The Physical Layer Security In Multi-antennas System

The wireless signal can be wiretapped easily because of the broadcast na-ture of the wireless communication channels,which brings terrific challenges to the security of networks.The traditional encrypted way on high layers is based on the fact that the computing power of eavesdropper is limited and the eaves-droppers could not break the secret key.However,with the rapid development of wireless devices,the key-based way is difficult to realize perfect security.Physical layer security is based on the information theoretic and can guarantee secrecy communication.It does not rely on the computing capacity of eaves-droppers.The basic idea of physical layer security is to exploit channel coding,precoding and other techniques to maximize the uncertainty of the information at eavesdroppers.On the other hand,the energy demand problem gets more and more focus because of the explosive growth of high speed wireless communication system.Portable devices are usually powered by batteries and their operating cycles are confined by battery capacity.This limits the lifetime of networks.Thus,the energy harvest technology is considered as a promising solution to the problem.Compared with traditional energy sources such as wind and solar,the ambient radio-frequency signals are location independent and more suitable for mobile networks to harvest energy.As a consequence,the scheme called simultaneous wireless information and power transfer(SWIPT)comes into being.Physical layer security and S WIPT are all new technologies and the combination of them is a hot research topic.For example,in interference network,the interference can not only be treat as jammer to eavesdroppers,but also can be treat as energy source to energy harvester.In this case,the joint design of the network security and the energy efficiency is extremely important to get optimal balance.Based on this situation,the thesis studies the physical layer security in interference channels first,and then the relay network combined with energy harvest.The main innovations and contributions of the paper are as follows.1)Considering two-users interference wiretap channel,the eavesdropper can wiretap both of the users.We propose an iterative algorithm to maximize the sum of secrecy rate subject to the transmission power constraint by designing beamforming vectors.To reduce computational complexity,we also design a zero-force scheme.Simulation results show the effectiveness of the proposed algorithms in enhancing the system security.2)Concerning more practical scenario,the network knows imperfect eaves-dropper's channel state information.Our goal is to maximize the worst-case achievable secrecy rate of the wiretapped node through designing the beam-forming and artificial noise vectors.In particular,this paper considers the chan-nel vectors and channel covariance matrices errors.With the help of rank re-laxation and one dimensional line search,the problem is solved efficiently.3)The green relay is investigated.We call it green relay because it is powered by the energy harvested from the relay observations.Furthermore,there are multiple eavesdroppers wiretapping the information.We propose an iterative algorithm,which can maximize the secrecy rate subject to the total transmit power constraint or minimize the total transmit power subject to the secrecy rate requirement by designing the power allocation and beamforming vector,.4)Considering the multicast green relay network,the transmitter only knows the eavesdropper's channel distribution.This paper propose an iterative algorithm to minimize the transmission power subject to the signal-to-noise ra-tio of legitimate users and the outage probability requirement of eavesdroppers.