Characterisation of GNSS carrier phase data on a moving zero-baseline in urban and aerial navigation

We present analyses of Global Navigation Satellite System (GNSS) carrier phase observations in multiple kinematic scenarios for different receiver types. Multi-GNSS observations are recorded on high sensitivity and geodetic-grade receivers operating on a moving zero-baseline by conducting terrestrial urban and aerial flight experiments. The captured data is post-processed; carrier phase residuals are computed using the double difference (DD) concept. The estimated noise levels of carrier phases are analysed with respect to different parameters. We find DD noise levels for L1 carrier phase observations in the range of 1.4–2 mm (GPS, Global Positioning System), 2.8–4.6 mm (GLONASS, Global Navigation Satellite System), and 1.5–1.7 mm (Galileo) for geodetic receiver pairs. The noise level for high sensitivity receivers is at least higher by a factor of 2. For satellites elevating above 30◦, the dominant noise process is white phase noise. For the flight experiment, the elevation dependency of the noise is well described by the exponential model, while for the terrestrial urban experiment, multipath and diffraction effects overlay; hence no elevation dependency is found. For both experiments, a carrier-to-noise density ratio (C/N0) dependency for carrier phase DDs of GPS and Galileo is clearly visible with geodetic-grade receivers. In addition, C/N0 dependency is also visible for carrier phase DDs of GLONASS with geodetic-grade receivers for the terrestrial urban experiment. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Schlussbericht des Instituts für Erdmessung der Leibniz Universität Hannover zum Verbundvorhaben Korrektur von GNSS-Mehrwegeffekten für die zuverlässige Eigenlokalisierung von hochautomatisierten Fahrzeugen in innerstädtischen Bereichen (KOMET)

Der vorliegende Schlussbericht fasst die Ergebnisse des dreieinhalbjährigen Verbundvorhabens KOMET zusammen, in dem skalierbare GNSS-Korrekturdaten für das autonome Fahren in innerstädtischen Bereichen entwickelt, analysiert und umgesetzt wurden. Der hier vorliegende Schlussbericht behandelt speziell die Forschungsanteile des Institut für Erdmessung im Kontext des Verbundvorhabens.Bundesministerium für Wirtschaft und Klimaschutz (BMWK) und Projektträger: TÜV-Rheinland/Neue Fahrzeugtechnologien (Leistungsplan: HA5010, Sicherheit im Straßenverkehr)/19A20002C/E

Multipath Characterization Using Ray-Tracing in Urban Trenches

Multipath in urban environments still represents a great challenge for Global Navigation Satellite System (GNSS) positioning as it is a degrading factor which limits the attainable accuracy, precision and integrity. In an urban trench, the dense building structures in the vicinity of the antenna cause reflections of the satellite signals resulting in multipath errors. Various work has been presented for simulating reflections for stations under laboratory conditions, yet the simulative analysis of multipath propagation in urban environments is currently developing. In this contribution, we enhanced an existing Ray-Tracing algorithm which identifies potentially multipath affected satellite signals. So far, it calculates reflection points on a plane ground and estimates the resulting multipath error. We extended it for the urban area case by introducing a 3D city building model with possible reflections on all surfaces of the buildings. Based on the geometry between the antenna position, satellite position and the reflection surface, the extra path delays, the characteristics of the propagation channel and the signal amplitudes are calculated. The resulting multipath errors are then estimated from the discriminator function using state of the art correlator parameters and antenna models. For a validation, the simulation results are compared with code-minus-carrier combination from a real GNSS experiment in a dense urban area in Hannover. We find that the simulated multipath errors fit the observations in terms of the amplitude, but with uncertainties in the building model, the multipath wave length is too large. The distance to the reflection surface is a key factor which influences the multipath wavelength

