The present invention estimates the maximum likelihood series of the output of the plurality of the complex differential discriminator so as to improve even the reception sensitivity if not the, more particularly, to modulation index estimated frequency deviation as a technique related to a receiving method and apparatus of the modulated signal (MLSE, Maximum It relates to using Likelihood Sequence Estimation) method, to a method and apparatus for recovering a frequency-shift keying signal (FSK, frequency shift Keying).
Receiver of the frequency shift modulated signals of the invention is a complex differential discriminator (Complex Differential Discriminator) and the complex differential having a plurality of order having a plurality of order using a complex conjugate (Complex Conjugate) of the baseband signal of the FSK received signal by applying a maximum likelihood sequence estimation (MLSE, maximum likelihood sequence estimation) method on the output value of the discriminator comprises a recovery circuit for recovering a symbol.