Research On Physical Layer Security For Wireless Communication Networks With Non-Orthogonal Multiple Access And Cognitive Radio

The rapid development of the Internet of Things and other emerging technologies not only bring great convenience to human life and work,but also put forward higher requirements for the new generation of wireless communication.The future improvement of wireless communication service capability,including 5G,will be carried out in three dimensions simultaneously: resource utilization,system throughput and finding new spectrum resources.In order to deal with these challenges,the new technologies of Non-orthogonal Multiple Access(NOMA)and Cognitive Radio(CR)have been paid much attention,and this thesis focuses on the power-domain NOMA.The core idea of power domain NOMA is to make use of power multiplexing at the transmitting node to serve multiple users at the same time and frequency band,so as to improve the system capacity and spectrum efficiency.On the other hand,CR technology enables unauthorized users to access authorized spectrum communication by sensing the working situation of authorized spectrum,which solves the problem of low spectrum utilization of authorized users and greatly improves the spectrum efficiency.Therefore,it is a natural choice to combine both,and it is also one of the key technologies for the future development of wireless communication.However,due to wireless communication uses electromagnetic wave to replace the traditional cable as the medium of information transmission,it has the characteristics of free and open transmission at the speed of light in space,but also provides a natural environment for attackers to carry out malicious eavesdropping.Therefore,we also need to consider the security of the communication system when we are looking for the communication target with high speed,high capacity and low delay.Physical Layer Security(PLS)technology can make eavesdroppers unable to correctly decode by using power control technology according to wireless channel's characteristics(fading and noise),so as to improve the secrecy capacity of the system without designing complex encryption and decryption algorithms,which has become a vital means to solve secrecy problems.Since power control is the main core technology in NOMA and CR,how to realize PLS technology in such network scenarios has become a research hotspot.This thesis mainly studies the PLS issues in the communication model combining CR and NOMA,and the main work and innovation points are summarized as follows:(1)Firstly,this thesis studies the PLS of the communication model combined with overlay CR and NOMA.Different from the transmission power of the secondary network needs to be constrained of the underlay CR,the core idea of the overlay CR is to make use of the spectrum hole,so as long as the authorized spectrum of the primary user is not occupied,the secondary network can access the communication network.According to this principle,the scheme is proposed in which the secondary network realizes the cooperative communication between the primary network and the secondary network by sensing whether the primary user occupies the authorized spectrum.The presence of eavesdroppers is considered.Artificial-noise-aided method is used in both primary and secondary networks to further improve the secrecy transmission performances of the systems.The secrecy outage performances of the systems are studied by deducing the expressions of secrecy outage probability(SOP)and secrecy throughput of primary network and secondary network respectively.Furthermore,the influence of artificial noise power allocation factor on system performance is given.The simulation results show that the proposed dynamic cooperative scheme can reduce the SOP and improve the secrecy throughput.The proposed cooperative scheme provides the design basis for CR-NOMA secrecy communication in overlay CR.(2)Then,the PLS of the communication model based on the combination of underlay CR and NOMA is studied.According to the principle of underlay CR,the secondary network accesses into the authorized spectrum of the main network with a very small power.Considering the problem of long-distance transmission in the actual scene,the secondary transmitter and the legitimate users communicate through the decode-and-forward(DF)relay.In the first time slot,the secondary transmitter sends the mixed signal of the legitimate users to the relay.After the relay receives the mixed signal,it decodes and forwards the mixed signal to the legitimate users in the second time slot.Meanwhile,the eavesdropper tries to intercept the message.In order to guarantee the communication quality of legitimate users,the joint of artificial-noise-aided and relay selection is adopted at the relay.The expressions of SOP and secrecy throughput are derived to evaluate the secrecy performance of the system.In addition,the asymptotic threshold value of SOP is derived.The simulation results show that the underlay CR-NOMA network is significantly better than the traditional underlay CR-OMA network in terms of secrecy outage performance,and the joint of artificial-noise-aided and the relay selection can effectively improve the secrecy throughput of the system.And the results provide an effective transmission scheme for the underlay CR network secrecy communication.