[1] Stotts L B, Stadler B, Lee G. Free space optical communications: coming of age. [C]∥Proceedings of SPIE Atmospheric Propagation V, 6951, 69510W(2008).

[2] Stotts L B, Andrews L C, Cherry P C et al. Hybrid optical RF airborne communications[J]. Proceedings of the IEEE, 97, 1109-1127(2009). http://ieeexplore.ieee.org/document/4939408/

[3] Bagley Z C, Hughes D H, Juarez J C et al. Hybrid optical radio frequency airborne communications[J]. Optical Engineering, 51, 055006(2012). http://spie.org/Publications/Journal/10.1117/1.OE.51.5.055006

[4] Anees S, Bhatnagar M R. Performance evaluation of decode-and-forward dual-hop asymmetric radio frequency-free space optical communication system[J]. IET Optoelectronics, 9, 232-240(2015). http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=7284796

[5] Zhao J, Zhao S H, Zhao W H et al. Performance analysis for mixed RF/FSO airborne communication systems over atmospheric turbulence and pointing error[J]. Chinese Journal of Lasers, 44, 0906001(2017).

[6] Trinh P V, Thang T C, Pham A T. Mixed mmwave RF/FSO relaying systems over generalized fading channels with pointing errors[J]. IEEE Photonics Journal, 9, 5500414(2017). http://ieeexplore.ieee.org/document/7797185/

[7] Soleimani-Nasab E, Uysal M. Generalized performance analysis of mixed RF/FSO cooperative systems[J]. IEEE Transactions on Wireless Communications, 15, 714-727(2016). http://ieeexplore.ieee.org/document/7247760/

[8] Zedini E, Ansari I S, Alouini M S. Performance analysis of mixed Nakagami-m and Gamma-Gamma dual-hop FSO transmission systems[J]. IEEE Photonics Journal, 7, 7900120(2015). http://ieeexplore.ieee.org/document/6987241/

[9] Miridakis N I, Matthaiou M, Karagiannidis G K. Multiuser relaying over mixed RF/FSO links[J]. IEEE Transactions on Communications, 62, 1634-1645(2014). http://ieeexplore.ieee.org/document/6775014/

[10] Zhao J, Zhao S H, Zhao W H et al. Performance of mixed RF/FSO systems in exponentiated Weibull distributed channels[J]. Optics Communications, 405, 244-252(2017). http://adsabs.harvard.edu/abs/2017OptCo.405..244Z

[11] Haykin S. Cognitive radio: brain-empowered wireless communications[J]. IEEE Journal on Selected Areas in Communications, 23, 201-220(2005). http://ieeexplore.ieee.org/document/1391031/

[12] Akyildiz I F, Lee W Y, Vuran M C et al. NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey[J]. Computer Networks, 50, 2127-2159(2006). http://dl.acm.org/citation.cfm?id=1162470

[13] Zhao Q, Sadler B M. A survey of dynamic spectrum access[J]. IEEE Signal Processing Magazine, 24, 79-89(2007). http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=4205091

[14] Ekin S, Abdallah M M, Qaraqe K A et al. Random subcarrier allocation in OFDM-based cognitive radio networks[J]. IEEE Transactions on Signal Processing, 60, 4758-4774(2012). http://ieeexplore.ieee.org/document/6213141/

[15] Lee J, Wang H, Andrews J G et al. Outage probability of cognitive relay networks with interference constraints[J]. IEEE Transactions on Wireless Communications, 10, 390-395(2011). http://dl.acm.org/citation.cfm?id=2218456

[16] Zhong C, Ratnarajah T, Wong K K. Outage analysis of decode-and-forward cognitive dual-hop systems with the interference constraint in Nakagami-m fading channels[J]. IEEE Transactions on Vehicular Technology, 60, 2875-2879(2011). http://ieeexplore.ieee.org/document/5872082/

[17] Ansari I S, Abdallah M M, Alouini M S et al. Outage performance analysis of underlay cognitive RF and FSO wireless channels. [C]∥IEEE 2014 3rd International Workshop in Optical Wireless Communications (IWOW), 6-10(2014).

[18] Varshney N, Jagannatham A K. Cognitivedecode-and-forward MIMO-RF/FSO cooperative relay networks[J]. IEEE Communications Letters, 21, 893-896(2017). http://ieeexplore.ieee.org/document/7803614/

[19] Al-Qahtani F S, El-Malek A H A, Ansari I S et al. . Outage analysis of mixed underlay cognitive RF MIMO and FSO relaying with interference reduction[J]. IEEE Photonics Journal, 9, 7902722(2017). http://ieeexplore.ieee.org/document/7883900/

[20] Hasna M O, Alouini M S. A performance study of dual-hop transmissions with fixed gain relays. [C]∥IEEE Transactions on Wireless Communications, 3, 1963-1968(2004).

[21] Lee E, Park J, Han D et al. Performance analysis of the asymmetric dual-hop relay transmission with mixed RF/FSO links[J]. IEEE Photonics Technology Letters, 23, 1642-1644(2011). http://ieeexplore.ieee.org/document/5999707/

[22] Han L Q, You Y H. Performance of multiple input multiple output free space optical communication under atmospheric turbulence and atmospheric attenuation[J]. Chinese Journal of Lasers, 43, 0706004(2016).

[23] Zhang H Y, Li H Z, Xiao D Y et al. Performance analysis of spatial-diversity reception over combined effects of atmospheric turbulence[J]. Chinese Journal of Lasers, 43, 0405002(2016).

[24] Popoola W O, Ghassemlooy Z. BPSK subcarrier intensity modulated free-space optical communications in atmospheric turbulence[J]. Journal of Lightwave Technology, 27, 967-973(2009). http://ieeexplore.ieee.org/document/4814759/

[25] Ekin S, Abdallah M M, Qaraqe K A et al. Random subcarrier allocation in OFDM-based cognitive radio networks[J]. IEEE Transactions on Signal Processing, 60, 4758-4774(2012). http://ieeexplore.ieee.org/document/6213141/

[26] Wolfram I. Mathematica Edition: Version 8.0[M]. Champaign, Illinois: Wolfram Research Inc(2010).

[27] Springer M D. The algebra of random variables[M]. New York: Wiley, 197-198(1979).

[28] Adamchik V S, Marichev O I. The algorithm for calculating integrals of hypergeometric type functions and its realization in REDUCE system. [C]∥Proceedings of the International Symposium on Symbolic and Algebraic Computation. ACM, 212-224(1990).

[29] Mathai A M, Saxena R K. The H function with applications in statistics and other disciplines[M]. New York: Wiley Eastern, 152(1978).

[30] Mittal P K, Gupta K C. An integral involving generalized function of two variables. [C]∥Proceedings of the Indian Academy of Sciences-Section A. Springer India, 75, 117-123(1972).

[31] Chatzidiamantis N D, Karagiannidis G K. On the distribution of the sum ofGamma-Gamma varieties and applications in RF and optical wireless communications[J]. IEEE Transactions on Communications, 59, 1298-1308(2011). http://ieeexplore.ieee.org/document/5719282/