7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 1/13

DIGITAL MODULATIONTECHNIQUES

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 2/13

Amplitude shift keying (ASK)Frequency shift keying (FSK)

Phase shift keying (PSK)

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 3/13

FREQUENCY SHIFT KEYING

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital

information is transmitted through discrete frequency changes of a carrier wave Frequency is varied to represent a 1 or 0

Frequency during bit duration is constant

Amplitude and phase remain constant

Avoids most of noise problems of ASK

Bandwidth required is equal to baud rate + frequency shift. (Larger bandwidth

requirement)

***Baud rate is the number of signal units per second that are required to represent bits

***Bandwidth, in terms of digital communication, is amount of data transferred from one

point to another in a given time period.

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 4/13

FSK :

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 5/13

Applications:

Most early telephone-line modems used audio frequency-shift keying (AFSK)

Caller ID devices

Storing data in audio casettes

Amateur Radios

Remote metering applications.

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 6/13

PHASE SHIFT KEYING

Phase-shift keying (PSK) is a digital modulation scheme that conveys

data by modulating, the phase of a reference signal (the carrier wave

)

Phase of carrier is varied to represent1 or 0

Peak amplitude and frequency remain constant

Phase remains constant during bit duration Not susceptible to noise degradation as ASK. i.e; robust against

interference

More complex

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 7/13

PSK :

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 8/13

Applications:

THE STANDARD WIRELESS LAN, WHICH WE USE TO PLAY PC GAMES IN HOSTELS

USES DIFFERENT TYPES OF PSK’S

BLUETOOTH 2.0 ( DQPSK)

 

-

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 9/13

AMPLITUDE SHIFT KEYING

Amplitude-shift keying (ASK ) is a form of modulation that represents digital data a

variations in the amplitude of a carrier wave

Amplitude of carrier signal is varied to represent a1 or 0

Frequency remain constant while amplitude is changed

Amplitude remains constant during bit duration

Highly susceptible to noise interference since noise usually affects amplitude

Minimum bandwidth required is equal to baud rate. (low-bandwidth requirement)

***Baud rate is the number of signal units per second that are required to represent bit

***Bandwidth, in terms of digital communication, is amount of data transferred from on

point to another in a given time period.

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 10/13

ASK :

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 11/13

Applications:

The ASK technique is commonly used :

to transmit digital data over optical fiber

For LED transmitters, binary 1 is represented by a short pulse of light andbinary 0 by the absence of light.

For Laser transmitters

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 12/13

ASK V/S FSK:

ASK IS MORE PRONE TO NOISEINTERFERENCE

LOW BANDWITH REQUIREMENT, WHICHIS EQUAL TO BAUD RATE.

FREQUENCY REMAINS CONSTANT

o LESS PRONE TO NOISE INTERFERENCE

o LARGER BANDWIDTH REQUIREMENT, WIS EQUAL TO BAUD RATE + FREQUENCY

SHIFT

o AMPLITUDE REMAINS CONSTANT

ASK FSK  

7/27/2019 digital modulation.pptx

http://slidepdf.com/reader/full/digital-modulationpptx 13/13

THANK YOU,SAI KIRAN, C1101-B29