| The rise and evolution of the mobile Internet and the internet of things(Io T)imposes new requirements and challenges on the current communication rate and diversified business.The 5G NR integrates multiple technologies to meet the miscellaneous service needs of the three application scenarios of e MBB,u RLLC and m MTC.The existing plane electromagnetic waves-based transmission technology and limited spectrum resources cannot meet the future demands of green communication with large bandwidth,large capacity,high density and low power consumption.As a new transmission technology,vortex electromagnetic waves carrying orbital angular momentum(OAM)can effectively solve the problems of shortage of spectrum resources and limited communication rate.However,there are still many problems to be solved in the process of practical application of vortex electromagnetic waves to future B5 G and 6G communication systems.Therefore,in order to solve the problem that the complete alignment of the transceiver restricts the practical application of OAM communication systems and divergent OAM beam limits the long-distance transmission of vortex electromagnetic waves.This thesis studies the broadband beam steering of misaligned multimode OAM communication systems and the concentric space division multiplexing technology based on vortex electromagnetic waves,which provide a certain theoretical basis for the realization of multi-mode OAM broadband wireless communication and the construction of green cellular Io T in the future.This thesis mainly contains the following research contents:(1)In an OAM wireless communication system,multiplexing a set of orthogonal OAM modes at the same frequency and the same time can increase the system capacity,but the harsh condition of the complete alignment of the transceiver limits the practical application of OAM in the wireless communication system.Therefore,in view of the future large-bandwidth and large-capacity communication requirements,this thesis combines OAM technology and OFDM technology to construct a multi-mode OAM-OFDM communication system model under arbitrary misalignment conditions,and quantitatively studies the impact of oblique angle and large-scale array on the transmission performance of OAM communication system.On this basis,the analog beam steering(ABS)and digital beam steering(DBS)schemes are proposed for the structure of RF analog and baseband digital transceivers,respectively.Both theoretical analysis and simulation results show that the spectrum efficiency(SE)of misalignment OAM system without beam steering is lower than 2bit/s/Hz.ABS and DBS can improve the SE to more than 20bit/s/Hz,and the SE of DBS is higher than ABS by 3bit/s/Hz.The advantage of DBS is more obvious with the increase of antenna number and deflection angle.In contrast,DBS is more suitable for the future OAM wireless communication system with large bandwidth and large antenna array.(2)The inherent divergence of OAM beams limits the long-distance transmission of vortex electromagnetic waves in the point-to-point communication scenarios.In addition,the current 120-degree sector beam coverage leads to poor communication quality of cell edge users.Therefore,in response to the future high-density and low-power communication requirements,this thesis divides all the cell users into multiple ring groups according to the distance to the base station.And then,analog-digital hybrid transmitter structure is employed to construct UCA-based OAM concentric space division multiplexing(CSDM)system,which realizes long-distance broadcast communication by beam steering and space division multiplexing of divergent multi-mode OAM beams.The system employs orthogonal frequency division multiple access(OFDMA)technology to eliminate intra-group interference(IAGA),and utilizes low-complexity space-frequency vector perturbation(SFVP)precoding to convert inter-group interference(IRGA)into space diversity and minimize emissions power.Both theoretical derivation and simulation results show that,in terms of bit error rate and energy efficiency,the CSDM-SFVP system with hybrid structure and low-complexity SFVP precoding is superior to the CSDM system with zero-forcing precoding(CSDM-ZF)and the full-digital system with zero-forcing precoding(FBZF).In contrast,the CSDM-SFVP system is more in line with the development concept and demand of green cellular Internet of things. |
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