Security Technology Research For Cognitive And Cooperative Relay Communications

Cognitive and cooperative communications technology not only can be used to improve the utilization rate of the radio spectrum,but also can be suitable for enhancing the quality of wireless communications.Meanwhile,it has been reported that an increasing number of wireless terminals are used for cyber criminals(i.e.,malicious attacks,malicious eavesdropping,data forging),which not only poses growing threats to peo-ple's daily life and social stability,but also causes a great economic losses.Hence,upgrading the security of wireless communications has been a key technology issue of cognitive and cooperative communications,and more attention should be dedicated to improving the security of wireless communications.This disser-tation deeply explores the performance of wireless physical-layer security for the cognitive and cooperative communications,including how to decrease the intercept probability of a cognitive and cooperative network relying on multiple OW-DF(One-way Decode and Forward)relays in the face of eavesdropping attacks,how to reduce the outage probability and intercept probability of a cognitive and cooperative system with the aid of multiple TW-DF(Two-way Decode and Forward)relays in the presence of the wiretapper,how to upgrade the security performance of a cognitive radio network relying on multiple OW-DF relays in the presence of an eavesdropper and channel estimation errors,how to enhance the ability of anti-eavesdropping of a cognitive system with the aid of multiple OW-AF(One-way Amplify and Forward)relays in the face of wiretapping and false detection of the presence of primary users.The specific research results and the main contributions are summarized as follows.First,for the security of a cognitive and cooperative network with multiple OW-DF relays in the presence of eavesdropping attacks,a secrecy rate maximization oriented relay selection scheme is proposed to improve the security of wireless communications.In the proposed scheme,a single relay with the maximal secrecy rate is selected among all relays to forward the source signal.Furthermore,in order to utilize all the relays that succeed in decoding,a multi-relay oriented relay selection scheme is also proposed,wherein all the relays that succeed in decoding will be selected to forward the source signal to the destination.Moreover,the intercept probability of the proposed schemes is analyzed over Rayleigh fading channels.For comparison purposes,the associated analysis of the conventional Max-Min relay selection is also presented.It is shown that the proposed schemes outperform the traditional Max-Min relay selection scheme in terms of the intercept probability.Additionally,the intercept probability of the proposed schemes decreases as the number of relays increases.Then,an artificial noise aided two-way opportunistic relay selection scheme is proposed for a cognitive and cooperative system consisting of multiple TW-DF relays in the face of the wiretapper.In the proposed scheme,one of the source nodes is used to transmit the artificial noise flexibly.Thus,one source node trans?mits its signal under the protection of artificial noise transmitted by the other source node.In addition,no artificial noise will be transmitted when a relay transmits.Moreover,the security and reliability performance of the proposed scheme is studied,where the security and the reliability are characterized by the intercept probability and the outage probability,respectively.It is shown that the intercept probability reduces as the outage probability increases,and the intercept probability increases as the outage probability decreases.Giv-en a specific outage probability constraint,the proposed scheme can obtain the lowest intercept probability.Additionally,in the low main-to-eavesdropper ratio region,the proposed scheme is capable of guaranteeing secure transmissions.Next,the channel estimation error oriented relay selection scheme is proposed to improve the security performance of a cognitive and cooperative network,consisting of multiple OW-DF relays in the presence of an eavesdropper and CSI estimation errors.In the proposed channel estimation error oriented relay selection scheme,a relay with the maximal instantaneous secrecy capacity will be selected to forward the signal to the destination.Furthermore,the security-reliability tradeoff performance of the proposed is analyzed over Rayleigh fading channels.For comparison and benchmarking purposes,the traditional direct transmission scheme is also analyze under the assumption of CSI errors.It is shown that the relationship between the intercept probability and the outage probability is represented by that the intercept probability upgrades as the outage probability degrades,and the intercept probability decreases as the outage probability increases.Given a specific outage probability,the security performance of the proposed scheme is better than that of the conventional direct transmission scheme.Finally,given a cognitive and cooperative radio network consisting of multiple OW-AF relays,in the face of wiretapping and the false detection of the presence of primary users,two relay selection schemes are proposed to improve the physical-layer security of cognitive transmissions against eavesdropping attacks,which are referred to as the global and partial channel state information based relay selection,respectively.In the global channel state information based relay selection scheme,both the CSI of the main links and that of the wiretap links are considered.In contrast to the global channel state information based relay selection scheme,only the CSI of the main links is taken into account in the partial channel state information based relay selection scheme.In addition,the intercept probability of the proposed schemes is analyzed over Rayleigh fading channels.For comparison purposes,the analysis of the convention round-robin transmission scheme is also provided.It is shown that the proposed schemes outperform the round-robin scheme in terms of the security of wireless communications.