Detection of Unknown Signals in a Fading Environment

In this letter we consider the effect of combined slow and fast fading on the energy detection. We model the received signal power distribution and propose a simplified approximation to this distribution. The approximation allows us to derive the distribution of the decision variable at the detector´s output in closed-form. By using the suggested distribution, we find that in the block fading channel the impact of slow fading is not significant. In the case of multiple independent fast fading realizations with commo.n slow fading value we can show how the slow fading starts to dominate the detection performance.