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.

Bayesian GNSS/IMU tight integration for precise railway navigation on track map

Abstract: The localization of a train on a railway network with onboard sensors has been usually tackled by matching an estimated position fix on a track map. In this paper, we face the navigation problem directly in the topological domain of the map without computing an initial global position. We develop a tightly coupled scheme to fuse the raw measurement of Global Navigation Satellite System (GNSS), Inertial Measurement Unit (IMU) and the information of a digital track map. We model this problem using a Dynamic Bayesian Network (DBN) and we derive a particle filter to handle the discrete and nonlinear nature of the map in the estimation process and to detect the correct path after a train switch. Real measurements are finally used to test the method and analyze the role of raw GNSS measurements and satellite geometry in precision. Results suggest that reliable navigation can be achieved even when less than four satellites are in view.

The GNSS Laboratory Tool Suite (gLAB) updates: SBAS, DGNSS and Global Monitoring System

Abstract: This work presents recent and ongoing updates to the free and open-source advanced interactive multi-purpose package for processing and analysing Global Navigation Satellite System (GNSS) data, named GNSS-Lab Tool suite (gLAB). The updates have been performed in the framework of two projects funded by the European Space Agency (ESA), namely, the “gLAB upgrade for European Geostationary Navigation Overlay System (EGNOS) Data processing” and “Upgrade of gLAB Tool for Double Frequency Multi-Constellation (DFMC)”. We examine various sets of results obtained with actual data using the Satellite Based Augmentation System (SBAS) corrections and the Differential GNSS (DGNSS) mode. Specifically, we introduce the Global Monitoring System (GMS) that routinely assesses the performance of the SBAS and DGNSS solutions using multiple station networks. That is, the Stanford-ESA integrity diagram, the Worst Integrity Ratio (WIR) maps, continuity risk, among other types of performance monitoring. Lastly, we present the ongoing update to the gLAB tool that focusses on the implementation of multi-frequency and multi-constellation data processing capabilities.

Performance analysis of duty-cycle power saving techniques in GNSS mass-market receivers

Abstract: The scope of this work is the analysis and assessment of power saving duty cycle techniques for GNSS receivers. One of the key design drivers of mass-market commercial GNSS devices is indeed power consumption. Different techniques are analyzed and a particular method, based on the alternation of active and sleep states, is implemented in a software receiver based on open-loop processing. The main issues related to the parameters re-initialization after the sleep state are described and a solution is proposed. Then, accuracy and performance are evaluated, for different signal power and in three different scenarios, simulating a static, a pedestrian and an automotive user. Results prove the good accuracy of the technique proposed in all conditions, confirming its validity also for applications different from the consumer market.