Intelligent Database Architecture for High-Integrity Urban Navigation

Accuracy, integrity and availability requirements are very stringent in urban navigation and autonomous driving. The GNSS sensor is the only one that provides self-localisation in a global coordinate system. The challenge ist to model non line-of-sight (NLOS) and multipath scenarios in urban areas. To meeth the high accuracy requirements, these distortions has to be known and corrected. Ray-tracing approaches are real-time capable but require a high computational load. The vision for this contribution is the correction of GNSS multipath for relaiable autonomous localisation of highly automated vehicles using an intelligent database structure

Coordinate Frames and Transformations in GNSS Ray-Tracing for Autonomous Driving in Urban Areas

3D Mapping-Aided (3DMA) Global Navigation Satellite System (GNSS) is a widely used method to mitigate multipath errors. Various research has been presented which utilizes 3D building model data in conjunction with ray-tracing algorithms to compute and predict satellites’ visibility conditions and compute delays caused by signal reflection. To simulate, model and potentially correct multipath errors in highly dynamic applications, such as, e.g., autonomous driving, the satellite–receiver–reflector geometry has to be known precisely in a common reference frame. Three-dimensional building models are often provided by regional public or private services and the coordinate information is usually given in a coordinate system of a map projection. Inconsistencies in the coordinate frames used to express the satellite and user coordinates, as well as the reflector surfaces, lead to falsely determined multipath errors and, thus, reduce the performance of 3DMA GNSS. This paper aims to provide the needed transformation steps to consider when integrating 3D building model data, user position, and GNSS orbit information. The impact of frame inconsistencies on the computed extra path delay is quantified based on a simulation study in a local 3D building model; they can easily amount to several meters. Differences between the extra path-delay computations in a metric system and a map projection are evaluated and corrections are proposed to both variants depending on the accuracy needs and the intended use

KOMET : Schlussbericht zum Verbundvorhaben Korrektur von GNSS-Mehrwegeffekten für die zuverlässige Eigenlokalisierung von hochautomatisierten Fahrzeugen in innerstädtischen Bereichen (KOMET)

Der vorliegende Schlussbericht fasst die Ergebnisse des dreieinhalbjährigen Verbundvorhabens KOMET zusammen, in dem skalierbare GNSS-Korrekturdaten für das autonome Fahren in innerstädtischen Bereichen entwickelt, analysiert und umgesetzt wurden.This final report compiles the results of the three-and-a-half-year joint project KOMET, in which scalable GNSS corrections for autonomous driving in urban areas were developed, analysed and implemented

Analysis of the Carrier Phase Multipath Error in the Context of Correction Maps for Urban Navigation

One of the most important functions for the safety of autonomous driving is the self-localisation of a moving platform. The GNSS (Global Navigation Satellite System) sensor is - compared to other sensors as, e.g., video, radar or camera - the only sensor that provides absolute positioning. Under clear sky conditions, GNSS positioning methods yield high level of accuracy and integrity. Poor signal propagation conditions make precise GNSS positioning challenging under urban conditions where multipath degrades the attainable accuracy and integrity. In the last decades, various correction or mitigation approaches for multipath errors have been developed and tested, but for carrier phase observations it is still the most critical error with magnitudes of up to a quarter of the wavelength. Since the carrier phase multipath error is location dependent, this property can be used to construct a correction map. In this paper, we report on the necessary steps to construct such a multipath correction map. The carrier phase error is a function of the multipath characteristics and the extra path delay. Hence, it is dependent on the distance to the reflection surface. Using a 3D building model, the geometry between the building and potentially multipath affected satellite signals is established to obtain one periodic cycle of the carrier phase error. A pseudo-kinematic experiment in an urban environment is planned and designed based on simulation studies of a ray-tracing algorithm to ensure ideal receiving properties for multipath signals in a realistic scenario. Two different approaches of carrier phase residuals will be compared to derive the multipath error from the observations. Firstly, double difference (DD) residuals are computed. Secondly, carrier phase residuals extracted from a positioning engine will be analysed. Finally, the developed functions are evaluated in the context of generating GNSS multipath correction maps for moving platformsBMWi / PT-TÜV Rheinland/Neue Fahrzeug- und Systemtechnologien/19A20002C/E