Global Navigation Satellite System Outages Research Articles

MEMS IMU Error Mitigation Using Rotation Modulation Technique.

Micro-electro-mechanical-systems (MEMS) inertial measurement unit (IMU) outputs are corrupted by significant sensor errors. The navigation errors of a MEMS-based inertial navigation system will therefore accumulate very quickly over time. This requires aiding from other sensors such as Global Navigation Satellite Systems (GNSS). However, it will still remain a significant challenge in the presence of GNSS outages, which are typically in urban canopies. This paper proposed a rotary inertial navigation system (INS) to mitigate navigation errors caused by MEMS inertial sensor errors when external aiding information is not available. A rotary INS is an inertial navigator in which the IMU is installed on a rotation platform. Application of proper rotation schemes can effectively cancel and reduce sensor errors. A rotary INS has the potential to significantly increase the time period that INS can bridge GNSS outages and make MEMS IMU possible to maintain longer autonomous navigation performance when there is no external aiding. In this research, several IMU rotation schemes (rotation about X-, Y- and Z-axes) are analyzed to mitigate the navigation errors caused by MEMS IMU sensor errors. As the IMU rotation induces additional sensor errors, a calibration process is proposed to remove the induced errors. Tests are further conducted with two MEMS IMUs installed on a tri-axial rotation table to verify the error mitigation by IMU rotations.

Performance analysis of IMU-augmented GNSS tracking systems for space launch vehicles

European space launch operators consider the potential of GNSS (global navigation satellite system) as a promising novel means of localization for the purpose of range safety of launch vehicles like Ariane and Vega, since it is expected that recurring costs are lower and accuracy is higher than currently existing systems like radar tracking. Range safety requires continuous information about the position and velocity of the launch vehicle to quickly detect the occurrence of catastrophic events. However, GNSS outages due, for example, to high jerks at fairing and stage jettisons or other external interferences like (un-)intentional jamming cannot be precluded. The OCAM-G experiment on Ariane 5 flight VA219 has provided evidence that GNSS is capable of providing a highly accurate position and velocity solution during most of the flight, but that outages of several seconds do occur. To increase the continuity of a GNSS-based localization system, it is proposed that the GNSS receiver is augmented by an inertial measurement unit (IMU), which is able to output a position and velocity solution even during GNSS outages. Since these outages are expected to be short, a tactical- or even consumer-grade IMU is expected to be sufficient. In this paper, the minimum IMU performance that is required to bridge outages of up to 10 s, and thereby meeting the accuracy requirements of range safety, is determined by means of a thorough simulation study. The focus of the analysis is on current generation microelectromechanical system (MEMS)-based IMU, which is lightweight, low-cost, available commercially and has reached acceptable maturity in the last decade.

Conceptual Issues Regarding the Development of Underground Railway Laser Scanning Systems

Mobile Laser Scanning (MLS) systems are widely applied for spatial data collection and support applications in many aspects. In recent years, MLS technology had been introduced to railway applications and greatly enhanced the spatial detail and efficiency when compared to traditional approaches. However, the advance of MLS technology is not completely applied to railway environment. Typical MLS systems rely on integrated navigation through the use of Inertial Navigation Systems (INS) and Global Navigation Satellite Systems (GNSS) for geo-referencing, while operation under long-term GNSS outages or even GNSS-free environments, such as underground railway or long tunnels, remains a challenging issue due to the degraded operation of standalone inertial navigation. Commercial MLS systems usually employ high performance inertial measurement units (IMU) and various strategies to manage GNSS outages, but GNSS components are still necessary prior to and after experiencing the loss of GNSS signals. To tackle the problem of permanent GNSS outages, alternative methods are introduced to replace the GNSS and so allow the use of MLS systems in GNSS-free underground railway environments. Such approaches encourage the MLS systems to be developed into the Underground Railway Laser Scanning (URLS) systems, which may provide several alternative operational functions for the management of underground railway operation.

