A self synchronizing digital FSK demodulator for applications with transmission rate comparable to the carrier frequencies

Frequency shift keying (FSK) finds application in low frequency transmission over band limited audio frequency channels, such as calling number identification, a service currently provided by telephone service providers. Conventional FSK demodulation techniques work well, when the transmitted frequencies are significantly higher than the baud rate. However, when the baud rate is comparable to the transmission frequencies, their implementation becomes prohibitively costly. This paper describes a mixed signal approach to FSK demodulation suitable in particular to the decoding of this type of signal, based on a self synchronizing digital FSK demodulator. The self-synchronizing behavior of the FSK demodulator is also analyzed.