奇异谱分析滤波法在消除GPS多路径中的应用

基于奇异谱分析(singularspectrumanalysis,SSA)的基本思想,利用噪声与信号的赫斯特(Hurst)指数有显著差异这一特性,提出了一种新的SSA滤波法,同时给定了嵌入维数犔与重构阶次犘的确定标准,并将该方法应用于GPS多路径的研究中。通过模拟数据及实测GPS坐标序列的数据分析,结果表明SSA滤波法是一种有效的去噪方法,其去噪效果与小波滤波与经验模态分解(empriricalmodedecomposition,EMD)滤波相当。针对多路径效应周日重复性的特点,利用该滤波方法建立改正模型,可有效地削弱多路径效应的影响,进而提高GPS动态变形监测的精度。     

基于经验模式分解的滤波去噪法及其在GPS多路径效应中的应用

经验模式分解(Empirical Mode Decomposition,EMD)是一种新的信号处理技术,它是基于数据本身的,且能在空间域中将信号进行分解,从而可以区分噪声和有用信号。根据EMD分解白噪声而得到的本征模式函数(IMF)分量的能量密度与其平均周期的乘积为一常量这一特性,建立一种新的基于EMD滤波去噪方法,并将该方法应用于GPS多路径效应的研究中。通过对模拟数据与GPS实测数据的处理分析,得出以下主要结论:①EMD滤波去噪法与小波方法都能最大限度地削弱测量的随机误差,但EMD滤波去噪法比小波方法更直接,且不受测不准原理及小波函数选择的影响;②相比小波方法,EMD能够更有效地剔除瞬时强噪声,从而能够提取更精确的多路径效应重复性误差改正模型。     

GPS多路径误差滤波方法比较研究

基于GPS多路径时间序列,分别采用Vondrak滤波、经验模式分解(EMD)和小波滤波3种方法构建了GPS多路径误差修正模型,并将其用于削弱多路径效应.通过对模拟数据及实测数据的分析表明,3种方法都能有效地分离不同噪声水平下时间序列中的信号和噪声.同时,利用3种方法构建的多路径修正模型可有效地削弱多路径效应的影响,提高GPS定位精度,但3种方法的优缺点各有不同.     

CVVF方法用于GPS多路径效应的研究

将交叉证认法与Vondrak数字滤波器相组合,提出一种分离测量资料中信号与噪声的新方法,即CVVF方法,并将该方法用于GPS多路径效应的研究中.对数字模拟试验和实际观测资料的分析表明,该方法能最大限度地削弱测量的随机误差,使资料序列中的信号和噪声合理分离.同时,利用GPS多路径效应周期性重复的特性,可有效地削弱多路径效应对观测结果的影响,从而提高GPS定位精度.     

GPS多路径重复性试验研究

信号衍射和多路径效应是限制GPS定位精度进一步提高的瓶颈,观测中两者往往同时存在。衍射效应具有不完全重复的特性,为了研究多路径重复性并使其不受信号衍射的影响,本文提出先应用SIGMA-Δ信噪比加权模型削弱信号衍射的影响,再运用改进恒星时滤波法分析多路径重复性。实验观测资料分析表明,SIGMA-Δ模型能有效削弱衍射信号对定位结果影响,并且保留主要的多路径信号;而改进恒星时滤波法能适应测站周围多路径环境的变化,从而最大限度地削减多路径误差。两者组合比传统的恒星时滤波更能有效提高GPS的动态定位精度。     

基于小波变换的GPS动态变形分析

介绍了小波滤波去噪的原理并讨论在动态环境下GPS多路径效应的重复性问题。首先利用小波方法对静态观测数据的残差进行去噪,提取具有系统性的多路径误差改正模型。然后,根据多路径误差重复性的特点,对后续动态观测的数据进行改正。通过实验证明:经重复性模型改正后残余的多路径噪声符合正态分布的特点。然后采用小波软阈值去噪方法,消除剩余的多路径误差,可进一步提高动态变形监测的精度。     

一种基于交叉证认技术的自适应小波变换及其在削减GPS多路径误差中的应用

多路径效应影响是目前限制GPS定位精度进一步提高的瓶颈。提出用交叉证认技术自动识别小波分解的信号层,再通过小波重构实现降噪和信号提取,并将该方法应用于GPS多路径误差的削减中。对模拟数据和实际GPS观测资料的分析表明,该方法能合理分离不同噪声水平下资料序列中的信号和噪声;当噪声水平小于信号振幅的一半时,能成功分离资料序列中的高频信号。同时,运用该方法得到的多路径改正模型和GPS多路径效应的重复性,可有效地削弱多路径效应的影响,提高GPS定位精度。     