On-the-fly Locata/inertial navigation system integration for precise maritime application

The application of Global Navigation Satellite System (GNSS) technology has meant that marine navigators have greater access to a more consistent and accurate positioning capability than ever before. However, GNSS may not be able to meet all emerging navigation performance requirements for maritime applications with respect to service robustness, accuracy, integrity and availability. In particular, applications in port areas (for example automated docking) and in constricted waterways, have very stringent performance requirements. Even when an integrated inertial navigation system (INS)/GNSS device is used there may still be performance gaps. GNSS signals are easily blocked or interfered with, and sometimes the satellite geometry may not be good enough for high accuracy and high reliability applications. Furthermore, the INS accuracy degrades rapidly during GNSS outages. This paper investigates the use of a portable ground-based positioning system, known as ‘Locata’, which was integrated with an INS, to provide accurate navigation in a marine environment without reliance on GNSS signals. An ‘on-the-fly’ Locata resolution algorithm that takes advantage of geometry change via an extended Kalman filter is proposed in this paper. Single-differenced Locata carrier phase measurements are utilized to achieve accurate and reliable solutions. A ‘loosely coupled’ decentralized Locata/INS integration architecture based on the Kalman filter is used for data processing. In order to evaluate the system performance, a field trial was conducted on Sydney Harbour. A Locata network consisting of eight Locata transmitters was set up near the Sydney Harbour Bridge. The experiment demonstrated that the Locata on-the-fly (OTF) algorithm is effective and can improve the system accuracy in comparison with the conventional ‘known point initialization’ (KPI) method. After the OTF and KPI comparison, the OTF Locata/INS integration is then assessed further and its performance improvement on both stand-alone OTF Locata and INS is shown. The Locata/INS integration can achieve centimetre-level accuracy for position solutions, and centimetre-per-second accuracy for velocity determination.

Tightly coupled MEMS based INS/GNSS performance evaluation during extended GNSS outages

Ubiquitous positioning using combined lowcost, Micro-electro-mechanical-systems (MEMS) Inertial Navigation Systems (INS) and Global Navigation Satellite System (GNSS) systems remains a challenge in difficult GNSS environments. This is due to the GNSS signals being partially or completely obstructed by building structures and consequently no information being available to calibrate the MEMS INS errors. In these environments although there may be insufficient signals for a two or three dimensional GNSS solution, some signals can still be received, particularly when utilizing high sensitivity GNSS receivers. These signals can be used to aid the INS/GNSS integrated system but can only be realized when it utilizes a tightly coupled (TC) as opposed to a loosely coupled (LC) integration architecture. This is particularly useful for MEMS based INS/GNSS integrated system as its performance can degrade rapidly over short period of GNSS outages. This paper aims to evaluate the capabilities of MEMS based INS/GNSS using TC integration architecture during extended period of GNSS outages. The results obtained show that TC integration architecture does help limit the error growth even when INS/GNSS integrated system experienced relatively long period of partial GNSS outages.

THE PERFORMANCE OF A TIGHT INS/GNSS/PHOTOGRAMMETRIC INTEGRATION SCHEME FOR LAND BASED MMS APPLICATIONS IN GNSS DENIED ENVIRONMENTS

Abstract. Nowadays the most common technologies used for positioning and orientation of a mobile mapping system include using Global Navigation Satellite System (GNSS) as a major positioning sensor and Inertial Navigation System (INS) as the major orientation sensor. The integration strategy of the most commercially system is the loosely coupled (LC) architecture, that has the simplest architecture using the GNSS solutions to aid the INS navigation information with proper optimization estimator. The LC does combine the two sensors’ solutions when the number of tracked satellite is more than four. In recent year, another commonly integration strategy is known as tightly coupled (TC) architecture. Because the TC uses the GNSS measurements to aid INS, it can integrate measurements provided by GNSS receiver and INS unless no GNSS satellite is tracked. Obviously, the TC architecture is a better candidate for land based mobile mapping applications than LC in Taiwan. Unfortunately, there are still many GNSS denied environment in the urban area, therefore the TC architecture is still not robust and stable enough for MMS application. The overall objective of this paper is to provide a scheme that tightly integrates INS/GNSS and Photogrammetric for land based MMS applications with sufficient and stable POS solutions during GNSS outages. In the traditional photogrammetry operation, numerous ground control points are applied to compute those Exterior Orientation Parameters (EOPs) of cameras by bundle adjustment. The key opinion is to derive the INS centre position and attitude and reconstruct 3-D tracking and 3-D object space by cameras EOPs. The proposed algorithm is verified using field test data collected in GNSS denied environments and the preliminary results presented in this study illustrated that the proposed algorithm is able to provide 60% improvement in terms of positioning and orientation accuracy in Taipei and Tainan cities.