| Nowadays,information security has become the core and key of wireless communication,especially when wireless communication technology is applied to financial services and military communication.A traditional way to solve security problems in wireless transmissions is based on key-based encryption,whose security depends heavily on key complexity.With the development of mobile Internet and supercomputers,the security risks are gradually exposed.The most significant advantage of physical layer security(PLS)is that it does not require complex digital keys to encrypt useful information.From the perspective of information theory,the security of information transmission has been studied,and secure transmission can be guaranteed only by using the physical characteristics of the wireless channel.Directional modulation(DM),as an emerging and promising physical layer security technology in wireless transmission,has received extensive attention from academia and industry.DM utilizes the difference between the main channel and the eavesdropping channel to send useful information to desired direction(s)while disrupting useful information in undesired directions,thereby enabling more secure information transmission.In view of the physical layer information security issue,PLS communication techniques based on DM have been deeply studied in this dissertation.The main work and innovative contributions of the dissertation include the following five parts:(1)Based on the basic principle of directional modulation based on the RF(Radio Frequency)frontend optimization method of array antennas,a synthesis technique of directional modulation signal based on hybrid Particle Swarm Optimization(PSO)and Genetic Algorithm(GA)is proposed.Compared with the traditional directional modulation signal,the directional modulation signal transmitted by the proposed method has a narrower information beamwidth,and the bit error rate(BER)pattern has fewer significant side lobes,which can further improve the security performance of wireless transmission.(2)A DM technique based on linear sparse array(LSA)is proposed,which uses random selection of sparse rate and array pattern to synthesize the DM signals.The simulation results show that the sparse array optimization DM technique can significantly increase the bit error rate in the undesired direction,which can significantly enhance the information transmission security,and the use of linear sparse array further reduces the system cost.(3)Two DM techniques based on single-carrier and multi-carrier multiple antenna arrays models are proposed,and it is composed of the structure of base station and legitimate users,which is designed in detail,and the performance analysis of the proposed DM schemes from three metrics: symbol error rate(SER),secrecy rate and robustness respectively.The simulation results show that the DM technology based on multiple antenna arrays can realize secure and accurate transmission of confidential information and partially solve the neighbourhood security problem of traditional DM schemes.(4)A DM technique based on multi-parameter weighted-type fractional Fourier transform(MP-WFRFT)and chaotic scrambling is proposed.Specifically,the basic principle and implementation method of MP-WFRFT technology and chaotic scrambling technology are introduced,and the performance of the proposed DM scheme is analyzed from four metrics:SER,secrecy rate,robustness and anti-interception performance.The simulation results show that the DM technology based on MP-WFRFT and chaotic scrambling can solve the neighbourhood security problem of traditional DM schemes.(5)A multi-beam DM technique based on polarization sensitive array is proposed from the perspective of sampling and signal processing,where the security performance of the polarization sensitive array based DM technique is analyzed according to the SER index under the two scenarios of eavesdropper knowing the origin polarization states and eavesdropper unknowing origin polarization states.The simulation results show that the DM technique based on a polarization sensitive array can enhance the security of traditional DM schemes. |
