Research On Physical Layer Secure Transmission Technology Based On Cooperative Jamming

Recently,wireless transmission networks have been widely applied in civilian and military scenarios,and emerged as indispensable part of our daily life.On one hand,with the rapid development of the wireless networks,an exponential growth in the number of connected devices has been occurred.On the other hand,due to the broadcast nature of wireless channels,any receiver within its coverage region are authorized to capture the signal emitted by source.Thus,providing an reliable and secure date transmission service is one of the most primary goal in the design and implementation of the 5G and future wireless communication networks.Different from the conventional upper-layer cryptographic techniques such as encryption,the basic principle of physical layer security schemes was investigated from an information-theoretic viewpoint,and it has been proved that a positive secrecy capacity can be achieved by utilizing the inherent randomness of the wireless channels and the difference between the legitimate channels and the wiretap channels.Therefore,physical layer security techniques owe superiority in terms of lower complexity and resource savings.Benefiting from the advantages of achieving spatial degrees of freedom and diversity gains,multiple antenna transmission technique have recognized as an efficient solution for realizing secure transmission in wireless networks.Specifically,in multi-antenna systems,transmit nodes can improve the signals received at the legitimate nodes while impair the signals received at eavesdroppers.Cooperative transmission technique can be regarded as an extension of multiple antenna transmission technique in space domain.In cooperative transmission networks,the cooperative nodes mainly act two roles including cooperative relaying(CR)and cooperative jamming(CJ)to further improve the security.Specifically,thanks to their benefit of easy deployment,the helper nodes can be adaptively selected to play different roles based on their location.However,the data transmission in relay networks requires two phases,i.e.,broadcasting phase and relaying phase,and this grants the potential secure information leakage.Therefore,it is challenging to guarantee secure transmission in relay networks.Different from CR scheme,in the CJ scheme,rather than improving the capacity of main channel,the friendly jammers degrade the capacity of the wiretap channel by emitting artificial noise with the aid of only statistical channel state information of the eavesdroppers to confuse the eavesdroppers.As such CJ scheme is shown to be much more reliable in enhancing secrecy performance,and intensive efforts have been devoted to focusing on physical layer security technique based on CJ.In this thesis,we focus on CJ scheme,and investigate secure transmission in unmanned aerial ve-hicle(UAV)-enabled and non-orthogonal multiple access(NOMA)cooperative transmis-sion networks.The main contents and contributions of this dissertation are summarized in the following(1)For the secrecy rate maximization(SRM)problem in a unmanned aerial vehicle(UAV)-aided cooperative transmission network,we propose a secure transmission scheme based on CJ.Firstly,we consider perfect channel state information(CSI),and reformulate the constriction of secrecy outage probability.Then the exact closed form expression of the secrecy outage probability(SOP)is derived,and the objective function of the SRM problem under certain is verified to be a concave one.Finally,an efficient scheme to obtain the optimal power allocation factor for maximizing the secrecy rate is developed.(2)We study secure cooperative transmission for the multiple-input-single-output multiple-eavesdropper(MISOME)systems.A more practical scenario is considered that the CSI of the channel between the UAV friendly jammer and the ground nodes is assumed to be imperfect.Specifically,we derive the exact closed form expression of the SOP under multiple eavesdroppers and develop an efficient power allocation strategy to guarantee secure transmission.Then,we examine the impact of specific parameters including the number of eavesdroppers,the altitude of the UAV,the transmit power of the UAV jammer and the channel estimation error on the secrecy performance of the considered system.Besides,a UAV placement strategy is developed for finding the best location of the UAV jammer to further improve the secrecy performance.(3)For the terrestrial cooperative NOMA networks,an adaptive CJ secure transmis-sion scheme is proposed.Firstly,perfect CSI is assumed,we discuss the constriction of the SOP for the user with high-level security requirement and the desired transmission rate for the other one,respectively.The exact closed form expression of the SOP and the upper bound of the power allocated to the primary user are derived.In addition,we have made a comprehensive discussion and developed an adaptive approach based on different cases to obtain the optimal power allocation factor for solving the SRM problem under certain SOP.Finally,the impact of the channel uncertainty on the secrecy performance if the considered system is demonstrated.(4)We investigate physical layer security in UAV-aided cooperative NOMA trans-mission networks.Specifically,for the considered system,in which a source intends to transmit confidential messages to one legitimate user with high-level security requirement,and serve another normal one simultaneously,an efficient approach consisting of adaptive power allocation adjustment for solving the SRM problem is developed.Besides,we also examine the impact of the channel uncertainties on system performance.Since the quality of service(Qo S)requirement must be satisfied,the upper bound of the power allocation factor is analyzed in detail,and an adaptive power allocation strategy for settling the SRM problem under certain SOP is proposed.Finally,We exploit the controllability and mobil-ity of the UAV jammer,and propose a placement strategy to optimize the position of the UAV jammer for further improving the effectiveness and the flexibility of our considered systems.Through both theoretical analysis and simulation experiments,the effectiveness of the CJ schemes proposed in this thesis have been confirmed.Numerical results are pro-vided to reveal the superiority and applicability of the proposed CJ schemes over bench-mark schemes in terms of secrecy performance and energy efficiency.Besides,these CJ schemes are verified to be promising in the practical wireless communication scenarios with imperfect CSI for the abilities of achieving relatively sufficient secrecy rate and en-ergy efficiency performance.