  This paper proposes simple moment based spectrum sensing algorithm for
cognitive radio networks in a flat fading channel. It is assumed that the
transmitted signal samples are binary (quadrature) phase-shift keying BPSK
(QPSK), Mary quadrature amplitude modulation (QAM) or continuous uniformly
distributed random variables and the noise samples are independent and
identically distributed circularly symmetric complex Gaussian random variables
all with unknown (imperfect) variance. Under these assumptions, we propose a
simple test statistics employing a ratio of fourth and second moments. For this
statistics, we provide analytical expressions for both probability of false
alarm (Pf) and probability of detection (Pd) in an additive white Gaussian
noise (AWGN) channel.We confirm the theoretical expressions by computer
simulation. Furthermore, under noise variance uncertainty, simulation results
demonstrate that the proposed moment based detector gives better detection
performance compared to that of energy detector in AWGN and Rayleigh fading
channels.
