Research On Key Technology Of Physical-layer Security Based On Frequency Diverse Array

Wireless communications has stepped into the era of 5G.The 5G era makes the interconnection of all things possible,but it also brings great challenges to information security.In recent years,the physical layer security has been playing an increasingly important role in information security.Different from the traditional encryption mechanism based on key exchange,physical layer security employs the inherent properties of wireless channels to guard the security of information transmission.Directional modulation(DM)has received great attention due to that it can enhance security by directionally sending confidential message.However,the traditional phased array(PA)based DM technique can safeguard security in the direction dimension only,but not in the distance dimension.Frequency diverse array(FDA)emerges as a new technique and can efficiently address this issue.It can produce a jointly direction-distance related beampattern due to imposing a frequency increment,which makes it potentially useful in the area of radar,physical layer security communications,etc.This dissertation focuses on FDA-based DM and some researches are carried out in the area of physical layer security.To be specific,the main contributions of this dissertation can be listed as follows:(1)FDA-based physical layer security scheme over fading channels is proposed.Fading is one of the intrinsic properties of wireless channels,and the study of FDA-based physical layer security over fading channels is of great significance.Time-variance of receive signal in FDA related application is an intractability problem.For this thorny issue,a new receive signal processing approach is proposed in this dissertation,which is capable of addressing the time-variant problem effectively.Since the receive signal-to-interferenceplus-noise ratio(SINR)of the eavesdropper is tedious to cope with,this dissertation derives an approximate expression for the SINR of the eavesdropper,which facilitates the performance analysis subsequently.Based on the preparation,the closed-form approximate expressions correspond to average secrecy capacity,probability of nonzero secrecy capacity and secrecy outage probability performances are derived,respectively.Besides,to have a deep insight into the system security,this dissertation further derives the upper bound of average secrecy capacity and lower bound of secrecy outage probability in high SINR regime,respectively.Specifically,to obtain the upper bound of average secrecy capacity,a useful approximate expression for exponential integral function is derived in this dissertation.Based on these performance expressions derived,this dissertation analyzes the corresponding performances,and then compares them with the performance of PA-based scheme.(2)Effects of key system parameters on FDA-based physical layer security are evaluated.To examine the effects of channel quality on security of FDA-based physical layer security system,this dissertation extends the FDA-based secure communication to a more general Nakagami-m fading scenario.Moreover,artificial noise(AN)aided method is employed to enhance security.Based on the channel model,this dissertation considers secrecy capacity,probability of nonzero secrecy capacity,secrecy outage probability,and secrecy throughput as performance metrics and derives the corresponding closed-form expressions,respectively.From these expressions,this dissertation analyzes the effects of distance,power allocation factor,frequency increment,fading parameter,direction difference of legitimate user and eavesdropper,and secrecy rate threshold on system performance theoretically.Further,this dissertation derives the potential zero eavesdropping areas and maximum eavesdropping areas,respectively,and the impact of potential eavesdropping location on secrecy outage performance is analyzed.(3)An FDA-based DF relaying SWIPT physical layer security model is proposed.Simultaneous Wireless Information and Power Transfer(SWIPT)and relay techniques have attracted widely attention due to the potentially remote charging and network coverage expanding abilities,respectively.This dissertation jointly considers the two techniques and proposes an FDA-based decoded-and-forward(DF)relaying SWIPT secure model.In this model,security is enhanced over two phases of the whole communication process.In the first phase,the legitimate user send AN to provide energy resource for the relay and to confuse the eavesdropper.In the second phase,the relay uses FDA DM technique to directionally forward information to enhance security,and sends AN to confuse the eavesdropper at the same time.Since the relay and legitimate user have a good knowledge of the channel state information(CSI)and nodes of the legitimate network,AN can be removed by the corresponding nodes when required to avoid unnecessary interference.Based on the model proposed,this dissertation considers time switching(TS)and power splitting(PS)relaying schemes,and derives the corresponding ergodic secrecy capacity expressions by employ moment generating function(MGF)approach together with the secrecy performances of both relaying schemes analyzed.(4)An FDA-based camouflaged and deceptive physical layer security scheme is proposed.The characteristic of FDA transmit signal makes the corresponding signal received similar to orthogonal frequency division multiplex(OFDM)in form.In this case,passive eavesdropper may recognize the receive signal as OFDM signal due to that the information of legitimate network is not available.Therefore,FDA has a function of masking its transmit signal and cheating the eavesdropper.Consider this scenario,this dissertation proposes an FDA-based camouflage and deception physical layer security scheme.In this scheme,the eavesdropper uses a different approach to address the receive signal comparing with the legitimate user,which differs from the existing literatures that all users have similar signal processing method(the conventional scheme).Besides,based on the secure scheme proposed,this dissertation analyzes the average secrecy rate,connection outage probability,secrecy outage probability,and secrecy throughput performances,and then compares them with those of corresponding conventional scheme and PA scheme.