A closed-form of the upper bound for the outage probability is derived in Nakagami-m channel model to effectively estimate the impact on outage probability of cognitive relay networks from the wireless channel fading exponent. Firstly
joint constraints of the spectrum underlay sharing and the best relay selection criteria are analyzed. Then
the probability density function and cumulative distribution function of the signal to noise ratio at the secondary receiver node are obtained using the subsection integral. The conditional integral of the probability density function is performed
and the closed-form of the upper bound for the outage probability is derived according to the implication rules. Simulation results and comparisons with the traditional Rayleigh channel model show that the outage probability performance with fading exponent greater than one can be effectively estimated by the Nakagami-m channel model. Furthermore
the outage probability is reduced because the power of cognitive users is limited under the constraint of the interference temperature of primary users.
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