Research On Physical Layer Security Performance For Ultra Dense Network

The rapid development of the 5G industry has brought innovation to various fields such as industry,finance,transportation,medical care,and life,and promoted the realization of the "Internet of Everything".Due to the higher frequency band used by 5G,the effective distance of signal propagation is shortened and the penetration of signal is greatly weakened,so the coverage of a single base station is reduced.Ultra dense networks can improve spectral efficiency and communication rates by deploying a large number of low-power small base stations in the area.However,due to the small difference in channel between adjacent base stations,the interference received by the user is relatively large,which reduces the performance of the ultra-dense network.In wireless communication,data security is the most basic requirement,especially when communicating in an ultra dense network,the eavesdropper may be closer to the micro small base station,or its channel may be better,making it easier for legitimate users to be eavesdropped.In the research of physical layer security,scholars have found that the confidentiality of messages can be guaranteed by using the physical characteristics of wireless channels.Compared with traditional encryption technology,physical layer security can greatly reduce the consumption of communication resources.In order to reduce energy consumption,energy harvesting technology has received great attention,and SWIPT can transmit energy and information at the same time,which is of great significance to improve the physical layer security performance in ultra dense networks.Based on the above background analysis,this thesis studies the security performance of physical layer in ultra dense network from the perspective of average security capacity.The specific work and main innovations are as follows:(1)Firstly,based on the active model of small base station in homogeneous ultra dense networks,its downlink is considered.The positions of small base stations,legitimate users and eavesdroppers are subject to mutually independent Poisson point processes.The typical user located at the origin is analyzed.Under the condition that the main channel is subject to Rician Fading,the closed expression of the average security capacity of typical user is derived by using stochastic geometry.Secondly,in order to reduce inter-cell interference,the idle mode is used to turn off the small base station without service users in the network,so that it can only retain the necessary ability to find service users and minimize the power consumption.Under the idle mode,the average security capacity of typical users is theoretically derived and simplified.Finally,under the two different modes,the theoretical numerical calculation and actual system simulation of different parameters affecting the security performance of the physical layer are carried out respectively,which verifies the correctness of the theoretical analysis.(2)Based on the idle mode,a communication mode in which the small base station and legitimate users use SWIPT is proposed,and the average security capacity of the typical user is analyzed.Under this mode,the small base stations and legitimate users work based on TS protocol.Legitimate users are equipped with dual antennas,which store energy in batteries during the energy harvesting phase,and operate in full-duplex mode during the information transmission phase.While receiving the information of the small base station,they transmit artificial noise to interfere with eavesdroppers and other users.An expression for the average security capacity of the typical user is derived using stochastic geometry under Rician fading channels.Then,the influence of the SWIPT mode on the security performance of the system under different parameters is analyzed by simulation,including the time switching factor,the density of small base station,legitimate user and eavesdropper.The simulation results show that under the appropriate time switching factor,legitimate users based on the SWIPT mode can effectively improve the average security capacity when the eavesdropper density is large.