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 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 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
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 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 = 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 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) = /2 = 3500 Hz
fc (backward) = – 5000/2 = 8500 Hz

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

51. Digital-to-Analog 부호화(cont’d)
FSK(Frequency Shift Keying)
the frequency of the signal is varied to represent binary 1 or 0.

52. Digital-to-Analog 부호화(cont’d)
FSK encoding

53. Digital-to-Analog 부호화(cont’d)
Bandwidth for FSK

54. Digital-to-Analog 부호화(cont’d)
PSK(Phase Shift Keying)
the phase is varied to represent binary 1 or 0.
bit
phase 1 1
180
Constellation diagram

55. Digital-to-Analog 부호화(cont’d)
PSK

56. Digital-to-Analog 부호화(cont’d)
QAM(Quadrature Amplitude Modulation)
means combining ASK and PSK in such a way that we have maximum contrast between each bit, dibit, tribit, quadbit, and so on.

57. Digital-to-Analog 부호화(cont’d)
000
001
011
010
100
101
110
111
Time domain for an 8-QAM signal
2 amplitudes, 4 phases

58. 5.4 Analog-to-Analog 부호화
is the representation of analog information by an analog signal.
Analog-to-Analog encoding

59. Analog-to-Analog 부호화(cont’d)
Type of analog-to-analog encoding

60. Analog-to-Analog 부호화(cont’d)
AM(Amplitude Modulation)
~ The frequency and phase of the carrier remain the same; only the amplitude changes to follow variations in the information.

61. Analog-to-Analog 부호화(cont’d)
Amplitude modulation

62. Analog-to-Analog 부호화(cont’d)
AM bandwidth
The total bandwidth required for AM can be determined from the bandwidth of the audio signal.

63. Analog-to-Analog 부호화(cont’d)
AM bandwidth

64. Analog-to-Analog 부호화(cont’d)
Audio signal(음성과 음악) bandwidth : 5 KHz
Minimum bandwidth : 10 KHz (bandwidth for AM radio station)
AM stations are allowed carrier frequencies anywhere between 530 and 1700 KHz(1.7 MHz)

65. Analog-to-Analog 부호화(cont’d)
AM band allocation

66. Analog-to-Analog 부호화(cont’d)
FM(Frequency Modulation)
as the amplitude of the information signal changes, the frequency of the carrier changes proportionately.

67. Analog-to-Analog 부호화(cont’d)
Frequency modulation

68. Analog-to-Analog 부호화(cont’d)
FM Bandwidth
The bandwidth of an FM signal is equal to 10 times the bandwidth of the modulating signal.

69. Analog-to-Analog 부호화(cont’d)
FM bandwidth

70. Analog-to-Analog 부호화(cont’d)
Bandwidth of an audio signal(음성과 음악) broadcast in stereo : 15 KHz
minimum bandwidth : 150 KHz
allows generally 200 KHz(0.2 MHz) for each station
FM station are allowed carrier frequencies anywhere 88 and 108 MHz(each 200 KHz)

71. Analog-to-Analog 부호화(cont’d)
FM band allocation
Alternate bandwidth allocation

72. Analog-to-Analog 부호화(cont’d)
PM(Phase Modulation)
~ is used in some systems as an alternative to frequency modulation.
The phase of the carrier signal is modulated to follow the changing voltage (amplitude) of the modulating signal