Research On The Physical Layer Security In Multihop Wireless Networks

Multihop wireless networks are kinds of networks based on wireless link to realize interconnection between nodes.They have a wide range of applications.Network security has been a key issue of the national strategy.Due to the broadcast nature of wireless channels,the security problem of wireless communication is more serious.This dissertation mainly studies the security problem in these kinds of networks from the perspective of physical layer security,and focuses on how to ensure the security of information transmission on multihop path in the absence of a priori knowledge of the eavesdropper,and realizes the security and reliability by joint optimization and so on.In the course of the study,the distribution of eavesdroppers is modeled by a widely-used homogeneous Poisson point process(PPP),and the mathematical methods such as random geometry and nonlinear optimization are used.At the same time,new means such as self-interference suppression technology in full-duplex(FD)communication and cooperative interference are adopted.All of these are used to carry out research on the physical layer security issues in complex network environment.Due to the general representation of multihop wireless networks,the research results of this dissertation have very great theoretical and practical significance.The main contributions of this dissertation are as follows:First,we study the problem of secure routing in a multihop wireless ad-hoc network in the presence of randomly distributed eavesdroppers.Specifically,the locations of the eavesdroppers are modeled as a homogeneous PPP and the source-destination pair is assisted by intermediate relays using the decode-and-forward(DF)strategy.We analytically characterize the physical layer security performance of any chosen multihop path using the end-to-end secure connection probability(SCP)for both colluding and non-colluding eavesdroppers.To facilitate finding an efficient solution to secure routing for the practical application,we derive accurate approximations of the SCP.Based on the SCP approximations,we study the secure routing problem,which is defined as finding the multihop path having the highest SCP.Second,we consider the secure connection problem in multihop wireless networks with FD jamming relaying,where the colluding eavesdroppers are randomly distributed following a homogeneous PPP.By applying FD,each legitimate node(including relay and destination)jams the eavesdroppers when it receives the desired signal from transmitter and adopts the self-interference cancelation technology in full-duplex at the same time.We adopt the end-to-end SCP as the secrecy metric to characterize the physical layer security performance.We first derive the exact expression of SCP for any given path.Then,an approximation of the SCP is proposed to facilitate efficient secure routing by using a revised Bellman-Ford algorithm.We show that a notable performance gain can be achieved by the proposed scheme compared to the half-duplex(HD)scheme.Third,we study the design and secrecy performance of linear multihop networks,in the presence of randomly distributed eavesdroppers in a large-scale two-dimensional space.Depending on whether there is feedback from the receiver to the transmitter,we study two transmission schemes: on-off transmission(OFT)and non-on-off transmission(NOFT).In the OFT scheme,transmission is suspended if the instantaneous received signal-to-noise ratio(SNR)falls below a given threshold,whereas there is no suspension of transmission in the NOFT scheme.We investigate the optimal design of the linear multiple network in terms of the optimal rate parameters of the wiretap code as well as the optimal number of hops to maximize the secure transmission throughput.By solving this combinatorial optimization problem,our analytical results provide useful guidelines for designing linear multihop networks with targeted physical layer security performance.