  In this paper, we investigate the performance of cooperative spectrum sensing
(CSS) with multiple antenna nodes over composite and generalized fading
channels. We model the probability density function (PDF) of the
signal-to-noise ratio (SNR) using the mixture gamma (MG) distribution. We then
derive a generalized closed-form expression for the probability of energy
detection, which can be used efficiently for generalized multipath as well as
composite (multipath and shadowing) fading channels. The composite effect of
fading and shadowing scenarios in CSS is mitigated by applying an optimal
fusion rule that minimizes the total error rate (TER), where the optimal number
of nodes is derived under the Bayesian criterion, assuming erroneous feedback
channels. For imperfect feedback channels, we demonstrate the existence of a
TER floor as the number of antennas of the CR nodes increases. Accordingly, we
derive the optimal rule for the number of antennas that minimizes the TER.
Numerical and Monte-Carlo simulations are presented to corroborate the
analytical results and to provide illustrative performance comparisons between
different composite fading channels.
