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Modulation detection of underwater acoustic communication signals through cyclostationary analysis

Modulation detection is important to many military communication and electronic warfare applications. Cyclostationary analysis has been proven to be an effective means to detect and identify modulation types of RF signals. It is highly desired to apply cyclostationary analysis to underwater acoustic communication signals to conduct modulation detection. However, due to the complex environment encountered by underwater acoustic communication, the cyclostationary features of such signals are significantly different from those of their RF counterparts. In this paper, we analyze the applicability of cyclotationay analysis in underwater acoustic communication signals for modulation detection purpose. Due to the severe and varying Doppler shift and phase noise, the cyclostationary features of underwater acoustic communication signals require very high resolution. Employing previously developed low-complexity short-term dynamic resolution cyclostationary analysis algorithm, we first obtain a meaningful spectrum correlation function (SCF) feature with sufficient resolution in the cyclic frequency range of interest. We then extract a simple parameter, namely the cyclic frequency/frequency peak ratio (CFFPR), to identify the modulation schemes of the signals. This feature proves to be statistically significant and stable in distinguishing BPSK modulation and QPSK modulation. Real experimental data collected at sea are used to validate the effectiveness of the proposed algorithm.