Research On Directional Modulation With Novel Array

Directional Modulation(DM),one of the promising multi-antenna techniques,has attracted a lot of interests for its ability of transmitting secure direction-dependent signals.With the evolution in the field of RF antennas,various types of novel arrays which can bring more design space for wireless communication have emerged.This thesis delves into the combination of directional modulation and novel array techniques to obtain higher security and transmission efficiency.In this thesis,spatial and directional modulation based on dual-polarization arrays is investigated to further improve spectral efficiency and security.Specifically,the polarization dimension of the dual-polarization array is used to modulate the polarization state depending on the information bits,which not only improves the spectral efficiency but also increases the system security.Furthermore,with the goal of maximizing the minimum Euclidean distance between polarization symbols,the polarization constellation diagram is geometrically optimized to improve the performance of the legitimate receiver.Moreover,a maximum likelihood signal detection scheme with joint baseband symbol,receive antenna index and polarization state symbol is designed,along with a low-complexity near-maximum likelihood detection method based on greedy algorithm is proposed for the legitimate receiver,based on which the theoretical bit error rate and security rate performance of the system are derived.The numerical simulation results verify that the proposed scheme outperforms the conventional spatial directional modulation in terms of transmission efficiency and security.In this thesis,an artificial-noise-aided directional modulation based on multi-log frequency diverse array is studied.Firstly,through analysis and simulation,it is found that the higher the degree of frequency shift nonlinearity among the frequencycontrolled array elements,the stronger its beam focusing capability.According to this feature,the multi-log frequency diverse array is selected as the transmit array.For its sidelobes,the artificial noise projection matrix is optimized with the objective of focusing the artificial noise power to the sidelobes region,under which the bit error rate and security rate are analyzed theoretically.Numerical simulation results demonstrate that,compared with the conventional spatially uniformly distributed artificial noise,the proposed artificial noise scheme suppresses the sidelobes leakage at the expense of smaller artificial noise without losing the secrecy capability in other regions,improving the system power efficiency and secrecy transmission capability.In this thesis,an artificial-noise-aided directional modulation based on reconfigurable intelligent surface is investigated.The angle difference of the reflective path from the reconfigurable intelligent surface is utilized to distinguish eavesdroppers in the same direction as the legitimate receiver.The beam assignment vector of the transmitter and the reconfigurable smart surface is jointly designed so that the legitimate side has a larger channel diversity gain.Aiming at maximizing the security rate,the joint optimization of beamforming and artificial noise is carried out by alternating iterations combined with semi-definite relaxation or genetic algorithm whether the eavesdroppers' channel is known or not.Numerical simulation results demonstrate that with the help of reconfigurable intelligent surface,the security and transmission performance can be enhanced even if the channel information of the eavesdropping party is unknown.