Research On Receiving Theory Of The Vortex Electromagnetic Wave In The Wireless Communication

With the rapid development of wireless communication technology,the congestion problem of radio frequency(RF)band is increasingly serious.Therefore,with limited spectral resource,how to further improve the spectrum utilization rate is a tough problem.The vortex electromagnetic wave based on orbital angular momentum multiplexing can simultaneously transmit multi-channel information in the same frequency band and increase the capacity of the channel,so it becomes a research hotspot in the field of wireless communication.In this paper,the receiving theory of the vortex electromagnetic wave in the wireless communication is mainly studied.First,this paper introduces the research background,significance and current research status of the vortex electromagnetic wave and summarizes the main work and structure of this paper.Then,this paper expounds the basic theory of orbital angular momentum and the vortex electromagnetic wave and explains the generation method and propagation characteristic of the vortex electromagnetic wave.Afterwards,this paper briefly describes two receiving methods: whole angular aperture receiving method and partial angular aperture receiving method and analyzes three frequently-used OAM modal detection methods.Firstly,the derivation process of single point measurement method is analyzed and the feasibility of the method is verified by the simulation results.Secondly,the theoretical derivation process of the traditional phase gradient method is described,and multi-antenna phase gradient methods with uniformly spaced antenna and paired-antenna are analyzed in detail.Then,the simulation performance of three methods is compared.Thirdly,the process of derivation of circular phase gradient method is described in detail,and the algorithm is simulated to verify that the simulation results of the method are in accordance with the theory.Then,for the problems where above-mentioned OAM modal detection methods do not explicitly involve the study of the receiving area with a relatively large electric field intensity and the distribution of the electric field intensity of the OAM wave is not uniform,based on the concentric circular arrays model,this paper innovatively proposes two methods of determining the common reception sampling area of multi-mode OAM waves in order to further improve the reception and detection performance of the vortex electromagnetic wave.The two methods are:(1)The method of calculating function formulas of the upper and lower boundaries of the common reception sampling area.When the LOS between the transmitting antenna array and the receiving antenna array is known,according to analyzing the data of high and low 3d B values of maximum value of the electric field intensity vector related to the OAM modality and LOS,we can find the overlap reception area,that is,the common reception sampling area of multi-mode OAM waves,and determine the function formulas of the upper and lower boundaries of the area.(2)The method of analyzing amplitudes and phases of the axial ratio of the optimal receiving position of multiple single-mode OAM waves.When the LOS between the transmitting antenna array and the receiving antenna array is unknown,according to analyzing the data of the maximum value of the electric field intensity vector related to the OAM modality and LOS,we can derive the polynomial of the optimal receiving position related to the OAM modality and LOS.Based on the above polynomial,by analyzing amplitudes and phases of the axial ratio,we can select two appropriate amplitudes and phases of the axial ratio as the criterion for judging the common reception sampling area.Then,we can compare amplitudes and phases of the axial ratio of the criterion with the measured amplitude and phase value of the axial ratio to determine whether the location of the receiving antenna is within the common reception sampling area of multi-mode OAM waves.Finally,this paper derives a theorem formula related to the optimal receiving position of OAM wave and frequency.When other parameters besides frequency are the same and the optimal receiving location of OAM wave at certain frequency is known,optimal receiving locations of OAM wave at any frequency can be confirmed easily,according to the formula.The ideas of two methods are also suitable for other multi-mode OAM arrays.