Physical Layer Security Issues In MIMO Cooperative Networks

The wireless communication techniques have been tremendously innovated in the past few decades.Besides the traditional need of transmission efficiency,the security need is fastgrowing for the wireless network users.However,due to the broadcast nature of wireless communication,the security issues in wireless communication must face more threats than wired.Thus,securing wireless networks has become a significant field both inside of industry and academia.Nowadays,the security of the wireless networks is mainly trusted to the cryptography approaches with continually proposing encryption schemes as well as security protocols.Besides the traditional cryptography approaches,the physical layer(PHY)security is an important approach with the potential to achieve perfect secrecy without shared key.Particularly,by integration two key techniques in wireless communication,i.e.,cooperative communication and Multiple-Inputs Multiple-Outputs(MIMO),more redundancy in physical layer could be provided to enhance the network security.Thus,it is desirable to consider the PHY security issues in MIMO cooperative networks.This thesis investigates the PHY security issues in MIMO cooperative communication networks.Three information exchange schemes have been proposed for basic channel models in MIMO cooperative communication.Furthermore,the proposed schemes have been adopted and applied into practical wireless networks.The main contributions of this thesis could be summarized as:Firstly,for MIMO multi-pair two-way relay channel,novel secure information exchange scheme has been proposed.Two approaches have been considered namely signal alignment approach and PHY encryption approach.For the signal alignment approach,summed signal will be obtained with key technique called Direction Rotation Alignment.With such summed signal,the untrusted relay or external eavesdropper cannot recover the separated original information transmitted from the users.For the PHY encryption approach,encryption vector has been nested into precoding matrix to conceal the original information.Secrecy capacity has been analyzed for the two approaches under three adversary models: untrusted relay attack model;trusted relay with eavesdropper attack model;and untrusted relay with eaves-droppers attack model.To the best of our knowledge,this work is the first secure method considering all these adversary models.Simulations have been conducted to demonstrate the performance of the proposed scheme.Secondly,for MIMO multi-hop relay channel,novel secure information exchange scheme has been proposed.The proposed scheme contains basic scheme and two evolutionary schemes.The basic scheme has been proposed for two n-hop distance users securely exchange information in n + 1 time slots.This time slots cost has been proved as a minimized number for half duplex model.Security analysis has been conduct analog to the stream cipher encryption.With the security analysis,two types of information leakage have been identified which are common leakages for the summed signal based security.The security analysis analog to the cryptography security is also our particular method for PHY security.Two evolutionary schemes have been proposed to prevent the identified information leakage.Following,the secrecy capacity of the basic scheme has been derived.Finally,simulation results are shown to evaluation the performance of the proposed scheme.Thirdly,for MIMO multi-way relay channel,novel secure group information exchange scheme has been proposed.In this scheme,a group of users securely exchange information with help of one relay.To prevent the attacks from the untrusted relay and external eavesdroppers,the signals of two neighbor users are aligned into a same direction to form summed signal at relay or external eavesdroppers.By regulating the transmission rate for each use,the information theoretic security could be achieved to prevent the attack from relay and external eavesdroppers.The secrecy capacity is analyzed following the scheme introducing,and theoretical analysis have been demonstrated by the simulations.Finally,the proposed PHY security schemes have been applied into three practical cooperative networks.For MIMO Mobile Ad Hoc networks,a protocol is proposed enabling two n-hop distance users exchange information without shared key.For Wireless Sensor Network,a protocol is proposed enabling source node transmit its gathered data to the sink node through a lot of untrusted helper nodes.For MIMO Vehicular Ad Hoc network,a protocol is proposed enabling a group of On Board Units securely exchange information through one Road Side Unit.