Outage performance of cognitive relay networks with underlay spectrum sharing

In cognitive relay networks with underlay spectrum sharing, the transmission power of secondary users is strictly confined, for protecting primary users quality of service (QoS). Hence, the transmission performance of secondary users is difficult to be guaranteed. Outage probability is one of the most important measurements to evaluate system performance. In this paper, the outage performance is analyzed in the multiple-relay cognitive radio networks, which employs "selective-best relay amplify-and-forward (AF)" scheme. And the exact outage probability expressions in both broadcasting phase and relaying phase are obtained. Moreover, the joint probability density function is derived when the received signal-to-noise ratios (SNRs) are dependent. Based on that, the lower bound on outage probability is given, in the case that interference power to primary users is limited. Finally, through numerical simulation, the theoretical analysis is validated.