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Modulation is a key process in the communication system. The idea behind the communication system is, to transmit the information through a long distance. The signals which carry the information is known as the base band signal. This signal may lose some of the information while transferring. To overcome this, we use modulations. It is a kind of mixing or superposition of two signal waves for effective transmission.

Modulation Definition

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Modulation is a process of superposition carrier signal with high frequency and modulating signal by adjusting the properties of carrier signal according to the modulating signal. The modulating signal includes all information which is going to transmit from one place to another. The device used for modulation is known as modulator.

Types of Modulation

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The main classification of modulation is
  • Analog modulation
  • Digital modulation

In analog modulation, the modulating signal that is the signal containing the information is in the form of analog. But in the case of digital modulation, the signal is in the form of digital. The detailed description is given in the next section.

Analog Modulation

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As mentioned earlier in analog modulation, analog signal is super impose with a carrying signal and transmit from one place to another. Amplitude modulation, frequency modulation and phase modulation are the important analog modulations.

1. Amplitude modulation:
In the case of amplitude modulation, amplitude of the carrier wave will change according to the signal wave. In this modulation, the amplitude of the carrier wave is not dependent.

2. Frequency modulation:
In frequency modulation, the frequency of the carrier wave is changing according to the information wave or signal wave. Given figure shows the changes in amplitude and frequency modulation of a wave.

Amplitude Frequency Modulation

3. Phase modulation:
Phase modulation is nothing but the changes in the phase of the carrier wave according to the signal while transmission.

Digital Modulation

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In digital modulation, the signal wave is in the form of digital signal. The carrier signal is changing such a way that the phase matching with that of the modulating wave. Digital modulation is commonly seen in computers. The important digital modulation is pulse code modulation and delta modulation

Pulse Modulation

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Pulse wave modulation is defined as the process of sampling the carrier signal according to the information signal. Mainly there are four types of pulse modulation. These are, pulse amplitude modulation, pulse position modulation, pulse width modulation and pulse code modulation. The given figure will helps to understand this concept.

Pulse Modulation

Modulation Index

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Modulation index is nothing but the depth of the modulation. It is given as the ratio between the amplitude of the signal wave and the amplitude of the carrier wave. If the signal amplitude is high, the modulation index is also high. It is denoted by m.

The mathematical expression for modulation index is,
m = $\frac{E_{m}}{E_{c}}$
$E_{m}$ is the amplitude of the modulating wave,
$E_{c}$ is the amplitude of the carrier wave.


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Demodulation is the process of extracting the signal wave from the modulating carrier wave without any attenuation of data. This process is just opposite to the modulation. In the normal demodulation process, the noise and type of channel reduces the signal quality. To improve the quality of output signal so many methods are implemented.