Centimeter-level Accuracy Research Articles

Exploiting Linear Structure for Precision Control of Highly Nonlinear Vehicle Dynamics

Drifting - operating a vehicle at a high sideslip angle - offers intriguing possibilities for controlling autonomous vehicles in critical situations. While drifting is a very dynamic process, occurring in a region of the state space with saturated tires and unstable equilibria, autonomous vehicles have been successfully controlled in this region. Previous control approaches to path tracking while drifting have relied on nonlinear vehicle models. In this paper, however, we demonstrate that linearized models capture the necessary dynamics for control in a large region surrounding a drift equilibrium. Using this linearized model, we develop a controller based on a linear quadratic regulator. This controller uses steering, throttle, and brakes to track both a desired path and a desired speed profile, making the system fully actuated. We demonstrate the fidelity of this linearized model and the utility of this controller by implementing this controller on MARTY, an electric DMC DeLorean, and accurately tracking equilibrium and quasi-equilibrium paths with centimeter-level accuracy that exceeds prior work.

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Topography reconstruction and evolution analysis of outlet glacier using data from unmanned aerial vehicles in Antarctica

Reconstruction of glacial topography is important for assessing the ice dynamics of glaciers in the past and understanding how they may respond to climate change in the future. As an emerging strategy, unmanned aerial vehicles (UAVs) have been successfully used in glaciology applications to reconstruct surface topography and monitor the short-term dynamics of glaciers. However, none of these studies have focused on the ice dynamics of outlet glaciers in Antarctica. In this study, based on a combination of UAVs and a base station, we investigated Dalk Glacier, a typical marine-terminating glacier in East Antarctica, during two Chinese National Antarctic Research Expeditions from 2019 to 2020. By applying structure-from-motion and multi-view-stereo photogrammetry, high-resolution orthomosaics and digital elevation models of the glacial topography were reconstructed with centimeter-level accuracy via in situ validation, thus marking the first application of UAV observations in the monitoring of Antarctic outlet glaciers. Topographic evolution of the glacier was quantitatively analyzed from various aspects including ice velocity, surface elevation, crevasses, and ice front calving. A maximum ice velocity of ∼ 310 m a-1 at its terminus was observed, which was ∼ 90 m a-1 greater than that in satellite-based studies. We analyzed in detail the spatially heterogeneous changes in the ice velocity and surface elevation of the glacier under the influence of an ice rumple at its calving terminus. Combined with satellite images and existing datasets, we hypothesize that the large ice rumples at the glacier terminus could deform the glacier and potentially damage its structural integrity, thereby limiting the growth of its terminus.

Passive Indoor Tracking Fusion Algorithm Using Commodity Wi-Fi

Recent studies have found the mapping relationship between channel state information used in commercial Wi-Fi devices and environmental changes in the indoor environment, which can be used for sensing purposes. With the advantages of low cost and wide deployment of Wi-Fi facilities, passive indoor tracking systems based on Wi-Fi have huge potential. This article proposes and builds a passive indoor tracking system using commercial Wi-Fi devices, which realizes the function of tracking the human body’s trajectory in indoor environment. The system uses only commercial Wi-Fi devices. It processes the collected channel state information data by sending and receiving two pairs of Wi-Fi devices, and extract the movement information the messy data to obtain the trajectory of the human body. The system conducts a geometric feature analysis in the complex plane to obtain accurate displacement information, and utilize a fusion algorithm, combining the AoA (Angle of Arrival) information obtained by MUSIC algorithm, to obtain accurate human trajectory. In the experiment, the complex plane geometric feature analysis algorithm reaches centimeter-level accuracy in obtaining displacement information, while the system reaches decimeter-level accuracy on in obtaining indoor human trajectory on a simulation dataset.

