Feasibility Analysis of LTE-Based UAS Navigation in Deep Urban Areas and DSRC Augmentation

The current autonomous navigation of unmanned aircraft systems (UAS) heavily depends on Global Navigation Satellite Systems (GNSS). However, in challenging environments, such as deep urban areas, GNSS signals can be easily interrupted, so that UAS may lose navigation capability at any instant. For urban positioning and navigation, Long Term Evolution (LTE) has been considered a promising signal of opportunity due to its dense network in urban areas, and there has recently been great advancement in LTE positioning technology. However, the current LTE positioning accuracy is found to be insufficient for safe UAS navigation in deep urban areas. This paper evaluates the positioning performance of the current network of LTE base stations in a selected deep urban area and investigates the effectiveness of LTE augmentations using dedicated short range communication (DSRC) transceivers through the optimization of the ground LTE/DSRC network and cooperative positioning among UAS. The analysis results based on simulation using an urban canyon model and signal line of sight propagations show that the addition of four or five DSRC transceivers to the existing LTE base station network could provide better than 4–6 m horizontal positioning accuracy (95%) in the selected urban canyon at a position of 150 ft above the ground, while a dense LTE network alone may result in a 15–20 m horizontal positioning error. Additionally, the simulation results of cooperative positioning with inter-UAS ranging measurements in the DSRC augmented LTE network were shown to provide horizontal positioning accuracy better than 1 m in most flight space, assuming negligible time-synchronization errors in inter-UAS ranging measurements.

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A New Asynchronous RTK Method to Mitigate Base Station Observation Outages

Sensors ◽

10.3390/s19153376 ◽

2019 ◽

Vol 19 (15) ◽

pp. 3376 ◽

Cited By ~ 2

Author(s):

Yuan Du ◽

Guanwen Huang ◽

Qin Zhang ◽

Yang Gao ◽

Yuting Gao

Keyword(s):

Real Time ◽

Base Station ◽

Global Navigation Satellite Systems ◽

Observation Data ◽

Post Processing ◽

Positioning Accuracy ◽

Real Time Processing ◽

Phase Measurements ◽

Satellite Systems ◽

Precise Ephemeris

Real-time kinematic (RTK) positioning is a satellite navigation technique that is widely used to enhance the precision of position data obtained from global navigation satellite systems (GNSS). This technique can reduce or eliminate significant correlation errors via the enhancement of the base station observation data. However, observations received by the base station are often interrupted, delayed, and/or discontinuous, and in the absence of base station observation data the corresponding positioning accuracy of a rover declines rapidly. With the strategies proposed till date, the positioning accuracy can only be maintained at the centimeter-level for a short span of time, no more than three min. To address this, a novel asynchronous RTK method (that addresses asynchronous errors) that can bridge significant gaps in the observations at the base station is proposed. First, satellite clock and orbital errors are eliminated using the products of the final precise ephemeris during post-processing or the ultra-rapid precise ephemeris during real-time processing. Then the tropospheric error is corrected using the Saastamoinen model and the asynchronous ionospheric delay is corrected using the carrier phase measurements from the rover receiver. Finally, a straightforward first-degree polynomial function is used to predict the residual asynchronous error. Experimental results demonstrate that the proposed approach can achieve centimeter-level accuracy for as long as 15 min during interruptions in both real-time and post-processing scenarios, and that the accuracy of the real-time scheme can be maintained for 15 min even when a large systematic error is projected in the U direction.

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GPS/BDS RTK Positioning Based on Equivalence Principle Using Multiple Reference Stations

Remote Sensing ◽

10.3390/rs12193178 ◽

2020 ◽

Vol 12 (19) ◽

pp. 3178

Author(s):

Jian Wang ◽

Tianhe Xu ◽

Wenfeng Nie ◽

Guochang Xu

Keyword(s):

