FSK Bit Synchronization by Combined AM

A bit-synchronization method in a frequency-shift-keying (FSK) data channel has been investigated experimentally and results are presented. The bit-timing information is conveyed by a square wave, with a frequency of half the data bit rate, modulated onto the signal amplitude. It has been shown that for a system using a peak-peak-to-peak frequency deviation of 0.7 times the bit rate and a receiver bandwidth restricted to 1 times the bit rate, the minimum error rates are obtained for an amplitude modulation index of 0.1. Further, in order for the system to have a performance comparable with an ordinary FSK system with the same values of frequency deviation and receiver predetection bandwidth and with perfect timing available at the receiver, an additional signal power of 0.9 dB is needed.