| Orbital angular momentum(OAM)is one of the potential key technologies for the beyond the 5th generation(B5G)and the 6th generation(6G)communication systems,since different modes of OAM beams are orthogonal to each other,OAM multiplexing can greatly improve the utilization of spectrum resources.Under the the reflection,diffraction and scattering of different building materials in the indoor environment,multipath propagation of OAM waves can cause OAM inter-modal crosstalk,which downgrades the OAM communication performance.To understand the OAM wave amplitude and phase distribution under the affection of building materials,and constructing an accurate OAM wave propagation and channel model are prerequisites for accurate design and evaluation of OAM communication systems.At present,most scholars mainly calculate the propagation path using the free space loss model based on the mirror principle,and establish a deterministic OAM channel model.On the one hand,the deterministic model relies on environmental information and material properties,and simulation computing power requirements are high,and application scenarios are limited.On the other hand,the existing OAM channel data is insufficient and the deterministic model verification work is insufficient.Few scholars have carried out research on statistical OAM channel modeling.Aiming at the problem of insufficient research on the statistical channel model of OAM communication,this thesis characterizes the propagation and fading characteristics of OAM beams in a real indoor wireless communication environment,and combines measurement data and statistical methods to carry out statistical modeling research on indoor 3.5 GHz OAM communication channels.The main research contents and innovations are as follows:1.A high-precision OAM wave reflection propagation model under the affection of indoor single-layer building materials is proposed.Firstly,taking the primary reflection of OAM wave as the research object,and by introducing the correction factor X of the material reflection field,an OAM wave primary reflection propagation model based on the mirror ray method is constructed;Then,an OAM amplitude and phase measurement platform based on a vector network analyzer is built,and the measured OAM amplitude and phase wavefronts database under the affection of seven common building materials is obtained;Finally,the accuracy of the model are verified by studying the modal purity characteristics of OAM wave.The results show that the accuracy of the OAM wave single-reflection propagation model under indoor building materials is improved to 0.1%comparing to that of ideal mirror model.2.A large-scale statistical channel model for indoor OAM full-angle domain is constructed.Firstly,an indoor OAM channel measurement scheme is designed.Then,a frequency domain measurement platform based on a vector network analyzer is built to obtain a large-scale channel measurement data set in the full-angle domain.Next,the constructed full-angle domain fitting function is used to fit the measured data,and the OAM amplitude correction parameters are obtained.The results show that the full-angle domain fitting function can well describe the full-angle domain amplitude characteristics of OAM waves.At last,a large-scale path loss model is used to linearly fit the channel data in the full-angle domain,and the results clarify the path loss of the +1 and-1 modal OAM beams in the range of 0°～90° rotation angle.The research work in this thesis clarifies the propagation law of 3.5 GHz OAM waves in indoor multipath scenarios,and provides basic theory and data support for B5 G and 6G indoor OAM communication system design,waveform design and evaluation of key technologies. |
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