Relative-Position Estimation Based on Loosely Coupled UWB–IMU Fusion for Wearable IoT Devices

Relative positioning is one of the important techniques in collaborative robotics, autonomous vehicles, and virtual/augmented reality (VR/AR) applications. Recently, ultra-wideband (UWB) has been utilized to calculate relative position as it does not require a line of sight compared to a camera to calculate the range between two objects with centimeter-level accuracy. However, the single UWB range measurement cannot provide the relative position and attitude of any device in three dimensions (3D) because of lacking bearing information. In this paper, we have proposed a UWB-IMU fusion-based relative position system to provide accurate relative position and attitude between wearable Internet of Things (IoT) devices in 3D. We introduce a distributed Euler angle antenna orientation which can be equipped with the mobile structure to enable relative positioning. Moving average and min-max removing preprocessing filters are introduced to reduce the standard deviation. The standard multilateration method is modified to calculate the relative position between mobile structures. We combine UWB and IMU measurements in a probabilistic framework that enables users to calculate the relative position between two nodes with less error. We have carried out different experiments to illustrate the advantages of fusing IMU and UWB ranges for relative positioning systems. We have achieved a mean accuracy of 0.31 m for 3D relative positioning in indoor line of sight conditions.

Open-Source Hardware-Based Three-Dimensional Positioning Device for Indoor Measurement and Positioning

Indoor private (local) wireless networks are considered key enablers for the industrial Internet of Things (IIoT). To ensure that a private network satisfies its own requirements and guarantees coverage, it is important to accurately measure the radio performance at the accurate position to further optimize the network. Additionally, as carrier frequencies increase, cellular network-based positioning becomes increasingly important, as it enables more accurate positioning. For example, centimeter-level accuracy is expected in beyond 5G systems owing to the sub-THz band carrier frequency. To accurately compare and assess various cellular network-based positioning methods, positioning devices, which can move along the same trajectory more accurately than at the centimeter-level, are required. To this end, we implemented a three-dimensional (3D) positioning device developed from open-source hardware, which is generally used to implement computer numerical control (CNC) machines and 3D printers. The implemented 3D pointing device is cost-effective and portable and can be freely configurable and resized in one, two, and three dimensions owing to the use of open-source hardware. The received signal strength indicator (RSSI) employing the LoRa module can be obtained using the implemented device. Using a very low carrier frequency system, it is possible to accurately measure the RSSI variations due to multipath propagation. After demonstrating the reproducibility of the data, the effectiveness of the implemented device was confirmed by showing that the RSSI variation and fading correlation coefficient are close to the Rayleigh fading variation.

PPP/PPP-RTK Message Authentication

<h3>Abstract</h3> This paper analyzes candidate schemes for PPP/PPP-RTK (precise point positioning/real-time kinematic) data authentication. Asymmetric schemes are proposed based on existing standards and compatible with GNSS messages. Post-quantum cryptographic signatures are also reviewed and discussed. Two schemes are selected for analysis: digital signature (DS) based on ECDSA, and delayed disclosure (DD) based on a hybrid scheme using the TESLA protocol. Each of them is described in detail for both Galileo high-accuracy service and QZSS centimeter-level accuracy service. The performance of the schemes in terms of time to receive the corrections message and increase in the age of data (ΔAOD) is analyzed. The analysis is complemented by a review of the CPU consumption at receiver level.

Estimation of 3D form of the Path for Autonomous Driving in Terrain*

3D path estimation, i.e., determining the height profiles of the path, is crucial in motion control for autonomous driving in terrains. It is essential to prevent rollover from abrupt peaks, dips, and briefly wet ground. In this study, wheel displacement measurements and height estimation of an off-road vehicle are presented. A calibration process is suggested to measure the instantaneous vertical displacement of each wheel. GNSS-pose-based methods are used to estimate the vehicle's geometry parameters yielding the centimeter-level accuracy of the 3D-path estimation method. The accuracy of the vehicle's instrumentation is examined on a test track to create a 3D terrain model of the path. The outcome of the proposed scheme is compared to a reference elevation profile created with structure from motion on the basis of machine vision and GNSS using data collected by an unmanned aerial vehicle. The comparison of the results demonstrates that the 3D path can be estimated with sufficient accuracy in open terrain using ground vehicles.

