Research On Physical Layer Security Issues Of Cooperative Relay Networks Under Co-Channel Interference

With the rapid development of wireless communication techniques,especially in recent years,diverse wireless communication systems,new wireless applications and kinds of communication data services are emerging.Meantime,the number of users and wireless mobile devices are sharply increased.However,the enabled spectrum face severe challenges,such as the spectrum scarcity problem,the low spectrum efficiency caused by the fixed and unreasonable spectrum allocation strategy and the severe electromagnetism environment.These facts further result in the crowd spectrum resource and the contradiction between the supplement and demand.In order to alleviate the spectrum scarcity problem,many promising techniques that aim for improve spectrum efficiency have been proposed,such as small cell,cognitive radio,multiple-input multiple output(MIMO),and cooperative relay,etc.Thereinto,cooperative relay that exploits the cooperation among different relay nodes to establish virtual MIMO antennas array,has the advantages in expanding the wireless coverage areas,achieving diversity gains,improving capacity and transmission rate.It can improve the performance of the user in the received end and achieve a high reliability for wireless communications.However,the cooperative relay network needs to address severe challenges caused by the open nature of the wireless channel.On the one hand,the confidential information can be easily eavesdropped due to the broadcasting nature of cooperative relay.Moreover,due to the massive relay nodes and complex structure,the high layer secure mechanisms based on the network protocol stack are difficult to be deployed.This further results in the severe security problem in cooperative relay networks.Thus,it is of great importance to improve he security of cooperative relay networks.Fortunately,physical layer security is promising to address this issue and has received increasing attention.It utilizes the diverse wireless channel characteristic,such as channel fading,to increase the mutual information of the desired users and decrease the mutual information of eavesdroppers.It can radically tackle the security problem of cooperative relay networks.Thus,it is envisioned that the investigation of physical layer security in wireless communications is inevitable trend.On the other hand,although cooperative relay techniques have potential to improve spectral efficiency,it introduces the interference in the same channel and results in the non-negligible interference problem in different increasingly complex communication scenarios.In this case,the wireless communication systems become interference-limited systems.The interference instead of noise is the mainfactor that significantly influences the performance of wireless communication systems,and the interference problem is ubiquitous in wireless communication systems and needs to be addressed.However,up to now,the existing cooperative relay models cannot well jointly study the relay selection,the interference problem and the wireless transmission security.In order to well study cooperative relay networks,it is required to jointly consider the physical layer security and the interference,and establish different secure communication frameworks under different interference condition for different communication scenarios.To address the above-mentioned problems,in this paper,we jointly consider the physical layer security and the interference in cooperative relay networks.We focus on improving the security of cooperative relay networks by using physical layer security and analyzing the reliability and security under the same channel interference.Moreover,the influence of interference on the security of cooperative relay networks is quantitatively analyzed.The achievements in this paper are beneficial for the design and optimization of cooperative relay networks in practical wireless communication systems.The main contributions of this paper are summarized as follows.Firstly,a cooperative wireless network is studied based on physical-layer security,where multiple co-channel interferers exist at relays,the destination and eavesdropper.Under the influence of multiple co-channel interferers,the tradeoff between the security and reliability of wireless communications against eavesdropping attacks is analysed in terms of the intercept probability and the outage probability.The exact closed-form expressions for the intercept probability and outage probability are derived for the direct transmission and the relay selection schemes over Rayleigh fading channels.The theoretical analysis is validated by numerical results.It is shown that the increase of the number of relays and(or)the number of co-channel interferers can efficiently improve the security–reliability tradeoff.Moreover,the relay selection strategy can achieve a higher SRT performance compared with the direct transmission strategy.Secondly,the physical-layer security of a multi-source multi-relay cooperative relaying communication network is investigated by considering the influence of co-channel interference from an security-reliability tradeoff perspective.Under the impact of multiple cochannel interferers,the intercept probabilities and the outage probabilities of both the conventional direct transmission strategy and relay selection strategy are derived in closed-form expressions over Rayleigh fading channels,respectively.Simulation results are provided to validate the theoretical analysis.It is shown that when the outage probability(reliability)requirement is relaxed,the intercept probability(security)performance improves and vice versa.It confirms that there is an SRT existing between the outage probability and the intercept probability.Meanwhile,a better SRT performance can be achieved by increasing the number of sources,relays and co-channel interferers.In addition,it is also shown that the relay selection strategy generally outperforms the conventional direct transmission strategy in terms of the product of the intercept probability and the outage probability.Thirdly,a two-way relay cooperative transmission model is investigated based on physicallayer security.A two-way relay selection scheme based on decode-and-forward opportunity relay is designed.Under the impact of multiple co-channel interferers,the exact closedform expressions for the intercept probability and outage probability are derived for the direct transmission and the relay selection schemes over Rayleigh fading channels,and the corresponding SRT performance analysis is given.The theoretical analysis is validated by numerical results and shows that the intercept probability performance(security)will improve correspondingly with the decrease of the outage probability(reliability),and vice versa.It confirms that there is an SRT existing between the outage probability and the intercept probability.The simulation results also show that the proposed two-way relay selection scheme can achieve a better SRT performance than the traditional direct transmission scheme.In addition,as the number of relays and the number of co-channel interferers increase,the SRT performance can be effectively improved.