Research On Anti-Multipath Technology Of Vortex Electromagnetic Wave Communication System

With the rapid popularization of Internet terminal equipment and communication terminal equipment,the call for new communication technology with large-capacity,high-spectrum is becoming more urgent.Vortex Electromagnetic Wave Communication with orbital angular momentum(OAM)has raised much attention because the orthogonality among different modes of OAM singles can be used to realize single-band multi-user multiplexing transmission.However,due to the divergence of vortex electromagnetic wave in the transmission process,multi-path effects cannot be ignored in OAM communication.In this context,we focus on two-path transmission model of vortex electromagnetic waves in the range of sight distance to solve the problem of mode crosstalk at the receiver.In order to find out the influence of multi-path transmission on vortex electromagnetic wave communication,this paper first uses metasurfaces to generate single-mode number of vortex electromagnetic waves and observes the phase distribution and mode purity on the cross-section perpendicular to the transmission direction at the same position in the single-path transmission model and the two-path transmission model.The analysis shows that in the two-path transmission model,the phase distribution is disordered due to the superposition of the reflected wave and the direct wave at the receiving end,which leads to the outward diffusion of single-mode numbers,which is called modal crosstalk.Inspired by the expression of the vortex electromagnetic wave signal,this paper establishes a domain transformation from the mode domain to the azimuth domain when solving the mode crosstalk problem caused by two-path transmission.The domain transformation process from generation to demodulation domain of vortex electromagnetic wave communication system is clarified.By comparing the characteristics of the channel matrix in the azimuth domain during single-path transmission and two-ray transmission,the causes of mode crosstalk at the receiving end of two-path transmission are analyzed.A method of eliminating mode crosstalk based on matrix decomposition is proposed,which can eliminate mode crosstalk in mode domain by adjusting the channel matrix in azimuth domain.In addition,it is verified by simulation that the method has universality under the two-path transmission model and more complex channel models.