Multi-platform Integrated Positioning and Attitude Determination using GNSS

Abstract: There is trend in spacecraft engineering toward distributed systems where a number of smaller spacecraft work as a larger satellite. However, in order to make the small satellites work together as a single large platform, the precise relative positions (baseline) and orientations (attitude) of the elements of the formation have to be estimated. Global Navigation Satellite System (GNSS, the general term for systems as GPS and Galileo) receivers can be utilized to provide baseline estimates with centimeter to millimeter level accuracy. These precise GNSS applications utilize the carrier phase observations, which are inherently ambiguous. While precise relative positioning using GNSS for surveying has been around for some time, precise relative navigation for moving applications on land, on water, in the air and even in space is still under development. The methods developed in this thesis can be applied for all these applications as no model for the user dynamics is applied (the methods are independent of the user motion). A functional model was developed, in which the difference between the topocentric distance at the GNSS system time and at the GNSS receiver time is taken into account. For users with high dynamics and/or large clock offsets, not taking this affect into account can cause time-varying offsets in the baseline estimate. The Doppler observation was reviewed and analysed for different types of applications. In most GNSS receivers, as the Doppler observation is generated from carrier phase observations, these observations are highly correlated with carrier-phase observations. For relative positioning applications, it was shown that inclusion of the Doppler observations in the model is only desirable 1. if the GNSS receivers have large clock offsets. Especially in a dynamic environment, the standard Double Difference model will result in an offset in the baseline estimation. 2. for applications were the relative position between two platforms is actively controlled, the relative velocity is generally required as input for the control loop. The Doppler observation will not improve the float solution of the relative positioning problem and therefore will not improve ambiguity resolution. The drawback of using the Doppler for relative velocity estimation is that the effect from the relative motion and the clock drift cannot be separated. If the relative velocity can be obtained offline, taking the time derivative of the baseline estimate can provide a more accurate relative velocity estimation. A single and multi-epoch data processing strategy was introduced that exploits the capability of the current GPS system, however, the tests are focused on its stand-alone, unaided, single-frequency, single-epoch performance, as this is the most challenging case for ambiguity resolution. A stronger model (larger number of observations, lower observation noise) will improve the performance of the developed approach in terms of the probability of correctly fixing the ambiguities. Multiple GNSS antennas mounted on one platform may be used to determine the attitude of the platform as well. In terms of accuracy not much room for improvement is expected in GNSS attitude determination, as the theoretical limit has been reached by the available techniques. However, for ambiguity resolution still a number of open challenges remain. Ideally, one would like to have an ambiguity resolution method with a high probability of correctly fixing the ambiguities even when a limited number of observations is available (weak models) which could work instantaneously, eliminating the need for a dynamics model, and is computational efficient. The method applied in this thesis is based on a constrained extension of the popular LAMBDA method, known as the Multivariate Constrained (MC-) LAMBDA method. The MC-LAMBDA method is a nontrivial modification of the standard LAMBDA method. In contrast to existing methods that make use of the known baseline length, the MCLAMBDA method does full justice to the given information by fully integrating the nonlinear baseline constraint into the ambiguity objective function. As a result, the a priori information receives a proper weighting in the ambiguity objective function, thus leading to higher success rates. The method was tested, using simulated as well as actual GPS data. The simulations cover a large number of different measurement scenarios, where the impact of measurement precision and receiver-GNSS satellite geometry was analysed. GNSS-based precise relative positioning between spacecraft normally requires dual frequency observations, whereas attitude determination of the spacecraft can be performed precisely using only single frequency observations. In this contribution, the possibility was investigated to use multi-antenna data in an integrated approach, not only for attitude determination, but also to improve the relative positioning between spacecraft. The rigorous inclusion of the known geometry of the antennas at the platform into the ambiguity objective function shows • dramatic improvements in the ambiguity resolution success rates for the baselines at and between the spacecraft. • improved precision of the baseline estimation for the baseline between the platforms. The theoretical improvement achievable for the baseline between the platforms as a function of the number of antennas on each platform was shown, both for ambiguity resolution and accuracy of the baseline solution. The obtained mathematical relationship was verified by software based, hardware-in-the-loop simulations and field experiments. The improved instantaneous ambiguity resolution will result in an even stronger reduction in time to fix (TTF). An additional benefit of the method is an improved robustness against multipath.

Advanced global navigation satellite systems (gnss) positioning using precise satellite information

Abstract: A method is provided for estimating parameters useful to determine the position of a global navigation satellite system (GNSS) receiver or a change in the position thereof. The method includes the steps of: obtaining at least one GNSS signal received at the GNSS receiver from each of a plurality of GNSS satellites; obtaining, from at least one network node, precise satellite information on: (i) the orbit or position of at least one of the plurality of GNSS satellites, and (ii) a clock offset of at least one of the plurality of GNSS satellites; identifying, among the obtained GNSS signals, a subset of at least one GNSS signal possibly affected by a cycle slip, the identified subset being hereinafter referred to as cycle-slip affected subset; and estimating parameters useful to determine the position of the GNSS receiver or a change in the position of the GNSS receiver using at least some of the obtained GNSS signals which are not in the cycle-slip affected subset, and the precise satellite information.