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1.
One of the key approaches to monitor the integrity of Global Satellite Navigation Systems (GNSS) is receiver autonomous integrity monitoring (RAIM). Existing RAIM algorithms utilise two tests in the position domain (for RAIM availability) and measurement domain (for failure detection). This paper proposes an alternative RAIM algorithm, which is based entirely in the measurement domain. This algorithm can be used for sensitivity analyses to support performance specification and system design. It can also be used during actual flight operations where the trigger is the phase of flight and its required navigation performance (RNP) parameters. This is made possible by computationally efficient calculation of the chi-squared parameters. The algorithm reverts to the current approach if the phase of flight is unknown. Simulation results for non-precision approach (NPA) have been used to demonstrate the effectiveness of the proposed algorithm. 相似文献
2.
Measurements consistency-based Receiver Autonomous Integrity Monitoring (RAIM) is the main technique for monitoring the integrity of global satellite navigation systems at the user-level. Existing RAIM algorithms utilize two tests, in the position domain a test for RAIM availability and in the measurement domain a test for failure detection. These tests involve the computation of three parameters: test statistic, decision threshold, and protection level. The test statistic is based on the actual measurements in the form of the sum of the squared errors (SSE). The decision threshold is chosen on the basis of the statistical characteristics of the SSE including the assumption that the errors are normally distributed. However, in practice residual, error distributions exhibit heavier tails than predicted by the Gaussian model. Therefore, this paper challenges the normality assumption of the residual navigation errors in three ways. First, real data are used to assess its impact on the traditional RAIM algorithm. Second, extreme value theory is applied to the tails, and the generalized extreme value (GEV) distribution is derived to capture residual navigation errors. Third, the performance of the traditional RAIM approach is compared with that employing the GEV distribution. The results demonstrate that the GEV model is a more accurate representation of the distribution of residual navigation errors than the conventional Gaussian model and should be used in the development of integrity monitoring algorithms. 相似文献
3.
Reliability testing, namely receiver autonomous integrity monitoring (RAIM), consists of statistical testing of least-squares residuals of observations, e.g., on an epoch-by-epoch basis aiming towards reliable navigation fault detection and exclusion (FDE). In this paper, classic RAIM and FDE methods are extended with testing of range-rate residuals to find inconsistent velocity solutions in order to contribute to the reliability of the system with special focus on degraded signal environments. Reliability enhancement efforts discussed include a Backward-FDE scheme based on statistical outlier detection and an iteratively reweighted robust estimation technique, a modified Danish method. In addition, measurement weighting assigned to code and Doppler observations is assessed in the paper in order to allow fitting a priori variance models to the estimation processes. The schemes discussed are also suitable in terms of computational convenience for a combined GPS/Galileo system. The objective of this paper is to assess position and velocity reliability testing and enhancement in urban and indoor conditions and to analyze the navigation accuracy conditions with high sensitivity GPS (HSGPS) tests. The results show the necessity of weighted estimation and FDE for reliability enhancement in degraded signal-environment navigation. 相似文献
4.
针对基于最小二乘残差估计的接收机自主完好性监测(RAIM)算法,结合伪距单点定位多采用观测量非等权模型,提出一种观测量非等权模型RAIM可用性算法,对实际计算具有借鉴意义。通过实测数据,分析了等权模型和非等权模型RAIM可用性算法对卫星几何分布的估计情况,验证了观测量非等权模型RAIM可用性算法的可行性。 相似文献
5.
把导航领域、军事领域和导航电子地图中广泛应用的圆概率误差(circular error probable,CEP)引入到HPL(horizontal protection level)的计算中,在最小二乘残差法基础上构建了基于圆概率误差的RAIM(receiver autonomous integrity monitoring)可用性算法。首先计算了在一定误警率、漏警率条件下多颗卫星发生故障时的水平定位偏差和一定置信度下的圆概率误差;然后以GPS导航星座为例,探讨了相关观测下计算HPL的新方法;最后把HPL与水平告警限差(horizontal alert limit,HAL)相比较,得到了基于圆概率误差的RAIM可用性,并通过算例验证了此方法的有效性和可行性。 相似文献
6.
