Multiple-Access Interference Mitigation and Iterative Demodulation of CPFSK in Asynchronous Slow FHSS Systems

In slow frequency-hop spread spectrum with nonorthogonal spreading sequences, multiple-access interference (MAI) occurs whenever two users transmit in the same frequency band. Schemes to mitigate such MAI have been previously developed for such systems when binary frequency-shift keying is used for modulation. It is desirable to instead use continuous-phase frequency-shift keying (CPFSK) to improve spectral efficiency, however, CPFSK is not a memoryless modulation and this complicates the problem of MAI mitigation. Previous work on CPFSK has been limited to ignoring the effects of MAI. In this paper, we develop an interference mitigation scheme for a slow FHSS system employing CPFSK and present performance results that show that our scheme significantly improves performance, especially in the presence of a strong interferers.