MODULATIE DIGITALA

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



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 .



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



$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 (



+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.



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.





• 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).



7PS&





Applications on 3&'

The !ireless ;A< standard



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.

http://en.wikipedia.org/wiki/IEEE_802.11

http://en.wikipedia.org/wiki/Wi-Fi

http://en.wikipedia.org/wiki/Wi-Fi

http://en.wikipedia.org/wiki/IEEE_802.11



=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



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.



$&' 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

http://dsp.stackexchange.com/questions/3400/psk-vs-fsk-for-noise-immunity







E b /N 0 (the energy per bit to noise power spectral density ratio



T*AN' 78U

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MODULATIE DIGITALA