【作者】 周鑫；

【导师】 钟章队；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2018， 博士

【摘要】 无线信道作为通信系统收发信号的媒介,其特性极大地影响着无线通信系统的通信质量。为评估乃至提升无线通信系统在衰落信道下的通信质量,必须对无线信道进行深入研究。而对无线信道的研究可分为两个部分,首先是掌握客观世界各个场景下无线信道的特性,这部分内容可通过信道测量的手段来完成。其次是在实验室条件下,模拟真实场景的信道特性,从而为评估衰落信道下通信系统的通信质量,提供可靠、可控、可重复的测试环境。尽管在过去数十年间,众多学者已经围绕无线信道开展了大量研究,但是现有研究仍然存在下述局限:1)对于真实场景的信道测量,目前在6 GHz以下的低频段做了较为充分的工作。然而,随着5G时代的到来,挖掘、利用高频段的频谱资源已成为业界共识,而对高频段信道特性的研究还严重不足,这使得高频段通信系统的研制缺乏依据。2)对于信道模拟,通过在混响室中加载不同数量的吸波材料,混响室可用来模拟不同多径效应强度的无线信道。在以往的工作中,为在混响室内达到某一期望的均方根时延扩展值,需要通过迭代的方式加载混响室内的吸波材料。即需要反复加载及测量不同吸波材料加载下的均方根时延扩展值。这一过程耗费大量时间,’显著降低混响室的工作效率。3)对于通信质量评估,目前的测试多是对整个通信产品性能的评估,难以从此测试结果中进一步独立分析各个影响因素。通信标准的物理层参数配置是影响衰落信道下通信质量的关键因素,针对通信标准抗衰性能的测量实验严重不足。这限制了通信标准物理层参数的优化。针对上述问题,以评估、提升衰落信道下的通信质量为目标,本文围绕无线信道的测量和模拟,采用实验测量、模型构建、理论分析等手段,开展了以下研究工作:1)本文的研究以测量实验为基础,为保障测量结果的准确性以及研究成果的可靠性,对信道测量系统及通信质量测量系统进行了研究。对信道测量系统,为定量地评估测量结果的准确度,基于蒙特卡洛法,分析了路径损耗和均方根时延扩展这两个关键信道特性参数的测量不确定度。此分析为测量系统的优化提供了依据。对通信质量测量系统,通过比对测量的方法,分析了不同测量仪表通信质量参数测量结果的一致性,通过对测量原理的研究,找出了目前不同厂家矢量信号分析仪在通信质量参数测量过程中的两个算法差异,使用更为合理的算法建立了测量系统。这一研究一方面提升了本文测量系统的准确性,同时促进了行业内通信质量参数的量值统一。2)针对室内场景,在厘米波频段这一下一代移动通信的备选频段上,进行了大量信道测量实验,系统分析了视距及非视距场景下路径损耗、均方根时延扩展、小尺度衰落等多个信道特性参数。针对载波频率对信道特性的影响,以真实场景的信道测量为基础,结合电波传播理论,并辅以混响室内的信道测量实验,分析了载波频率与信道特性的关系。这一研究有助于掌握高频段信号的电波传播规律。3)针对混响室这一信道模拟装置内的信道特性,对路径损耗和均方根时延扩展进行了大量测量。并对此测量的不确定度进行了分析,这一不确定度反映了信道模拟的准确程度,也就决定了混响室内进行的通信质量评估的准确程度。基于测量结果和理论分析,重点研究了混响室内吸波材料特性与时延扩展的数学关系,提出了根据吸波材料特性预测混响室内均方根时延扩展的估计方法。使用此估计方法可有效提高混响室的配置效率。4)提出了一种基于调制质量参数测量的,在混响室内评估信号通信质量的方法。测量结果反映了通信标准物理层配置抗击信道衰落的性能。综合混响室内的信道特性及通信质量测量结果,研究分析了混响室内吸波材料特性、桨叶位置这两个关键物理属性对信道特性以及通信质量的影响,揭示了混响室内信道特性对通信质量的影响机理。综上,本论文围绕信道测量与模拟展开研究,整个研究服务于评估衰落信道下无线通信系统的通信质量这一应用。信道模拟所构建的衰落信道是通信质量评估的基础,而信道测量除对真实场景进行信道建模外,还起到为信道模拟系统赋值、校准的作用。因此,信道测量是信道模拟的基础。信道测量和信道模拟两部分研究内容密不可分,共同组成衰落信道下通信质量评估的技术支撑。更多还原

