The Interception of Spread Spectrum Waveforms with the Amplitude Distribution Function
Geraniotis, Evaggelos A.
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Within the research effort related to unfriendly detection and interception of secure communications, an innovative concept called the Amplitude Distribution Function (ADF) is used to construct a detector that is an enhancement to the radiometer. The ADF is introduced and shown to be roughly the average probability distribution of a random process. The significance of ADF in the is that, under most spreading modulations, e.g. phase and frequency, the ADF is invariant. This suggests that a detector built around the ADF idea would be robust and of general purpose.<P>To develop the ADF methodology, a mathematical foundation is laid consisting of a sequence of definitions, lemmas, and theorems, an outline of which is included in the paper. The most significant result is that the ADF of signal plus noise is the convolution of the ADF of signal and the ADF of noise taken separately. These ideas are applicable through the definition of the Amplitude Moment Statistic (AMS), a statistical transform that converges to the moment generating function of the ADF. Hence, the AMS is the vehicle for indirectly estimating the ADF from observations. For the particular problem of detecting a modulated sinusoid in stationary Gaussian noise, a detector is developed around the AMS. The detector's performance is analyzed, compared with that of a radiometer, and shown superior for small (10) time-bandwidth products.<P>T