Research On Directional Modulation Technology In Wireless Communication Transmission

In recent years,with the rapid development of MIMO antenna systems,the role of wireless communication technologies has become more and more important.The wireless networks provide people with a convenient life,but at the same time,the security issues in the transmission have attacted much attention.In this thesis,it focus on the beamforming direction modulation technology,analysis the radiation function distribution of antenna array and optimized the target function of direction modulation,thereby improving the system's bit error rate performance.The main works of this thesis are as follows:(1)The direction modulation algorithm based on the target genetic algorithm is researched and improved.The direction modulation synthesis method based on target genetic algorithm is to change the direction constellation map by adjusting the phase shift value of the phase shifter to achieve the direction modulation.In this thesis,we improve the objective function of genetic algorithm.By designing the objective function reasonably,the width of the information beam of the directional modulation signal is narrowed and the directionality of the information beam is improved,which improves the security of the physical layer.(2)The direction modulation algorithm based on Fourier transform is researched and improved.Although the direction modulation algorithm based on Fourier transform can reduce the complexity of the algorithm,but the width of the main lobe of the information beam is wide,which can causes thr information leakage.In this thesis,the objective function of far-field distribution is optimized and weighted based on the Fourier transform algorithm,so as to reduce the main lobe width of the information beam and solve the problem of side lobe information leakage.(3)A directional modulation algorithm based on Woodward-Lawson is proposed.The Woodward-Lawson sampling method is applied to the method of linear approximation in a linear array.The method is simple in principle and has a small amount of calculation.In this thesis,combined with directional modulation technique and Woodward-Lawson sampling method,the far-field distributed objective function,which has been optimized,can achieve better performance of physical layer secure communication.