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Digital CommunicationEcE 4034
B.Tech. Second Year for EcE
Date: 14.3.08
Dr. K a!t Khin"rofe##or and $eadDe%artment of Electronic Engineering
and &nformation TechnologYangon Technological 'ni(er#it
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Chapter 12
Digital Communication Concepts12.1 Digital Information
Bit Coding Coding Efficiency
One bit can define 2 objects2 bit can define 2 of 2 = 2 . 2 = 2 2 = 4 object3 bit can define 2 of 2 of 2 = 2 . 2 . 2 = 2 3 = 8 object4 bit can define 2 of 2 of 2 of 2 = 2.2.2.2 = 2 4 = 16 object
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2n = Mthe number of required bits = ndifferent things or levels =
M n 2log=
!ctual number of digits used
"#act number of digits required$oding "fficienc% =
& bits6.46 bitse.g $oding "ff ' = = (.)23 = )2.3*
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12.2 Information Transfer rate (f i
+nit bit, sec or b-se.g erial digital /ord 1(1((1 06 bits
ime ta en = 6 ms
1sec0,(((416
6kbpsbit
ms
bits f i ==
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12.! "ignaling (B#$D %ate (f &
1 3 4 5 6 & 8 )
ignal level 0
t 0ms
b = 1 ms f &= 1'T & = 1 baud
7ote n a -urel% binar% s%stemthe bit rate = the baud rateig 12.1 Binary transmission
(
1
(
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e.g.9inar% message 1 ( 1 ( ( 1 1 1
:uaternar% transmission 2 2 1 3
f b = 1 baud 0bit,sec
f i= 1 b-s
olts
1(
2
3
4
1 4 5 62 3
t 0ms
f i 0transfer rate = 8 bits,4ms = 2 b-s
f b 0band rate = 4 s%mbols,4ms =1 baud
ig 12.2 our le)el transmission of a&inary message
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12.* "ystem Capacity (+% Imformation Capacity (C)
$ = information # 0 1, m = 01, b
M f C c 20min log2=
/here m is the message time
1, b is the signaling rate
log 2 is the number of bits 0 +%
,artly -a $ - B T
;here $ = information ca-acit%
9 = band/idth
= transmission time
bps N S BC 10log 2 +=
M 2log
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12./ Band idth Considerationsthe minimum -ossible band/idth required for a given -ulse rate
ho/ -ulses can be sha-ed to minimi
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$ontinued
b = 1, f b
f = 1, = 1, 2 b = f b
9; min = f b
f b = the transmission line bitArate 0baud rate
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!
olts
ime domain descri-tion
t
+
+
+= .........22cos2sin
211
2cossin2
0 t T T
t T T
A
T t v
he -ulse re-etition rate is f = 1, 0s%mbols,sec
!m-litude0 olts
10sin2 volts
T
A
( )( )T n
T nT
A,
,sin2
( 1, 2,
f = 1,f = 2,
Brequenc% domain descri-tion
f 0@esolution is the smallest analog in-ut voltage changethat can be distinguished b% !,F converter. q = Bs , 2 n
/here q = resolution n = number of bits in the digital code /ord Bs = fullAscale voltage range for the analog signal
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Dynamic %ange( D%
!F$ -arameters = Bs, q
= 2 n = F> = ma#, min = 2 n
F> 0d9 = 2( log ma#, min2( log 2 n= 2(n log 2 = 6.(2n
or F>0d9 6nBor linearl% encoded H$ s%stem F>0d9 = 6 d9, bit
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"ignal to
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CompandingIinear quanti
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!
(((
((1
(1(
((1
1((
1(1
11(
111 Iinear analogAtoAdigital converter
transfer characteristic.
7
Bull scale or B
F i g i t a
l o u
t - u
t c o
d e
q
am-le voltage in-ut0 olts ma#0 olts
J q(K q , 2
A q , 29. :uantum uncertaint% or quanti
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eference#
1. Advanced Electronic Communication Systems byWA !E "#$AS%& $esa Community College&Second Edition
'. rinciples o Digital and Analog Communicationsby *erry D. +ibson& "e,as A - $ niversity
/. Electronic Communication "ec ni ues by aul2.. oung& .E. & Ari3ona State niversity
4. Advanced Electronic Communication Systems byWA !E "#$AS%& 5i t Edition
6. %ntroduction to Digital and Data Communication