In the Global Positioning System, there is no provision for real-time integrity information within the Standard Positioning Service, by design. However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved using the special augmentation systems or RAIM (Receiver Autonomous Integrity Monitoring) or both. RAIM, the most cost-effective method relies on data consistency, and therefore requires redundant measurements for its operation. An external aid to provide this redundancy can be in the form of an Inertial Navigation system. This should enable continued performance even when no redundant satellite measurements are available. An algorithm presented in previous papers by the authors detects the rate of slowly growing errors. The algorithm was shown to be effective for early detection of slowly growing errors that belong to the class of most difficult to detect errors. Firstly, rate detector is tested for varying faults. Secondly, real data are used to validate the rate detector algorithm. The data are extensively analyzed to ascertain whether it is suitable for integrity and fault diagnostics. A modification to the original rate detector algorithm is suggested by addition of a bias state to the dynamic model. The performance is then compared with the existing techniques and substantial improvement is shown. 相似文献
7.
In the global positioning system (GPS), code division multiple access (CDMA) signals are used. Because of the known spectral
characteristics of the CDMA signal, continuous wave (CW) interference has a predictable effect on the different pseudo random
noise (PRN) spreading codes (unique to each satellite) depending on the Doppler frequency of the signal. The Doppler frequency
for each signal is also predictable once the receiver position is known. As different satellite signals have different Doppler
frequencies, the effect on the signal quality is also different. In this paper first the effect is studied analytically. The
concept of an “exclusion zone” is defined and analyzed for each satellite. This exclusion zone, where that satellite should
not be used due to interference degradation, is shown to be predictable for each satellite as a function of time. Using this
prediction, the CW interference effect on the positioning quality of the receiver can be mitigated by ignoring the affected
satellites within exclusion zones when performing position evaluation. The threshold beyond which a satellite should be excluded
is then derived by studying the mutual effects of the geometry and the signal quality of that satellite on the positioning
quality. Receiver autonomous integrity monitoring (RAIM) uses redundancy in measurements to perform an internal consistency
check to see if all of the measurements are satisfactory. In this paper this technique is also used to mitigate the effect
of CW interference on the positioning accuracy. Finally it is shown that the prediction of the exclusion zone for each satellite
outperforms the RAIM algorithm in mitigation the effect of the interference when 5 satellites are visible.
An erratum to this article can be found at 相似文献
8.
Pseudorange-based integrity monitoring, for example receiver autonomous integrity monitoring (RAIM), has been investigated
for many years and is used in various applications such as non-precision approach phase of flight. However, for high-accuracy
applications, carrier phase-based RAIM (CRAIM), an extension of pseudorange-based RAIM (PRAIM) must be used. Existing CRAIM
algorithms are a direct extension of PRAIM in which the carrier phase ambiguities are estimated together with the estimation
of the position solution. The main issues with the existing algorithms are reliability and robustness, which are dominated
by the correctness of the ambiguity resolution, ambiguity validation and error sources such as multipath, cycle slips and
noise correlation. This paper proposes a new carrier phase-based integrity monitoring algorithm for high-accuracy positioning,
using a Kalman filter. The ambiguities are estimated together with other states in the Kalman filter. The double differenced
pseudorange, widelane and carrier phase observations are used as measurements in the Kalman filter. This configuration makes
the positioning solution both robust and reliable. The integrity monitoring is based on a number of test statistics and error
propagation for the determination of the protection levels. The measurement noise and covariance matrices in the Kalman filter
are used to account for the correlation due to differencing of measurements and in the construction of the test statistics.
The coefficient used to project the test statistic to the position domain is derived and the synthesis of correlated noise
errors is used to determine the protection level. Results from four cases based on limited real data injected with simulated
cycle slips show that residual cycle slips have a negative impact on positioning accuracy and that the integrity monitoring
algorithm proposed can be effective in detecting and isolating such occurrences if their effects violate the integrity requirements.
The CRAIM algorithm proposed is suitable for use within Kalman filter-based integrated navigation systems.
相似文献
| Shaojun FengEmail: |
9.
