Forouzan Chp5

8/16/2019 Forouzan Chp5

1/57

McGraw-Hill © The McGraw-Hill Companies, Inc., 2004

Chapter 5

Analog Transmission


2/57


5.1 Modulation of Digital Data

Digital-to-Analog Conversion

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK)

hase Shift Keying (SK)

!uadrature Amplitude "odulation #it$#aud Comparison


3/57


Figure 5.1 Digital-to-analog modulation


4/57


Figure 5.2 Types of digital-to-analog modulation


5/57


#it rate is the num%er of %its per

second& #aud rate is the num%er ofsignal units per second& #aud rate is

less than or equal to the %it rate&

Note: Note:


6/57


'ample 'ample

An analog signal carries 4 bits in each signal unit. If 1000

signal units are sent per second, find the baud rate and the

bit rate

Solution Solution

Baud rate = 1000 bauds per second (baud/s)Baud rate = 1000 bauds per second (baud/s)

Bit rate = 1000 x 4 = 4000 bpsBit rate = 1000 x 4 = 4000 bps


7/57


'ample * 'ample *

The bit rate of a signal is 3000. If each signal unit carries

6 bits, what is the baud rate?

Solution Solution

Baud rate = 3000 / 6 = 500 baud/sBaud rate = 3000 / 6 = 500 baud/s


8/57


Figure 5.3 ASK


9/57


Figure 5.4 +elationship %et,een %aud rate and %and,idth in ASK


10/57


'ample 'ample

Find the minimum bandwidth for an ASK signal

transmitting at 2000 bps. The transmission mode is half-

duplex.

Solution Solution

In !" the baud rate and bit rate are the sa#e$ %he baud

rate is there&ore '000$ n !" sina re*uires a#ini#u# band+idth e*ua to its baud rate$ %here&ore, the

#ini#u# band+idth is '000 -.$


11/57


'ample . 'ample .

Given a bandwidth of 5000 Hz for an ASK signal, what

are the baud rate and bit rate?

Solution SolutionIn !" the baud rate is the sa#e as the band+idth,

+hich #eans the baud rate is 5000$ But because the baud

rate and the bit rate are aso the sa#e &or !", the bitrate is 5000 bps$


12/57


'ample / 'ample /

Given a bandwidth of 10,000 Hz (1000 to 11,000 Hz),

draw the full-duplex ASK diagram of the system. Find

the carriers and the bandwidths in each direction. Assume

there is no gap between the bands in the two directions.

Solution Solution

or &udupex !", the band+idth &or each direction is

B = 10000 / ' = 5000 -.

%he carrier &re*uencies can be chosen at the #idde o&

each band (see i$ 5$5)$

&c (&or+ard) = 1000 2 5000/' = 3500 -.

&c (bac+ard) = 11000 5000/' = 500 -.


13/57


Figure 5.5 Solution to 'ample /


14/57


Figure 5.6 FSK


15/57


Figure 5.7 +elationship %et,een %aud rate and %and,idth in FSK


16/57


'ample 0 'ample 0

Find the minimum bandwidth for an FSK signal

transmitting at 2000 bps. Transmission is in half-duplex

mode, and the carriers are separated by 3000 Hz.

Solution Solution

or !"

B = baud rate 2 & B = baud rate 2 & c1c1 −− & & c0c0

B = bit rate 2 &c1B = bit rate 2 &c1−−

&c0 = '000 2 3000 = 5000 -.&c0 = '000 2 3000 = 5000 -.


17/57


'ample 1 'ample 1

Find the maximum bit rates for an FSK signal if the

bandwidth of the medium is 12,000 Hz and the difference

between the two carriers is 2000 Hz. Transmission is in

full-duplex mode.

Solution Solution

Because the trans#ission is &u dupex, on 6000 -. is

aocated &or each direction$

B = baud rate 2 &c1B = baud rate 2 &c1−−

&c0&c0

Baud rate = BBaud rate = B −− (&c1(&c1 −− &c0 ) = 6000&c0 ) = 6000 −− '000 = 4000'000 = 4000

But because the baud rate is the sa#e as the bit rate, the

bit rate is 4000 bps$


18/57


Figure 5.8 SK


19/57


Figure 5.9 SK constellation


20/57


Figure 5.10 The .-SK method


21/57


Figure 5.11 The .-SK characteristics


22/57


Figure 5.12 The 8-PSK characteristics


23/57


Figure 5.13 +elationship %et,een %aud rate and %and,idth in SK


24/57


'ample 2 'ample 2

Find the bandwidth for a 4-PSK signal transmitting at

2000 bps. Transmission is in half-duplex mode.

Solution Solution

or 7!" the baud rate is the sa#e as the band+idth,

+hich #eans the baud rate is 5000$ But in 7!" the bit

rate is 3 ti#es the baud rate, so the bit rate is 15,000 bps$


25/57


'ample 3 'ample 3

Given a bandwidth of 5000 Hz for an 8-PSK signal, what

are the baud rate and bit rate?

