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Advanced Integration of GNSS and External Sensors for Autonomous Mobility Applications
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Evaluation and definition of a reference maritime multipath model for GNSS receivers
No full textThe purpose of this paper is to define a reference maritime multipath model for supporting analysis and simulation in GNSS receivers. A maritime multipath model considering specular and diffuse scattering, depending on sea state as implemented in ESA activity Physical-Statistical Models for Mobile Satellite Communication Systems Below 10 GHz (PhyStat) has been used for the analysis of GNSS receivers performance in maritime environment considering different dynamics, platforms and sea state conditions. A number of realisations of the model were generated varying the range of model parameters. The realisations of the communication channel were adapted into a Spirent GNSS constellation simulator for receiver testing. The assessment considered a sensitivity analysis of the number of echoes versus effects on fading, carrier phase and pseudorange errors. The paper presents a recommendation for model parameters to be used for the implementation in the constellation simulator in order to evaluate the expected GNSS receiver performance for COTS receivers. The work is validated comparing the model implementation applied to a receiver through Spirent simulator, to the measurements collected by a GNSS receiver installed on a medium vessel
The Record and Replay Approach for GNSS Receiver Performance Assessment in Road Environment
No full textNowadays the concept of smart transport, that exploits Intelligent Transport Systems (ITS) technology, plays a fundamental role in our society. The Global Navigation Satellite Systems (GNSS) have significant potential in the development of ITS where the estimation of the vehicle's position represents a key role. However, in strongly constrained environments, such as city centers, the definition of positioning performances is a challenge due to the variability of the different urban scenarios, the modeling of the dynamics as well as the architecture of the positioning platform, which might embed other sensors and aiding means to the GNSS unit. Moreover, the performance metrics of interest are not just position and speed but metrics related to the integrity/reliability concept, properly defined for the road environment. These performance metrics are becoming of paramount interest, as safety-critical application emerging, and have to be assessed. This framework asks for a deep understanding by the ITS sector of the achievable performance by GNSS systems in the different scenarios for automotive. In fact, positioning is taken as a fully reliable and accurate information, based on which more and more automated driving operations are performed. For this reason, the need of standardized performance metrics for GNSS-Based Positioning Terminal (GBPT) and the associated performance assessment procedures and scenarios assume considerable importance. The main focus of the paper is to introduce a performance evaluation procedure based on a record and replay approach able to represent meaningful and realistic scenarios. This approach requires proper data collections that allow the replay phase and data postprocessing to test the GBPT performance. The paper presents also some results obtained on a set of field tests related to different scenarios, selected as representative of reference scenarios for the Key Performance Indicators (KPIs) assessment
A collaborative method for positioning based on GNSS inter agent range estimation
Get PDFThe limited availability and the lack of continuity in the service of Global Positioning Satellite Systems (GNSS) in harsh environments is a critical issue for Intelligent Transport Systems (ITS) applications relying on the position. This work is developed within the framework of vehicle-to-everything (V2X) communication, with the aim to guarantee a continuous position availability to all the agents belonging to the network when GNSS is not available for a subset of them. The simultaneous observation of shared satellites is exploited to estimate the Non-Line-Of-Sight Inter-Agent Range within a real-time-connected network of receivers. It is demonstrated the effectiveness of a hybrid localization algorithm based on the the integration of standard GNSS measurements and linearised IAR estimates. The hybrid position estimation is solved through a self-adaptive iterative algorithm to find the position of receivers experiencing GNSS outages
Design of a Configurable Monitoring Station for Scintillations by Means of a GNSS Software Radio Receiver
