ENHANCING KALMAN FILTERING–BASED TIGHTLY COUPLED NAVIGATION SOLUTION THROUGH REMEDIAL ESTIMATES FOR PSEUDORANGE MEASUREMENTS USING PARALLEL CASCADE IDENTIFICATION

Integrated global positioning system (GPS) solutions that utilize micro-electro-mechanical systems (MEMS)-based inertial sensors provide a more accurate navigation solution than stand-alone GPS in challenging scenarios. To keep the integrated solution less affected by sensor errors and to decrease the cost, a reduced inertial sensor system (RISS), which consists of only one gyroscope and two accelerometers, together with an odometer and integrated with GPS, is proposed. Tightly coupled integration is a better choice in demanding scenarios, as it can provide GPS aiding even when the number of visible satellites is three or less. However, inaccuracies of pseudoranges measured by the GPS receiver and used as aiding in the RISS/odometer/GPS integration solution will affect the overall positioning accuracy. This article explores the benefits of using parallel cascade identification (PCI), a nonlinear system identification technique that improves the overall navigation solution by modeling residual pseudorange correlated errors to be used by a Kalman filter (KF)–based tightly coupled RISS/odometer/GPS navigational solution. When less than four satellites are visible, the identified parallel cascade model for the still visible satellites is used to predict the residual pseudorange errors for these respective satellites, and the corrected pseudorange value is provided to KF. The performance of PCI for correcting the pseudoranges is examined and verified using road test trajectories and compared to a traditional tightly coupled RISS/odometer/GPS KF solution. The results demonstrate the advantages of this technique in correcting the pseudoranges and enhancing the positional solution.     

A derivative UKF for tightly coupled INS/GPS integrated navigation

The tightly coupled INS/GPS integration introduces nonlinearity to the measurement equation of the Kalman filter due to the use of raw GPS pseudorange measurements. The extended Kalman filter (EKF) is a typical method to address the nonlinearity by linearizing the pseudorange measurements. However, the linearization may cause large modeling error or even degraded navigation solution. To solve this problem, this paper constructs a nonlinear measurement equation by including the second-order term in the Taylor series of the pseudorange measurements. Nevertheless, when using the unscented Kalman filter (UKF) to the INS/GPS integration for navigation estimation, it causes a great amount of redundant computation in the prediction process due to the linear feature of system state equation, especially for the case with system state vector in much higher dimension than measurement vector. To overcome this drawback in computational burden, this paper further develops a derivative UKF based on the constructed nonlinear measurement equation. The derivative UKF adopts the concise form of the original Kalman filter (KF) to the prediction process and employs the unscented transformation technique to the update process. Theoretical analysis and simulation results demonstrate that the derivative UKF can achieve higher accuracy with a much smaller computational cost in comparison with the traditional UKF.     

全球定位系统(GPS)接收机的原理及应用

GPS接收机得到广泛应用,本文介绍其绝对定位和相对定位的原理,分析GPS接收机硬件性能和软件功能。并介绍国产HD8200 GPS接收机的性能指标及其使用。     

自学习式GPS车辆自主导航仪的研究

提出一种用GPS接收机通过自学习方式进行车辆自主导航和引导的方法。该方法首先对GPS接收机接收的定位信息通过回归算法进行线性化处理，然后以线性相关系数判断为准则对路径信息进行分段，再将这些线性相关的分段直线信息进行压缩和记录就形成了可以自主导航的路径信息。在导航过程中，利用这些线性相关的分段直线信息，通过矢量夹角计算和矢量方向判断的方法可以预测出前方路径的行驶方向，从而完成自主导航。这种由自学习方式获取的导航路径信息具有很高的导航精度和方向判别性。     

INS/SFGPS PPP紧组合系统动态补偿滤波算法

惯性/卫星组合导航系统结合精密单点定位技术可有效提高导航定位精度。但精密单点定位技术一般需采用双频接收机,成本较高;同时该系统中采用载波相位作为部分或全部观测量,极容易受到周跳的影响而导致精度下降和系统不稳定。针对上述问题,设计了一种惯性/卫星精密定位紧组合导航系统以及基于动态周跳补偿的鲁棒滤波算法。该系统采用低成本的单频接收机(SFGPS),以精密单点定位技术(PPP)处理过的伪距和载波相位作为观测信息,与惯性导航系统(INS)等效观测量进行紧组合,建立了相应紧组合观测模型并引入周跳作为信息融合滤波状态模型中的状态量,以滤波器信息构建周跳检测统计量并对周跳幅值进行识别和估计,实时补偿观测量以提高观测信息精度,同时以前述周跳估计的结果对状态模型中周跳状态量部分滤波参数进行实时调节。上述方法通过动态补偿周跳误差提高导航精度,通过滤波器参数自适应调节提高滤波稳定性。仿真结果验证了该系统模型及算法的有效性。     