Solution Solutionor 7!" the baud rate is the sa#e as the band+idth,

+hich #eans the baud rate is 5000$ But in 7!" the bit

rate is 3 ti#es the baud rate, so the bit rate is 15,000 bps$


26/57


!uadrature amplitude modulation is a

com%ination of ASK and SK so that amaimum contrast %et,een each

signal unit (%it4 di%it4 tri%it4 and so on)

is achieved&

Note: Note:


27/57


Figure 5.14 The .-!A" and 2-!A" constellations

Fi 5 15 Ti d i f 2 !A" i l


28/57


Figure 5.15 Time domain for an 2-!A" signal

Fi 5 16 0 !A" ll i


29/57


Figure 5.16 0-!A" constellations

Fi 5 17 #it d % d


30/57


Figure 5.17 #it and %aud


31/57


Ta%le /& #it and %aud rate comparison

ModulationModulation UnitsUnits Bits/BaudBits/Baud Baud rateBaud rate Bit Rate

A!" F!" 2#$! A!" F!" 2#$! Bit 1 % %

4#$!" 4#&AM4#$!" 4#&AM 'i(it 2 % 2%

8#$!" 8#&AM8#$!" 8#&AM )ri(it 3 % 3%

16#&AM16#&AM &uad(it 4 % 4%

32#&AM32#&AM $enta(it 5 % 5%

64#&AM64#&AM *e+a(it 6 % 6%

128#&AM128#&AM e,ta(it 7 % 7%

256#&AM256#&AM -ta(it 8 % 8%


32/57


'ample 5 'ample 5

A constellation diagram consists of eight equally spaced

points on a circle. If the bit rate is 4800 bps, what is the

baud rate?

Solution Solution

%he consteation indicates 7!" +ith the points 45

derees apart$ !ince '3 = , 3 bits are trans#itted +ith

each sina unit$ %here&ore, the baud rate is 400 / 3 = 1600 baud


33/57


'ample 'ample

Compute the bit rate for a 1000-baud 16-QAM signal.

Solution Solution

1689 sina has 4 bits per sina unit sinceo'16 = 4$

%hus,

(1000)(4) = 4000 bps


34/57


'ample * 'ample *

Compute the baud rate for a 72,000-bps 64-QAM signal.

Solution Solution

6489 sina has 6 bits per sina unit sinceo' 64 = 6$

%hus,

'000 / 6 = 1',000 baud


35/57


5.2 Telephone Modems

"odem Standards


36/57


A telephone line has a %and,idth of

almost *.55 67 for data transmission&

Note: Note:

Figure 5 18 Telephone line %and,idth


37/57


Figure 5.18 Telephone line %and,idth


38/57


"odem stands for

modulator$demodulator&

Note: Note:

Figure 5 19 "odulation$demodulation


39/57


Figure 5.19 "odulation$demodulation

Figure 5 20 The 8 * constellation and %and,idth


40/57


Figure 5.20 The 8&* constellation and %and,idth

Figure 5 21 The 8 *%is constellation and %and,idth


41/57


Figure 5.21 The 8&*%is constellation and %and,idth

Figure 5.22 Traditional modems


42/57


Figure 5.22 Traditional modems

Figure 5.23 /0K modems


43/57


Figure 5.23 /0K modems


44/57


5.3 Modulation of Analog Signals5.3 Modulation of Analog Signals

Amplitude "odulation (A")

Frequency "odulation (F")

hase "odulation (")

Figure 5.24 Analog-to-analog modulation


45/57


Figure 5.24 Analog to analog modulation

Figure 5.25 Types of analog-to-analog modulation


46/57


g yp f g g


47/57


The total %and,idth required for A"

can %e determined from the %and,idthof the audio signal9

#:t ; * #:m&

Note: Note:

Figure 5.26 Amplitude modulation


48/57


g p

Figure 5.27 A" %and,idth


49/57


g

Figure 5.28 A" %and allocation


50/57


g


51/57


'ample 'ample

We have an audio signal with a bandwidth of 4 KHz.

What is the bandwidth needed if we modulate the signalusing AM? Ignore FCC regulations.

Solution Solution

n 9 sina re*uires t+ice the band+idth o& the

oriina sina:

B = ' x 4 "-. = "-.


52/57


The total %and,idth required for F"

can %e determined from the %and,idthof the audio signal9

#:t ; 5 #:m&

Note: Note:

Figure 5.29 Frequency modulation


53/57


Figure 5.30 F" %and,idth


54/57



55/57


The %and,idth of a stereo audio signal

is usually / K67& Therefore4 an F"

station needs at least a %and,idth of/5 K67& The FCC requires the

minimum %and,idth to %e at least *55

K67 (5&* "67)&

Note: Note:

Figure 5.31 F" %and allocation


56/57


' l .' l .


57/57

'ample . 'ample .

We have an audio signal with a bandwidth of 4 MHz.

What is the bandwidth needed if we modulate the signalusing FM? Ignore FCC regulations.

Solution Solution

n 9 sina re*uires 10 ti#es the band+idth o& the

oriina sina:

B = 10 x 4 9-. = 40 9-.

Documents

Forouzan Chp5