Outage performance of relay assisted hybrid overlay/underlay cognitive radio systems

In this paper, considering a relay assisted hybrid overlay/underlay cognitive radio system with peak interference power constraints for protecting the primary system, the upper bound of outage probability of secondary system with power limit is derived. The results show that the outage performance of secondary system improves with the increase of maximum tolerated interference power before a specific threshold, but it keeps unchanged after the threshold. The results also show that more relays can provide higher diversity gain to get better outage performance in this kind of cognitive radio system. It is also indicated that the outage performance of secondary system is affected by the activity behavior of primary network, and relay cooperation can decrease this kind of affection.