新型网络结构下MIMO信道测量与建模研究

【作者】 聂欣；

【导师】 刘泽民； 张建华；

【作者基本信息】 北京邮电大学 ， 电路与系统， 2010， 博士

【摘要】 为了满足IMT-Advanced系统高数据率传输的需要,首先需要为IMT-Advanced系统寻找足够的频谱,其次需要使用MIMO等高频谱利用率的物理层传输技术,最后则需要采用新的网络结构。基于中继的通信系统与传统蜂窝网络相比,具有降低功耗、改善覆盖、提高数据率和增强分集增益的优点,被认为是最有效的IMT-Advanced候选方案之一无线信道的测量和建模是传输技术研究与评估、通信系统实现与部署的基础,因此在IMT-Adavanced分配或者候选频段内,以及在新型网络结构下,进行信道测量和建模是非常必要的。本论文主要围绕中继系统的宽带MIMO信道测量和建模,按照实地测量、统计分析、模型建立的思路,理论分析与实地测量相结合完成研究工作。论文的主要工作和创新点包括：(1)基于实测数据的信道性能分析方法和框架：MIMO和中继性能的研究吸引了广泛的关注,但是目前的理论研究所假设的信道状况较为理想,导致理论预测的性能与系统在真实传播环境中所能达到的实际性能存在偏差。现场测量获得的信道包含了传播环境的细节,因此基于实测信道进行的性能分析和预测具有较高的准确性,但是关于如何从实测信道获得系统的性能,目前还没有完整的方法和框架。为了对MIMO和中继在实际传播环境中的性能进预测和验证,提出并建立了基于实测信道进行性能分析的方法和框架,推导了重要信道性能的表达式,从信道增益、信号相关性、特征值分布、容量、分集复用折中等角度对实测信道的性能进行分析。基于建立的性能分析框架,研究了室内热点和室外中继场景信道的统计特性和性能,比较了三种传输方案(直接传输、放大转发和解码转发)在实际传播环境的信噪比、空间分集和容量,分析了传播环境对于系统性能的影响。(2)倾斜极化天线阵列的空间和互极化联合相关性研究：倾斜极化天线阵列利用了空间和互极化带来的解相关效果,可以有效降低信号相关性,提高系统性能。但是由于目前尚没有相应的理论表达式,倾斜极化天线阵列不同天线的信号相关性只能通过仿真或者测量得到,信道参数对相关性的影响也未完全明确。针对MIMO系统使用倾斜极化天线阵列的情况,基于3GPP SCM模型,推导了任意天线倾角和间距时,由空间相关性和互极化性联合贡献的信号相关性的表达式,并给出了大角度扩展和小角度扩展时的低复杂度近似表达式。推导了信号相关性随天线配置(间距、倾角)和信道参数(角度扩展、交叉极化鉴别率)变化的表达式。通过仿真验证了表达式的正确性,分析了准确表达式和近似表达式的应用范围,研究了不同天线配置信号相关性的变化规律。最后推导了天线倾角与天线间距的等效关系。(3)中继信道统计特性研究：中继天线一般低于基站天线,高于移动台天线。天线高度的改变导致传播环境不同于传统的基站与移动台链路。但是目前还没有在IMT-Advanced频段内进行MIMO中继信道测量的结果。对于MIMO中继系统性能有着重要影响的极化和空间特性还没有相关研究,因此,基于传统的基站与移动台链路获得的信道参数统计特性的适用性,以及中继信道参数的新特性值得深入探讨。根据实测数据和信道参数估计的结果,比较了中继信道三条链路的空间和极化特性,使用最小二乘估计获得交叉极化鉴别率和角度功率谱的分布。提出了使用多簇拉普拉斯分布描述角度功率谱。给出了交叉极化鉴别率随距离变化的经验公式。推导了信号相关性关于多簇拉普拉角度功率谱和交叉极化鉴别率的公式。根据推导的公式和实测获得的参数值,分析了不同链路的天线配置在实际传播环境中的信号相关性,为基站、中继和移动台的天线配置提供了指导。(4)簇内统计统计特性和传播机制研究以及簇识别和簇跟踪方法的改进：目前主要的信道模型均基于簇,最新的信道模型根据传播机制对不同类型的簇分配不同的参数。但现有的测量和研究尚未涉及RS(?)MS链路的簇内统计特性和传播机制。因此,根据信道参数估计的结果,对多经分量进行簇识别和簇跟踪。基于簇分析了RS(?)MS链路的簇内统计特性和传播机制。提出了多维距离簇心初始化方法,使用归一化正交距离作为距离的量度。提出了基于反射机制和自动跟踪相结合的簇跟踪算法。本部分工作为基于簇的信道建模和参数化提供基础。本文涉及室内热点场景和室外中继场景的测量结果分别被ITU-R和3GPP-LTE+组织接受,提出的方法可以广泛应用于信道测量和建模工作,测量和分析结果可以为IMT-Advanced性能评估和系统部署提供参考。以上研究工作可以为中国未来IMT-Advanced系统的仿真、评估和网络规划提供可靠的研究基础。更多还原

