Research On Secure Beamforming Technology In Satellite Communication Systems

Satellite communication has many advantages,such as wide coverage,large communication capacity and no geographic restrictions.It will play an increasingly important role in the next generation mobile communication system.However,the wide area coverage of satellite communication makes information security transmission a more challenging research topic in this field.As one of the main means to achieve physical layer security,Beamforming(BF)improves the security performance of the system in spatial dimension by adjusting the direction of the antenna to increase the received signal power of legitimate users and significantly reduce the received signal quality of eavesdroppers.This paper mainly studies the secure beamforming technology in satellite communication systems,as follows:(1)We propose a secure beamforming algorithm for satellite communication in multicast transmission mode for the two cases of accurately known eavesdropper CSI and error.Firstly,for multicast transmission systems with multiple eavesdroppers,the transmission power minimization problem under safe rate constraint is constructed.Then,assuming that the Channel State Information(CSI)of both legitimate user and eavesber is known,a beamforming method combining semi positive definite programming and penalty function is proposed.Furthermore,a robust security BF algorithm based on iteration is proposed under the condition of error of eavesdropper CSI.The simulation results show that the proposed two BF algorithms can effectively improve the physical layer security performance of the multi-beam satellite communication downlink multicast transmission system.(2)We propose a robust secure beamforming algorithm for satellite communication in unicast transmission mode for the condition that only the approximate position of eavesdropper is known.Firstly,in the non-cooperative eavesdropping scenario,an optimization problem is established with the objective function of maximizing the safe rate of legitimate users and the constraint of transmitting power of single antenna.Then,the log-sum-exp function is used to approximate the objective function,and Dinkelbach and the Alternating Direction Method of Multipliers(ADMM)algorithm are combined to solve the problem iteratively.The robust safety BF algorithm is obtained.Furthermore,the algorithm is extended to cooperative eavesdropping scenarios.Finally,the simulation results show that the performance of the proposed robust security BF algorithm is superior to the traditional Maximum Ratio Transmission(MRT)BF algorithm and the non-robust security BF algorithm(3)We propose a robust secure beamforming algorithm for satellite communication based on Layered Division multiplexing(LDM)transmission under the condition that only the approximate position of eavesdropper is known.Firstly,for the LDM transmission satellite system with multiple eavesdroppers,the expressions of security rate under unicast and multicast transmission of legitimate users are derived respectively.Then,the transmission power minimization problem with safe rate constraint is constructed.Furthermore,a robust secure BF algorithm based on SCA iteration is proposed by approximating non-convex constraints and transforming them into convex constraints under the condition that only the approximate location of eavesdropping is known.Finally,simulation results verify the effectiveness and superiority of the proposed robust safety BF algorithm.