【作者】 蒙静；

【导师】 张乃通；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2010， 博士

【摘要】 随着数据业务和多媒体业务的快速增加,人们对位置信息感知的需求也日益增大。在短距离高速率无线通信技术的支撑下,作为一项新兴技术,脉冲超宽带(Impluse Radio Ultra Wideband, IR-UWB)技术可满足无线室内定位高精度、低功耗和低复杂度的实现要求,结合基于到达时间(Time-of-Arrival, TOA)的测距算法可以充分利用IR-UWB信号时间分辨率高的优点获得很好的定位精度,从而迅速成为短距离无线室内定位研究的热点。与高速通信系统所关注的无线信号时延扩展不同,IR-UWB定位系统主要关注直达路径(Direct Path, DP)的传播特性,相应的性能衡量标准也由误码率变为距离误差。复杂室内环境下,IR-UWB信号传播过程中的多径和非视距(Non-Line-of-Sight, NLOS)现象是造成定位测距误差的主要原因。虽然IR-UWB信号本身所具备的纳秒级时间分辨率可降低多径对DP路径的干扰,但受系统带宽的限制,也同样存在多径误差。NLOS误差则为DP受到障碍物的阻挡,对非直达径的检测所产生的额外传播时延而导致的距离误差。可见,IR-UWB无线定位系统的性能是与IR-UWB信号的传播特性密切相关的。现有的IR-UWB信道模型均是从统计的角度给出IR-UWB信号传播过程中的幅度和时延信息,无法有效的反映IR-UWB单径信号与具体空间环境的相互作用机理,而这对于关注DP信号传播特性的TOA测距定位系统尤为重要。本文在明晰IR-UWB单径信号传播机制的基础上,以分析多径传播所造成的TOA测距误差为切入点,以探索完全非视距环境下的脉冲信号定位机理为目标,深入系统地研究了IR-UWB信号的传播特性,同时建立了基于IR-UWB的定位测距误差模型,可为IR-UWB无线定位系统的设计与基础算法提供参考依据。本文的研究内容主要包括以下几方面:(1) IR-UWB无线定位系统基础理论研究。首先分析了现有超宽带系统中常用脉冲信号的特点及其用于TOA定位的优劣,作为研究定位环境下IR-UWB信号传播机理的基础。重点介绍了IEEE 802.15工作组给出的针对脉冲超宽带信号在不同应用环境下的3a和4a信道模型详细参数。最后研究了无线室内定位系统的总体结构框架,包括定位原理、测距算法性能限、以及结合IR-UWB信号进行无线室内定位的可行性。(2)提出了IR-UWB单径信号传播的研究方案,研究了室内LOS环境下IR-UWB信号的传播特性。由于IR-UWB信号为超宽频谱基带瞬态窄脉冲,传统窄带调制连续波信号基于中心频率的传播理论已不适合分析IR-UWB信号,而目前针对IR-UWB单径信号传播特性的研究一直没有定论,本文提出了研究IR-UWB单径信号传播特性的修正的确定性时频域方法。同时,鉴于IR-UWB信号在复杂室内环境中传播的易反射现象,本文在对室内LOS环境下IR-UWB信号传播建模的基础上,重点研究了IR-UWB单径信号的反射特性。最后通过对不同收发机环境下的接收信号的分析,利用两径模型中直达径与反射径的传播时延差,从理论上明确了TOA测距多径误差与环境参数和系统参数的相互关系。为IR-UWB定位测距误差的建模提供了理论依据。(3)从理论建模和实际测量两方面研究了NLOS环境下IR-UWB信号的穿墙传播特性。鉴于IR-UWB信号潜在的强穿透障碍物能力,通过对其在有限厚度障碍物内传播过程的描述及相应系数的修正,给出了IR-UWB穿墙透射系数的时频域闭合表达式。在此基础上,结合相干TOA测距系统对IR-UWB信号穿墙传播的要求,明晰了脉冲超宽带信号的透射性能与环境参数和系统参数的相互关系,重点分析了IR-UWB信号波形失真对相干TOA测距性能的影响。为选择合理的脉冲信号完成NLOS环境下的高精度定位提供了理论参考。最后利用哈尔滨工业大学深圳研究生院通信工程研究中心自主研发设计的IR-UWB样机完成了IR-UWB信号的穿墙传播实测,通过与理论结果的比较验证,完善了IR-UWB信号的穿墙传播理论。(4)针对IR-UWB无线室内定位测距误差的建模研究。在明确与IR-UWB信号传播特性有关的测距多径误差和NLOS误差产生原因的基础上,根据多径误差与环境参数和系统参数的理论关系,研究了不同信道环境下与系统带宽有关的多径误差,给出了500MHz~8GHz带宽范围的多径误差分布参数。针对现有信道模型无法描述IR-UWB信号在NLOS环境下的额外传播时延,基于IR-UWB信号穿透有限厚度障碍物传播的空间几何结构,推导了IR-UWB信号穿墙测距NLOS几何距离误差限,明晰了收发节点距离和障碍物参数等对几何距离误差的影响。最后研究了完全NLOS环境下利用距离误差信息的IR-UWB穿墙定位性能,提出了基于确定误差信息和信道环境分布的简易的TOA测距误差修正方法。更多还原

