Application of Sub-Sample Dithering to Reduce Probability of Signal Detection

Abstract

Communications Security is Achieved in the Physical Layer with the utilization of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI) Modulation Techniques. Standard modulation techniques have cyclical time varying properties that can be exploited by signals intelligence (SIGINT) for signal detection, traffic analysis, and signal interception. There is a large body of analysis on wide-sense cyclostationary features of these modulation techniques with the conclusion that the primary cause of periodic cyclostationary features is the modulation symbol rate. Deterministic variability in the symbol rate can be used to reduce or eliminate cyclostationary features. Several techniques have been proposed, including DAC clock dithering. In this paper we provide a description of a polyphase resampler application to provide symbol rate dithering and an analysis of the dithering on the second, and higher order cyclostationary features. Multiple modulation types are included in the analysis. ADC de-dithering is typically not an option at the receiver - the delays inherent in standard receiver architectures prohibit real-time control of the ADC during signal demodulation while the polyphase resampler can be applied digitally within the receiver at matched filter sample rates.