非均匀散射空时频相关MIMO信道建模与仿真研究
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摘要
多输入多输出（Multiple-input Multiple-output, MIMO）技术可显著提高系统的信道容量、传输速率与频谱利用率，近年来已成为第四代移动通信系统的关键技术之一。无线传播环境对通信系统性能起着决定性作用，收发天线阵元间距不够大及环境散射不充分导致各信道衰落具有相关性，因此研究相关MIMO信道的建模与仿真对于MIMO系统的参数设计、算法优化和性能分析具有重要的理论意义与应用价值。本文重点研究了非均匀散射环境下相关MIMO衰落信道建模仿真，MIMO信号空时频相关性计算以及阴影多径复合衰落下MIMO系统性能。
首先，介绍了无线衰落信道传播特性和建模仿真研究现状。针对传统均匀散射环境下瑞利衰落谐波叠加(Sum-of-Sinusoids, SoS)信道模型在平稳和统计独立性等方面的不足，提出一种基于最佳到达角的简化SoS模型，该模型各种统计性能优于现有模型。同时，基于入射角概率面积等分方法提出一种适用于非均匀散射的SoS推广模型，并将该模型应用于更为通用的Nakagami衰落信道情况，为Nakagami-MIMO信道仿真实现奠定基础。
其次，分析了瑞利衰落下MIMO系统各支路接收信号之间的空时频相关性，推导了接收端移动情况下空时联合相关性的解析表达式。针对实际中空域相关性非常重要但数值计算较复杂的问题，提出一种基于角度域脉冲采样的简化计算模型，该模型误差小于0.01，但运算时间远小于数值积分及其它方法。通过详细分析Nakagami与瑞利衰落相关性的内在联系，推导给出Nakagami-MIMO信号包络之间的空时频相关性解析式，以及相干距离(时间、频率）的近似表达式，为MIMO信道建模与系统性能分析奠定理论基础。
结合上述单输入单输出信道仿真建模方法和MIMO信道相关性分析，本文随后给出了一种空时频相关Nakagami衰落的MIMO信道模型。该模型首先利用实际测量的数据或统计信息得到各种信道参数，然后利用理论分析方法获得信道空时频相关性矩阵，最后产生具有特定自相关性和互相关性的Nakagami随机过程，从而获得相关Nakagami-MIMO信道。针对大规模多支路MIMO信道实时仿真需求，还提出了一种高效的舍弃法模型用于产生任意衰落系数Nakagami随机序列，新方法效率优于目前文献报道的同类方法。
最后，针对多径阴影复合衰落分布复杂难以获得系统性能精确解析式的问题，基于矩匹配思想推导给出了相关复合衰落系统的近似性能。为验证近似性能表达式的正确性，本文还提出了一种新的相关复合衰落信道仿真模型，并基于该模型仿真获得了相关复合衰落下MIMO信道的遍历容量。
MIMO technology can be used to improve system capacity, transmission rate and spectralefficiency and becomes one of the key solutions for the4thgeneration wireless communication system.It is well known that the performance of MIMO system is greatly influenced by the wirelesspropagation environment. The correlation between channel fadings cannot be ignored for the compactantenna array and non-ideal propagation. Therefore, it is very important for parameters design,algorithms optimization and performance analysis of MIMO system to study the modeling and thesimulating MIMO channels with space-time-frequency correlation. This dissertation focuses oncorrelated MIMO channel model in non-isotropic scattering environment, space-time-frequencycorrelation between MIMO signals and MIMO system performance analysis for composite fading.
Firstly, the wireless propagation properties and the researches on channel model and simulationare reviewed. The stability and statistically independence of the traditional SoS models are not good,so an improved model based on optimal angle of arrival (AoA) is proposed, whose statisticalperformance is better than other models. Based on the method of equal probability areas of AoA, anextended SoS model for non-isotropic scattering conditions is presented. It is then applied onmodeling the Nakagami fading channel which is more flexible than Rayleigh fading. Thus it lays thefoundation of Nakagami-MIMO channel model.
Secondly, this paper analyzes the space-time-frequency correlations of MIMO system underRayleigh fading and derives the expression of spatial-temporal joint correlation with mobile antenna.The evaluation of spatial correlation is very important but also complicated for needing numericalcomputation, so a simple spatial correlation calculation method based on pulse sampling principle inangle domain is presented. The maximum error of the new method is less than0.01while thecomputation time is far less than numerical integration method or other methods. Based on therelationships between Rayleigh and Nakagami fading, a general close-form expression of thespace-time-frequency correlation for Nakagami fading, as well as coherence time and coherencebandwidth, are derived. These results are useful and important for MIMO channel model andperformance analysis.
Thirdly, based on the SoS model proposed and correlation properties derived, this paper thenpresents a new correlated MIMO channel model with Nakagam fading. It obtains the channelparameters from field data or statistical information, and then calculates the space-time-frequencycorrelation matrix by theoretical method. Finally, the Nakagami-MIMO channels are obtained by generating Nakagami stochastic processes with specific auto-correlation and cross-correlation. Inorder to realize the large-scale and real-time MIMO channel simulation, a new rejection method isalso presented for generating Nakagami sequences with arbitrary fading factor, which has higherefficiency than other methods reported.