Equivalence Principle ◽

Urban Areas ◽

Unmanned Vehicles ◽

Global Navigation Satellite Systems ◽

Reference Station ◽

Unknown Parameters ◽

Positioning Accuracy ◽

Kinematic Positioning ◽

Parameter Constraints ◽

Multiple Reference

Reliable real-time kinematic (RTK) is crucially important for emerging global navigation satellite systems (GNSSs) applications, such as drones and unmanned vehicles. The performance of conventional single baseline RTK (SBRTK) with one reference station degrades greatly in dense, urban environments, due to signal blockage and multipath error. The increasing use of multiple reference stations for kinematic positioning can improve RTK positioning accuracy and availability in urban areas. This paper proposes a new algorithm for multi-baseline RTK (MBRTK) positioning based on the equivalence principle. The advantages of the solution are to keep observation independent and increase the redundancy to estimate the unknown parameters. The equivalent double-differenced (DD) observation equations for multiple reference stations are firstly developed through the equivalent transform. A modified Kalman filter with parameter constraints is proposed, as well as a partial ambiguity resolution (PAR) strategy is developed to determine an ambiguity subset. Finally, the static and kinematic experiments are carried out to validate the proposed algorithm. The results demonstrate that, compared with single global positioning system (GPS) and Beidou navigation system (BDS) RTK positioning, the GPS/BDS positioning for MBRTK can enhance the positioning accuracy with improvement by approximately (45%, 35%, and 27%) and (12%, 6%, and 19%) in the North (N), East (E), and Up (U) components, as well as the availability with improvement by about 33% and 10%, respectively. Moreover, the MBRTK model with two and three reference receivers can significantly increase the redundancy and provide smaller ambiguity dilution of precision (ADOP) values. Compared with the scheme-one and scheme-two for SBRTK, the MBRTK with multiple reference receivers have a positioning accuracy improvement by about (9%, 0%, and 6%) and (9%, 16%, and 16%) in N, E, and U components, as well as the availability improvement by approximately 10%. Therefore, compared with the conventional SBRTK, the MBRTK can enhance the strength of the kinematic positioning model as well as improve the positioning accuracy and availability.

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Implementation and Performance of a Deeply-Coupled GNSS Receiver with Low-Cost MEMS Inertial Sensors for Vehicle Urban Navigation

Sensors ◽

10.3390/s20123397 ◽

2020 ◽

Vol 20 (12) ◽

pp. 3397 ◽

Cited By ~ 1

Author(s):

Xin Feng ◽

Tisheng Zhang ◽

Tao Lin ◽

Hailiang Tang ◽

Xiaoji Niu

Keyword(s):

Urban Areas ◽

Weight Control ◽

Low Cost ◽

Field Tests ◽

Urban Environments ◽

Global Navigation Satellite Systems ◽

Measurement Unit ◽

Positioning Accuracy ◽

Gnss Receiver ◽

Tracking Loops

In urban environments, Global Navigation Satellite Systems (GNSS) signals are frequently attenuated, blocked or reflected, which degrades the positioning accuracy of GNSS receivers significantly. To improve the performance of GNSS receiver for vehicle urban navigation, a GNSS/INS deeply-coupled software defined receiver (GIDCSR) with a low cost micro-electro-mechanical system (MEMS) inertial measurement unit (IMU) ICM-20602 is presented, in which both GPS and BDS constellations are supported. Two key technologies, that is, adaptive open-close tracking loops and INS aided pseudo-range weight control algorithm, are applied in the GIDCSR to enhance the signal tracking continuity and positioning accuracy in urban areas. To assess the performance of the proposed deep couple solution, vehicle field tests were carried out in GNSS-challenged urban environments. With the adaptive open-close tracking loops, the deep couple output carrier phase in the open sky, and improved pseudo-range accuracy before and after GNSS signal blocked. Applying the INS aided pseudo-range weight control, the pseudo-range gross errors of the deep couple decreased caused by multipath. A popular GNSS/INS tightly-coupled vehicle navigation kit from u-blox company, M8U, was tested side by side as benchmark. The test results indicate that in the GNSS-challenged urban areas, the pseudo-range quality of GIDCSR is at least 25% better than that of M8U, and GIDCSR’s horizontal positioning results are at least 69% more accurate than M8U’s.

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A New Faulty GNSS Measurement Detection and Exclusion Algorithm for Urban Vehicle Positioning

Remote Sensing ◽

10.3390/rs13112117 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2117

Author(s):

Qi Cheng ◽

Ping Chen ◽

Rui Sun ◽

Junhui Wang ◽

Yi Mao ◽

...

Keyword(s):