Accuracy Assessment of Direct Georeferencing for Photogrammetric Applications Based on UAS-GNSS for High Andean Urban Environments

Unmanned Aircraft Systems (UAS) are used in a variety of applications with the aim of mapping detailed surfaces from the air. Despite the high level of map automation achieved today, there are still challenges in the accuracy of georeferencing that can limit both the speed and the efficiency in mapping urban areas. However, the integration of topographic grade Global Navigation Satellite System (GNSS) receivers on UAS has improved this phase, leading to a reach of up to a centimeter-level accuracy. It is therefore necessary to adopt direct georeferencing (DG), real-time kinematic positioning (RTK)/post-processed kinematic (PPK) approaches in order to largely automate the photogrammetric flow. This work analyses the positional accuracy using Ground Control Points (GCP) and the repeatability and reproducibility of photogrammetric products (Digital Surface Model and ortho-mosaic) of a commercial multi-rotor system equipped with a GNSS receiver in an urban environment with a DG approach. It was demonstrated that DG is a viable solution for mapping urban areas. Indeed, PPK with at least 1 GCP considerably improves the RMSE (x: 0.039 m, y: 0.012 m, and z: 0.034 m), allowing for a reliable 1:500 scale urban mapping in less time when compared to conventional topographic surveys.

LSAB: Enhancing Spatio-temporal Efficiency of AoA Tracking Systems

Estimating the angle-of-arrival (AoA) of an RF source by using a large-sized antenna array is a classical topic in wireless systems. However, AoA tracking systems are not yet used for Internet of Things (IoT) in the real world due to their unaffordable cost. Many efforts, such as a time-sharing array, emulated array, and sparse array, were recently made to cut the cost. This work introduces a log-spiral antenna belt ( LSAB ), a new novel sparse “planar array” that could estimate the AoA of an IoT device in 3D space by using a few antennas connected to a single timeshare channel. Unlike the conventional arrays, LSAB deploys antennas on a log-spiral-shaped belt in a non-linear manner, following the theory of minimum resolution redundancy newly discovered in this work. One physical 8 × 8 uniform planar array (UPA) and four logical sparse arrays, including LSAB , were prototyped to validate the theory and evaluate the performance of sparse arrays. The extensive benchmark demonstrates that the performance of LSAB was comparable to that of a UPA, with similar degree of resolution; and LSAB could provide over 40% performance improvement than existing sparse arrays. We also prototyped a second LSAB adapted to an RFID system for localizing RFID tags at centimeter-level accuracy.

Use of real time localization systems (RTLS) in the automotive production and the prospects of 5G – A literature review

ABSTRACT Numerous challenges in automotive production lead to an increased need for transparency and optimization. Real-Time-Location-Systems (RTLS) is a key tool for achieving this goal. They enable intelligent and automated production processes. Existing solutions such as Ultra-Wideband, Bluetooth-Low-Energy, or Radio-Frequency-Identification have drawbacks in costs, range, or accuracy. 5G is a newly developing standard, recently including high-accuracy positioning. It is unclear, however, if 5G positioning has reached industrial maturity. This contribution aims to determine the state-of-the-art of 5G positioning by performing a systematic literature review and comparing its findings to industrial positioning requirements. 143 articles were analyzed and categorized as: the fundamentals of radio-frequency positioning, an overview of existing solutions, the state-of-the-art, and the maturity of 5G as an industrial positioning system. Results show that, theoretically, centimeter-level accuracies are pursued. However, practical tests are rarely conducted. Concluding, 5G positioning shows great potential, but industrial pilots are required to validate the theoretical characteristics.

Carrier Phase Based Autonomous Coordinate Evolution for Narrowband Positioning Systems

Ground-based positioning systems (GBPSs), such as cellular networks and pseudolites, can provide high-precision positioning services through carrier phase positioning (CPP). Most existing methods are based on having accurate coordinates of all transmitters (TXs). In some applications, however, it could be too expensive and time-consuming to measure the coordinates of all TXs accurately, and requiring precise manual measurements severely degrades the flexibility of GBPSs. In this paper, we propose a carrier phase based autonomous coordinate evolution (CPACE) method for GBPSs, which uses the observations of multiple users to continuously improve the accuracy of TX coordinates. We first propose a Batch CPACE (B-CPACE) method and analyze its theoretical advantages over traditional single-point positioning (SPP). In the case of a large number of users, to avoid heavy burden on data transmission and calculation, we propose two distributed CPACE (D-CPACE) methods which have the same asymptotic performance with B-CPACE. Our numerical simulations prove that both B-CPACE and D-CPACE have better accuracy than SPP and reach the Cramer-Rao lower bounds. A real-world experiment shows that the proposed method can achieve centimeter-level accuracy.

