Topic
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.
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20 Sep 2013
TL;DR: In this article, the authors present the main challenges of a GNSS receiver in different phases of a mission to the moon including Moon Transfer Orbit and Low Lunar Orbit, including expected signal strengths, DOP and number of visible satellites.
Abstract: INTRODUCTION
Reception of weak GNSS signals in challenging environments using techniques such as Assisted GNSS has become a reality and today such techniques are considered important enablers of GNSS receivers in mobile devices [1]. Furthermore, the use of GPS and Galileo signals for indoor navigation is also receiving increased attention in recent studies which push the limits of minimum signal to noise ratios [2].
Space users have also seen remarkable achievements, where GPS signal reception has been confirmed and reported in GEO orbits [3] and seen as enabler for increased spacecraft autonomy in GEO orbits [4]. The study of weak GNSS signal reception techniques for lunar missions appears as a logical sequential step which is further supported by the growing international efforts for lunar exploration, which typically involve radiometric range and Doppler measurements from the earth to perform orbit determination.
CONTEXT AND MOTIVATION
The first missions flying to the Moon after the Apollo era were the NASA's Clementine (launched in 1994) and Lunar Prospector (launched in 1998). Both missions searched for lunar polar ice deposits and explored unknown areas thus producing more detailed surface maps.
The interest in Lunar exploration missions then started to spread out in the international community and SMART-1, the first European mission to the Moon, was launched in 2003. Since then, the European Space Agency has fostered investigation on Lunar Exploration Missions. Lunar Lander is an example of such mission [5], which has reached CDR in 2012 for which DEIMOS has been actively involved as co-prime for the G&C subsystem during this descent phase and prime for the HDA subsystem. ESA’s interest in moon exploration continues with the recent agreement for the provision of a service module for NASA Orion uncrewed spacecraft Exploration Mission-1 (EM-1) in 2017.
Additionally, DEIMOS has lead the GNSSGEO feasibility study for ESA, for the use of GNSS in high orbits (GEO, GTO, HEO) for autonomous orbit determination. In this study, a GNSS receiver simulator and receiver design has been developed including detailed design of signal processing algorithms. Orbit Determination (OD) in GEO and large portions of HEO orbits down to 18 dB-Hz was as shown as an alternative to traditional radiometric based OD, with potential cost savings and simplifications in the mission.
SIGNIFICANCE OF WORK
In the frame of an ESA study, the Lunar GNSS project investigates the use of weak GNSS signals from existing GPS and future Galileo towards future lunar exploration missions for real-time position, navigation and timing information. More specifically, GNSS signals could be used if receivers are complemented with advanced processing signal and filtering techniques, allowing acquisition and tracking down to very weak signal to noise ratios.
The paper presents the main challenges of a GNSS receiver in different phases of a mission to the moon including Moon Transfer Orbit and Low Lunar Orbit, including expected signal strengths, DOP and number of visible satellites. Factors such as GNSS antenna radiation patterns (transmitter and receiver), frequency, constellations, spacecraft attitude, integration times and TT&C link characteristics are considered. Requirements for the Lunar Lander mission based on conventional radiometric measurements from the earth as well as onboard sensors and then presented.
An overview of selected high sensitivity techniques which take benefit of Galileo signals and modernized GPS to cope with the challenges is then presented followed by the description of an orbital filter complementing GNSS measurements in closely-coupled fashion.
The paper also describes a dedicated test platform which allows demonstrating the main functional and performance capabilities for weak signal navigation. Such platform includes both the capability to use realistic IF data and to execute high fidelity simulations of the signal processing and navigation functions of an AGGA4 based chipset (ESA’s future generation GNSS receiver). A first batch of simulation results for a selected trajectory of the Lunar Lander mission is presented, highlighting the achievable navigation performance throughout the trajectory.
In conclusion, this paper contributes to the understanding of how GPS and Galileo could be used for orbit determination in lunar missions, which may have an impact on the use of ground segment assets (ground station use times, operations manpower and equipment, etc.).
REFERENCES
[1] Mulassano P., Dovis F. “Assisted Global Navigation Satellite Systems: An Enabling Technology for High Demanding Location-Based Services”. In: Location-Based Services Handbook / Ahson S. A., Ilyas M. CRC Press, Boca Raton, FL (USA), pp. 279-298. ISBN 9781420071962, 2011
[2] Vecchione et al., “DINGPOS, A GNSS-based Multi-sensor Demonstrator for Indoor Navigation”, IEEE/ION PLANS 2010, Myrtle Beach, USA, April 2010
[3] Moreau M. C. et al, “Results from the GPS Flight Experiment on the High Earth Orbit AMSAT OSCAR-40 Spacecraft”, ION GNSS, Sept. 2002
[4] Lorga J.F.M et al., ”Autonomous orbit determination for future GEO and HEO missions”. In: 5th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing (NAVITEC), 2010, Noordwijk (NL), 8-10 Dec. 2010.
