Minimum-shift keying
From Wikipedia, the free encyclopedia
Minimum-shift keying (MSK) is a type of continuous phase frequency-shift keying.
Similarly to OQPSK, MSK is encoded with bits alternating between quarternary components, with the Q component delayed by half a bit period. However, instead of square pulses as OQPSK uses, MSK encodes each bit as a half sinusoid. This results in a constant-modulus signal, which reduces problems caused by non-linear distortion.
The resulting signal is represented by the formula
<math>S(t) = a_{I}(t)\cos{(\frac{{\pi}t}{2T})}\cos{(2{\pi}f_{c}t)}+a_{Q}(t)\sin{(\frac{{\pi}t}{2T})}\sin{(2{\pi}f_{c}t)}</math>
where <math>a_{I}(t)</math> and <math>a_{Q}(t)</math> are the square pulses as shown in QPSK.
A similar modulation scheme is Gaussian minimum shift keying, which uses Gaussian instead of sinusoidal pulse shapes.
