Research On Key Technologies Of Directional Modulation Based On Frequency Diverse Array

With the continuous expansion of wireless networks and the development of new applications,the number of active mobile users is increasing rapidly.At the same time,security has become a key issue in wireless applications.The traditional security methods based on encryption algorithms face challenges due to the complexity and the improve-ment of computer computing power.Physical layer security technology realizes secure communication by means of wireless channel fading,interference and path diversity,and does not need key encryption.It shows different characteristics from upper layer en-cryption technology.As an important technology in physical layer security,directional modulation has been widely studied by many scholars,but this method can only achieve directional security.As a new system array,frequency diverse array(FDA)can produce beam pattern related to direction and distance,so it can be combined with directional mod-ulation to solve the above problems.This thesis focuses on the key technologies of directional modulation based on FDA.The specific research contents and main conclusions are as follows:(1)The transmitter structures of beamforming FDA communication and directional modulation FDA communication are proposed,and their parameter calculations are trans-formed into optimization problems.Due to the non convexity of the optimization function,heuristic algorithms such as genetic algorithm are usually used to solve them.The pro-posed scheme can improve the communication security of eavesdropping users and target users in the same direction.Finally,through simulation,the performance of the two trans-mitter structures in physical layer security is compared and analyzed,and it is found that directional modulation FDA communication has better security in general.(2)The model of multipath fading channel is given and the alignment statistical char-acteristics are analyzed.A physical layer secure communication scheme based on direc-tional modulation FDA in multipath fading channel is proposed.The scheme estimates the channel based on the pilot signal,and the pilot structure adopts the block structure,and then reduces the influence of channel fading through channel equalization at the receiver.Simulation results show that the scheme can effectively ensure the communication quality and safety performance of directional modulation FDA under the condition of multipath channel.(3)An implementation scheme of space division multiple access based on directional modulation FDA communication is proposed,and a method to simplify the solution pro-cess of optimization problems is given.In Quadrature Phase Shift Keying(QPSK)mod-ulation communication system,this method can reduce the original 16 optimization prob-lems to one,and effectively improve the efficiency of parameter calculation.This scheme can realize subchannel division not only in the direction dimension,but also in the dis-tance dimension.Finally,the simulation results show that the scheme can effectively realize space division multiple access.