NAR AGC adaptive detection of nonoverlapping signals in noise with fluctuating power

In order to detect a deterministic signal in nonstationary noise with slow power fluctuations and obtain a constant false alarm rate, an automatic gain control (AGC) system is generally used at the input of the matched filter. But this AGC system does not differentiate between signal and noise and, in general, limits the amplitudes of strong signals. In this paper we present another AGC system possessing an interesting property called the noise alone reference (NAR) property. It means that the NAR AGC system acts only on the noise even in the presence of signal. The performance of the NAR AGC system is compared with that of the classical one in the presence of localized signals (as in communication problems) or unlocalized signals (as in radar and sonar problems). We show that the NAR AGC system provides better contrast and more reliable amplitude classification at the output of the receiver. Finally, computer simulation results are presented to show the effects of NAR AGC systems in adaptive detection.