Research On Performance Analysis Of Physical Layer Security For Cognitive Cooperative Relay Networks

Recently,people's growing demand for bandwidth and the scanty spectrum resources have become a pair of contradiction which urgently needs to be solved,Thus the cognitive cooperative relay networks come out.However,due to the broadcast nature of wireless communication,the information is easy to be intercepted by illegal eavesdroppers.Compared with traditional cryptographic techniques which are employed above the physical layer to protect the transmission confidentiality from intercept,physical layer security demands less computation and can secure the transmission in a low complexity.Therefore,besides the study on outage performance of the cognitive cooperative relay networks,the study on physical layer security in cognitive cooperative relay networks is also very important.This thesis studies the outage performance of multi-antenna cognitive cooperative relay networks based on underlay spectrum sharing scenario,which lays the foundation for the following research.Then,the physical layer security in multi-antenna cognitive cooperative relay network is studied.In consideration of the practical situation,the perfect channel state information(CSI)is difficult to be obtained,so this thesis also studies the physical layer security in cognitive cooperative relay network with imperfect CSI.The main contributions of this thesis are as follows.1.The outage performance of multi-antenna multiuser cognitive cooperative relay network is studied.In order to obtain multi-antenna diversity and multiuser diversity to combat fading,this thesis studies the cooperative relay networks with multiple antennas and multiple cognitive users.Under this decode-and-forward(DF)protocol based networks,we derive both the exact closed-form expression of outage probability and asymptotic expression of which in high signal-to-noise ratio(SNR)region.The results show that the outage performance of the system will be improved with the increase of both the number of antennas and SDs.Meanwhile,if the numbers of antennas for cognitive transmitter and relays are both N,and the number of cognitive destinations is L,then the diversity order of the system is N×min(N,L).Besides,when the number of antennas is less than the number of secondary users,the diversity order of the system is completely decided by the number of antenna,and has nothing to do with the number of secondary users.However,when the antenna number is larger than or equal to the number of secondary users,the diversity order is relevant with both number of antennas and secondary users.2.The physical layer security in cognitive cooperative relay network with multiple antennas is studied.Under this spectrum sharing scenario,we derive both the exact and asymptotic expressions of secrecy outage probability over Rayleigh fading channels and give the reliability-security tradeoff analysis.The results show that the loss of the secrecy outage performance caused by an increase of eavesdroppers number can be totally overcome by multiple antenna diversity.It's illustrated that increasing the number of antennas can also improve both reliability and security of the system.Besides,the asymptotic analysis indicates the secrecy diversity order is only determined by number of antennas and is independent with number of eavesdroppers.The secrecy array gain is relevant with both number of antennas and eavesdroppers.In other words,the existence of eavesdroppers will degrade the secrecy outage performance but will not affect the diversity order of the system.3.The physical layer security in cognitive cooperative relay network with imperfect CSI is studied.In practical situation,it is difficult to know the perfect CSI between the primary system and the secondary system,so the research of this aspect is very significant.This thesis gives the exact outage probability of cognitive cooperative relay network with imperfect CSI in Underlay spectrum sharing scenario.The results indicate that the imperfect CSI can increase the outage probability of the system,but the situation can be improved by increasing the number of relays.With the increase of relays,the gaps on outage probability between perfect and imperfect CSI are becoming bigger.In addition,the affects on outage probability caused by the first hop is much bigger than that of by the second hop.Besides,the imperfect CSI only affects the outage probability,and will not affect the diversity order of the system.