An adaptive navigation method for a small unmanned aerial rotorcraft under complex environment

Focusing on low navigation performance of small unmanned aerial rotorcraft under complex environment, a composite navigation method combined with adaptive Kalman filtering and radial basis function neural network prediction method is proposed to improve navigation performance during GPS outages. When the GPS signal is available, an adaptive Kalman filter based on covariance scaling is introduced to deal with the process noise in real time. Meanwhile, a radial basis function neural network is trained on line to construct the projection among input (output of the inertial measurement unit, attitude and GPS losing time) and output (position error and velocity error). During GPS outages, the radial basis function neural network can provide high performance error estimation for position and velocity to improve state information. Finally, a land vehicle test and a flight test have confirmed that the proposed method can improve the navigation performance largely under complex environment.     

Real-time averaging of position data from multiple GPS receivers

Making GPS more accurate and/or reliable by combining it with other sensors and applying sophisticated data processing techniques has been attempted many times. Our approach to enhancing the performance of GPS is much simpler than most. We combine multiple (up to eight) consumer-grade GPS receivers into a system that averages their data in real time, requiring no other sensors, augmentation technologies, or powerful processors. The results show significant improvement in both accuracy and reliability of the data over that of a single receiver, and the distribution of error more closely resembles the normal distribution (as compared to a single receiver). Our multi-GPS system shows potential to be an inexpensive way to achieve better GPS performance with only “off-the-shelf” equipment.     

A method for indoor navigation based on magnetic beacons using smartphones and tablets

Outdoor navigation using GPS receivers installed in various types of consumer electronics devices, especially smartphones and tablet computers has become very common. However, indoor navigation can be problematic as GPS signals are blocked by ceilings and building walls and accuracy is on the order of building dimensions. In present work we propose using an array of magnetic beacons for localizing a receiver equipped with a magnetic sensor. A smartphone or a tablet computer with an internal magnetometer can be employed as a receiver. Exploiting smartphones and tablets for indoor navigation is a great advantage when considering convenience, simplicity and low cost. The navigation area is covered by magnetic beacons deployed in known locations. Each beacon generates an AC magnetic field with a unique signature enabling the receiver to distinguish between beacons. The signature may feature a specific single frequency tone, a combination of frequencies, or any other modulated signal. A software application running on the receiver enables self-localization by means of detection and identification of the nearest beacon. A system prototype has been developed and used to test the proposed method in field conditions. Experimental results show successful localization, which paves the way for a full scale development of an effective indoor navigation system. The good results together with simple implementation make the proposed method attractive for a wide range of indoor localization applications, including: pedestrian and robot navigation, inbuilding rescue missions, vision impaired assistance, and location aware services, just to mention a few.     

恶劣环境下GPS接收机定位算法研究

为了解决在恶劣环境下卫星信号被遮挡时GPS接收机无法定位的问题,将接收机钟差等效为可见卫星,并根据钟差预测值辅助GPS接收机进行定位解算.提出了基于时间序列分析理论的接收机钟差组合预测模型,然后将钟差预测值引入到GPS接收机中,通过扩充观测方程以实现接收机三维定位解算功能.分别在静态以及动态情况下应用实测数据进行验证,结果表明:该模型适合于钟差序列预测;在仅有3颗卫星的恶劣环境下,该方法可以提供满足导航定位精度要求的GPS接收机三维定位信息.     

基于MCMC粒子滤波的GPS接收机自主完好性监测算法研究

提出将马尔可夫蒙特卡罗方法与标准的粒子滤波算法有机结合应用于接收机自主完好性监测(RAIM)中.通过状态观测概率密度似然比方法建立一致性检验统计量进行卫星故障的检测与隔离.对算法进行了数学建模,描述了算法的流程.通过实测数据验证,结果表明,该方法在非高斯测量噪声情况下可以对状态进行精确的估计,成功检测和隔离故障卫星,克服了卡尔曼滤波的RAIM算法在处理非高斯测量噪声时性能下降的问题,从而验证了MCMC粒子滤波在接收机自主完好性监测中的有效性.     