[5] Richard Fisackerley, Alain Pradier: “The ESA Lunar Lander Mission”, AIAA, 2011
17 citations
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05 Sep 2008TL;DR: This paper presents the complexity evaluation of a FFT-based acquisition technique, suitable for new GNSS signals and for both software and hardware implementations, and compares the results obtained with a Xilinx FPGA board and a software receiver implemented on a general-purpose processor.
Abstract: The first step of the digital processing within a Global Navigation Satellite System (GNSS) receiver is the signal acquisition. The receiver has to detect the satellites in view, and for each of them, has to estimate the Doppler shift and the code phase of the received signal. In order to speed up the acquisition process, modern receivers use fast acquisition technique based on the Fast Fourier Transform (FFT). This paper presents the complexity evaluation of a FFT-based acquisition technique, suitable for new GNSS signals and for both software and hardware implementations. After the description of the algorithm, the focus will be on the comparison of the results obtained with a Xilinx FPGA board and a software receiver implemented on a general-purpose processor.
17 citations
01 Aug 2007
TL;DR: An overview of GBAS integrity verification is provided, explaining how integrity risk is allocated to various potential safety threats and how monitors are used to meet these allocations.
Abstract: The Local Area Augmentation System (LAAS) or, more generally, the Ground Based Augmentation System (GBAS), has been developed over the past decade to meet the accuracy, integrity, continuity and availability needs of civil aviation users. The GBAS utilizes a single reference station (with multiple GNSS receivers and antennas) within an airport and provides differential corrections via VHF data broadcast (VDB) within a 50-km region around that airport. This paper provides an overview of GBAS integrity verification, explaining how integrity risk is allocated to various potential safety threats and how monitors are used to meet these allocations. In order to illustrate GBAS integrity monitoring in detail, this paper examines the potential threat of ionospheric spatial anomalies (e.g., during ionospheric “storms”) to GBAS and how GBAS protects users against this threat. In practice, the need to mitigate potential ionospheric anomalies is what dictates CAT I GBAS availability.
17 citations
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TL;DR: In this article, the authors proposed a new multi-feature support vector machine (SVM) signal classifier-based weight scheme for GNSS measurements to improve the kinematic GNSS positioning accuracy in urban environments.
Abstract: High-precision positioning with low-cost global navigation satellite systems (GNSS) in urban environments remains a significant challenge due to the significant multipath effects, non-line-of-sight (NLOS) errors, as well as poor satellite visibility and geometry. A GNSS system is typically implemented with a least-square (LS) or a Kalman-filter (KF) estimator, and a proper weight scheme is vital for achieving reliable navigation solutions. The traditional weight schemes are based on the signal-in-space ranging errors (SISRE), elevation and C/N0 values, which would be less effective in urban environments since the observation quality cannot be fully manifested by those values. In this paper, we propose a new multi-feature support vector machine (SVM) signal classifier-based weight scheme for GNSS measurements to improve the kinematic GNSS positioning accuracy in urban environments. The proposed new weight scheme is based on the identification of important features in GNSS data in urban environments and intelligent classification of line-of-sight (LOS) and NLOS signals. To validate the performance of the newly proposed weight scheme, we have implemented it into a real-time single-frequency precise point positioning (SFPPP) system. The dynamic vehicle-based tests with a low-cost single-frequency u-blox M8T GNSS receiver demonstrate that the positioning accuracy using the new weight scheme outperforms the traditional C/N0 based weight model by 65.4% and 85.0% in the horizontal and up direction, and most position error spikes at overcrossing and short tunnels can be eliminated by the new weight scheme compared to the traditional method. It also surpasses the built-in satellite-based augmentation systems (SBAS) solutions of the u-blox M8T and is even better than the built-in real-time-kinematic (RTK) solutions of multi-frequency receivers like the u-blox F9P and Trimble BD982.
17 citations
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TL;DR: In this article, an adaptive orbital filter that fuses the GNSS observations with an orbital forces model was proposed to improve the achievable GNSS performance in MTOs, which showed a navigation accuracy significantly higher than that attainable individually by a standalone GNSS receiver or by means of a pure orbital propagation.
Abstract: Numerous applications, not only Earth-based, but also space-based, have strengthened the interest of the international scientific community in using Global Navigation Satellite Systems (GNSSs) as navigation systems for space missions that require good accuracy and low operating costs. Indeed, already successfully used in Low Earth Orbits (LEOs), GNSS-based navigation systems can maximise the autonomy of a spacecraft while reducing the burden and the costs of ground operations. That is why GNSS is also attractive for applications in higher Earth orbits up to the Moon, such as in Moon Transfer Orbits (MTOs). However, the higher the altitude the receiver is above the GNSS constellations, the poorer and the weaker are the relative geometry and the received signal powers, respectively, leading to a significant navigation accuracy reduction. In order to improve the achievable GNSS performance in MTOs, we consider in this paper an adaptive orbital filter that fuses the GNSS observations with an orbital forces model. Simulation results show a navigation accuracy significantly higher than that attainable individually by a standalone GNSS receiver or by means of a pure orbital propagation.
17 citations