Investigation On The Reliability And Security Of Cognitive Cooperative Communication

The dilemma between the low utilization of the available spectrum and the growing wireless applications is becoming the key factor that constraining the development of wireless communications.Cognitive radio technique which can make full use of wireless spectrum resource provides efficient way for the limited spectrum resource to be used by more users.Cooperative relay communications can efficiently increase the transmission rates,enhance the coverage rang of wireless communications,and improve the outage performance of the communications systems by multiple nodes forming the virtual multiple-input multiple-output array.Presently,spectrum sharing cognitive radio technique and multiple nodes cooperative transmission have been the core technology of the new generation wireless communications.The reliability and the security of the cognitive radio network can be improved by the cooperation between the cognitive secondary nodes and the licensed primary nodes or by the cooperation by the cognitive secondary nodes and cognitive secondary nodes.The traditional cooperative communication technique has been widely studied in the past years.However,for the cognitive cooperative transmission,the unlicensed cognitive secondary user can access the licensed spectrum only when the cognitive secondary users sense the spectrum hole or the cognitive secondary users don't cause harmful interference for the licensed primary users.Hence,due to the different priority owned by the licensed primary users and the unlicensed cognitive secondary users,the theory on reliability and security in traditional wireless cooperative communication networks cannot be directly used in cognitive communication networks.With this regards,this thesis focuses on the investigation of reliability and security of cognitive cooperative communications.The main contents and contributions are as follows:Firstly,the underlay cognitive cooperative relay transmission is investigated when there exists single primary receiver's interference.As long as the communication of the primary user is not interfered,the multiple nodes cooperative communication scheme is designed under the joint limits of the peak interference power and average interference power of the primary receiver to improve the reliable transmission performance of the cognitive network as much as possible.Undertaking the correlation among the received signal-to-noise ratio caused by the spectrum sharing,the performance of the selective cooperative relay transmission in underlay spectrum sharing environment is evaluated by deriving the exact expressions of the outage probability and the channel capacity.It is shown that although the correlations among the received signal-to-noise have a non-negligible influence on the communication performance of outage probability and channel probability,the diversity gain of the understudy underlay cognitive cooperative communication is not influence.Secondly,the impacts of the cooperative spectrum sensing on the cooperative data communication is investigated when there exist multiple cognitive secondary sources and multiple relays.According to the cooperative spectrum sensing results of cognitive secondary sources and relays,cognitive secondary user can access the licensed spectrum and transmit information to the cognitive secondary destination only when the multiple cognitive secondary sources and relays sense the spectrum hole.For the scenario that there exist multiple cognitive secondary sources,only the cognitive secondary source node which have the best channel quality with the cognitive secondary destination is selected as the best cognitive secondary source node.The best cognitive secondary source communicates with the cognitive secondary destination with the aid of multiple selective cooperative relay nodes.A basis for the practical application of the cognitive cooperative communications and the efficient utilization of licensed spectrum can be lied by deeply analyzing the impacts of the cooperative spectrum sensing on the cooperative data communication.Thirdly,the underlay cognitive multiple relay cooperation is studied when there exist primary transmitter and primary receiver.The selective cooperation decode-and-forward transmission scheme is designed based on the signal-to-noise-plus-noise to improve the system reliability and security.The exact outage probability and interference probability of the cognitive secondary user are respectively analyzed for the scenario when the direst secondary link is unavailable,the scenario when the cognitive secondary destination(eavesdropper)use selective combing technique to combine the information received from the cognitive secondary source and the best relay,the scenario when the cognitive secondary destination(eavesdropper)use maximum ratio combining technique to combine the information received from the cognitive secondary source and the best relay.Further,the impact of primary user on the reliability and security of cognitive network is discussed.It is shown that there exist trade-off between the reliability and security of cognitive cooperative communication network with primary transmitters and primary receiver.Finally,the security of the multiple-input single-output cognitive cooperative communication network is studied under a practical non-linear energy harvesting model.In order to improve the security of both the primary network and the secondary network,a cooperative jamming scheme is proposed.A robust artificial noise aided beamforming design problem is formulated under the bounded channel state information error model.The formulated problem is non-convex and challenging to be solved.Using S-Procedure and the semidefinite relaxation method,a suboptimal beamforming can be obtained.It is also shown that the security of the primary network and the secondary network can be simultaneous improved.