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What Is Modulation in Communication?

In communication systems, modulation is the technique of superimposing one signal, known as the message signal, on top of another, known as the carrier signal. In other words, modulation is the process by which a property or parameter of the carrier signal is varied in proportion to the message signal. Modulation is performed by the transmitter, while the reverse process, known as demodulation, is performed by the receiver.

Purpose
- Communication channels, such as those in telephone cable, Ethernet cable and optical fiber, only operate with certain frequency bands. Modulation converts a signal from its original frequency band, or baseband, to the operating range of the communication channel. Modulating different signals to different frequency bands allows them to be transmitted simultaneously on a single communications channel.
Amplitude Modulation
- Many different types of modulation technique exist, but they all fall into one of three categories, known as amplitude modulation, frequency modulation and phase modulation. Amplitude modulation refers to modulation is which the amplitude, or strength, of the carrier signal is modulated, or varied, in proportion to the message signal, while keeping the frequency and phase constant. The changes in signal strength may represent the sounds to be reproduced by a loudspeaker or the light intensity of the picture elements, or pixels, on a TV screen among other applications.
Frequency Modulation
- Frequency modulation refers to modulation in which the frequency of the carrier signal is modulated while keeping the amplitude and phase constant. The fact that the amplitude of the carrier signal does not change means that frequency modulation is less susceptible to noise than amplitude modulation and improves the overall signal-to-noise ratio of a communications system. Frequency modulation is often used at very high frequencies, between 30 and 300 megahertz, for high fidelity radio broadcasts of speech and music.
Phase Modulation
- Phase modulation refers to modulation in which the phase of the carrier signal is modulated, while keeping the amplitude and frequency constant. In other words, phase modulation is a technique for impressing data onto an alternating current waveform, by modulating the phase of the wave. Phase is a measured of how far the wave is through its cycle; at one quarter of its cycle, its phase is 90 degrees, at one half of its cycle its phase is 180 degrees and so on. Phase modulation can easily be adapted to data modulation applications and is commonly used in remote controls.

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