基于自适应噪声抵消与小波滤波的GPS监测误差分析

对GPS载波相位测量误差进行了理论分析和试验研究。根据噪声特征以及它们对载波相位测量结果的影响，提出了基于自适应噪声抵消与小波滤波相结合的GPS噪声抑止方法。对具有强相关特性的多路径误差采用自适应噪声抵消方法，而对于不相关的高频噪声则通过合理选择小波分解层数对信号进行分解，对作用闽值后的小波系数进行重构，得到最后的变形信号。实测数据分析表明，该方法能有效地削弱多路径效应及测量随机噪声，较用单一方法对GPS数据进行消噪处理有较大的优越性。     

基于CEEMD-Wavelet-SavGol模型的GPS多路径修正算法

针对GPS多路径提取过程中EMD算法存在模态混叠效应及小波（Wavelet）去噪局限性的问题,提出了一种基于CEEMD-Wavelet-SavGol模型的多路径提取算法。为了能够充分提取高频和低频中的有用信息,该算法利用完备经验模态分解（CEEMD）对信号进行分解,得到一系列从高频到低频的模态函数（IMF）,并根据模量标准化累计均值法对尺度进行区分,然后分别采用Wavelet和SavGol滤波对高频分量和低频分量进行降噪,将降噪后的IMF进行重构,得到降噪后的信号。最后将该模型用于GPS多路径误差提取的实例中,并与Wavelet、EMD、CEEMD模型进行对比,证明了新模型的有效性。     

EEMD滤波技术在GPS动态监测数据去噪中的应用

为了削弱结构动态监测中GPS随机噪声的影响,本文研究了一种基于集成经验模态分解(EEMD)技术的滤波方法。根据信号自身尺度分解信号,基于分解产生的本征模态函数(IMF)的Fourier变换频谱特征,构造了EEMD时空滤波器。对不同信噪比的仿真非平稳数据进行去噪处理并与小波去噪法相比较,各项指标表明基于EEMD滤波器的去噪方法与小波去噪方法效果相当,但避免了小波基的选择,具有更大的自适应性。应用于GPS动态监测数据的去噪结果表明该方法能有效分解信号消除GPS高频噪声及低频噪声的影响,提取有用振动信号,为进一步结构分析提供有效数据。     

Filtering GPS time-series using a Vondrak filter and cross-validation

Multipath disturbance is one of the most important error sources in high-accuracy global positioning system (GPS) positioning and navigation. A new data filtering method, based on the Vondrak filter and the technique of cross-validation, is developed for separating signals from noise in data series, and applied to mitigate GPS multipath effects in applications such as deformation monitoring. Both simulated data series and real GPS observations are used to test the proposed method. It is shown that the method can be used to successfully separate signals from noise at different noise levels, and for varying signal frequencies as long as the noise level is lower than the magnitude of the signals. A multipath model can be derived, based on the current-day GPS observations, with the proposed method and used to remove multipath errors in subsequent days of GPS observations when taking advantage of the sidereal day-to-day repeating characteristics of GPS multipath signals. Tests have shown that the reduction in the root mean square (RMS) values of the GPS errors ranges from 20% to 40% when the method is applied.     

GPS多路径误差处理技术

GPS高精度定位和授时中存在多路径效应。本文介绍了多路径效应产生的原理、作用特性,并着重从三个方面归纳、分析比较了目前国内多种关于多路径误差的处理技术。本文在北京基站进行了GPS单站定时实验,分析实验结果认为,多路径效应是GPS授时中不可忽视的误差因素。     

GPS码跟踪环自适应多径消除算法

根据多径信号的产生机理,在对GPS接收机中的码跟踪环多径信号模型研究的基础上,提出了采用自适应滤波的来消除GPS多径效应的算法。自适应滤波的方法不需要估计模型的系统参数,而直接通过自适应滤波将多径信号滤除。在有噪声的情况下,自适应滤波的RLS算法是最小二乘意义下的最优估计,仿真的结果表明采用自适应滤波算法可以快速的消除多径的影响,修正鉴相函数的过零点偏差,提高码跟踪环的跟踪精度。由于自适应滤波算法是递推算法,易于软、硬件实现。     

Quantitative evaluation of multipath rejection capabilities of GNSS antennas

Multipath error remains the largest error source in many high precision GPS applications. To counteract this problem, solutions at both software and hardware level have been studied. Software processing by means of measurement redundancy or error predictability can be used in order to mitigate the multipath effects. In general, these techniques work properly only when the length of a reflection path exceeds that of the direct path by more than 10–20 m. Unfortunately, in most cases, reflections are generated in the area near the receiving antenna. For this reason, multipath rejection actuated at the antenna level is one of the most valid means to improve the accuracy of GPS systems. The scope of this work is twofold. First, a review of low-multipath reception requirements will be proposed for comparing different classes of high precision GNSS antennas. Based on this discussion, we introduce a quantitative evaluation of multipath rejection capabilities of a GNSS antenna. The proposed assessment technique is focused on the antenna pattern, but, in contrast to other parameters evaluating the antenna radiation characteristics, it is specifically conceived to capture the effects of multipath signals.     

