Research On The Technologies Of Physical Layer Security In Wireless Relay Networks

PopularityoftheInternetandthelarge-scaleapplicationofwirelessnetwork,havegreatly facilitated people’s lives. However, the interception and malicious use of infor-mationcausedseriouslosstothesociety. Wirelesscommunication,duetoitsbroadcastproperty, is particularly vulnerable to eavesdropping. Nowadays，we pay more atten-tiontothesafetyofwirelesscommunicationinadditionofthereliabilityandefciency.The physical layer security, based on information theory, is perfectly secure and robustto the exhaustive search attack. Thus, it is attracting more and more attention.Cooperative relaying is one of the key technologies in current wireless commu-nication system. In the future, there will be more and more data transmit in the relaynetworks. To deal with the security concern in relay networks, we study how to utilizethe physical layer security technique to enhance the security of the relay networks.First, we analyze the relay placement in one-way secret communication system.For diferent relay strategies, decode-and-forward, randomize-and-forward, we derivethe optimal power allocation in the four-node(source, relay, destination and eavesdrop-per)system. Inaddition, weshowthattheoptimalrelaypositionisaroundthemidpointof the source and the destination. In single-cell cellular network, we analyze the secureoutage probability of the mobile user with the base station. We show that without therelay station, it is difcult to establish a secure connection between the base station andthe mobile user. In these two systems, randomize-and-forward strategy is better thandecode-and-forward strategy. Moreover, we analyze the efects of path loss on secureconnection and fnd that the relay transmission is especially helpful when path loss isseverer.Second，we analyze the secure beamforming design for MIMO two-way com- munications with an untrusted relay. The untrusted relay may intentionally eavesdropthe signal when relaying. The two source nodes exchange message through the relaynode while shielding the messages being decoded by the relay. Three transmissionschemes, direct transmission, two-and three-phase two-way relaying are proposed andstudied. We propose the optimal structure of the relay beamforming and iterative algo-rithmstojointlyoptimizethesourceandrelaybeamforming. Furthermore,Weconductasymptotical analysis when the powers of the source or/and relay nodes approach ze-ro or infnity. Specifcally, when the powers of the source and relay nodes approachinfnity, the two-phase scheme achieves the maximum secrecy rate if the transceiverbeamformers are designed such that the received signals at the relay can be aligned tobe parallel. It also lowers the requirement of numbers of antennas at the source nodesfor ensuring security.