NovAtel OEM4主板的GPS原始数据解码

GPS快速定位需要对实时的卫星导航数据和接收机观测数据进行处理,解码GPS接收机原始数据是实时获得以上数据的主要方法。文章介绍了GPS接收机原始数据转换为标准化数据格式(Rinex)的解码方法以及具体操作中的注意事项。叙述了GPS原始数据的获得途径、分析了Rinex2.10导航文件和观测文件的格式。通过对NovAtel OEM4主板GPS接收机获得的原始数据进行解码,证明解码方法的正确性与有效性。     

Noise characteristics of high-frequency,short-duration GPS records from analysis of identical,collocated instruments

High-rate (>1 Hz) GPS, currently used for measurement of dynamic processes and as a universal time and frequency standard, is usually assumed to be affected by site-specific errors and only limited studies of the error properties of high-frequency (10 Hz), short-duration (<100 s) GPS records exist. Preliminary studies, provided evidence of instrument-specific errors, which were investigated on the basis of systematic experiments with various types of stationary, collocated, identical GPS units. This analysis revealed differences between couples of receiver/antenna units, while spectral analyses revealed low-frequency colored noise, statistically significant below 0.2 Hz and, gradually decaying with increasing duration of observations, so that above 2.5 Hz measurements are contaminated only by white noise.     

Combining multiple Large Volume Metrology systems: Competitive versus cooperative data fusion

Large Volume Metrology (LVM) tasks can require the concurrent use of several measuring systems. These systems generally consist of set of sensors measuring the distances and/or angles with respect to a point of interest so as to determine its 3D position. When combining different measuring systems, characterized by sensors of different nature, competitive or cooperative methods can be adopted for fusing data. Competitive methods, which are by far the most diffused in LVM, basically perform a weighted mean of the 3D positions determined by the individual measuring systems. On the other hand, for cooperative methods, distance and/or angular measurements by sensors of different systems are combined together in order to determine a unique 3D position of the point of interest.This paper proposes a novel cooperative approach which takes account of the measurement uncertainty in distance and angular measurements of sensors of different nature. The proposed approach is compared with classical competitive approaches from the viewpoint of the metrological performance. The main advantages of the cooperative approach, with respect to the competitive one, are: (i) it is the only option when the individual LVM systems are not able to provide autonomous position measurements (e.g., laser interferometers or single cameras), (ii) it is the only option when only some of the sensors of autonomous systems work correctly (for instance, a laser tracker in which only distance – not angular – measurements are performed), (iii) when using systems with redundant sensors (i.e. photogrammetric systems with a large number of distributed cameras), point localization tends to be better than that using the competitive fusion approach.     

Self-powered wireless thermoelectric sensors

Sensors capable of measuring various performance parameters of an operational power generation unit could help improve system performance and overall efficiencies. For example, measurement of temperatures, temperature differences, or exhaust gas concentrations could provide both a quick quantitative and qualitative assessment of system health and allow for operation of power units with smaller safety margins and therefore higher efficiencies. For this study a technique is presented that can transmit data about an operational system wirelessly in real-time to an external location. For these experiments thermoelectric element leads were connected to a solenoid coil. When the thermoelectric was exposed to a temperature difference a current was generated in the thermoelectric and solenoid coil resulting in a magnetic field. A receiver was then used to measure the changes in magnetic field of the system. Two primary configurations were developed to test this wireless sensor configuration: dynamic and static. For dynamic measurements a pendulum and pneumatic air cylinder were used to simulate a moving component that may pass the external Hall sensor such as a fan or turbine blade. For dynamic measurements it was determined that for accurate results it is very important to maintain the distance constant between the Hall sensor and solenoid coil. For stationary measurements the temperature difference across the thermoelectric was related to output measurements from the Hall sensor. Overall, results show that data can be wirelessly transmitted to an external location using this method.     

