Modulation is characterized as converting data to radio waves by adding it to an optical or electronic carrier signal. In turn, a carrier signal has a steady waveform – frequency and constant amplitude, or height. The primary modulation concept is as follows: the original form of a message signal cannot be transmitted without getting distorted through the channel. Hence, the message signal should be superimposed over a carrier with high energy, amplitude, and frequency. The main aim of modulation in terms of a communication system is to generate a modulated signal adapted to the transmission channel’s characteristics. For instance, in radio communications, the transmission systems need modulation for the message to be transferred to the available radio channel of high frequency. Modulation provides an opportunity of sending signals over the passband frequency range. A single channel simultaneously transmits multiple signals in case each has its frequency range, and the frequency ranges used by them are different (“Modulation,” n.d.). Moreover, modulated signals allow using smaller antennas.
The three basic modulation types are amplitude modulation, phase modulation, and frequency modulation. Each of them has its main characteristics defining its peculiarities. Amplitude modulation is characterized by changing its amplitude with each symbol. It is frequency constant and has relatively low bandwidth requirements. Finally, its main advantage is that amplitude modulation is highly susceptible to interference, and therefore, its susceptibility to noise is very high. It is typically used for digital data transmission over optical fiber. In amplitude modulation, one binary is characterized by the carrier presence at constant amplitude, whereas another binary digit is characterized by the carrier absence (Tipper, n.d., p. 7). In turn, phase modulation is defined by changing phase with each symbol, higher complexity, and being robust against interference. Frequency modulation is known for changing frequency for each symbol and its need for a larger bandwidth.
References
Modulation. (n.d.).
Tipper, D. (n.d.). Digital modulation.