Using modern techniques, the analysis of amateur photographs yields results with almost the same accuracy level as with metric photographs. This paper gives a classification of data processing techniques for amateur photographs and presents a well proven method for the treatment of existing amateur photographs, known as Metric Photo Perspective Transformation (MPPT). Data processing is particularly convenient and efficient if on line techniques are used. Operational procedures for the treatment of additional parameters and for the detection of blunders in a time critical on line triangulation system are proposed. 相似文献
10.
In integrated systems for accurate positioning, which consist of GNSS, INS, and other sensors, the GNSS positioning accuracy has a decisive influence on the performance of the entire system and thus is very important. However, GNSS usually exhibits poor positioning results in urban canyon environments due to pseudorange measurement errors caused by multipath creation, which leads to performance degradation of the entire positioning system. For this reason, in order to maintain the accuracy of an integrated positioning system, it is necessary to determine when the GNSS positioning is accurate and which satellites can have their pseudorange measured accurately without multipath errors. Thus, the objective of our work is to detect the multipath errors in the satellite signals and exclude these signals to improve the positioning accuracy of GNSS, especially in an urban canyon environment. One of the previous technologies for tackling this problem is RAIM, which checks the residual of the least square and identifies the suspicious satellites. However, it presumes a Gaussian measurement error that is more common in an open-sky environment than in the urban canyon environment. On the other hand, our proposed method can estimate the size of the pseudorange error directly from the information of altitude positioning error, which is available with an altitude map. This method can estimate even the size of non-Gaussian error due to multipath in the urban canyon environment. Then, the estimated pseudorange error is utilized to weight satellite signals and improve the positioning accuracy. The proposed method was tested with a low-cost GNSS receiver mounted on a test vehicle in a test drive in Nagoya, Japan, which is a typical urban canyon environment. The experimental result shows that the estimated pseudorange error is accurate enough to exclude erroneous satellites and improve the GNSS positioning accuracy. 相似文献
11.
A tightly coupled filter integrating GPS and ultra-wideband (UWB) observations for high-precision position applications is
implemented and tested to survey several external corner points of an eight story building. The filter uses GPS pseudoranges,
GPS carrier-phase measurements, and UWB ranges and includes in-run estimation of UWB bias and scale factor states. The filter
employs inequality constraints and innovation testing to mitigate the effects of unmodeled errors. The tightly coupled solution
is compared to GPS-only, UWB-only, and loosely coupled solutions. The ability of each solution to detect measurement blunders
is compared. Sub-meter level position solutions are maintained using tight-coupling in conditions where the solutions from
the other three approaches are either unavailable or unreliable. 相似文献
12.
针对运动航天器收到的脉冲星信号受Doppler效应影响,难以准确测量脉冲到达时间的问题,提出了基于三阶小波互累积量的脉冲星累积脉冲轮廓时间延迟测量算法。结果表明,当信号受到Doppler效应影响时,该算法测量精度优于现有算法,适用于脉冲星导航系统中脉冲到达时间的测量。 相似文献
13.
14.
针对GNSS接收机在室内环境中面临的强烈的信号衰减、非视距传播和互相关效应的问题,提出了一种基于粗时段导航和RAIM算法解决A-GNSS室内定位问题的方法,并利用BDS数据验证了该方法的可靠性。结果表明,粗时段导航算法能够提供连续可靠的定位结果,应用于微弱信号环境;基于组合FDE的RAIM算法能够增加定位结果可用率,解决室内卫星信号存在的非视距传播和互相关效应的问题。基于粗时段导航与RAIM算法的A-GNSS定位技术能够应用于室内定位,仿真定位结果水平方向RMS在10 m以内。 相似文献
15.
针对目前房屋建筑面积测量外业工作强度大、测量精度低、成图效率低等主要问题,本文提出了基于无人机倾斜摄影测量的房屋建筑面积测算方法。首先从无人机倾斜摄影、实景三维建模、数字正射影像制作、三维数字化测图、图件制作和面积指标计算等方面进行了研究,然后对试验结果进行了精度评定。结果表明,地形图平面位置中误差为4.6 cm,高程中误差为4.2 cm,房角点点位中误差为4.6 cm,建筑物边长中误差为4.5 cm,房屋建筑物面积较差小于城市商品房二级精度面积限差,各项精度均符合国家标准规范要求,该方法用于房屋建筑面积测算是可行的。 相似文献
16.
