【作者】 陈靖峰；

【导师】 周杰；

【作者基本信息】 南京信息工程大学 ， 信号与信息处理， 2012， 硕士

【摘要】 MIM0通信系统在提高频谱效率和增大信道容量上表现出卓越的优越性,MIM0系统的性能主要由表征着天线阵列与信道特征的空间相关性函数所决定。随着紧凑型天线的发展,互耦效应对于系统的影响更加显著,因此分析互耦效应对于MIMO系统的影响具有重要的意义。本文重点研究了不同入射信号分布与相关性的关系以及互耦效应对于MIMO系统的影响。全文具体工作包括以下几个方面。第一,以均匀分布的圆形天线阵列为模型,入射信号分别为均匀、高斯和拉普拉斯能量分布和三种双边带分布时,推导出其空间相关性的精确和近似表达式,分析了在入射信号为双边分布时各种因素对于其空间相关性的影响。仿真分析结果表明,双边带分布时相关性波动幅度和差值取决于中心到达角之间的差值。第二,分析了互耦效应对多天线性能的影响,通过网络等效分析法对天线模型进行简化分析,得出阻抗矩阵和收发端的耦合矩阵。推导出互耦效应时天线阵元空间相关性的通用表达式,并论证了它与无互耦时空间相关性的关系。研究了互耦效应分别对平行天线阵列和共线天线阵列阵元间空间相关性的影响。仿真分析表明,互耦效应对于两种天线阵列的影响显著不同,适当的选择天线阵列可以有效地改善互耦效应对于系统性能的影响。第三,针对在互耦效应影响下,均匀线形天线阵列在阵元间距较小时信道容量急剧下降的问题,提出一种具有空域对称结构的均匀圆型天线阵列。在建立网络等效模型的基础上,推导出互耦效应下空间相关性的通用表达式,并在来波角谱为高斯分布的情况下与均匀线型天线阵列的容量性能作仿真比较。仿真结果表明：均匀圆型阵列的空间对称性排布结构使其具有良好的互补性,这种天线阵列具有非常稳定的信道容量,可以有效地改善互耦效应对于系统性能的影响。第四,针对非频率选择性瑞利衰落的MIMO信道,建立接收天线的空间三维信道模型,将信道建模推广到空间域。建立了天线阵列间在互耦效应下的等效网络模型,推导出三维模型下的互耦相关性的通用表达式。应用该公式分析了当接收端为不同的天线阵列时,入射信号中扩展角和俯仰角的中心到达角和角度扩展分别对于互耦效应下信道容量的影响。数值分析验证了不同的角度扩展对于互耦相关性的影响,仿真结果表明互耦效应下影响系统容量的主要因素为入射信号的平均中心到达角。更多还原

【Abstract】 MIMO(Multiple-input multiple-output)wireless systems, in which multiple antennas are used at both transmitter and receiver, have demonstrated the great potential for increased spectrum efficiency and channel capacity.The major issue of MIMO systems is that capacity gain is highly dependent on the spatial correlation,which is a function of the antenna array and channel characteristics.In order to achieve a compact array,mutual coupling becomes particularly significant as the interelement spacing is decreased.Therefore,it is of great value to analyze the impacts of mutual coupling on the properties of MIMO channel.In this paper,the relation between different energy distributions and spatial correlation and the effect of mutual coupling on the performance of MIMO systems are studied.The main work of this paper detailed as follows.Firstly, we derive spatial correlation functions of a uniform circular antenna arrays for three type of angle-arrival(AOA) distributions and their bi-modal distributions.Three different AOA distributions are considered in this papena uniform angular distributions Gaussian angle distribution,and a Laplacian angle distribution.The generalized spatial correlation functions are investigationed carefully by exact and approximate analyses.Results show that the oscillation of correlation function depends on the difference between the AOA’s of the two modes.Secondly, the impacts of mutual coupling on the performance of MIMO wireless channel are analyzed. From the analysis of the antenna model by network equivalent analysis, the impedance matrix and the mutual coupling matrices of transmitter and receiver are obtained. A general expression of the spatial correlation between a pair of mutually coupled antennas is explicitly derived, and the conditions under which mutual coupling has no effect on the spatial correlation are also identified. The effects of mutual coupling on the parallel antenna array and the collinear antenna array are investigated. Simulation results show that the impacts of mutual coupling on parallel antenna array and collinear antenna array are quite different in the performance of MIMO channel, and the performance of MIMO system affected by mutual coupling can be improved effectively by properly selecting antenna array.Thirdly, considering the effect of mutual coupling, the channel capacity of a uniform linear array (ULA) will decrease rapidly with the decreasing of distance between antenna array elements, this paper provides a uniform circular array (UCA) with symmetric structure. A general expression of the spatial correlation between a pair of mutually coupled antennas is explicitly derived base on the established equivalent model, then the stability of the channel capacity of ULA and UCA are also compared in the case of truncated Guassian distribution of power azimuth spectrum. Simulation results show that this symmetric UCA can provide more stable channel capacity than ULA due to its complementary properties among the antenna array elements. The effect of mutual coupling on the performance of MIMO system can be improved effectively by selecting UCA.Fourthly, a three-dimensional antenna array channel model for frequency nonselective Rayleigh fading channel is set up and the channel model setting is extended to space. This paper analyzes mutual coupling between antenna arrays and obtains the equivalent network model of the multiple-antenna. The general spatial correlation expression of channel model with the impact of mutual coupling is derived. When the receivers are different antenna arrays, the effects of the angular parameters associated with the mean azimuth of arrival(MAOA),azimuth spread(AS),mean elevation of arrival(MEOA)and elevation spread(ES) on the system capacity is investigated. Numerical results verify the different angle spread impact on spatial correlation. The simulation results indicate that the system capacity with the mutual coupling is more dependent on the MAOA and MEOA than the AS and ES.更多还原