Research On The Physical Layer Security For Cooperative Relay-based In SWIPT System

At the present time,with the popularity of smart terminals and the increasing growth of wireless multimedia services,while the information and communications industry is developing rapidly,the stagnant battery technology has been unable to meet the urgent energy needs of energy-constrained devices in wireless networks.The emergence of simultaneous wireless information and power transfer(SWIPT)has opened a new direction for solving this problem.Different from the traditional wireless communication technology that only transmits information or energy,SWIPT technology can realize stable energy for wireless devices while exchanging information with wireless devices.However,due to the openness of the wireless channel,the transmission information is easily intercepted and monitored by illegal devices,and the information security of legitimate receivers is difficult to be guaranteed.Taking the security of the SWIPT system as the starting point,this paper conducts related research on several different communication scenarios,and further designs the corresponding physical layer security transmission schemes.The main contributions are as follows:Firstly,aiming at the resource allocation problem in the SWIPT multi-relay system under the condition of eavesdropping channels,combined with the amplify forwarding and cooperative jamming methods,the physical layer security transmission schemes of static power splitting and dynamic power splitting were studied respectively.Considering the difficulty of solving the high-dimensional multi-objective model,and using the differences between the channels of legitimate receivers and illegal eavesdroppers,two zero-forcing relay cooperation algorithms are proposed.These algorithms project the target vector into the zero space of the receiver or eavesdropper channel,thereby simplifying complex models and reducing the amount of computation.Simulation experiments illustrate that the two algorithms can provide secrecy rates close to the upper bound of the optimal performance with lower computational complexity.Secondly,considering that different engineering objectives require the algorithm to be flexible in some practical application scenarios.The algorithm must solve the problem of a reasonable trade-off between secrecy rate and computational complexity.Aiming at the performance trade-off problem in SWIPT multi-relay system under the condition of eavesdropping channel,and using the prior information of illegal eavesdropper channel,an improved zero-forcing cooperation algorithm is proposed.The algorithm divides eavesdroppers into strong and weak subsets based on the determined compromise weight,and uses the zero-forcing precoding method to avoid strong eavesdroppers and cooperative jamming method to suppress weak eavesdroppers.Simulation researches represent that the algorithm can determine its reachable secrecy rate and computational complexity according to the performance index requirements,and provide controllable system performance,which is obviously more suitable for practical engineering application scenarios.Finally,aiming at the near-far effect in the SWIPT multi-user system under the condition of eavesdropping channel,a physical layer secure transmission scheme based on user cooperation is proposed,where a user with a strong channel condition acts as an energy-harvesting relay and transmit information to a weak user.The power splitting scheme is adopted at the energy-harvesting relay.By jointly optimizing the beamforming vectors and the power splitting ratio,the design objective is to minimize the transmission power of the base station while satisfying the secrecy rates of users.The analysis of the results demonstrate clearly that the proposed scheme can effectively balance the near-far problem and reduce the energy consumption of the base station.