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In this paper, we investigate the performance of asymmetric radio frequency (RF) and free space optical (FSO) dual-hop cooperative relay network along with a direct RF link between source and destination. The FSO link experiences double generalized Gamma turbulence in the presence of the generalized non-zero boresight pointing errors, and RF links experience non-identically distributed Nakagami-m fading. Moreover, considering both cognitive radio and non-cognitive scenarios, a partial relay selection (PRS) strategy has been employed. Furthermore, both relay selection and underlay power restriction are governed with the outdated channel state information (CSI). We also assume both heterodyne and intensity modulation/direct detection methods in the FSO receiver. Under the assumption of amplify-and-forward relaying and PRS, we derive closed-form expressions for outage probability (OP) of both scenarios, while bit-error probability and ergodic capacity of the non-cognitive scenario are also obtained. The asymptotic expressions of OP and diversity order of this network are derived for both perfect CSI and outdated CSI cases. It is demonstrated that the diversity order is a function of the fading severity of the RF links, turbulence parameters of the FSO link, and pointing error, regardless of interference channel parameter of the primary user. INDEX TERMS Cognitive radio network, double generalized Gamma, free space optical communications, non-zero boresight pointing errors, outdated channel state information, partial relay selection. The associate editor coordinating the review of this manuscript and approving it for publication was Wei Wang. the log-normal, log-normal Rician, I-K distribution, Malaga, Gamma-Gamma (G 2) and Double-Weibull [2]. The G 2 is widespread distribution for modeling FSO turbulence channel in the literature, however, G 2 distribution is not completely match with experimental data particularly in tails [2]. Recently, a novel statistical model called Double Generalized Gamma (DGG) distribution has been introduced by [2], where irradiance fluctuations are given by production of small-scale and large-scale fluctuations, both of which are function of generalized Gamma distribution. This model precisely describes the signal propagation under all conditions, (i.e., from weak to strong turbulence conditions) added to the fact that it generalizes other distributions. B. NON-ZERO BORESIGHT MISALIGNMENT Additionally, the building sway phenomenon leads to the vibration of transmitter beam that causes a misalignment between transmitter and receiver known as pointing error.

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Fast reliable spectrum sensing (SS) is a crucial problem in the cognitive radio systems. To address this issue, cyclostationarity-based detection methods, which are generally more complex but more reliable than energy detection methods, have been proposed. This paper presents a new method to detect the presence of the second-order cyclostationarity in the OFDM-based primary user (PU) signals. The proposed method has a low computational complexity, while it presents a close performance as compared to the well-known GLRT-based Dandawaté-Giannakis's method. Moreover, since the proposed low-complexity method is robust against the noise uncertainty, it can be a good alternative to the energy detection method. In order to be able to perform the hypothesis test, we derive the asymptotic distribution of the test statistic under the null hypothesis. We further propose some cooperative spectrum sensing methods to improve the detection performance. An approximate threshold selection method is proposed for performing statistical test at the fusion center (FC). Extensive simulation results confirms the superiority of the proposed schemes.