GNSS augmentation

About: GNSS augmentation is a research topic. Over the lifetime, 2478 publications have been published within this topic receiving 28513 citations. The topic is also known as: SBAS & Satellite Based Augmentation System.

Performance Analysis of Two-Dimensional Dead Reckoning Based on Vehicle Dynamic Sensors during GNSS Outages

Abstract: Recently, to improve safety and convenience in driving, numerous sensors are mounted on cars to operate advanced driver assistant systems. Among various sensors, vehicle dynamic sensors can measure the vehicle motions such as speed and rotational angular speed for dead reckoning, which can be applied to develop a land vehicle positioning system to overcome the weaknesses of the GNSS technique. In this paper, three land vehicle positioning algorithms that integrate GNSS with vehicle dynamic sensors including a wheel speed sensor (WSS), a yaw rate sensor (YRS), and a steering angle sensor (SAS) are implemented, and then a performance evaluation was conducted during GNSS outages. Using a loosely coupled strategy, three integration algorithms are designed, namely, GNSS/WSS, GNSS/WSS/YRS, and GNSS/WSS/YRS/SAS. The performance of the three types of integration algorithm is evaluated based on two data sets. The results indicate that both the GNSS/WSS/YRS integration and the GNSS/WSS/YRS/SAS integration could estimate the horizontal position with meter-level accuracy during 30-second GNSS outages. However, the GNSS/WSS integration would provide an unstable navigation solution during GNSS outages due to the accuracy limitation of the computed yaw rate using WSS.

Performance Boundaries for Cooperative Positioning in VANETs

Abstract: The concept of Cooperative Positioning (CP) has emerged recently to improve the quality of positioning, provided by Global Navigation Satellite System (GNSS), in terms of accuracy and availability. This is necessary to meet the requirements of the vehicular position-based applications such as collision avoidance, which cannot rely only on GNSS performance. CP systems are based on fusing data from different sources, including GNSS, for positioning quality improvement. A typical class of CP is based on the GNSS-based position estimates and distances between the participating vehicles. Inter-vehicle ranging and GNSS errors are limiting factors for achievable performance using CP systems. Inter-vehicle range-rate is also a potential observable for CP systems. In this article, the performance boundaries for range-based and range-rate-based CP systems are investigated. The limits on the achievable performance with different topologies and observations are investigated. Also, the required bandwidth is considered for evaluating the performance of the discussed CP structures.

Assessment of Single-difference Ionospheric Residuals in a Regional Network for GBAS

Abstract: In current Global Navigation Satellite System (GNSS) differential single-frequency data processing, ionospheric delays are considered to be considerably reduced for short baselines in regional network. However, under strong ionosphere activities the remaining ionospheric effects on the single-difference level and their short-term variations may not be neglected and may become critical for, e.g., the approach and landing of airplanes using a Ground Based Augmentation System (GBAS). In this paper, the single-difference ionospheric residuals and spatial gradients are studied as a function of the Ionosphere Pierce-Point (IPP) distance under diverse ionosphere activities using data of the Automated GNSS Network for Switzerland (AGNES) over 15 years. A similar study has been performed by Lee et al. (2006) using the Wide Area Augmentation System (WAAS) “supertruth” data and the Jet Propulsion Laboratory (JPL) post-processed Continuously Operating Reference Stations (CORS) data by leveling the carrier-phase-based ionospheric measurements with the help of the code observables. Here, we provide an alternative method to estimate the single-difference ionospheric residuals and spatial gradients based on double-difference phase observations with resolved ambiguities. After pre-processing of the phase observations, the phase ambiguities can be resolved with the help of the Bernese GPS Software. The geometry-free (GF) linear combination of the phase observations is then generated on the double-difference level without the code-related error sources like differential code biases (DCBs) and arc-wise biases resulting from code smoothing. Only the ionospheric delay, the phase noise and biases like multipath remain in the residuals. However, singularities exist when deriving single-difference ionospheric delays from double-difference residuals. This is corrected for by imposing, e.g., a zero-mean condition on the single-difference residuals per baseline and per observation epoch. In order to correct for the lack of absolute information in the double-difference residuals mentioned above, model values of the ionospheric delays are generated for each observation using the CODE’s global ionosphere maps. A mean model ionospheric offset is then added epoch-wise to the estimated single-difference ionospheric delays per baseline to supply absolute information and the zero-mean condition is then applied to the deviations from the mean ionospheric offset. Local ionosphere maps may be considered in the future to produce more appropriate mean model ionospheric offset. It should be mentioned that small epoch-wise biases may still exist in each of the ground baselines because of the spatial and temporal smoothing effects of the ionosphere model. The single-difference spatial ionospheric gradients are estimated with the single-difference ionospheric delays and the pierce-point baseline length, namely the distance between the two pierce points of the “thin-shell” ionosphere model. We categorize the ionosphere activity into different levels based on geomagnetic indices, e.g., the Kp and Dst Index (see Lee et al. 2006), and analyze the correlation between the slant differential ionospheric delays and the geomagnetic indices as well as the daily Total Electron Content (TEC) provided by the Center for Orbit Determination in Europe (CODE). Using an elevation-dependent mapping function, the vertical single-difference ionospheric delays and gradients are also calculated and studied for all available days except the very stormy days. Very short ground baselines for the purposes of investigation of the non-ionospheric biases and ground baselines longer than 300 km are included in the study. Studies with long-term time series and the entire network of the AGNES stations have delivered a general relationship between the ionospheric delays, gradients and the ionosphere activity. The differential slant and vertical ionospheric delays and gradients were calculated and analyzed from 1999 to 2013. We see that the change of the differential ionospheric delays and gradients corresponds to the ionosphere activities. For very short baselines, the mean single-difference ionospheric residuals are at mm-level with a standard deviation at cm-level. In the end, the vertical ionospheric gradients are normalized in specific distance bins and an inflated sigma which bounds all the outliers and non-Gaussian tails of the normalized vertical ionospheric gradients has been determined. This part of the analysis is based on the work of Lee et al. (2006) for all the ionosphere nominal and active days. The daily peak slant ionospheric gradients are further analyzed for all available days under different ionosphere conditions with the help of the Conterminous United States (CONUS) ionosphere anomaly threat model (see Pullen et al. 2009). This work has been financed by Flughafen Zurich AG as part of the Skyguide (Swiss Air Navigation Services Ltd.) project "Impact of Ionospheric Activities onto GNSS Signal during Approach and Landing" within the frame of the Swiss-wide program to implement new technologies (CHIPS). We would also like to thank swisstopo for providing the AGNES data for the processing. References: Lee J., Pullen S., Datta-Barua S. and Enge P.: Assessment of Nominal Ionosphere Spatial Decorrelation for LAAS; Position, Location, and Navigation Symposium, 2006 IEEE/ION, Coronado, CA, USA, pp. 506-514, April 2006. Pullen S., Park Y.S. and Enge P.: Impact and mitigation of ionospheric anomalies on ground-based augmentation of GNSS, Radio Science 44, 2009, doi:10.1029/2008RS004084.

