Analysis Of Transmission Capability And Security Performance In Distributed Cognitive Radio Networks

The emerging communication technologies and traffics increasingly expand the demands on the network capacity and the information security,and highlight the spectrum scarcity.The cognitive radio networks(CRNs)and the physical-layer security(PLS)are regarded as potential solutions to improve the transmission capability and the security performance of the wireless networks.Based on the cognitive radio technology,CRNs will significantly improve spectrum efficiency and network capacity by continuously optimizing network parameters in the process of perceiving external environment.To secure transmission of confidential messages,PLS makes use of diversity and time variation characteristics rooting in wireless channels to ensure the communication quality of legitimate users while preventing eavesdroppers from intercepting the confidential information.This dissertation focuses on two kinds of performance for DCRNs on the base of stochastic geometry technique.The first one is the transmission capability,which is affected by many factors including the network topology,the nodes spatial distributions and the accumulative interference,and the research on transmission capability emphasizes the capacity of the wireless network.The second one is the secrecy performance,the network security has always been regarded as one of essential problem in the evolution of wireless networks.And the issue on PLS has become a new research hot spot in recent years.The main contributions of this paper are summarized as follows:In the first part,the analytical framework of transmission performance metrics is established for DCRNs.We derive the achievable rate coverage probability of the secondary network(SN)by modeling the outage probability of DCRNs based on the stochastic geometry technique,and present the upper bound of the achievable throughput for the SN under double constraints including outage probability and achievable rate coverage probability.The maximum achievable throughput of the SN is achieved through optimizing the achievable rate coverage probability satisfying the connectivity requirement of the primary network(PN).Compared with the existing average rate,the achievable rate provides a helpful supplement to evaluate the transmission rate completely.In the second part,an secrecy framework of DCRNs is established based on the stochastic geometry theory and the physical layer security method.We give the connection outage probability(COP)and secrecy outage probability(SOP),and derive the closed-form expression of secrecy transmission capacity for both the PN and the SN.In the PN,the maximum secrecy transmission capacity is achieved by optimizing the density of the PN.It is shown that the cognitive interference is helpful to improve the security of the PN,only if the average channel condition of the PN is better than that of the eavesdropping network.In the SN,we obtain the transmission capacity by modeling the COP of the PN and the SOP of the SN,and propose the achievable secrecy rate to reflect the effect of nodes random distribution on the security.Compared with the ergodic secrecy rate,which only indicating the average value of the security,the achievable secrecy rate better characterizes the security of the DCRNs.In addition,the cognitive secrecy gain is proposed to evaluate the advantageous effect from the SN on the secrecy capacity of whole CRNs.In the final part,the joint security strategy of the hybrid wiretap network is studied.We propose a hybrid wiretap model,which simultaneously considers colluding and no-colluding eavesdropping way,and derive the connection probability and the secrecy outage probability based on joint security strategy exploiting guard zone and artificial noise to enhance the network security.We maximize the security by optimizing the power distribution factor under the constraint of the connection probability.In addition,the threshold value of eavesdropper's density is proposed to determine whether it is necessary to adopt the joint security strategy to enhance the security,and the secrecy zone of the hybrid wiretap network is provided considering the constraint of the secrecy outage probability.Compared with existing security strategy,the proposed joint security strategy significantly improves the security of the hybrid wiretap network at high eavesdropping density.Above all,we research on the transmission capability and the secrecy performance of DCRNs,and derive the closed-form expressions including the outage probability,the transmission capacity and the cognitive secrecy gain for the PN and the SN,respectively.In addition,the joint security strategy is proposed to improve the security of the hybrid wiretap network.All of the above results provide theoretical guidance for the distributed wireless network.