Research On The Physical Layer Security And Swipt For Relay Cooperative Systems

With the rapid development of the Internet of Things(IoT),large quantities of sensors need to be deployed in smart home,smart city and smart industry application scenarios to monitor the environment and equipment in real-time.The high-speed increase on the number of IoT devices and sensors will inevitably lead to massive energy consumption.The limited battery capacity of wireless sensor will hinder the development of the Internet of Things.Moreover,IoT devices are applied to health monitoring,smart home,industry process control and other aspects,so that bulk private and sensitive data(such as real-time location and health status)is transmitted through the wireless channel,causing serious security risks.In addition,the energy and resources of IoT devices and sensors are limited.It is unrealistic to rely on increasing the complexity of security algorithms to ensure security.Therefore,in view of the energy shortage and security problems,this thesis mainly focuses on the secure communication in energy-constrained relay cooperative systems based on simultaneous wireless information and power transfer(SMWIPT)and physical layer security.The main contributions are described as follows.Firstly,for cognitive relay systems,a secure transmission model with SWIPT based on Decode-and-Forward(DF)protocol and destination-assisted Jamming is established.Under the constraints of power and the minimum rate demand of the secondary user(SU),an optimization problem is established to maximize the secrecy rate of the primary user(PU).Since the optimization problem is a complex non-convex problem,this thesis adopts a two-stage step-by-step algorithm to solve the problem by using the Semi-Definite Relaxation(SDR)method and Charnes-Cooper transformation.And the optimal beamforming vectors and power split ratio are obtained.Finally,the relationships between the secrecy rate of PU and the rate of SU,transmission power and the number of antennas are studied.The experimental results show that the proposed algorithm can improve the security performance in cognitive relay systems.Secondly,for cognitive relay systems,a secure transmission model with SWIPT based on Amplify-and-Forward(AF)protocol is established.The optimization problem of maximizinig the rate of SU by jointly optimizing beamforming vector,relay processing matrix and power split ratio under the constraints of power and the secrecy rate of PU is constructed.Furthermore,an alternating iterative algorithm,which utilizes SDR method,Lagrangian method and rank-reduction method to solve the non-convex problem is adopted.Finally,the relationships between the rate of SU and the secrecy rate of PU and the location of relay is studied through simulation experiments.The simulation results show that the proposed algorithm can effectively guarantee the secure transmission.Finally,for the untrusted two-way relay cooperative systems,a secure transmission model with SWIPT combining Multiple-Input Multiple-Output(MIMO)technology is established.Under the constraint of power,the optimization problem of maximizing the secrecy rate of two-users is established by jointly designing the relay processing matrix,beamforming vectors and power split ratio.The coupling between multiple optimization variables makes the optimization problem a complex non-convex.In this thesis,rate allocation method,Taylor expansion and Alternating Direction Method of Multipliers(ADMM)are used to solve the optimization problem.In addition,the dimension-reduction method is adopted to reduce the complexity of the algorithm.Finally,the relationships between the secrecy rate of two-users and transmitting power,the relay location and power allocation ratio are studied.The experimental results show that the proposed algorithm can effectively improve the secure transmission performance of the untrusted two-way relay cooperative systems.