基于电磁轨道角动量的无线传输系统建模与性能分析

发布时间：2018-06-28 18:50

  本文选题：电磁波 + 轨道角动量　； 参考：《浙江大学》2017年硕士论文

【摘要】：近年来因波前为涡旋形状而具备轨道角动量(OAM)的电磁波所展现的信息携带能力越来越受关注。作为电磁场的基本物理量,OAM在物理层提供了信息调制的额外自由度,利用不同OAM模态之间的正交特性来承载信息有望提升系统的频谱效率。鉴于OAM电波固有的传输特性,如何将其利用于无线传输并对可能带来的实际增益进行分析意义重大。本文围绕OAM在无线传输领域的应用展开研究,根据不同的场景进行系统建模和性能分析,主要内容概述如下:本文建立和分析了基于均匀环形阵列(UCA)的OAM复用传输模型。UCA作为一种能灵活辐射和接收OAM电波的方式,在OAM复用传输方面发挥着重要作用,而相同的配置也可基于传统的MIMO方式传输,我们期望分析这两种传输方式的差异和性能关系,进而揭示在在不同阵列配置和发送端信道边信息(CSI)假设下各自的优势和不足。模型中发送端单个UCA通过馈电叠加同时辐射多路涡旋电波,通过对UCA的接收信号进行DFT变换或基于MMSE准则来检测信号。以传输速率为参考,结果表明在发端已知CSI时如果两个平行的UCA有相同的阵元个数则两种传输方式等效,OAM的优势体现在发端未知CSI且收发阵列对齐时,DFT检测方式达到信道本身提供的最大传输速率。考虑到不同模式值的OAM电波具备的内在正交特性,本文的第二部分,我们希望将其正交性利用在自干扰消除方面并建立了基于OAM的同时同频全双工传输模型。模型中利用不同模式的OAM电波分别作为收发信号的载波,收发天线放置于同一个参考轴但彼此之间存在倾角。由于馈电偏差等因素导致辐射的OAM波束含有寄生分量,和接收模式一致的OAM分量将会被本地节点接收并作为残留干扰而存在。以最大化双工系统和速率为度量,在不同的模式纯度和白噪声强度下分析了最佳的双工模式选择。结果表明,在残留干扰起主导作用时双工模式选择为可选模式集中的最大或最小值;在干扰和噪声同时起作用时,模式选择在干扰和噪声单独存在时的极端值间过度变化。本文最后研究了OAM和MIMO相融合的传输系统。OAM和MIMO结合相当于拓展了原有的MIMO传输维度,在每个MIMO支路复用多路OAM有望进一步提升系统频谱效率。与此同时,OAM波束的发散效果相比平面波更加严重,导致接收功率快速衰减,基于此,我们建立了通用的复用传输模型以分析在这两个矛盾因素的影响下融合传输可能带来的增益。结果表明,在接收天线能覆盖波束有效拓展半径的前提下,近距离时复用传输的维度越多传输的容量也越大,而由于功率衰减在远距离时OAM-MIMO的传输速率不如MIMO。
[Abstract]:In recent years, more and more attention has been paid to the information carrying ability of electromagnetic waves with orbital angular momentum (OAM) due to the vortex-shaped wavefront. As the basic physical quantity of electromagnetic field, OAM provides additional degree of freedom for information modulation in physical layer. It is expected to improve the spectral efficiency of the system by using the orthogonal characteristic of different OAM modes to carry information. In view of the inherent transmission characteristics of OAM waves, it is of great significance to apply them to wireless transmission and to analyze the possible actual gain. In this paper, the application of OAM in wireless transmission is studied, and the system modeling and performance analysis are carried out according to different scenarios. The main contents are summarized as follows: in this paper, OAM multiplexing transmission model based on uniform ring array (UCA) is established and analyzed. UCA plays an important role in OAM multiplexing transmission as a flexible way to radiate and receive OAM radio waves. The same configuration can also be based on the traditional MIMO transmission. We expect to analyze the differences and performance relationships between the two transmission modes, and then reveal their respective advantages and disadvantages under different array configurations and channel side information (CSI) assumptions. In the model, a single UCA at the transmitter simultaneously radiates multi-channel vortex waves through the feed superposition, and detects the signal by DFT transform or based on MMSE criterion. Taking the transmission rate as a reference, The results show that if two parallel UCA have the same number of elements when the CSI is known at the source, the advantage of the two transmission modes is that the CSI is unknown and the receiver array is aligned to achieve the maximum transmission rate provided by the channel itself. Considering the inherent orthogonality of OAM waves with different mode values, in the second part of this paper, we hope to use the orthogonality in self-interference cancellation and establish a full-duplex transmission model based on OAM. In the model, OAM waves of different modes are used as carriers of the transceiver signal, and the antenna is placed in the same reference axis, but there are obliquity between them. Due to the error of the feed, the OAM beam contained parasitic component, and the OAM component which is consistent with the receiving mode will be received by the local node and will exist as a residual interference. Based on the maximization of duplex system and rate, the optimal duplex mode selection is analyzed under different mode purity and white noise intensity. The results show that the duplex mode is the maximum or minimum value in the optional mode set when residual interference is dominant, and the extreme value between interference and noise is excessive when the interference and noise are acting simultaneously. Finally, this paper studies the OAM and MIMO transmission system. The combination of OAM and MIMO is equivalent to extending the original MIMO transmission dimension, and multiplexing multiple OAM in each MIMO branch is expected to further improve the spectral efficiency of the system. At the same time, the divergence effect of OAM beam is more serious than that of plane wave, which leads to the fast attenuation of receiving power. A universal multiplexing transmission model is established to analyze the possible gains from the fusion transmission under the influence of these two contradictory factors. The results show that under the condition that the receiving antenna can effectively extend the radius of the beam, the larger the transmission capacity of the dimension of close-range multiplexing transmission is, the lower the transmission rate of OAM-MIMO is when the power attenuates at a long distance.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN92
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本文编号：2078992