Research On Physical Layer Security Technology In Millimeter Wave Communication

The next-generation mobile communication system(5G)pursues higher throughput and faster transmission rate,but security and privacy protection are also important concerns for users.Traditional wireless communication systems mainly rely on the encryption technology of the upper layer to achieve secure communication,but it has encountered great challenges in key distribution for a large number of users in 5G.The physical layer security technology uses the inherent randomness of the wireless channel to ensure the security of the communication,regardless of the user's computing power.It can be used to solve the security issues of data transmission for the next generation of mobile communication or key distribution of a lage number of distributed access users.Firstly,this paper proposes an adaptive transmission scheme based on artificial noise and secrecy performance analysis in millimeter wave systems.It assumes that the eavesdropper's part of the channel state information(CSI)is known at the transmitter and improves the secrecy throughput by optimizing the power allocation factor under the constraint of the secrecy outage probability.Simulation results show that the scheme works well.Secondly,taking into account the complexity of applying traditional digital precoding in large scale antenna arrays,RF precoding technology is adopted to ensure the safety of millimeter wave communication.When the full channel CSI is known at the transmitter,the RF precoder is optimized based on semidefinite relaxation and gradient ascent algorithm.For partial CSI is known at the transmitter,the RF precoder is optimized to improve the secrecy performance under secrecy outage constraint.The simulation results show that the proposed method can improve the secrecy rate.Finally,considering the trade-off between performance and complexity,a hybrid precoding scheme combining joint digital baseband precoding and RF precoding is proposed based on the previous work.When the full channel CSI is know at the transmitter,an iterative hybrid precoder based on gradient ascent algorithm is proposed to maximize the secrecy rate.When the partial channel CSI is known at the transmitter,a secrecy outage probability upper is derived.The secrecy throughput maximization problem is converted into a sequence of secrecy outage probability minimization problems.The hybrid precoder is proposed to minimize the secrecy outage probability by an iterative hybrid precoder scheme based on gradient descent,so as to improve the secrecy throughput.