Advanced LPI (Low-Probability-of-Intercept) Intercept Detector Research.

摘要

We examine in this report the problem of wideband detection of a spread spectrum signal from an interceptor's viewpoint; our aim is to derive, evaluate and compare various detector structures whose purpose is to intercept a spread-spectrum communication transmitter. The transmitter under surveillance employs a variety of modulation/spreading/transmission techniques which are invariably assumed to emit the message-bearing signal in deep background noise or interference. Thus, the challenging task of the intercepting detector is to reveal as best as possible any transmission of the unknown spread waveform in the presence of an obscuring noisy environment. Naturally, the degree of success achieved by the interceptor when detecting the presence of the communicator's spread signal depends on the amount of information available to him regarding the structure of that signal. At one extreme, the interceptor's most fortunate situation would be to acquire the spreading code itself ('crack' the code). If this is too demanding, he must settle for less, such as approximate knowledge of the signal's carrier center frequency, code rate, code epoch, spreading bandwidth, etc., or a subset thereof. At the other extreme, he might know almost nothing, in which case, he could resort to a simple energy discriminator device (i.e., radiometer) since it is, on many occasions, a low-SNR asymptotically optimal detector. In this report our main interest is to investigate the possibility that the interceptor could do better by optimally processing whatever information is available to him between the two extremes cited above.