On FSK Demodulation Technology With Improved Frequency Offset Immunity Performance

The Frequency Shift Keying modulation is widely used in HF digital communication. This paper is mainly on the FSK demodulation algorithms suitable for HF frequency hopping signal interception. Firstly, the spectrum properties of FSK signal are introduced and the principle of spectrum estimation for FSK signal detection is discussed in detail. Secondly, a DSTFT(Discrete Short Time Fourier Transform )-based demodulation method for the 2FSK signal is studied and algorithms for symbol synchronization and symbol decision are analysed. An improved algorithm for symbol synchronization and symbol decision are proposed. Their performance at different level of SNR and frequency offset are discussed by simulations. At last, this paper analyses the delay correlation properties of 2FSK signal, and proposes a new algorithm for symbol synchronization, which shows better performance when frequency offset exists.