Frequency Shift Keying (FSK), Minimum Shift Keying (MSK)

FREQUENCY SHIFT KEYING (FSK) , MINIMUM SHIFT KEYING (MSK)

Minimum Shift Keying (MSK) : The minimum frequency space that allows the 2 fsk representing symbols 0s and 1s. Thus CP (Continuous Phase) FSK signal with a deviation ratio if one half is defined as MSK.

Frequency Shift Keying (FSK) : Frequency Shift Keying is the as changing amplitude of the carrier signal with respect to the binary information or digital signal.

The advantages of Minimum Shift Keying :

MSK baseband waveform are smoother compared with QPSK MSK signals have continuous phase It does not have any amplitude variation

Frequency Shift Keying (FSK)

Transmitter

The ‘N’ successive bits are presented in parallel to digital to analog converter. These ‘N’ bits forms a symbol at the output of digital to analog converter. There will be total 2^N = M possible symbols. The symbol is presented every T_s = N T_b period. The output o digital to analog converter is given to a frequency modulator. Thus depending upon the value of symbol, the frequency modulator generates the output frequency. For every symbol, the frequency modulator produces different frequency output. This particular frequency signal remains at the output or one symbol duration. Thus for ‘M’ symbols, there are ‘M’ frequency signals at the output of modulator. Thus the transmitted requencies are f₀, f₁, f₂,………. F_M-1, depending upon the input symbol to the modulator.

Receiver

The M-ary PSM signal is given to the set of ‘M’ bandpass filters. The center frequencies of those filters are f₀, f₁, f₂,………. F_M-1,. These filters pass their particular frequency and alternate others. The envelope detectors outputs are applied to a decision device. The decision device produces its output depending upon the highest input. Depending upon the particular symbol, only one envelope detector   will have higher output. The outputs of other detectors will be very low. The output of the decision device is given to ‘N’ bit symbol in parallel. These bits are then converted to serial bit stream by parallel to serial converter. In some cases the bits appear in parallel. Then there is no use serial to parallel and parallel to serial converters.