Research On Multiple Antenna Directional Modulation For Physical Layer Security Transmission

Directional modulation(DM)is an important technology for physical layer security transmission,which can distort the signal along undesired directions to prevent eavesdroppers from eavesdropping information,while the legitimate receiver at desired direction can realize a normal communication.Many scholars have made an active exploration for DM in recent years.However,this technology is still in its infancy,there are still many problems worth of research.With the spatial scrambling DM and the switched antenna DM as the entry point,the chief contents of this paper are as follows:1.This article has conducted research on spatial scrambling DM.To improve the security performance of spatial scrambling DM,two kinds of interference excitation are designed and optimized.One of the interference excitation is designed based on orthonormal base vectors,another excitation is based on the combination of orthonormal base vectors and Gaussian vectors.Under the constraint of transmitter efficiency,the optimization model is measured by the maximum of eavesdropper's symbol error rate in a certain area which surrounds legitimate receiver.Then the optimization problem is solved by augmented Lagrangian genetic algorithm.Simulation results show that,compared with general directional modulation signal,those two methods have a better security performance and own a narrower security beam width.2.The switched antenna subset directional modulation is studied.The equal probability continuous position switching antenna mode and the probability-weighted random position switching antenna mode are proposed to enhance the security performance.Then the security rate formula have been derived under the condition that the switching speed equals to the symbol rate.Those three switching modes of equal probability random position,equal probability continuous position and probability-weighted random position are compared by simulation.Simulations results show that equal probability continuous position mode has the best security performance when signal to noise ratio is low,and the probability-weighted random position always has a better performance over equal probability random position mode.3.Research has been carried out on direct sequence spread spectrum directional modulation based on switched antenna.The problem that the existing method can betray confidential message in particular directions is found,then a spread spectrum directional modulation method based on irrelevantly switched antenna is presented to solve this problem.The existing spread spectrum directional modulation method has the dispreading effect in some particular directions,therefore,eavesdroppers equipped with a traditional receiver can get the confidential message without obtaining the spreading sequence.Those particular directions are calculated and a security-enhanced method is proposed through separating the antenna switching from the spectrum spreading to eliminate the security vulnerabilities.Finally,simulation results show that the proposed method has a better security performance and anti-jamming capability.4.The frequency-hopping directional modulation technology is studied.In order to increases the carrier estimation difficulty for eavesdropper,a kind of directional modulation technology with frequency-hopping feathers is proposed according to the Doppler effect.By quickly switching antenna elements with a varying speed,frequency hopping signal can be produced in undesired directions due to period variation of the phase,while the carrier frequency of a pre-specified direction keeps constant.The time-frequency spectrograph in different directions is analyzed and simulated together with the communication performance of eavesdropper to validate the frequency-hopping directional modulation method.5.A switched antenna directional modulation experiment system is designed and established.The structure is mainly based on GNU Radio and USRP software radio platform.This system,which has the function of video transmission from point to point,is based on the use of high speed switch,FPGA control board,network group and array antenna.The structure of switched antenna subset DM transmitter is optimized to reduce the complexity of implementation.Feasibility of the switched antenna DM system is validated by testing the performance of video transmission and constellations patterns along different directions.