Comparison of Optimum Demodulation of CPFSK With Limiter-Discriminator Performance in Jamming, Interference and Noise

Abstract

This study examines the potential performance benefits and implementation issues associated with using a maximum likelihood demodulator in place of the commonly employed limiter-discriminator to demodulate a Continuous-Phase Frequency Shift Keyed (CPFSK) signal in jamming, interference and thermal noise.The comparison is based on the results of running detailed computer simulations. The types of jamming that are considered include noise, tone, and follower jamming. The results show that the optimum demodulator can perform significantly better than the limiter-discriminator, ranging from an improvement of approximately 2 dB in thermal noise to as much as 7 dB in certain types of jamming environments. The results also show that the optimum demodulator provides better immunity against adjacent channel interference. In addition to considering performance advantages of optimum demodulation, the practicality of implementing the optimum demodulator is also addressed. Results are presented showing the relationship between data rate and the size and cost needed to implement the optimum demodulator using FPGA technology.