1 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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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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Unipolar~ uses only one level of value(1: positive value, 0: i

dle)

Unipolar encoding

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Unipolar encoding problems DC(Direct Current)Component : 직류 Synchronization( 동기 )

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Polar~ uses two levels (positive and negative) of

amplitude.

Types of polar encoding

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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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NRZ-L and NRZ-I encoding

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RZ(Return to Zero)~ use three value(positive, negative, zero)

1 : positive-to-zero

0 : negative-to-zero

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RZ encoding

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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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Bipolar~ uses three voltage levels(positive, negative,zero)

zero level : binary 0 positive and negative voltage : 1(alternate)

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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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B8ZS(Bipolar 8-Zero Substitution)~ is the convention adopted in North America to

provide synchronization of long strings of 0s.

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B8ZS encoding

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HDB3(High-Density Bipolar 3)~ is the convention adopted in Europe and Japan.

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HDB3 encoding

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Example 5.1 compare the bandwidth needed for unipolar encodi

ng and RZ encoding.

Solution RZ need twice the bandwidth of unipolar encoding.

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Solution to Example 5.1

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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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PAM

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PCM(Pulse Code Modulation)~ Quantization is a method of assigning interal value

s in a specific range to sampled instances.

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

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Quantized sample

Quantizing using and magnitude

Assign sign and magnitude value(seven-bit binary equivalent)

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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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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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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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ASK(Amplitude Shift Keying)~ Both frequency and phase remain constant while

the amplitude changes.

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ASK encoding

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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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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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QAM(Quadrature Amplitude Modulation)~ means combining ASK and PSK in such a way tha

t we have contrast between each bit, dibit, tribit, quadbit, and so on.

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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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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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Amplitude modulation

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AM bandwidth~ The total bandwidth required for AM can be

determined from the bandwidth of the audio signal.

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AM bandwidth

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Audio signal( 음성과 음악 ) bandwidth : 5 KHz

Minimum bandwidth : 10 KHzAM stations are allowed carrier frequencies

anywhere between 530 and 1700 KHz(1.7 MHz)

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AM band allocation

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FM(Frequency Modulation)~ as the amplitude of the information signal

changes, the frequency of the carrier changes proportionately.

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Frequency modulation

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FM Bandwidth~ is equal to 10 times the bandwidth of the

modulation signal.

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FM bandwidth

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Bandwidth of an audio signal( 음성과 음악 ) broadcast in stereo : 15 KHz

minimum bandwidth : 150 KHzallows generally 200 KHz(0.2 MHz) for each

stationFM station are allowed carrier frequencies

anywhere 88 and 108 MHz(each 200 KHz)

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FM band allocation

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PM(Phase Modulation)~ is used in some systems as an alternative to

frequency modulation.

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1 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