Impact of Maximum Transmit Power Limit on the First-Order and Second-Order Performance of Cognitive Opportunistic Relaying

This paper focuses on the first-order and second-order performance of dual-hop underlay cognitive radio systems with opportunistic relaying（UCR-OR） over independent and non-identically distributed（i.ni.d）Rayleigh fading channels.For the UCR-OR systems,the tolerable maximum interference power（TMIP） Q at primary users（PUs） and the allowable maximum transmission power limit（AMTP） Pmax at secondary users（SUs）are considered,simultaneously.We first obtain the closed-form solutions to the first-order performance such as outage probability,average symbol error ratio（SER）,and ergodic capacity（EC）.Secondly,we investigate the second-order statistical performance,i.e.,average outage rate（AOR） and average outage duration（AOD）.With the consideration that in practice implementation the receiver performance is primarily influenced by the signalto-noise ratio（SNR）(not the signal envelope),the second-order statistical performance is investigated based on the equivalent instantaneous end-to-end SNR.Finally,we present the detailed performance comparison analysis of UCR-OR systems by defining a random variable μ=Pmax/Q.The results show that the effect of μ on the first-order and second-order performances is different greatly.For the first-order performance,the performance gap is negligible when the value of μ is relatively large.However,for the second-order one,the gap is distinct.