Minimum-shift keying

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. Similar to OQPSK, MSK is encoded with bits alternating between quadrature components, with the Q component delayed by half the symbol period.

However, instead of square pulses as OQPSK uses, MSK encodes each bit as a half sinusoid. Mapping changes in continuous phase. Each bit time, the carrier phase changes by ±90°.]]

The resulting signal is represented by the formula:

: <math>s(t) = a_{I}(t)\cos{\left(\frac