A Physical Layer Security Scheme For Mobile Eavesdroppers

With the technology developing,wireless communications have played a more and more important role in individuals' daily lives.Wireless channels provide users with convenience.However,due to the broadcast nature and superposition nature of wireless channels,wireless communications are very susceptible to the security threat from malicious users,which makes security in wireless communications a vital issue to cope with.Traditional cryptographic techniques are employed at the upper layers of wireless networks,whose security performance is guaranteed at the cost of high computational complexity of algorithms and keys.As a complement,physical layer security is studied from the aspect of information theory and signal processing.It is to exploit the inherent randomness of noise and communication channels to enforce security.Recently,about the jamming strategy in the physical layer security field,there has not been a systematic comprehensive survey yet.And most of current physical layer security schemes assume that the eavesdropper's channel state information is known to legitimate users,while the study without the eavesdropper's channel state information is on-going.Especially,there are few studies on mobile eavesdroppers,whose channel state information is unknown.Besides,most of current physical layer security schemes choose to operate the security measure during the whole communication process.The design may cost a large number of resources,and may make the scheme not suitable for the resource-constrained systems.Aiming at these three issues,the thesis has studied the physical layer security in the network with a mobile eavesdropper and focused on jamming strategies,which is one of main stream physical layer security techniques.The scheme is also expected to save resources as many as possible.The main contents and contributions of this thesis are listed as follows:First,the thesis focuses on the jamming strategy,and gives a comprehensive analysis and summary of current main stream jamming schemes.The thesis proposes the classification of jamming strategies,and gives an analysis and evaluation of each kind of jamming strategies.The thesis discusses challenges,potential future works and applications in this field.The thesis gives a survey of the jamming strategy.Second,the thesis aims at the wireless network with mobile eavesdroppers,and proposes a prediction scheme on the eavesdropper to predict the security risk in legitimate users' communications,which can make the physical layer security scheme more suitable for the resource-constrained system.By judging whether the eavesdropper will harm the communication security between legitimate users or not,legitimate users can decide whether to take security measures or not.Because in this scheme,security measures are not taken during the whole communication process,this method can save many resources.Last,on the premise of the above-mentioned prediction scheme,the thesis proposes a physical layer security scheme based on the cooperative jamming strategy,including the jammer selection scheme and the optimal power allocation algorithm.By sending artificial noise signal to the network space,the jammer can prevent the eavesdropper from effective eavesdropping,thus to guarantee legitimate users'communication security.