Research Of Physical Layer Security Transmission Technology For Millimeter Wave Wireless Communications

Security performance is an important index in wireless communication systems.The traditional encryption secure transmission technology is to encrypt the information in the upper layer of the system and then transmit it to the target user through the wireless channel.However,due to the broadcast feature of wireless signal,eavesdropper can easily eavesdrop the encrypted wireless signals and use high performance computer to decode.Thus,the traditional method still has hidden dangers.Physical layer security(PLS)technology utilizes the channel features to achieve secure wireless communications without encryption in the upper layer.Due to the exhaustion of low-band spectrum resources,the development of carrier frequencies in new generation wireless communication system towards higher frequency millimeter wave(mmWave)has become inevitable for wider bandwidth and higher rate.The increase of communication frequency band has caused changes of channel characteristics.The unique mm Wave channel characteristics of large path loss,strong reflection and weak diffraction make the wireless communication method change from single antenna to large-scale antenna array beamforming,which brings new challenges to the PLS.Although the increase in the number of array antennas improves the PLS performance of mm Wave beam,when the eavesdropper's receive gain increases infinitely or the eavesdropper is in the direction of mainlobe propagation,the PLS technology will still fail.Thus,studying and solving the sensitive eavesdropping problem in the sidelobe area and eavesdropping problem in the mainlobe is of great significance to improve the PLS performance of mm Wave beamforming transmission system.Motived by these,aiming at the problems of sensitive eavesdropping in the sidelobe regions and the mainlobe eavesdropping,this thesis proposes three PLS transmission schemes,which are programmable amplitude weight fixed angular beamforming(FAB),rotating angular beamforming(RAB)and fixed region beamforming(FRB),by exploiting the amplitude,frequency and phase degrees of freedoms(DOFs)of the phased antenna array.The main research works and the contributions are summarized as follows.1.FAB PLS transmission technology based programmable amplitude weight phased array(PAWPA).In order to increase the randomization of sidelobe leakage signals and solve the problem of sensitive eavesdropping in the sidelobe directions,the FAB PLS technology schemes of inverted amplitude antenna subset and optimal amplitude weight subset based PAWPA are proposed.The mathematical statistical characteristic theorems of beamforming gain of amplitude antenna subset and finite phase shifter resolution are derived,and then the approximate Gaussian distribution characteristic of the sidelobe randomized signal and the optimized design model of antenna subset with maximum sidelobe artificial noise power are obtained.An optimized scheme of sidelobe peak is proposed by constructing a high-quality antenna subset vector codebook with simulated annealing particle swarm optimization algorithm.The simulation results show that the proposed schemes can provide better robust sidelobe secrecy rate(SR).2.RAB PLS transmission technology.To solve the eavesdropping problem in the direction of mainlobe,an angular range dual-parameters controlled RAB PLS transmission technology is proposed by exploiting the frequency DoF of the frequency diverse phased array.The beam rotation theorem is proposed,and the propagation trajectory equations of beam mainlobe,grating lobe and zero lobe are formulated.The optimization design method of FOI to reduce the influence of grating lobe is analyzed.Beam zero sidelobe rotation technology is used to generate a signal receiving blind region to solve the eavesdropper with known position information.The beam dynamic rotation technology is used to reduce the average sidelobe gain,so as to prevent eavesdropper with unknown position information from capturing the mainlobe of beam and eavesdropping.The SR performance of the proposed schemes is analyzed through simulation.3.FRB PLS transmission technology.In order to solve the PLS threat of the main beam of FAB,FRB PLS technique is proposed to control the FOI vector of frequency diverse subarray(FDSA)to effectively superimpose the sub-beams in the target region and cancel each other out of the target region.A seeker optimization algorithm and a block coordinate descend linear approximation algorithm are proposed to solve the non-deterministic polynomial hard(NP-hard)problem of FOI selections of FDSA for unknown eavesdropping position information and known eavesdropping position information,respectively.The relationships between the antenna subarray division scheme,the maximum FOI setting range and the SR are analyzed.PLS performances of the proposed scheme are analyzed through theoretical analysis and simulation.In summary,the thesis proposes three types of beamforming technologies for secure transmission in view of the challenging problems of PLS transmission,which solve the problem of sensitive eavesdropping in the sidelobe region and the zero SR problem at the mainlobe position.The simulation results verify the effectiveness of the proposed schemes.