A trajectory similarity-based method to evaluate GNSS kinematic precise positioning performance with a case study

There is a lack of effective testing methods to evaluate high-precision global navigation satellite system (GNSS) kinematic positioning solutions, such as GNSS real-time kinematic (RTK) or post-processed kinematic (PPK), with centimeter-level accuracy. Current methods either process static GNSS data in kinematic mode to perform a pseudo-kinematic test or use a precise motion table to make a real-kinematic test but within a very limited travel distance. This study proposes a trajectory similarity method by moving a track trolley platform along a railway track, which can match the GNSS positioning trajectory and the pre-surveyed reference track. The GNSS trajectory offsets from the reference track along the cross-track and vertical directions are regarded as GNSS kinematic positioning errors. Lever-arm compensation is applied to achieve millimeter-level accuracy for this evaluation method. A case study was conducted to evaluate the positioning performance of the Global Positioning System/BeiDou Navigation Satellite System (GPS/BDS) PPK using the proposed method. The results indicate that the proposed method can provide a reference trajectory on the order of a few millimeters, which is sufficiently accurate even for PPK positioning performance evaluation and error source tracing in wide regions. In this case, cycle slips as small as 10 cm in the carrier phase measurements can be detected and studied based on the proposed method.

An elevation stochastic model constrained by C/N0 for GNSS real-time kinematic positioning in harsh environments

When the global navigation satellite system (GNSS) is used for positioning in harsh environments with high occlusion and strong reflection, the signals are easily reflected, diffracted, or even blocked, which can lead to multipath and non-line-of-sight (NLOS) errors. Existing stochastic models do not fully consider the significant unmodeled errors, such as multipath and NLOS, in specific scenarios such as canyons. This paper systematically establishes the carrier-to-noise ratio (C/N0) template functions of the low-cost receiver for the first time and proposes an elevation stochastic model constrained by C/N0 (elevation-C/N0 model) by combining the two indicators (elevation angle and C/N0) with the idea of robust estimation. Then, real-time kinematic positioning (RTK) experiments are conducted to verify the effectiveness of the new model, and both static monitoring and urban kinematic situations are included. The results showed that: (a) in the static data, the average ambiguity fixed rate of the elevation-C/N0 model is 95.79%, which is 10.05%, 15.74%, and 12.57% higher than that of the equal-weight, elevation-based, and C/N0-based stochastic models, respectively. At the same time, only the new model consistently meets centimeter-level accuracy requirements in harsh environments. (b) In the kinematic data, compared with the three traditional stochastic models, the ambiguity fixed rate of the elevation-C/N0 stochastic model is increased by 58.33%, 19.79%, and 28.13%, respectively. The motion trajectory calculated by the elevation-C/N0 model is the smoothest out of all the models. In conclusion, compared with the traditional stochastic models, the elevation-C/N0 stochastic model is more applicable to both static and kinematic measurements in harsh environments. It can effectively mitigate the adverse effects of errors such as multipath and NLOS, increase the ambiguity fixed rate, and improve the positioning reliability to a certain extent, hence the proposed method has a better positioning performance.

Designing an outdoor machinery monitoring device with integrated real-time kinematic positioning

Accurate positioning ofoutdoor vehicles and machinery is of the top importance inmanagement, tracking, analysis, and control applications. However, most of the current vehicle tracking devices have an error of a few meters to several tens of meters,which is not enough for applications requiring high accuracy. This paper presents the design of an outdoor machinery monitoring device that integrates precise positioning technology of real-time kinematic (RTK). The device uses U-Blox’s Zed F9P module as the core to perform the high accuracy positioning function. Thanks to the integration of RTK positioning technology, the device can monitor the location of machinery outdoors with centimeter-level accuracy.

Mobile Feature Enhanced High-Accuracy Positioning Based on Carrier Phase and Bayesian Estimation

The mobile feature and the moving positions are important for mobile communications and Internet of Things. Inspired by the potentially excellent precision of carrier phase positioning, this article proposes a mobile feature enhanced high-accuracy positioning algorithm based on the carrier phase and Bayesian estimation. The mobile feature is first estimated using time-differential carrier phase measurements. By combining the estimated position changes with instant ranging and carrier phase measurements, the factorized posterior probability of positioning is established based on the Bayes theorem. In turn, a factor graph-based positioning method is proposed to obtain precise positioning results. The numerical simulation results show that the proposed algorithm can achieve centimeter-level accuracy, and the positioning error can approach the Cramer–Rao lower bound.

