Frequency-shift keying

Frequency-shift keying (FSK) encodes digital data by switching a carrier among distinct frequencies. A receiver recovers symbols by distinguishing those frequencies.

Frequency modulation: A modulation method that conveys information by varying a carrier wave’s instantaneous frequency. FSK uses discrete frequency changes, a digital form of frequency modulation.
Amplitude-shift keying: A digital modulation method that represents symbols by selecting among carrier amplitudes. ASK changes amplitude where FSK changes frequency.
Frequency-shift keying in telecommunications: The use of FSK to transmit digital data over wired or wireless communication channels. FSK has carried data across radio links, telephone lines, and other constrained channels.
Carrier wave: A periodic signal whose properties are varied to convey information. FSK communicates by selecting among frequencies of a carrier wave.
Spectral efficiency: The rate of information transmission per unit bandwidth, usually measured in bits per second per hertz. FSK’s frequency spacing and symbol rate determine how efficiently it uses spectrum.
Binary frequency-shift keying: An FSK scheme that represents binary symbols with two distinct frequencies. It is the simplest FSK form: one frequency per binary value.
Phase-shift keying: A digital modulation method that represents symbols by selecting among carrier phases. PSK encodes symbols in phase rather than in distinct frequencies.
Bell 103 modem: A 300-bit-per-second full-duplex modem standard that uses audio-frequency FSK over telephone lines. Bell 103 is a canonical example of FSK transporting data through voice-band telephone circuits.
Frequency: The number of cycles of a periodic process completed per unit time. The selected frequency is the signal property that carries each FSK symbol.
Bandwidth (signal processing): The range of frequencies occupied by a signal or passed by a system. Separating FSK tones improves detection but can increase occupied bandwidth.

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