Research On Power Control To Optimize Security Performance In Full-Duplex Untrusted Relay System

In wireless communication scenarios,when the transmission is blocked by obstacles,which will result in inability to transmit directly and poor transmission quality,the use of relay nodes for forwarding information is one of technical solutions to this problem.However,when the transmitted information needs to be kept secret from the relay node,which is an untrusted node,it is necessary to rely on the untrusted relay to provide amplification and forwarding services while avoiding the confidential information being obtained by it.This thesis addresses the optimization problem of maximizing the achievable secrecy transmission rate for full duplex untrusted relay communication system.The main contents are as follows:1.For a full-duplex untrusted relay transmission system with collaborative interference sent by the destination node,the power of the source node sending the information signal and the destination node sending artificial noise is optimized to improve the secrecy rate in the presence of errors in the estimated channel state information.The total power of source node and destination node is limited,the untrusted relay amplifies and forwards signal came from the source node while receiving it,and the destination node sends artificial noise to the untrusted relay while receiving to prevent relay from acquiring secrecy information.Due to the random errors in the channel coefficients between the relay and the destination node obtained by the destination node,the artificial noise at the destination node cannot be eliminated completely,and its signalto-noise ratio and the achievable secrecy rate of the system are random variables.An upper bound on the expected average achievable secrecy rate of the system is first derived with respect to the random channel coefficient errors,based on which the power allocation factor between source node and destination node is optimized with the objective of maximizing this upper bound.The proposed scheme has a more significant gain in system performance than the scheme that ignore channel coefficient error.The more severe the error is,the more significant the gain is.2.For a full duplex time switching simultaneous wireless information and energy transfer(SWIPT)relay system,the three main factors of optimization are thoroughly investigated,including time switching factor,power allocation factor of source node and power allocation factor of destination node.The source and destination nodes are powered by the conventional grid,and the relay node is a time switching SWIPT node.During the first stage,the relay node works in energy harvesting mode,collecting energy from the signals sent by the source and destination nodes.During the second stage,the relay uses the collected energy to forward the signal from the source node while the destination node sends collaborative jamming.The achievable secrecy rate is maximized by jointly optimizing time switching factor,power allocation factor of source node and power allocation factor of destination node.Compared with partial parameters optimization schemes,joint optimization scheme always gets better system performance gains.