Generalized likelihood adaptive detection of signals deformed by unknown linear filtering in noise with slowly fluctuating power

The adaptive detection of signals deformed by unknown linear filtering in noise with slowly fluctuating power is considered. A generalized likelihood ratio test is derived. This test leads to two AGC receivers having the same detection performance. The first receiver is comprised of a classical AGC that cannot distinguish signal from noise and limits the amplitudes of strong signals. The other receiver incorporates a noise-alone reference (NAR) AGC which is insensitive to strong signals and guarantees a better contrast and more reliable amplitude classification. The output contrasts of the two receivers and of a third hypothetical perfect measurement likelihood ratio receiver are compared by means of computer simulations for different signal waveforms and different impulse responses of the linear filter deforming the signal. These simulations show that the performance of the second receiver is quite near to the ultimate performance achieved only theoretically by the third receiver. Moreover, unlike the quasi-NAR AGC receiver with the generalized matched and antimatched filters which was defined in a previous paper, the NAR property of the second receiver is not established at the expense of an increased false alarm probability.