Research On Orbital Angular Momentum Radio Multiplexing Communication Technology Based On Uniform Circular Array

All current 1G-5G wireless communications are built on planar electromagnetic waves.However,electromagnetic waves have not only linear momentum,but also angular momentum,which contains spin angular momentum(SAM)and orbital angular momentum(OAM).OAM is one of the physical properties of electromagnetic wave propagation,and OAM wavefronts have spiral waves instead of plane waves.OAM has a large number of topological charges,i.e.,OAM modes,and due to the continuous phase shift of each OAM mode,the beams of different OAM characteristic modes are orthogonal to each other,and they can be together multiplexed/demultiplexed,thus increasing capacity without relying on conventional resources such as time and frequency.Multiple OAM modal signals transmitted simultaneously on the same channel can be separated and demodulated at the receiver.Therefore,in addition to frequency division multiplexing,time division multiplexing,polarization division multiplexing,and code division multiplexing,OAM provides a new dimension for wireless communication networks-OAM modal division multiplexing(MDM)to increase communication capacity,providing a new way to significantly improve spectrum efficiency,which is expected to be used in 6G and even more future wireless communication networks.In order to improve channel capacity and spectral efficiency,vortex electromagnetic waves carrying orbital angular momentum have been widely studied in wireless communications.However,the current research on eddy EM waves in wireless frequency bands mainly focuses on the generation and modal characteristics of eddy EM waves and their channel system capacity,and the research on OAM communication systems is not enough.This paper mainly focuses on the research of Uniform Circular Array(UCA)antenna carrying multimodal OAM multiplexing communication system,and the main research content and innovation points of the paper are divided into the following three parts:(1)Uniform circular array antennas offer the potential to realize planar compact solutions for simulating vortex electromagnetic waves.First,the cumulative electric field distribution based on the electric field points in the UCA is derived in a cylindrical coordinate system,and the OAM-UCA factorrelated parameters are simulated by Matlab software,which can give correct radiation maps and phase distribution results within seconds compared to time-consuming electromagnetic simulations,and second,the effect of the UCA factor-related parameters on the generation of ripple-free radiation maps is investigated to provide a basis for generating UCA-based A simple method to check the OAM modal purity is then introduced to further verify the generated OAM modal purity.(2)The multimodal OAM radio multiplexing communication system based on single-loop UCA is investigated,and its communication channel is modeled and analyzed in two communication scenarios with strictly parallel alignment and parallel non-aligrunent of single-loop UCA transceivers and transmitters,respectively,and the simulation results show that the capacity of its communication system is better than that of the conventional MIMO system.The BER analysis is performed after adding QPSK modulation to the multimodal OAM signal of single-loop UCA in combination with the conventional communication method,and the results show that the system BER is low when single-loop UCA singlemode OAM is used for communication transmission,however,with the increase of the number of carried modes,the performance of the transmission system decreases significantly,especially affected by the high BER of the carried higher-order modal vortex electromagnetic wave signal.To address this issue,we propose to fit the system transmission BER performance by normalizing the variance of the OAM channel gain matrix to obtain the optimal gain launch angle for single-loop UCA multimodal OAM multiplexed communications.(3)Secondly,the multiplexing transmission performance can also be optimized by establishing a multimodal OAM multiplexing communication system with concentric uniform circular arrays,according to the BER simulation results,the BER of the system is lower when multiplexing communication transmission with multi-loop UCA multimodal OAM,and the increase of BER with the increase of the number of carried modes is smaller compared with the single-loop UCA multimodal OAM multiplexing communication system,where the modal multiplexing The BER performance of each single-mode OAM under modal multiplexing is similar to that of single-loop UCA with single-mode OAM,and the concentric uniform circular array-based multimode OAM multiplexing transmission system provides good channel gain for MDM communication and low crosstalk between OAM modal channels.