Fault Detection ◽

Real Time ◽

Urban Areas ◽

Least Square ◽

Global Navigation Satellite Systems ◽

Positioning Accuracy ◽

Detection Scheme ◽

Multiple Faults ◽

Ground Vehicle ◽

Vehicle Positioning

The performance requirements for Global Navigation Satellite Systems (GNSS) are becoming more demanding as the range of mission-critical vehicular applications, including the Unmanned Aerial Vehicle (UAV) and ground vehicle-based applications, increases. However, the accuracy and reliability of GNSS in some environments, such as in urban areas, are often affected by non-line-of-sight (NLOS) signals and multipath effects. It is therefore essential to develop an effective fault detection scheme that can be applied to GNSS observations so as to ensure that the vehicle positioning can be calculated with a high accuracy. In this paper, we propose an online dataset based faulty GNSS measurement detection and exclusion algorithm for vehicle positioning that takes account of the NLOS/multipath affected scenarios. The proposed algorithm enables a real-time online dataset based fault detection and exclusion scheme, which makes it possible to detect multiple faults in different satellites simultaneously and accurately, thereby allowing real-time quality control of GNSS measurements in dynamic urban positioning applications. The algorithm was tested with simulated/artificial step errors in various scenarios in the measured pseudoranges from a dataset acquired from a UAV in an open area. Furthermore, a real-world test was also conducted with a ground-vehicle driving in a dense urban environment to validate the practical efficiency of the proposed algorithm. The UAV based simulation exhibits a fault detection rate of 100% for both single and multi-satellite fault scenarios, with the horizontal positioning accuracy improved to about 1 metre from tens of metres after fault detection and exclusion. The ground vehicle-based real test shows an overall improvement of 26.1% in 3D positioning accuracy in an urban area compared to the traditional least square method.

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Initial Assessment of BDS PPP-B2b Service: Precision of Orbit and Clock Corrections, and PPP Performance

Remote Sensing ◽

10.3390/rs13112050 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2050

Author(s):

Zhixi Nie ◽

Xiaofei Xu ◽

Zhenjie Wang ◽

Jun Du

Keyword(s):

Global Navigation Satellite Systems ◽

Convergence Time ◽

Initial Assessment ◽

Satellite Orbits ◽

Navigation Satellite ◽

Positioning Accuracy ◽

Global Navigation ◽

Kinematic Ppp ◽

Global Navigation Satellite ◽

Better Than

On 31 July 2020, the Beidou global navigation satellite system (BDS-3) was officially announced as being commissioned. In addition to offering global positioning, navigation, and timing (PNT) services, BDS-3 also provides precise point positioning (PPP) augmentation services. The satellite orbit correction, clock correction and code bias correction of BDS-3 and other global navigation satellite systems (GNSS) are broadcast by the BDS-3 geostationary earth orbit (GEO) satellites through the PPP-B2b signal. The PPP-B2b service is available for users in China and the surrounding area. In this study, an initial assessment of the PPP-B2b service is presented, with collected 3-day PPP-B2b messages. Based on broadcast ephemeris and PPP-B2b messages, the precise satellite orbits and clock offsets can be recovered. This precision is evaluated with the precise ephemeris from the GeoForschungsZentrum Potsdam (GFZ) analysis center as references. The results indicate that the accuracy of BDS-3 satellite orbits in the direction of radial, along-track, and cross-track is 0.138, 0.131, and 0.145 m, respectively, and for GPS a corresponding accuracy of 0.104, 0.160, and 0.134 m, respectively, could be obtained. The precision of clock offsets can reach a level of several centimeters for both GPS and BDS-3. Both the performance of static PPP and kinematic PPP are evaluated using the observations from four international GNSS monitoring assessment service (iGMAS) stations. Regarding static PPP, the average convergence time is 17.7 minutes to achieve a horizontal positioning accuracy of better than 0.3 m, and a vertical positioning accuracy of better than 0.6 m. The average positioning accuracy in the direction of east, north, and up-directions are 2.4, 1.6, and 2.3 cm. As to kinematic PPP, the average RMS values of positioning errors in the direction of east, north, and up are 8.1 cm, 3.6 cm, and 8.0 cm after full convergence.

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Road Tests of the Positioning Accuracy of INS/GNSS Systems Based on MEMS Technology for Navigating Railway Vehicles

Energies ◽

10.3390/en13174463 ◽

2020 ◽

Vol 13 (17) ◽

pp. 4463 ◽

Cited By ~ 3

Author(s):

Mariusz Specht ◽

Cezary Specht ◽

Paweł Dąbrowski ◽

Krzysztof Czaplewski ◽

Leszek Smolarek ◽

...

Keyword(s):

