Research On Channel Capacity And Security Of Millimeter Wave Multimode OAM System

Orbital angular momentum(OAM)wireless communication is one of the key technologies of the sixth generation of mobile communication.OAM carries a large number of orthogonal eigenstates,and its combination with millimeter waves is expected to improve the antenna physical size,high-mode beam divergence,and transmission capacity.At the same time,the millimeter wave OAM beam has strong directivity and has the potential to improve the security of the communication system.This paper focuses on millimeter wave multi-mode OAM communication,and launches channel capacity and security research.The main research contents are as follows:(1)Firstly,the OAM channel model of aligned scene is constructed,and the amplitude and phase distributions of single-mode and multi-mode vortex electromagnetic waves in full angle domain are derived and analyzed,and the channel capacity under the influence of different system parameters is studied;The measurement platform of OAM wave-front radiation and channel is built,and the amplitude and phase distribution of vortex electromagnetic wave and channel are measured,which provides theoretical and experimental basis for the performance analysis of OAM system in the following misaligned scene.(2)Based on the aligned channel model,the channel model of vortex electromagnetic wave in the misaligned scene is constructed.The amplitude and phase distribution,modal power spectrum and channel capacity of vortex electromagnetic wave in the two relative positions of the receiving and transmitting array are studied;A twopath OAM channel measurement platform is built,and the millimeter wave vortex electromagnetic wave channel experiment is carried out in the reflection scene.Based on the measured channel data,the channel capacity performance of millimeter wave vortex electromagnetic wave system is analyzed.(3)Based on the characteristics of line-of-sight propagation and spiral phase structure of vortex electromagnetic wave,a vortex electromagnetic wave eavesdropping system is constructed.The security capacity of vortex electromagnetic wave eavesdropping system is derived,and the security capacity of vortex electromagnetic wave system under different eavesdropping distance,eavesdropping angle,eavesdropping array radius and eavesdropping power ratio is studied.The results show that due to the divergence of vortex electromagnetic wave beam,the safe communication of vortex electromagnetic wave system can be realized by designing the array radius and transmitting mode according to the beam propagation distance.