digital comm concepts.pdf

8/10/2019 digital comm concepts.pdf

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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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)1

"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

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