【Abstract】 As the development of short range wireless communications technology, the demands of accuracy positioning in complicated environments were also increased dramatically in recent years. The impulse radio ultra wideband (IR-UWB) technology can fully satisfied the requirements of high accuracy, low power consumption and low complexity in indoor localization system, based on the time-of-arrival (TOA) ranging algorithm, the IR-UWB positioning system can achieve centimeter degree position accuracy, which rapidly became a research focuses in short range localization.Different from the telecommunication applications which interested in the behavior the multipath spread of the wireless channel, the indoor positioning applications place greater emphasis on the behavior of the direct path (DP) between the transmitter and the receiver node, the correspondence performance criteria is defined as the distance error. In complicated indoor environment, ranging measurements are typically corrupted by the multipath and non-line-of-sight (NLOS) blockage. IR-UWB signal have the capability to resolve multipath components in nano-seconds, which greatly reduce the multipath interference to DP in correlation receiver, however, considered the limitation of sampling rate in actual system realization, there are also multipath error in IR-UWB positioning system due to different system bandwidth. On the other hand, the NLOS blockage makes only reflection or transmission signals can reach to the IR-UWB receiver, which lead to the TOA ranging estimation larger than the true distances, and consequently cause a positive ranging error. Apparently, the propagation characteristics of IR-UWB signal determined the performance of indoor positioning system. Although the IEEE 802.15.4a channel model has already given the statistical information of multipath in IR-UWB propagation, it can not effectively reflected the interaction mechanism between IR-UWB propagation properties and the specific environments, which are very important for the localization system concerning the DP chanracteristics. This paper mainly focuses on investigate the propagation characteristics of IR-UWB per-path signal, explore the IR-UWB positioning mechanism in completely NLOS envronments, establish the ranging error model caused by IR-UWB propagation in indoor environments, then give a system framework about the error mitigation in TOA ranging. The contents of this dissertation are summarized as follows.Firstly, the basic principles of IR-UWB positioning system are studied. Three types of pulse waveforms designed to fit the FCC spectrum mask in IR-UWB system are analyzed under the restrictions of high time resolution for short range localization. The statistical channel models of IEEE 802.15.3a and 4a proposed by IEEE 802.15TG are comprehensively introduced, with its characteristics in CM1~CM4 channel environments. The two-step positioning receiver structure was chose to achieve low complexity, and the ranging algorithms based on received-signal-strength (RSS), TOA and angle-of-arrival (AOA) are described and compared with its CRLB. Also the feasibility studies of these three algorithms in IR-UWB ranging are carried out.Secondly, the research schemes of IR-UWB per-path signal propagation is proposed and IR-UWB propagated in indoor line-of-sight (LOS) environments are analyzed. Due to the huge bandwidth of IR-UWB signal, the classical central frequency theory in narrowband system was no longer suit for the study of IR-UWB transient pulse, here a deterministic method in both time domain (TD) and frequency domain (FD) is raised to cope with the frequency dependence of IR-UWB signal in propagation. As the wavelength of IR-UWB signal is comparable to the stuffs commonly in indoor environment, which makes the relatively easier reflection phenomenon for IR-UWB signal compared with the 2G/3G mobile signals, the IR-UWB propagated in LOS situation is modeled by the LOS direct path and reflected paths from walls in a 3D environment. The reflection mechanism of IR-UWB signal is emphasized with closed form expression in both TD and FD methods, the reflected waveforms in different conditions are analyzed. In order to make sure the relationship between the multipath ranging error and environments/system parameters (transceiver height, transceiver distance and pulse duration time), the two-ray model is used to study the impacts of reflected path on DP in TOA estimation.Thirdly, the IR-UWB signal through wall propagation mechanism in NLOS environment is established in both theoretical and experiments study. The closed form of transmission coefficients in both TD/FD are derived on considering the multi-reflection phenomenon in slab. Based on the requirements of wireless localization system on IR-UWB signal, the through wall ability and range resolution of different Gaussian pulse are studied. And the IR-UWB signal waveform distortions as propagatting through common obstacles in indoor environment are investigated with its impacts on TOA ranging performance. Then the through wall propagation experiments of IR-UWB signal are accomplished using the IR-UWB system designed by the Communication Research Center of Harbin Institute of Technology Shenzhen Graduate School, a novel data process scheme was proposed to filter the transceiver antenna’s responses from the experiment data. The measurement data which only contain the wireless channel response were compared with the theoretical results.Fourthly, researches on model the ranging error of IR-UWB positioning system are carried out. The principles of multipath error and NLOS error due to IR-UWB propagation are analyzed. Based on the statistical information of IEEE 802.15.4a channel model, the influences of system bandwidth on multipath ranging error in coherent TOA estimation is studied. As the recent researches can’t give a uniform NLOS error model, according to the propagation charateristics of IR-UWB signal, the NLOS error are modeled by geometrical error caused by the geometrical structure of IR-UWB through wall propagation and the correlation peak biased error due to IR-UWB waveform distortions. The geometrical ranging error is derived using the equivalent source method, and the impacts of transceiver distance and wall parameters on geometrical error are discussed. Finally, based on the coherent TOA estimation and trilateration positioning algorithm, the positioning performance modification using the NLOS prior information in completely NLOS environment are studied, then a generalized distance error model is proposed based on the deterministic ranging error and the distribution characteristics of channel environments.更多还原