Transcript Modulation_Techniques

Modulation?
Modulation is the addition of information (or the signal) to an
electronic or optical signal carrier.
In electronics, modulation is the process of varying one or more properties of a
high frequency periodic waveform, called the carrier signal, with respect to a
modulating signal.
In telecommunications, modulation is the process of conveying a message
signal, for example a digital bit stream or an analog audio signal, inside another
signal that can be physically transmitted.
Modulation Techniques
Carrier frequency
A carrier frequency is an electronic wave that
is combined with the information signal and carries it across the
communication channel.
A carrier signal is a single frequency that is used to carry the intelligence
(data).
For digital, the intelligence is either a 1 or 0. When we modulate the
carrier , we are changing its characteristics to correspond to either a 1 or
0.
Modulation aspects and technologies
There are three aspects of the basic carrier wave that can be
modulated:
-Amplitude
-Frequency
-Phase (or angle)
Modulation aspects and technologies
(contd…)
The three corresponding techniques are as follows:
-Amplitude Modulation(AM)
-Frequency Modulation(FM)
-Phase Modulation(PM)
Other modulation techniques are:
- Amplitude shift keying(ASK)
- Frequency shift keying(FSK)
- Phase shift keying(PSK)
Amplitude Modulation (AM)
Amplitude modulation (AM) is a method of impressing data onto an alternatingcurrent (AC) carrier waveform.
Amplitude Modulation (AM) contd..
In the above example, a 1 is represented by the presence of the carrier for a
predefined period of 3 cycles of carrier. Absence or no carrier indicates a 0.
In AM, the carrier itself does not fluctuate in amplitude. Instead, the
modulating data appears in the form of signal components at frequencies
slightly higher and lower than that of the carrier.
Frequency Modulation (FM)
Frequency modulation (FM) is a method of impressing data onto an
alternating-current (AC) wave by varying the instantaneous frequency of the
wave.
Frequency Modulation (FM) contd…
Frequency Modulation modifies the frequency of the carrier to represent the 1s or
0s.
In the above example, a 0 is represented by the original carrier frequency and
a 1 by a much higher frequency ( the cycles are spaced closer together).
Phase Modulation (PM)
Phase modulation (PM) is a method of impressing data onto an alternatingcurrent (AC) waveform by varying the instantaneous phase of the wave.
Phase Modulation (PM) contd…
The carrier phase is switched at every occurrence of a 1 bit but remains
unaffected for a 0 bit.
The phase of the signal is measured relative to the phase of the preceding bit.
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