A method for correcting discharge of boat-mounted ADCP measurements

GPS data are usually used to measure boat velocity during boat-mounted acoustic Doppler current profiler (ADCP) measurements when bottom tracking is biased by moving bed. GPS cannot provide consistently accurate boat velocity reference because of multipath errors, satellite signal reception problems, and heading errors. In addition, the computation of water velocity from an ADCP mounted onto a moving boat is a vector-algebra problem, thus the discharge calculation is subject to the compass error when GPS is used for boat velocity reference. This paper proposes a method for correcting discharge based on the idea that the discharge calculation is independent of the boat path. The processing of two sets of boat-mounted ADCP measurements integrated with differential GPS and non-differential GPS was simulated to verify the method. The results show that the proposed method performs well in both differential and non-differential GPS conditions. The relative errors range from 0.1% to 1.5% for all measurements with the mean relative errors of 0.7%. Analytical assessment of the GPS errors shows the proposed method is insensitive to the positioning accuracy of GPS, but positioning error of non-differential GPS may induce relative discharge error of more than 1% when the river or stream is narrow. On the contrary, a relatively small compass or heading error can cause a significant error in water velocity and discharge when using GPS as the boat velocity reference. Therefore, integrating a differential GPS and maintaining a slow boat speed are best practices for discharge measurement, especially for narrow streams or short boat paths.     

双频实时动态GPS接收机的设计与研制

双频实时动态GPS(全球定位系统)接收机可提供当前的三维坐标等位置,因其动态、实时而高效的显著特点,越来越多地应用于测绘领域。阐述了GPS系统的组成和GPS接收机的工作原理,提出了国产双频实时动态GPS接收机的设计思想和实现方案。     

Vehicle position estimation using nonlinear tire model for autonomous vehicle

To achieve technical perfection of the Advanced driver assistant system (ADAS), accurate analysis of the vehicle’s position is essential. For this, conventionally, sensor fusion has been carried out using a general GPS and general Inertial measurement unit (IMU), but the position accuracy decreases because of inertial sensor accumulation. Furthermore, because a vehicle tire model is analyzed by linearization and using a bicycle model, the position error increases. To solve this, in this study, a fusion algorithm was proposed by using an extended Kalman filter based on the non-linear tire model for the vehicle state information and by using the general GPS position information provided by the electric stability program of the vehicle. The fusion algorithm proposed in this study allowed us to suggest a position error correction method corresponding to a high precision Differential global positioning system (DGPS) within 1 m.     

全球定位系统用户定位的数学模型

以卫星时钟、系统时钟、用户接收机时钟同步为条件,建立起用户接收机位置求法定性分析的基本原理;又从三者时钟非同步开始建立起用户接收机位置求解的数学模型,在线性化的基础上,用迭代法进行位置求解的定量分析,使之对全球定位系统用户定位有一个比较清晰的认识.     

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry technique flow are presented. The hot-wire calibration is based on the determination of the acoustic velocity reference value through an acoustic pressure measurement and their relationship using a linear acoustic model. In this model, an analytical approach involving the coupling between the sound source and the resonant cavity effects and the viscous and the thermal effects in the boundary layers is used. The amplitude and phase calibrations are reported for the first time, simultaneously, either by varying the sound source input voltage for a fixed frequency, or by varying the frequency for a given source input voltage. The amplitude calibration is detailed by using a filtering technique to eliminate either the acoustic streaming effects or the anemometer basic electric voltage variations effects. This provides a simple way to an amplitude calibration with good accuracy when measuring an average of a stationary oscillating velocity. The phase calibration is proposed here by considering the phase difference between the microphone and the hot-wire anemometer output signals. The results obtained by using a simple fluid-filled resonant cavity are encouraging on the feasibility of this method to carry out a first-order acoustic velocity measurement. However, the complexity of the dynamic calibration due to that of the heat transfer mechanism around the hot-wire probe in various frequency ranges clearly merits more investigation.     

Experimental assessment of high-rate GPS receivers for deformation monitoring of bridge

The bridge engineer has long needed methods of accurate global displacement measurement for use in construction and more recently in the areas of bridge health monitoring. In this paper, the reliability and practicability of using high-rate carrier phase global positioning system (GPS) receivers are investigated to characterize dynamic oscillations of bridges. Initially, the short baseline trial is conducted to study the precision and characteristics of such kind of receivers as well as the potential applications of such a high-frequency data rate. After that, the performance of high-rate GPS receivers for dynamic response tracking is validated against accelerometers through controlled experimental tests and a novel kind of wavelet packet-based filtering method is also proposed. Finally, on-site dynamic experiments are carried out to measure the bridge deck oscillation induced by different external loads. Observed data are compared with predicted values derived from modeling undertaken with the finite element (FE) analysis software. The results of all the experiments proved to be very encouraging, and showed that high-rate GPS receiver is successful in quantifying both environmental induced bridge vibrations and high-frequency transient motion caused by vehicle loading, providing the ability for verification and/or improvement of structural design and modeling.