  Energy detection is a widely used method of spectrum sensing in cognitive
radio and Radio Detection And Ranging (RADAR) systems. This paper is devoted to
the analytical evaluation of the performance of an energy detector over Weibull
fading channels. This is a flexible fading model that has been shown capable of
providing accurate characterization of multipath fading in, e.g., typical
cellular radio frequency range of 800${/}$900 MHz. A novel analytic expression
for the corresponding average probability of detection is derived in a simple
algebraic representation which renders it convenient to handle both
analytically and numerically. As expected, the performance of the detector is
highly dependent upon the severity of fading as even small variation of the
fading parameters affect significantly the value of the average probability of
detection. This appears to be particularly the case in severe fading
conditions. The offered results are useful in evaluating the effect of
multipath fading in energy detection-based cognitive radio communication
systems and therefore they can be used in quantifying the associated trade-offs
between sensing performance and energy efficiency in cognitive radio networks.
