Time-frequency analysis of FSK digital modulation signals using the smooth lag-windowed Wigner-Ville distribution

Digital modulation signals such as FSK are time-varying signals that can be represented in the time-frequency representation. The smooth lag-windowed Wigner-Ville distribution (SLWWVD) is proposed as a method to obtain accurate time-frequency representation of FSK signals used in HF (high frequency) radio communications. Unlike existing time-frequency distributions such as the windowed Wigner-Ville distribution (WWVD) or the smooth windowed Wigner-Ville distribution (SWWVD), the proposed time-frequency distribution does not require priori knowledge of the signal modulation parameters such as the bit-duration and subcarrier frequencies. The algorithm generates the time-frequency representation directly based on the signal characteristics. Comparison based on mainlobe width and signal-to-interference ratio shows the SLWWVD generate accurate time-frequency representation for simulated and actual communication signals.