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An example of binary FSK. Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. [1]
When a digital signal is to be transmitted over an analogue baseband channel, the modulation technique is termed line coding. Several keying techniques exist, including phase-shift keying, frequency-shift keying, and amplitude-shift keying. Bluetooth, for example, uses phase-shift keying to exchange information between devices.
Multiple frequency-shift keying (MFSK) is a variation of frequency-shift keying (FSK) that uses more than two frequencies. MFSK is a form of M-ary orthogonal modulation , where each symbol consists of one element from an alphabet of orthogonal waveforms.
Some examples of constant envelope modulations are as FSK, GFSK, MSK, GMSK and Feher's IJF - All constant envelope modulations allow power amplifiers to operate at or near saturation levels. [1] Although, the power spectrum efficiency of a non-constant amplitude envelope [ 2 ] is always higher than that of a constant envelope modulation.
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The frequencies may represent digits, such as '0' and '1'. FSK is widely used in computer modems such as fax modems, telephone caller ID systems, garage door openers, and other low-frequency transmissions. [1] Radioteletype also uses FSK. [2] Frequency modulation is widely used for FM radio broadcasting.
In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s by Collins Radio employees Melvin L. Doelz and Earl T. Heald. [1]
However, many modulation schemes make this simple approach impractical because most signal power is devoted to modulation—where the information is present—and not to the carrier frequency. Reducing the carrier power results in greater transmitter efficiency. Different methods must be employed to recover the carrier in these conditions.