5 장 부호화(Encoding)
5.1 Digital-to-Digital
5.2 Analog-to-Digital
5.3 Digital-to-Analog
5.4 Analog-to-Analog
5.5 요약
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부호화(cont’d)
Information must be encoded into signals
before it can be transported across
communication media.
Different encoding schemes
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5.1 Digital-to-Digital 부호화
~ is the representation of digital information by a
digital signal.
Digital-to-Digital encoding
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Digital-to-Digital 부호화(cont’d)
Types of digital-to-digital encoding
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Digital-to-Digital 부호화(cont’d)
Unipolar
~ uses only one level of value(1: positive value, 0:
idle)
Unipolar encoding
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Digital-to-Digital 부호화(cont’d)
Unipolar encoding problems
DC(Direct Current)Component : 직류
Synchronization(동기)
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Digital-to-Digital 부호화(cont’d)
Polar
~ uses two levels (positive and negative) of
amplitude.
Types of polar encoding
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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
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Digital-to-Digital 부호화(cont’d)
NRZ-L and NRZ-I encoding
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Digital-to-Digital 부호화(cont’d)
RZ(Return to Zero)
~ use three value(positive, negative, zero)
1 : positive-to-zero
0 : negative-to-zero
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Digital-to-Digital 부호화(cont’d)
RZ encoding
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Digital-to-Digital 부호화(cont’d)
Biphase
~ is implemented in two different ways.
Manchester
Differential Manchester
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Digital-to-Digital 부호화(cont’d)
Manchester and Differential Manchester
encoding
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Digital-to-Digital 부호화(cont’d)
Bipolar
~ uses three voltage levels(positive, negative,zero)
zero level : binary 0
positive and negative voltage : 1(alternate)
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Digital-to-Digital 부호화(cont’d)
Types of bipolar encoding
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Digital-to-Digital 부호화(cont’d)
Bipolar AMI(Alternate Mark Inversion)
~ is the simplest type of bipolar encoding
Bipolar AMI encoding
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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.
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Digital-to-Digital 부호화(cont’d)
B8ZS encoding
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Digital-to-Digital 부호화(cont’d)
HDB3(High-Density Bipolar 3)
~ is the convention adopted in Europe and Japan.
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Digital-to-Digital 부호화(cont’d)
HDB3 encoding
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Digital-to-Digital 부호화(cont’d)
Example 5.1
compare the bandwidth needed for unipolar
encoding and RZ encoding.
Solution
RZ need twice the bandwidth of unipolar
encoding.
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Digital-to-Digital 부호화(cont’d)
Solution to Example 5.1
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Digital-to-Digital 부호화(cont’d)
Example 5.2
compare the bandwidth needed for Manchester
and Differential Manchester encoding.
Solution
~ are the same.
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Digital-to-Digital 부호화(cont’d)
Example 5.3
using B8ZS, encode the bit stream
10000000000100. Assume that polarity of the first
1 is positive.
Solution
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Digital-to-Digital 부호화(cont’d)
Example 5.4
using HDB3, encoded the bit stream
10000000000100. Assume that the number of 1s
so far is odd and the first 1 is positive.
Solution
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5.2 Analog-to-Digital 부호화
~ is the representation of analog analog
information by a digital signal.
Analog-to-Digital Encoding
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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.
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Analog-to-Digital 부호화(cont’d)
PAM
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Analog-to-Digital 부호화(cont’d)
PCM(Pulse Code Modulation)
~ Quantization is a method of assigning interal
values in a specific range to sampled instances.
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Analog-to-Digital 부호화(cont’d)
Quantized PAM signal
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Analog-to-Digital 부호화(cont’d)
Quantized sample Assign sign and magnitude value
(seven-bit binary equivalent)
Quantizing using and magnitude
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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
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Analog-to-Digital 부호화(cont’d)
From analog signal to PCM digital code
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5.3 Digital-to-Analog 부호화
ASK(Amplitude Shift Keying)
FSK(Frequency Shift Keying)
PSK(Phase Shift Keying)
QAM(Quadrature Amplitude Modulation)
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Digital-to-Analog 부호화(cont’d)
Types of Digital-to-Analog encoding
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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.
반송신호(Carrier Signal)
base signal for the information signal
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Digital-to-Analog 부호화(cont’d)
ASK(Amplitude Shift Keying)
~ Both frequency and phase remain constant while
the amplitude changes.
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Digital-to-Analog 부호화(cont’d)
ASK encoding
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Digital-to-Analog 부호화(cont’d)
FSK(Frequency Shift Keying)
~ the frequency of the signal is varied to represent
binary 1 or 0.
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Digital-to-Analog 부호화(cont’d)
FSK encoding
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Digital-to-Analog 부호화(cont’d)
PSK(Phase Shift Keying)
~ the phase is varied to represent binary 1 or 0.
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Digital-to-Analog 부호화(cont’d)
PSK
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Digital-to-Analog 부호화(cont’d)
QAM(Quadrature Amplitude Modulation)
~ means combining ASK and PSK in such a way
that we have contrast between each bit, dibit, tribit,
quadbit, and so on.
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Digital-to-Analog 부호화(cont’d)
Time domain for on 8-QAM signal
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5.4 Analog-to-Analog 부호화
~ is the representation of analog information by
an analog signal.
Analog-to-Analog encoding
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Analog-to-Analog 부호화(cont’d)
Type of analog-to-analog encoding
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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.
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Analog-to-Analog 부호화(cont’d)
Amplitude modulation
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Analog-to-Analog 부호화(cont’d)
AM bandwidth
~ The total bandwidth required for AM can be
determined from the bandwidth of the audio signal.
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Analog-to-Analog 부호화(cont’d)
AM bandwidth
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Analog-to-Analog 부호화(cont’d)
Audio signal(음성과 음악) bandwidth : 5
KHz
Minimum bandwidth : 10 KHz
AM stations are allowed carrier frequencies
anywhere between 530 and 1700 KHz(1.7
MHz)
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Analog-to-Analog 부호화(cont’d)
AM band allocation
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Analog-to-Analog 부호화(cont’d)
FM(Frequency Modulation)
~ as the amplitude of the information signal changes,
the frequency of the carrier changes
proportionately.
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Analog-to-Analog 부호화(cont’d)
Frequency modulation
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Analog-to-Analog 부호화(cont’d)
FM Bandwidth
~ is equal to 10 times the bandwidth of the
modulation signal.
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Analog-to-Analog 부호화(cont’d)
FM bandwidth
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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)
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Analog-to-Analog 부호화(cont’d)
FM band allocation
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Analog-to-Analog 부호화(cont’d)
PM(Phase Modulation)
~ is used in some systems as an alternative to
frequency modulation.
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