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8/16/2019 MODULATIE DIGITALA
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An Najah National University
Telecommunication Engineering Department
comparison of binary shift keying techniques
Prepeared by : Suhad Malayshi
Raghad foqha
Ola mashaqi
submitted to Dr. Allam Mousa
8/16/2019 MODULATIE DIGITALA
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What is digital modulation?
The techniques used to modulate digital information so that it can be transmitted
ia micro!ae" satellite or do!n a cable pair are di#erent to that of Analogue
transmission .
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Metode fundamentale de modulare digitala:
Binary Amplitude shift keying
on!o" keying# adantage: simplicity %disadantage: AS& isery susceptible to noise
interference' noise usually(only)a#ects the amplitude"
therefore AS& is themodulation technique most
a#ected by noise%application: AS& is used
to transmit digital data oeroptical *ber
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$re%uency &hift 'eying+requency Shift &eying (+S&) is a frequency modulationscheme (conveys information over a carrier wave byvarying its instantaneous frequency) in !hich digitalinformation is transmitted through discrete frequencychanges of a carrier !ae (
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+S& is the most common form of digital modulation in the highfrequency radio spectrum" and has important applications intelephone cct.
A modem conerts the binary data from a computer to +S& fortransmission oer telephone lines" cables" or !ireless media.
Shifts are usually in the range of ,- to ---/0.
demodulation:
demodulator must be able to determine !hich of t!o possiblefrequencies is present at a gien time
advantage:
+S& is less susceptible to errors than AS& ' receier loo1s for
speci*c frequency changes oer a number of interals" sooltage (noise) spi1es can be ignoreddisadvantage:
+S& spectrum is 2 3 AS& spectrum
application:
oer oice lines" in high4freq. radio transmission" etc.
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B$&' Binary $re%uency &hift 'eying #
)eneral form of B$&' is :
=
0),2cos(1),2cos()(
2
1
binaryt f Abinaryt f At s
π
π
*ere + in B$&'+ the ,-. is called the mark fre%uency and the,/. is called the space fre%uency(
The optical 0eld of $&' form is :
The total B(1 of $&' isgiven 2y :25f 6 27" !here 7 is the bit rate.
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• Phase4shift 1eying (PS&) is a method of digital communication in
!hich the phase of a transmitted signal is aried to transmitinformation. There are seeral methods that can be used to do PS&.
3hase &hift 'eying
• The simplest PS& technique is called binary phase4shift 1eying(7PS&). 8t uses t!o opposite signal phases (- and 9- degrees).
The digital signal is bro1en up time!ise into indiidual bits (binarydigits).
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Applications on 3&'
The !ireless ;A< standard
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A 4ireless local area net4ork (15AN)lin1s t!o or more deices using some!ireless distribution method "and usuallyproiding a connection through an accesspoint to the !ider 8nternet. This gies users
the mobility to moe around !ithin a localcoerage area and still be connected to thenet!or1. Most modern =;A<s are basedon 8>>> 9-2. standards" mar1eted under
the =i4+i brand name. =;A<s !ere oncecalled ;A=<s (for local area !irelessnet!or1) by the Department of Defense.
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=ireless ;A<s hae become popular in thehome due to ease of installation" and in
commercial comple3es o#ering !irelessaccess to their customers? often for free
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Dierences+S& s PS&
less susceptible to interference .
easier to generate !ith modern electronics
7+S& requires t!ice the band!idth of 7PS&
power fsk is better compared to psk
but
it is e3pensie
AS& Simplicity
lo! implementation costs
consering po!er.
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$&' vs 3&' noise immunity6
you need to de*ne a quantitatie metric that has aleel playing *eld bet!een the t!o" such asmeasuring the systems@ bit4error rate ersus thesignal to noise ratio
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E b /N 0 (the energy per bit to noise power spectral density ratio