【Abstract】 To meet the requirement of high data rate transmission, adequate fre-quency bands should be allocated to the IMT-Advanced system. Moreover, more effords should be devoted to the reformation of the network structure and the improvement of the transmission technique. Relay is considered as one of the most promising candidate techniques because of its various advantages over the conventional cellular system regarding the enhancement of coverage range, diversity, and achievable rates. Since the channel measurement and modeling are vital for the research of the transmission technology and the deployment of the communication system, it is very necessary to carry out the channel mea-surement and modeling in the frequency bands that have been or probably will be allocated to the IMT-Advanced, as well as in the emerging network struc-ture. The research in this paper mainly focuses on the channel measurement and modeling in relay system. The main line of the research consists of three steps, namely field measurement, parameter estimation and statistics, as well as modeling. The main contributions are as follows.(1) The performances of MIMO and relay have been attracting a wide range of concerns. However, most of current theoretical literature hypothesize relatively simple channel conditions, resulting in a deviation between the the-oretically predicted performance and the actual performance that system can achieve in the real propagation environment. The field measurement can ac-quire details from the propagation environment, so the performance analysis and prediction based on the measured channel can achieve high accuracy. Nev-ertheless there are no complete methodology and framework on how to assess the system performance from the measured channel at present. A framework for the performance evaluation based on the measured channel is established. The expressions for performance indices of the measured channel are derived. Based on the framework, the performances of the measured channel in indoor hotspot and outdoor relay scenarios are analyzed in terms of channel gain, channel correlation, eigenvalue statistics, capacity and diversity-multiplexing tradeoff. The achievable signal-to-noise ratio, spatial diversity and capacity of three transmission schemes, i.e., direct transmission, amplify-and-forward and decode-and-forward relaying, are investigated. The impact of the propagation environment on the performance is also analyzed.(2) The slant polarized array can utilize the decorrelation effect introduced by both the space and orthogonal polarization, thus can reduce the signal cor-relation and improve system performance. However, because currently there is no corresponding theoretical solution, the signal correlation in the slant po-larized array can only be gotten by measurement or simulatin. The influence of the channel parameters on the correlation is not entirely clear. For the case where the slant polarized arrays are used, the solution of the correlation con-tributed by both the spatial and cross-polarization correlation with arbitrary an-tenna spacing and slant angle is derived. The approximations for the large and small angular spread are also given to reduce the simulation complexity. The derivative of channel correlation on the angular spread, slant angle and cross-polarization descrimination are obtained. The application scope of exact and approximate expressions are validated by simulation. Finally, the equivalent relationship between the antenna spacing and slant angle is revealed.(3) Generally, the antenna of relay is lower than that of the base station, and higher than that of the mobile station. A change in antenna height makes the propagation environment different from the traditional link between base station and mobile station. However, there are no related measurement re-sults on MIMO relay channel measurement in frequency bands allocated to the IMT-Advanced system. Moreover, the polarization and spatial characteristics, which have an important impact on the system performance are not revealed. Therefore, the applicability of channel properties obtained from the traditional base station and mobile station link and new features of the relay channel pa- 北京邮电大学博士学位论文rameters need to be examined. The spatial and polarization characteristics in the three link constituting the relay channel are compared. The distributions for fitting the cross-polarization descrimination and power azimuth spectrum are obtained by the least-square estimation. The expression of channel corre-lation is extended to the case where the power azimuth spectrum follows the multi-cluster Laplacian distribution. Substituting the measured values describ-ing the statistics of channel parameters into the derived expression, the channel correlation of different antenna configurations is studied in the real propagtion environment.(4) Most of the popular channel models are based on the cluster, and the latest models assign different parameters to the clusters generated by differ-ent propagation mechanisms. However, existing measurements and research have not covered the statistical characteristics and propagation mechanisms in RS(?)MS link. For the propgation mechanism in the RS(?)MS link, the cluster identification and tracking are carried out based on the results of parameter esti-mation. Based on the clustering results, the statistics in cluster and correspond-ing propagation mechanisms are investigated. The methods for improving the cluster identification and tracking are also presented.The analysis and modelling methods proposed in this thesis can be applied widely to channel measurements and modeling. The presented measurement and analysis results can provided references and guidelines for performance evaluation and deployment of the IMT-Advanced system. The measurement results in indoor hotspot and outdoor relay scenarios are adopted by the ITU-R and 3GPP-LTE+ standardization, respectively. All the contributions in this the-sis provide a reliable research base for the simulation, evaluation and network planning of IMT-Advanced system in China.更多还原