A fast and efficient integrity computation for non-precision approach performance assessment 总被引：1，自引：0，他引：1
The level of safety to be expected from global positioning system (GPS) must be known in order to use it to support safety
critical operations such as air navigation. This is captured by the navigation performance parameter of integrity which includes
the ability of the navigation system to deliver a warning to the user in the event of a significant failure and within a specified
time-to-alert. Given the high percentile requirement associated with integrity, assessment of expected system performance
both in the nominal case and during failure events, requires the application of analytical techniques. This paper identifies
the weaknesses of the current methods for assessing the level of performance to be expected of GPS for non-precision approaches
and proposes ways to address them including a novel application of a mathematical integration technique that greatly reduces
the computational load associated with integrity performance calculations. Results based on computation times show that the
new method reduces computational load by a factor of 500+ with a high accuracy and associated high level of confidence. It
is shown that in some cases, the technique presented is able to improve GPS RAIM availability beyond the gains achieved by
measurement weighting. 相似文献
17.
Supervised classification of quad-polarimetric SAR images is often constrained by the availability of reliable training samples. Active learning (AL) provides a unique capability at selecting samples with high representation quality and low redundancy. The most important part of AL is the criterion for selecting the most informative candidates (pixels) by ranking. In this paper, class supports based on the posterior probability function are approximated by ensemble learning and majority voting. This approximation is statistically meaningful when a large enough classifier ensemble is exploited. In this work, we propose to use extreme learning machines and apply AL to quad-polarimetric SAR image classification. Extreme learning machines are ideal because of their fast operation, straightforward solution and strong generalization. As inputs to the so-called active extreme learning machines, both polarimetric and spatial features (morphological profiles) are considered. In order to validate the proposed method, results and performance are compared with random sampling and state-of-the-art AL methods, such as margin sampling, normalized entropy query-by-bagging and multiclass level uncertainty. Experimental results for four quad-polarimetric SAR images collected by RADARSAT-2, AirSAR and EMISAR indicate that the proposed method achieves promising results in different scenarios. Moreover, the proposed method is faster than existing techniques in both the learning and the classification phases. 相似文献
18.
接收机自主完好性监测(receiver autonomous integrity monitoring,RAIM)是终端用户高可靠导航定位的保障,低轨卫星的发展为完好性监测带来新的机遇,然而不同低轨星座增强下的终端RAIM性能可能会存在显著差异。基于高轨道倾角(80颗)、中轨道倾角(120颗)和混合轨道倾角(168颗)3种典型的低轨星座,系统评估了低轨卫星增强下的北斗卫星导航系统（BeiDou navigation satellite system,BDS）RAIM可用性及故障检测效果。仿真计算结果表明：对于高纬区域,高轨道倾角增强下的RAIM可用性效果最好,而在中、低纬区域,中轨道倾角星座增强下的RAIM可用性效果最优;在全球范围内,高轨道倾角、中轨道倾角和混合轨道倾角星座增强下非精密进近阶段的RAIM可用性较BDS分别提升30.5%、29.0%和41.0%。由此可知,由不同轨道倾角组成的混合星座可较好地弥补可视卫星在空间覆盖上的缺陷,其全球RAIM可用性增强效果最优,增强下的RAIM可检测到的最小伪距偏差较之前平均减小33.3 m。 相似文献
19.
王新洲 《武汉大学学报(信息科学版)》1996,(4)
首先给出了标准化残差受粗差污染的隶属函数，进而导出了观测误差与残差之间的模糊逻辑关系，以及观测误差属于粗差的隶属函数。最后提出了顾及模糊逻辑关系的稳健估计算法。计算结果表明，顾及模糊逻辑关系的稳健估计能有效地抵制粗差的影响，并能正确地定位粗差 相似文献
20.