minimum shift keying (MSK)
Minimum Shift Keying (MSK) is a special form of Frequency Shift Keying(FSK) that operates very bandwidth-efficiently, resulting in more efficient utilization of the available bandwidth.
In MSK keying, the modulation index, which is determined from the ratio of the angular frequency of the frequency deviation to the angular frequency of the modulation signal, is 0.5; in contrast, the modulation index of Orthogonal Frequency Shift Keying (OFSK) is 1. Since a frequency changeaccompanies each bit period, Minimum Shift Keying (MSK) is also referred to as Fast Frequency Shift Keying( FFSK).
With the MSK method, frequency shift keying always occurs at the same phase position.