Physical Layer Security Of Relay Systems In The Finite Blocklength Regime

With the popularization of mobile communication technology,modern society urgently needs a new generation of communication techniques to meet the demands for low latency,wide coverage,and high speed.In recent years,full duplex has been extensively investigated.Compared with the commonly used half-duplex,full-duplex improves the utilization of increasingly scarce spectrum resources,and thus becomes a hot point.However,since the performance of full-duplex is not as good as half-duplex when the self-interference cancellation ability is not good,hybrid duplex,that is,switching between full-duplex and half-duplex has become a hot research direction.Cooperative communication is a method that uniformly controls multiple wireless devices through a cooperation protocol to achieve better performance than independent work.Multiple relays that perform cooperative communication with each other are called cooperative relays.Cooperative relays use the independence of the channels where each relay is located to obtain spatial diversity,while expanding the effective working range of the communication system.Real-time communication is a demand that has emerged in recent years.For this reason,it is necessary to ensure low latency of information transmission.Due to the limitation of packet length caused by this demand,traditional communication performance indicators such as channel capacity deviate from actual performance.Meanwhile,more private information entering the wireless network of open medium transmission will also attract more eavesdropping and cracking of wireless signals.Physical layer security has received widespread attention as an auxiliary technology for cryptographic encryption.However,the traditional physical layer security is based on the assumption of infinite packet length,and there is no evaluation index for accurately evaluating the physical layer security of low-latency systems.Therefore,this theory needs to be improved.This dissertation investigates the physical layer security theory of short packet relay systems,and applies relay selection,hybrid duplex,resource optimization allocation,cooperative beamforming and artificial noise technology,while improving the coverage and spectrum utilization of existing communication systems Rate,and the accuracy of measuring the security of the short packet communication system.First of all,this work establishes a system for a hybrid duplex single-relay short packet communication system,combines this system with the short packet communication physical layer security theory,and derives the approximate closed-loop system security throughput suitable for computer solutions.Expressions.Secondly,this work established a hybrid duplex optimal relay selection short packet communication system,using the secret throughput expression of a single-relay system as the system performance index to be optimized,and transmitting in different duplex modes of relay work The power distribution and packet length are optimized jointly with the relay end,and this nonconvex optimization problem is transformed into an iteration of the convex optimization problem,and a hybrid duplex optimal relay selection scheme is given.Finally,this work established a multi-relay cooperative beamforming short packet communication system based on the hybrid duplex optimal relay selection system,and derived an approximate closed-form expression for the confidential throughput.Multiple relays of this system form a virtual multi-antenna system through a collaboration protocol,and forward signals to the receiver directionally through beamforming.While forwarding,the relay emits artificial noise with a certain power in the null space of the transmitted signal,which increases the interference to eavesdroppers to improve security.