Data Encoding Part III Digital to Analog Conversion Surasak - - PDF document

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Data Encoding

Part III Digital to Analog Conversion

Surasak Sanguanpong nguan@ku.ac.th http://www.cpe.ku.ac.th/~nguan

Last updated: 25 November 2004 Applied Network Research Group Department of Computer Engineering, Kasetsart University 2/13

FSK FSK PSK PSK

Types of Digital-Analog Encoding

ASK ASK

Digital-Analog encoding

QAM QAM

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Digital data, Analog signal

Transmitting digital data through PSTN Modem is used to convert digital data to analog

signal and vice versa

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Modulation techniques

ASK FSK PSK

1 1 1 1

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ASK

Vd(t) Vc(t) VASK(t)

1 1 1 1 1

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FSK

Carrier 2 Carrier 1

vd(t) v1(t) v2(t) vFSK(t) 1 1 1 1

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PSK

Data Signal Carrier Phase coherent

vc(t) vc(t) vPSK(t) 180=0 0=1

phase diagram

bit rate = signaling rate

1 1 1 1

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4-PSK

1 1 1 0 0 1 1 0 1 1 0 0 1

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Signal Constellation

distance = C2+D2

D C

C C2+D2 sin-1 point defines a legitimate signal change

distance defines signal’s amplitude angle defines phase shift

angle =

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N-PSK constellation diagram

bit rate = 2xsignaling rate

+90ฐ=01 0ฐ=00 +270ฐ=11 +180ฐ=10 000 001 010 011 100 101 110 111

bit rate = 3xsignaling rate

4-PSK 8-PSK

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Quadrature Amplitude Modulation

00 10 01 11 001 011 010 111 100 101

4-QAM 8-QAM

1 amplitude, 4 phases 2 amplitude, 4 phases

000 110

Both amplitude and phase are combined

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16-ary QAM

Sample of 16-ary QAM

WE 209 : 3 amplitudes 12 phases V.29 : 4 amplitudes 8 phases 2 amplitudes 8 phases

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Bit rate and Baud rate

Bit rate : A number of bits that are transmitted in a second Baud rate : A number of line signal changed variation per

second If a modem transmits 1 bit for every signal change bit rate = baud rate If a signal change represents n bits bit rate = n*baud rate