北斗导航卫星系统测距信号的精度分析

基于单测站和短基线实验的伪距相位差值 (Code-minus-phase Combination, CC)和多路径(Multipath, MP)两类组合观测值,对比分析了北斗（BD）和GPS测距信号质量,并检验了多路径误差对CC模糊度固定的影响。结果表明：BD GEO卫星(Geostationary Earth Orbit)的测距信号质量优于IGSO卫星(Inclined Geosynchronous Satellite Orbit),且两类测距信号的多路径误差分别包含长、短期的变化趋势。针对CC模糊度固定,当采用较长时间段（如本文中的600s）时,GPS L1/L2和BD B1/B2四个频段上的成功率均超90%;而对于快速模糊度固定（如仅采用120秒）,由于受强多路径误差影响,BD IGSO卫星的固定成功率最低,不超过50%。     

GPS多路径误差分析及探测方法

多路径误差严重影响动态GPS测量精度,且很难将其彻底消除.介绍多路径效应的机理及特性,利用相同环境下、连续卫星周期间数据取差以及连续历元坐标序列的移动平均方法削弱多路径误差,提高定位精度.     

参考经验模态分解-独立分量分析及其在GPS多路径误差处理中的应用

多路径误差在绝大部分应用中,其测站间相关性很弱,不能通过差分观测得到有效削弱,成为高精度GPS动态变形监测中的主要误差源。针对GPS多路径误差的特点,结合具有良好多尺度分解能力的经验模式分解方法(EMD)和具有良好盲分离能力的独立分量分析(ICA)方法,提出带参考信号的EMD-ICA方法来削弱多路径效应的影响。应用实例的结果证明了该方法的有效性。     

削弱GNSS多路径效应的半天球格网点建模方法

多路径效应与测站观测环境相关,无法利用差分的方式消除或削弱,是GPS精密数据处理时的主要误差源。为此,本文提出了一种利用半天球格网点模型削弱测站多路径误差影响的新方法MHGM(multi-point hemispherical grid model)。该方法对以测站为球心的半天球进行格网点划分,通过格网点的参数化描述,实现测站处多路径误差建模,可适用于现有各类GPS数据处理的软硬件设备和观测环境。本文算例的测试结果表明,采用新方法建模后双差观测值残差的RMS均值改善率平均在73.9%左右,较传统恒星日滤波方法的改善效果平均可提升26.9%,对于静态观测数据,按实时动态相对定位处理模式可获得平面精度约1.7 mm,高程精度约3.0 mm的定位结果。此外,MHGM模型还可进一步用于对测站周边可能存在的多路径误差源进行方位评估,对从物理意义上消除多路径误差源的影响给出一定的指导性意见。     

A new method to mitigate multipath error in single-frequency GPS receiver with wavelet transform

One of the major errors in high-precision GPS positioning is multipath. Multipath effect modeling and reduction have been a challenging issue in high-accuracy GPS positioning applications due to its special properties. Different methods have been employed to mitigate this error including hardware and software approaches. We reduce C/A code multipath error by adopting an efficient software method which uses wavelet transform as a basic data processing trend. The key idea of the proposed method is using stationary wavelet transform (SWT) in GPS signal data processing. Since we have used SWT, there is complete access to high-frequency and low-frequency terms in both time and frequency domains, and we can apply appropriated procedures to mitigate this error. The multipath error mostly is a low-frequency term. In our proposed method, the double difference (DD) residuals are applied to the SWT to identify the multipath disturbance. The extracted multipath is then used to correct DD observations. Our experiments include three data sets to investigate the proposed method and compare it with existing algorithms. We used simulations for two of these data sets. The results indicate the efficiency of the proposed method over existing algorithms.     

Development and testing of a new ray-tracing approach to GNSS carrier-phase multipath modelling

Multipath is one of the most important error sources in Global Navigation Satellite System (GNSS) carrier-phase-based precise relative positioning. Its theoretical maximum is a quarter of the carrier wavelength (about 4.8 cm for the Global Positioning System (GPS) L1 carrier) and, although it rarely reaches this size, it must clearly be mitigated if millimetre-accuracy positioning is to be achieved. In most static applications, this may be accomplished by averaging over a sufficiently long period of observation, but in kinematic applications, a modelling approach must be used. This paper is concerned with one such approach: the use of ray-tracing to reconstruct the error and therefore remove it. In order to apply such an approach, it is necessary to have a detailed understanding of the signal transmitted from the satellite, the reflection process, the antenna characteristics and the way that the reflected and direct signal are processed within the receiver. This paper reviews all of these and introduces a formal ray-tracing method for multipath estimation based on precise knowledge of the satellite–reflector–antenna geometry and of the reflector material and antenna characteristics. It is validated experimentally using GPS signals reflected from metal, water and a brick building, and is shown to be able to model most of the main multipath characteristics. The method will have important practical applications for correcting for multipath in well-constrained environments (such as at base stations for local area GPS networks, at International GNSS Service (IGS) reference stations, and on spacecraft), and it can be used to simulate realistic multipath errors for various performance analyses in high-precision positioning.