GPS/BDS precise point positioning with B2b products for high-rate seismogeodesy: application to the 2021Mw 7.4 Maduo earthquake

SUMMARYPrecise point positioning (PPP) can measure ground motions with a centimetre-level accuracy using only one receiver. It has been widely used in earthquake monitoring and earthquake early warning (EEW) systems. However, traditional PPP highly depends on well-established and robust internet infrastructure for data communication. Along with the broadcast ephemeris, the orbit and clock corrections transmitted by the B2b signals of BeiDou Navigation Satellite System (BDS) can be used to recover the precise products of GPS and BDS. Since the B2b products, namely the satellite state parameter messages, are accessible even without internet infrastructure, PPP with B2b signals is more suitable for real-time applications. This study witnesses the application of PPP with B2b products in seismic monitoring for the first time. The shake table experiments demonstrate that PPP with B2b can reach a millimetre-level accuracy in horizontal in earthquake monitoring for GPS-only, BDS-only and GPS/BDS combination. The application to the 2021 Mw 7.4 Maduo earthquake shows that the accuracies of seismic displacements derived from GPS-only PPP with B2b products are 1.7, 2.4 and 1.7 cm in east, north and vertical components, compared with those from GPS-only PPP with final precise products. We therefore conclude that PPP with B2b products has a promising prospect in seismogeodesy and related applications such as EEW and rapid hazard response.

A Signal-Multiplexing Ranging Scheme for Integrated Localization and Sensing

Precise range information plays a role in acquiring high-precision position awareness, but its accuracy will be severely degraded by clock errors. This letter devises a signal-multiplexing ranging scheme for integrated localization and sensing, which exploits the reflecting non-line-of-sight signals for sensing and jointly determines the node and the target positions with the range estimates. Specifically, we design a ranging protocol with a minimum number of signal transmissions via signal multiplexing and propose a maximum likelihood (ML) range estimate with effective clock error elimination. Simulation results show that the proposed method can achieve centimeter-level accuracy even in the presence of large clock errors.

Performance Evaluation of Different GNSS Positioning Modes

This paper gives a comparison of different GPS positioning modes using RTKLIB which is free and open-source software. The modes tested in this work are Single point positioning ( SPP), precise point positioning (PPP), Satellite-based augmentation system ( SBAS), Differential GPS (DGPS), and Real-Time Kinematic (RTK). The data for tests were obtained from NetR9 receivers, these types of receivers are multi-frequencies and multi-constellation receivers that provide carrier and phase measurements. The SPP mode is the very simplest mode, it can be used for applications where accuracy is not less than 5m, and it can be improved to achieve 1m by using SBAS corrections but only in the coverage area of the system. The DGPS can also provide 1m accuracy using a second receiver as a base station which can increase the cost of the operation. For applications that need very high accuracy, RTK and PPP can be used to reach centimeter-level accuracy. RTK needs a base station in addition to the rover receiver used for the positioning; PPP uses precise orbital and clock solutions which are not available in real time for all users.

The Role of GNSS-RTN in Transportation Applications

The Global Navigation Satellite System—Real-Time Network (GNSS-RTN) is a satellite-based positioning system using a network of ground receivers (also called continuously operating reference stations (CORSs)) and a central processing center that provides highly accurate location services to the users in real-time over a broader geographic region. Such systems can provide geospatial location data with centimeter-level accuracy anywhere within the network. Geospatial location services are not only used in measuring ground distances and mapping topography; they have also become vital in many other fields such as aerospace, aviation, natural disaster management, and agriculture, to name but a few. The innovative and multi-disciplinary applications of geospatial data drive technological advancement towards precise and accurate location services available in real-time. Although GNSS-RTN technology is currently utilized in a few industries such as precision farming, construction industry, and land surveying, the implications of precise real-time location services would be far-reaching and more critical to many advanced transportation applications. The GNSS-RTN technology is promising in meeting the needs of automation in most advanced transportation applications. This article presents an overview of the GNSS-RTN technology, its current applications in transportation-related fields, and a perspective on the future use of this technology in advanced transportation applications.