Research On Cooperative Relay Transmission Technology In Physical Layer Security

Cooperative communication has attracted wide attention because it can achieve the same spatial gain as multiple-input multiple-output(MIMO),solve the problem that terminals need to equip multi-antennas for transmission performance,and expand the coverage of communication.This paper focuses on the amplify-and-forward(AF)relay system for low hardware cost and data integrity and studies cooperation technologies from two aspects: power allocation and relay selection based on the physical layer security.Increasing attention has been concentrated on the information-theoretic secrecy in physical layer.Considering that both reliability and validity are important design targets for wireless network design,therefore,the goal of this paper in the first part is to maximize the system capacity while satisfying the secure quality of service(Qo S)and the total power transmit constraints.In other words,the tradeoff between system capacity and secrecy capacity is taken into consideration.An optimal power allocation is explored for an AF relaying system,and closed-form solutions are obtained.Simulation results highlight the effectiveness of the proposed power allocation and have shown that the intercept probability is also improved.In the second part,this paper first investigates the physical-layer security in wireless communication with multiple eavesdroppers.Considering the importance of the fairness among multiple relays,this paper presents the sub-optimal relay selection protocol based on cumulative distribution function(CDF)of the ratio of channel coefficients,which satisfies the security requirement at the same time.Relay fairness is analyzed by obtaining the expression of relay selection probability and numerical results prove the strict fairness among multiple relays.Meanwhile,the expression of the intercept probability is also presented.Since the half-duplex relay can result in low spectrum efficiency,the third part focuses on the issue of secrecy capacity optimization of amplify-and-forward-based energy harvesting two-way relaying systems.Utilizing the statistical channel information(CSI),a two-way relaying model which is applicable to practical environments under fast fading channels is established.The untrusted relay in this model will cause communication security problems.Then,a power allocation problem for users and the power splitter is formulated to maximize the secrecy capacity under the constraints of total power.Through the differential method,closed-form solution is achieved,thus providing valuable guideline into practical system designs.For wider applications,this paper has shown that the results can be extended to multi-relay multi-user scenario.Simulation results highlight the effect of the analytical results.