Finally, it is very difficult to analyze the system performance with the complicated distribution ofcomposite fading, so an approximate method based on moments match is proposed. In order toconfirm the validity of the new method, a novel simulation model for composite fading channel isthen presented. Moreover, it is applied on getting the ergodic capacity of correlated composite fadingMIMO channels.
首先，介绍了无线衰落信道传播特性和建模仿真研究现状。针对传统均匀散射环境下瑞利衰落谐波叠加(Sum-of-Sinusoids, SoS)信道模型在平稳和统计独立性等方面的不足，提出一种基于最佳到达角的简化SoS模型，该模型各种统计性能优于现有模型。同时，基于入射角概率面积等分方法提出一种适用于非均匀散射的SoS推广模型，并将该模型应用于更为通用的Nakagami衰落信道情况，为Nakagami-MIMO信道仿真实现奠定基础。
其次，分析了瑞利衰落下MIMO系统各支路接收信号之间的空时频相关性，推导了接收端移动情况下空时联合相关性的解析表达式。针对实际中空域相关性非常重要但数值计算较复杂的问题，提出一种基于角度域脉冲采样的简化计算模型，该模型误差小于0.01，但运算时间远小于数值积分及其它方法。通过详细分析Nakagami与瑞利衰落相关性的内在联系，推导给出Nakagami-MIMO信号包络之间的空时频相关性解析式，以及相干距离(时间、频率）的近似表达式，为MIMO信道建模与系统性能分析奠定理论基础。
结合上述单输入单输出信道仿真建模方法和MIMO信道相关性分析，本文随后给出了一种空时频相关Nakagami衰落的MIMO信道模型。该模型首先利用实际测量的数据或统计信息得到各种信道参数，然后利用理论分析方法获得信道空时频相关性矩阵，最后产生具有特定自相关性和互相关性的Nakagami随机过程，从而获得相关Nakagami-MIMO信道。针对大规模多支路MIMO信道实时仿真需求，还提出了一种高效的舍弃法模型用于产生任意衰落系数Nakagami随机序列，新方法效率优于目前文献报道的同类方法。
最后，针对多径阴影复合衰落分布复杂难以获得系统性能精确解析式的问题，基于矩匹配思想推导给出了相关复合衰落系统的近似性能。为验证近似性能表达式的正确性，本文还提出了一种新的相关复合衰落信道仿真模型，并基于该模型仿真获得了相关复合衰落下MIMO信道的遍历容量。
MIMO technology can be used to improve system capacity, transmission rate and spectralefficiency and becomes one of the key solutions for the4thgeneration wireless communication system.It is well known that the performance of MIMO system is greatly influenced by the wirelesspropagation environment. The correlation between channel fadings cannot be ignored for the compactantenna array and non-ideal propagation. Therefore, it is very important for parameters design,algorithms optimization and performance analysis of MIMO system to study the modeling and thesimulating MIMO channels with space-time-frequency correlation. This dissertation focuses oncorrelated MIMO channel model in non-isotropic scattering environment, space-time-frequencycorrelation between MIMO signals and MIMO system performance analysis for composite fading.
Firstly, the wireless propagation properties and the researches on channel model and simulationare reviewed. The stability and statistically independence of the traditional SoS models are not good,so an improved model based on optimal angle of arrival (AoA) is proposed, whose statisticalperformance is better than other models. Based on the method of equal probability areas of AoA, anextended SoS model for non-isotropic scattering conditions is presented. It is then applied onmodeling the Nakagami fading channel which is more flexible than Rayleigh fading. Thus it lays thefoundation of Nakagami-MIMO channel model.
Secondly, this paper analyzes the space-time-frequency correlations of MIMO system underRayleigh fading and derives the expression of spatial-temporal joint correlation with mobile antenna.The evaluation of spatial correlation is very important but also complicated for needing numericalcomputation, so a simple spatial correlation calculation method based on pulse sampling principle inangle domain is presented. The maximum error of the new method is less than0.01while thecomputation time is far less than numerical integration method or other methods. Based on therelationships between Rayleigh and Nakagami fading, a general close-form expression of thespace-time-frequency correlation for Nakagami fading, as well as coherence time and coherencebandwidth, are derived. These results are useful and important for MIMO channel model andperformance analysis.
Thirdly, based on the SoS model proposed and correlation properties derived, this paper thenpresents a new correlated MIMO channel model with Nakagam fading. It obtains the channelparameters from field data or statistical information, and then calculates the space-time-frequencycorrelation matrix by theoretical method. Finally, the Nakagami-MIMO channels are obtained by generating Nakagami stochastic processes with specific auto-correlation and cross-correlation. Inorder to realize the large-scale and real-time MIMO channel simulation, a new rejection method isalso presented for generating Nakagami sequences with arbitrary fading factor, which has higherefficiency than other methods reported.
Finally, it is very difficult to analyze the system performance with the complicated distribution ofcomposite fading, so an approximate method based on moments match is proposed. In order toconfirm the validity of the new method, a novel simulation model for composite fading channel isthen presented. Moreover, it is applied on getting the ergodic capacity of correlated composite fadingMIMO channels.
引文
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