Enhanced Inter-Vehicular relative positioning

Abstract: Intelligent Transportation System (ITS) applications for integral and cooperative vehicle safety as well as some Advanced Driver Assistance Systems (ADASs) benefit from precise determination of relative positions between dynamic traffic objects. With conventional Global Navigation Satellite System (GNSS) measurements, e.g. using Global Positioning System (GPS), the required accuracy cannot be achieved. For this reason, an exchange of GNSS observations via Vehicular Ad-Hoc Network (VANET) is proposed in this paper. In particular, the European Inter-Vehicle Communication (IVC) protocol stack ITS-G5 is employed. With these exchanged GNSS observations, Differential GNSS (DGNSS) or Real-Time Kinematic (RTK) calculations provide a precise relative position vector. However, due to relative movement of traffic objects, this position vector becomes obsolete for increasing transmission delays. For this reason, a mitigating kinematic model is set up and validated experimentally. With respect to fixed RTK solutions, this kinematic model reduces the errors by an average of 61% compared to position calculations ignoring IVC latency.

Enhanced SBAS Integration Method Using Combination of Multiple SBAS Corrections

Abstract: In this paper, we propose a new way of improving DGNSS service using combination of multiple SBAS information. Because SBAS uses Geostationary Earth Orbit (GEO) satellites, it has very large coverage but it can be unavailable in urban canyon because of visibility problem. R. Chen solved this problem by creating Virtual Reference Stations (VRS) using the SBAS signal [1]. VRS converts SBAS signal to RTCM signals corresponding its location, and broadcast the converted RTCM signals over the wireless internet. This method can solve the visibility problem cost effectively. Furthermore it can solve DGNSS coverage problem by creating just a transmitter instead of a reference station. Developing above method, this paper proposes the methods that integrate two or more SBAS signals into one RTCM signal and broadcast it. In Korea, MSAS signal is available even though it is not officially certified for Korean users. As a Korean own SBAS-like system, there is the internet-based KWTB (Korean WADGPS Test Bed) which we developed and released at ION GNSS 2006. As a result, virtually two different SBAS corrections are available in Korea. In this paper, we propose the integration methods for these two independent SBAS corrections and present the test results using the actual measurements from the two systems. We present the detailed algorithm for these two methods and analyze the features and performances of them. To verify the proposed methods, we conduct the experiment using the logged SBAS corrections from the two systems and the RINEX data logged at Dokdo monitoring station in Korea. The preliminary test results showed the improved performance compared to the results from two independent systems, which shows the potential of our proposed methods. In the future, the newly developed SBASs will be available and the places which can access the multiple SBAS signals will increase. At that time, the integration or combination methods of two or more SBASs will become more important. Our proposed methods can be one of the useful solutions for that. As an additional research, we need to extend this research to the system level integration such as the concept of the decentralized WADGPS.