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Transcript of digital modulation.pptx
7/27/2019 digital modulation.pptx
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DIGITAL MODULATIONTECHNIQUES
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Amplitude shift keying (ASK)Frequency shift keying (FSK)
Phase shift keying (PSK)
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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.
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FSK :
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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.
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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
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PSK :
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Applications:
THE STANDARD WIRELESS LAN, WHICH WE USE TO PLAY PC GAMES IN HOSTELS
USES DIFFERENT TYPES OF PSK’S
BLUETOOTH 2.0 ( DQPSK)
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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.
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ASK :
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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
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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
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THANK YOU,SAI KIRAN, C1101-B29