Research On Highly Energy Efficient And Secure Transmission Of Full Duplex Relay Communication Systems

In recent years,full-duplex relay communication systems have been widely concerned by researchers from home and abroad due to the capacity to improve the spectrum efficiency and data rate based on expanding the coverage of communication systems.However,with the practical application of 5G technology,the contradiction between the rapid growth of wireless data traffic and energy cost has become the bottleneck problem which is restricting the practical application of fullduplex relay communication systems.Meanwhile,the openess and broadcasting characteristics of wireless channel make the data transmission of full-duplex relay systems suffer the eavesdropping threat from the illegal users.Therefore,this paper focused on the energy efficiency and security problem of full-duplex relay communication systems and proposed the performance target of secrecy energy efficiency(SEE)for full-duplex relay communication systems by combing the definition of physical layer security and energy efficiency for wireless communication systems.For two common scenarios,i.e.,the channel state information(CSI)of eavesdroppers is available and not available,we desgined two corresponding secure and energy efficient transmission schemes based on beamforming(BF)and artificial noise(AN)technologies respectively,which can effectively improve energy efficiency and security of systems and achieve well trade-off between the performance of the energy efficiency and the security.The main research contents are listed follows:(1)For the case with eavesdroppers' CSI,we first derived the destination signal-to-noise ratio of full-duplex relay communication systems based on the self-interference(SI)zero-forcing constraint and thus defined the SEE of full-duplex relay systems.Then,we formulated the optimization problem to maximize the SEE by optimizing the relay BF matrix.Due to the non-convex form of the considered SEE maximization problem,the equivalent expression was given by introducing auxiliary variables and applying the equivalent matrix transformation approach,and an approximation convex form of the equivalent SEE optimization problem was derived by applying sequential convex approximation(SCA)and penalty function method.Finally,an effective iterative optimization algorithm was designed to find the optimal solution of the original optimization problem in few iteration numbers.In addition,to reduce the computational complexity of the proposed iterative algorithm,a second order cone programming(SOCP)based iterative algorithm was proposed by recasting the approximation convex form of SEE problem into the second order cone form.Finally,the simulation results shown the effectiveness and superiority of the proposed algorithm and its SOCP form.(2)For the case without eavesdroppers' CSI,the AN technology was employed to interfere the eavesdroppers and thus improve the security of the full-duplex relay communication systems.First,we used the zero-forcing constraint to eliminate the SI at relay and the AN at destination,and simplified the SEE expression of the considered systems.Then,based on the power minimization criterion,we formulated the joint relay BF matrix and AN power allocation optimization problem with transmit zero-forcing constraints of SI and AN.Subsequently,we derived the approximate convex form of the power minimization problem by jointly employing equivalent matrix transformation simplification,SCA approximation and penalty function methods,and proposed a convergence-well iterative optimization algorithm and its SOCP approximation algorithm to find the optimal solution of the original power minimization problem.Finally,simulation results were given to show that although the SEE of the case without eavesdroppers' CSI is worse than the case with eavesdroppers' CSI,the AN can still guarantee the security of considered systems.