Urban Areas ◽

Land Development ◽

Global Navigation Satellite Systems ◽

Rolling Stock ◽

Navigation Systems ◽

Positioning Accuracy ◽

Positioning Systems ◽

Satellite Systems ◽

Wide Range ◽

Mems Technology

Thanks to the support of Inertial Navigation Systems (INS), Global Navigation Satellite Systems (GNSS) provide a navigation positioning solution that, in the absence of satellite signals (in tunnels, forest and urban areas), allows the continuous positioning of a moving object (air, land and sea). Passenger and freight trains must, for safety reasons, comply with several formal navigation requirements, particularly those that concern the minimum acceptable accuracy for determining their position. Depending on the type of task performed by the train (positioning a vehicle on a route, stopping at a turnout, stopping at a platform, monitoring the movement of rolling stock, etc.), the train must have positioning systems that can determine its position with sufficient accuracy (1–10 m, p = 0.95) to perform the tasks in question. A wide range of INS/GNSS equipment is currently available, ranging from very costly to simple solutions based on Micro-Electro-Mechanical Systems (MEMS), which, in addition to an inertial unit, use one or two GNSS receivers. The paper presents an assessment of the accuracy of both types of solutions by testing them simultaneously in dynamic measurements. The research, due to the costs and logistics complexity, was made using a passenger car. The surveys were carried out in a complex way, because the measurement route was travelled three times at four different speeds: 40 km/h, 80 km/h, 100 km/h and 120 km/h on seven representative test sections with diverse land development. In order to determine the positioning accuracy of INS devices, two precise GNSS geodetic receivers (2 cm accuracy, p = 0.95) were used as a reference positioning system. The measurements demonstrated that only INS/GNSS systems based on two receivers can meet the requirements of most railway applications related to rail navigation, and since a solution with a single GNSS receiver has a much lower positioning accuracy, it is not suitable for many railway applications. It is noted that considerable differences between the standards defining the navigation requirements for railway applications. For example, INS/GNSS systems based on two receivers meet the vast majority of the expectations specified in the Report on Rail User Needs and Requirements. However, according to the Federal Radionavigation Plan (FRP), it cannot be used in any railway application.

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Shadow Matching: A New GNSS Positioning Technique for Urban Canyons

Journal of Navigation ◽

10.1017/s0373463311000087 ◽

2011 ◽

Vol 64 (3) ◽

pp. 417-430 ◽

Cited By ~ 134

Author(s):

Paul D. Groves

Keyword(s):

Urban Areas ◽

Tall Buildings ◽

Global Navigation Satellite Systems ◽

Positioning System ◽

Positioning Accuracy ◽

Satellite Systems ◽

Building Models ◽

Satellite Visibility ◽

Global Navigation Satellite ◽

Cross Track

The Global Positioning System (GPS) is unreliable in dense urban areas, known as urban canyons, which have tall buildings or narrow streets. This is because the buildings block the signals from many of the satellites. Combining GPS with other Global Navigation Satellite Systems (GNSS) significantly increases the availability of direct line-of-sight signals. Modelling is used to demonstrate that, although this will enable accurate positioning along the direction of the street, the positioning accuracy in the cross-street direction will be poor because the unobstructed satellite signals travel along the street, rather than across it. A novel solution to this problem is to use 3D building models to improve cross-track positioning accuracy in urban canyons by predicting which satellites are visible from different locations and comparing this with the measured satellite visibility to determine position. Modelling is used to show that this shadow matching technique has the potential to achieve metre-order cross-street positioning in urban canyons. The issues to be addressed in developing a robust and practical shadow matching positioning system are then discussed and solutions proposed.

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Zonation of Landslide Susceptibility in Ruijin, Jiangxi, China

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18115906 ◽

2021 ◽

Vol 18 (11) ◽

pp. 5906

Author(s):

Xiaoting Zhou ◽

Weicheng Wu ◽

Ziyu Lin ◽

Guiliang Zhang ◽

Renxiang Chen ◽

...

Keyword(s):

