplex • Solution • In ASK the baud rate and bit rate are the same. The baud rate is therefore 2000. An ASK signal requires a minimum bandwidth equal to its baud rate. Therefore, the minimum bandwidth is 2000Hz

  49. Digital-to-Analog 부호화(cont’d) • Example 5.10 • Given a bandwidth of 10,000 Hz (1000 to 11,000 Hz), draw the full-duplex ASK diagram of the system. Find the carriers and the bandwidth in each direction. Assume there is no gap between the bands in two directions. • Solution • Bandwidth for each direction : 10000/2 = 5000 Hz • Carrier frequencies : fc (forward) = 1000 + 5000/2 = 3500 Hz fc (backward) = 11000 – 5000/2 = 8500 Hz

  50. Digital-to-Analog 부호화(cont’d) Solution to Example 5.10

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