Research On Application Of Directional Modulation For Security Communication Based On The Arrays

Nowadays,researchers pay a lot attention to the directional modulation technology which is one of the key technologies of wireless communication system for physical layer security.The basic principle of the directional modulation technology is optimizing the signal direction(spot)of arriving and beamforming of the phased array(or frequency diverse array,FDA).So the signal would form a stable constellation in the desired direction(spot)and a distorted constellation in other spots.The main work of this thesis can be summarized as follows:1.The main characteristics of the FDA‘s beam are analyzed in terms of theoretical derivation and computer simulation.The FDA‘s beam has the distance periodicity and is helical outward diffused from the array‘s emission position.The realization method of "S" shaped beam is proposed,and this beam can be used as the interference source,which shows the advantage of FDA.And the feasibility of "S" shaped beam and dot beam method is verified by MATLAB software simulation.2.After researching and analyzing the principle of directional modulation technology which uses the genetic algorithm to calculate the phase shift,this thesis apply the particle swarm optimization to calculate the phase shift.This method has been further improved compared to the existing algorithm in calculating the phase shift,and guaranteed that the optimal solution can be obtained every time.Based on the existing phased array directional modulation,a directional modulation method using frequency diverse array as the transmitting array is proposed.This method can achieve more accurate selection of the position of the receiver(direction and distance double selection).Especially when the eavesdropping receiver and the desired receiver lie in the same direction,using FDA can achieve secure communication.Finally the computer simulation verify its correctness.3.After analyzing the directional modulation spread spectrum technology using a switched antenna array,the bit error rate and the security performance are compared in the case of using a single array element and subarray as the switched unit.Because of the existence of array gain,the security performance of a single antenna is not as good as that of subarray,but the antenna utilization of the existing switching scheme is low.This thesis proposes a new antenna(array)switching scheme.Comparing to a single antenna as the switch unit,this method improves the security performance,and to the existing sub-array,this method improves the utilization of the antenna.The effectiveness of this method eventually passes the simulation verification.4.A point-to-point secure communication software system using the directional modulation technology is built on the MATLAB platform.In this system,the phased array and FDA are used as the transmitting array respectively.The system simulates and tests the theoretical and actual bit error rate of the two modes.The simulation results show that by increasing the number of array elements and the length of spread spectrum code could improve security performance.