Environmental Factors ◽

Landslide Susceptibility ◽

Urban Areas ◽

Support Vector ◽

Susceptibility Map ◽

Human Society ◽

Learning Approaches ◽

Prevention Measures ◽

Landslide Occurrence ◽

Better Than

Landslides are one of the major geohazards threatening human society. The objective of this study was to conduct a landslide hazard susceptibility assessment for Ruijin, Jiangxi, China, and to provide technical support to the local government for implementing disaster reduction and prevention measures. Machine learning approaches, e.g., random forests (RFs) and support vector machines (SVMs) were employed and multiple geo-environmental factors such as land cover, NDVI, landform, rainfall, lithology, and proximity to faults, roads, and rivers, etc., were utilized to achieve our purposes. For categorical factors, three processing approaches were proposed: simple numerical labeling (SNL), weight assignment (WA)-based and frequency ratio (FR)-based. Then 19 geo-environmental factors were respectively converted into raster to constitute three 19-band datasets, i.e., DS1, DS2, and DS3 from three different processes. Then, 155 observed landslides that occurred in the past decades were vectorized, among which 70% were randomly selected to compose a training set (TS1) and the remaining 30% to form a validation set (VS1). A number of non-landslide (no-risk) samples distributed in the whole study area were identified in low slope (<1–3°) zones such as urban areas and croplands, and also added to the TS1 and VS1 in the same ratio. For comparison, we used the FR approach to identify the no-risk samples in both flat and non-flat areas, and merged them into the field-observed landslides to constitute another pair of training and validation sets (TS2 and VS2) using the same ratio of 7:3. The RF algorithm was applied to model the probability of the landslide occurrence using DS1, DS2, and DS3 as predictive variables and TS1 and TS2 for training to obtain the SNL-based, WA-based, and FR-based RF models, respectively. Verified against VS1 and VS2, the three models have similar overall accuracy (OA) and Kappa coefficient (KC), which are 89.61%, 91.47%, and 94.54%, and 0.7926, 0.8299, and 0.8908, respectively. All of them are much better than the three models obtained by SVM algorithm with OA of 81.79%, 82.86%, and 83%, and KC of 0.6337, 0.655, and 0.660. New case verification with the recent 26 landslide events of 2017–2020 revealed that the landslide susceptibility map from WA-based RF modeling was able to properly identify the high and very high susceptibility zones where 23 new landslides had occurred, and performed better than the SNL-based and FR-based RF modeling, though the latter has a slightly higher OA and KC. Hence, we concluded that all three RF models achieve reasonable risk prediction, but WA-based and FR-based RF modeling deserves a recommendation for application elsewhere. The results of this study may serve as reference for the local authorities in prevention and early warning of landslide hazards.

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Filtering Link Outliers in Vehicle Trajectories by Spatial Reasoning

ISPRS International Journal of Geo-Information ◽

10.3390/ijgi10050333 ◽

2021 ◽

Vol 10 (5) ◽

pp. 333

Author(s):

Junli Liu ◽

Miaomiao Pan ◽

Xianfeng Song ◽

Jing Wang ◽

Kemin Zhu ◽

...

Keyword(s):

Urban Areas ◽

Spatial Reasoning ◽

Sampling Interval ◽

Global Navigation Satellite Systems ◽

Quality Analysis ◽

Ancillary Data ◽

Satellite Systems ◽

Positioning Errors ◽

Vehicle Trajectories ◽

Global Navigation Satellite

Vehicle trajectories derived from Global Navigation Satellite Systems (GNSS) are used in various traffic applications based on trajectory quality analysis for the development of successful traffic models. A trajectory consists of points and links that are connected, where both the points and links are subject to positioning errors in the GNSS. Existing trajectory filters focus on point outliers, but neglect link outliers on tracks caused by a long sampling interval. In this study, four categories of link outliers are defined, i.e., radial, drift, clustered, and shortcut; current available algorithms are applied to filter apparent point outliers for the first three categories, and a novel filtering approach is proposed for link outliers of the fourth category in urban areas using spatial reasoning rules without ancillary data. The proposed approach first measures specific geometric properties of links from trajectory databases and then evaluates the similarities of geometric measures among the links, following a set of spatial reasoning rules to determine link outliers. We tested this approach using taxi trajectory datasets for Beijing with a built-in sampling interval of 50 to 65 s. The results show that clustered links (27.14%) account for the majority of link outliers, followed by shortcut (6.53%), radial (3.91%), and drift (0.62%) outliers.

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Vocational Rehabilitation Transition Outcomes of Youth With Disabilities From a Midwestern State

Rehabilitation Research Policy and Education ◽

10.1891/2168-6653.30.1.48 ◽

2016 ◽

Vol 30 (1) ◽

pp. 48-64 ◽

Cited By ~ 3

Author(s):

Jessica M. Awsumb ◽

Fabricio E. Balcazar ◽

Francisco Alvarado

Keyword(s):

Vocational Rehabilitation ◽

Urban Areas ◽

Transition Program ◽

Small Towns ◽

System Level ◽

Youth With Disabilities ◽

Transition Outcomes ◽

Rehabilitation Agency ◽

Better Than ◽

Gender Type

Purpose: To examine the outcomes (rehabilitated vs. nonrehabilitated) of youth with disabilities (ages 14–22 years) participating in the transition program from a midwestern state.Method: Five years of vocational rehabilitation transition data (N = 6,252) were analyzed to determine what demographic and system-level factors were related to rehabilitated or nonrehabilitated outcomes.Results: Postsecondary and employment outcomes were predicted by race, gender, type of disability, office region, total number of services, and case expenditure. Hispanic youth had the highest percentage of rehabilitation; males faired significantly better than females and participants in small towns were significantly more likely to be rehabilitated than participants living in large urban areas.Conclusions: Based on the data findings, it was recommended that the vocational rehabilitation agency alters and updates its transition program. Strategies to help youth with disabilities achieve positive employment and postsecondary educational outcomes are discussed.

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