Look up: MSK

1. MSK
   Minimum Shift Keying. A radio modulation technique. MSK is a form of FSK (frequency shift keying) or phase shift keying (PSK), MSK uses changes in phase to represent 0's and 1's, with the phase shift used depending on the previous phase value. MSK acts like FSK with minimum difference between the frequencies of the two FSK signals, resulting in a power spectral density that falls off much faster than QPSK (quadrature phase shift keying) so MSK can operate in a smaller radio bandwidth than QPSK. GSM uses a variant of MSK and QPSK, GMSK (Gaussian MSK)
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