【Abstract】 As the wireless channel is the medium over which wireless communication system transmits and receives signals,the channel characteristics significantly affect the com-munication quality.In order to evaluate the communication quality under fading channel-s,it is necessary to conduct an in-depth research on the wireless channel.Corresponding research can be divided into two parts.The first is to obtain the characteristics of the wireless channel under various real scenarios.This work can be accomplished by con-ducting channel measurements.The second is to simulate the channel under laboratory conditions in order to provide a reliable,controllable,and repeatable test environment for the communication quality evaluation under certain fading channels.In the recent decade,a significant progress on the insight to the channel measurement and simulation has been achieved after the great effort of global researchers;however,there are still the following limitations in the previous research:1)In terms of channel measurement in real scenarios,with the advent of the fifth-generation(5G)system,utilizing spectrum resources in the high frequency bands(above 6 GHz)has become a consensus.However,the research on channel character-istics in the high frequency is still inadequate,which severely limits the development of communication systems.2)In terms of channel simulation,reverberation chambers(RCs)can be used to simu-late different multipath environments by loading the RCs with different amounts of RF absorbers.In past research work,RCs were iteratively loaded with RF absorber-s for reaching a desired root mean square(RMS)delay spread.For every loading case,the RMS delay spread was measured.These repeated measurements were time consuming and inefficient.3)In terms of the communication quality evaluation,the current research focuses on the overall communications product performance.From the test results,it is difficult to analyze the various influencing factors separately.The physical layer parameters of communication standards are the key factors affecting the communication quality.The research on the physical layer performance is seriously inadequate,which limits the optimization of communication standards.In order to break these existing limitations,this dissertation conducts a research on channel measurement and channel simulation by means of experimental measurement,model construction,and theoretical analysis.The innovation of this dissertation mainly includes:1)The research in this dissertation is based on experimental measurement.In order to ensure the accuracy of the measurement results and the reliability of the research re-sults,the channel measurement system and the communication quality measurement system are studied first.With regard to the channel measurement system,in order to quantitatively evaluate the accuracy of the measurement results,the measurement un-certainties of two key channel characteristic parameters,i.e.,path loss and RMS delay spread,are analyzed based on Monte Carlo method.This analysis provides scientific references for the optimization of the channel measurement system.With regard to the communication quality,it is analyzed by measuring the modulation quality parame-ters.And by means of the comparison measurement,the consistency of measurement results of the modulation quality parameters for current main stream instruments is analyzed.It is found that the differences of the measurement results between different instruments are caused by different algorithms.This research is benefit to improving the accuracy and consistency of the measurement results,and lays a foundation for promoting the quantity unification of the modulation quality parameters.2)In terms of the channel characteristics in high frequency bands,the indoor channel at centimetre-wave bands(which are the candidate bands for the future communication systems)is investigated.Based on channel measurements,large-scale and small-scale statistics of line-of-sight(LOS)and non-LOS(NLOS)channels are analyzed.Of par-ticular interest is the impacts of the frequency on the channel characteristics.Based on the channel measurement results in the indoor scenarios,combined with the the-oretical analysis and the experiments in the RC,the relationship between the carrier frequency and the channel characteristics is studied.This research gives insight into propagation mechanisms in the high frequency bands.3)In terms of the channel characteristics in the RC,path loss and RMS delay spread are measured.Furthermore,the uncertainties of these measurements are evaluated.These uncertainties reveal the accuracy of the channel simulation.Based on the measure-ment results and theoretical analysis,a model is proposed to explain the quantitative relationship between the RMS delay spread and the parameters of loading.With this model,complex wireless channel with certain RMS delay spread can be quantitatively and effectively simulated with certain loading.4)A method to measure the communication quality in the RC is proposed based on the modulation quality measurement system.The measurement results reveal the per-formance of communication standard physical layer in fading channels.Based on measurement,the correlations between channel characteristics,communication quali-ty,and the two key configurations,i.e.,paddle position and absorber loading in the RC are investigated.The research reveals the action mechanism of channel characteristics on communication quality.In summary,this research focuses on channel measurement and channel simulation.The results of the research are useful for evaluating the communication quality under fading channels.The channel simulation is the basics of communication quality eval-uation.And the channel measurement is the basis of channel simulation,because the channel simulation device need to be configured according to the channel measurements.The channel measurement and channel simulation together form a technical support for communication quality evaluation.更多还原