Get PDFThis letter addresses the design and implementation of a monitoring station for Global Navigation Satellite Systems signals based on the software-defined radio paradigm. The monitoring platform exploits a digital data grabber based on the use of Universal Software Radio Peripheral devices and a satellite navigation fully software receiver; with respect to a traditional commercial receiver, this implementation solution grants a higher level of flexibility for the processing strategy, enabling the possibility of a deeper analysis of the signals in case of meaningful events, such as ionospheric scintillations or radio frequency interference, through the storage of raw samples. Such an implementation approach yields valuable advantages in critical and remote areas, such as polar regions, where resources are limited and installation, maintenance, and replacement of hardware may be critical
Benefits and Limitations of the Record and Replay Approach for GNSS Receiver Performance Assessment in Harsh Scenarios
Get PDFGlobal navigation satellite systems play a significant role in the development of intelligent transport systems, where the estimation of the vehicle’s position is a key element. However, in strongly constrained environments such as city centers, the definition of quality metrics and the assessment of positioning performances are challenges to be addressed. Due to the variability of different urban scenarios, the modeling of the dynamics as well as the architecture of the positioning platform, which might embed other sensors and aiding means to the GNSS unit, make it hard to define unambiguous positioning metrics. Performance assessment through analytical models and simulators can be ineffective in terms of cost, complexity, and general validity and scalability of the results. This paper shows how a record and replay approach can be an efficient solution to grant fidelity to a realistic scenario. This work discusses advantages and disadvantages with emphasis on the case study of harsh scenarios. Such an approach requires proper data collections that allow the replay phase to test the GNSS-based positioning terminals. This paper presents the results obtained on a set of field tests related to different scenarios, selected as representative for the key performance indicators assessment
On the Use of an Ultra-Tight Integration for Robust Navigation in Jammed Scenarios
Get PDFWith the advent of new services and the evolution of transportation systems the need of a reliable and accurate knowledge of the position information became of paramount importance. Among the multiple technologies and sensors that might be used for positioning, Global Navigation Satellite System (GNSS) can be considered as the core technology and a superior system capable to provide the user with estimates of his own position in a global reference frame. Unfortunately, received GNSS signals are extremely weak and thus vulnerable to non-intentional and intentional Radio Frequency Interference. In particular, the malicious intentional interference produced by jammers is proliferating and it is becoming a serious threat for GNSS receivers. The integration of GNSS and external sensors with complementary characteristics, is the key for overcoming the weaknesses and enhancing the strengths of each sub-system. In this paper, the design of an ultra-tight hybrid navigation system is proposed with the aim to enhance the robustness of the navigation system in presence of jamming. A GNSS unit has been integrated with external sensors, namely Inertial Navigation Systems, visual sensor and odometer. Exploiting the “record and replay” of real GNSS signal artificially augmented with jamming interference within the L1 GNSS bandwidth, the performance has been assessed in controlled scenarios. The results presented in this paper show that the multi-sensor integrated system can sustain the navigation even in presence of severe jamming, although such a strong interference completely masks the GNSS signal denying the navigation of a GNSS stand-alone system. Moreover, the test procedures suitability of the record and replay approach for the jamming scenario generation and combination with real datasets are discussed and analyzed
Performance Assessment of the New L2C CNAV GPS Signal
No full textL2C is a relatively new GPS signal which is part of the GPS modernization program. In April 2014, the Air Force began broadcasting a valid L2C CNAV navigation message. When combined with the L1 C/A legacy signal in a dual-frequency receiver, L2C enables interesting features such as improved reliability, PVT solution accuracy and robustness in weak signal environments. Based on L1 C/A signal, our software receiver has been adapted to the L2C signal structure. This paper suggests methods for acquisition, tracking and PVT computation for the L2C signal exploiting the benefits of double frequency receiver
On the Use and Performance of New Galileo Signals for Ionospheric Scintillation Monitoring over Antarctica
No full textIrregularities in the ionosphere cause Global Navigation Satellite Systems (GNSS) signals to experience fluctuations in amplitude and phase called scintillations. Given the global and permanent availability of Global Positioning System (GPS) signals, they have become one of the preferred methods to monitor ionosphere activity. With the coming completion of new GNSS systems like the European Galileo, which is to be interoperable and compatible with GPS, a greater number of signals will be available for monitoring purposes. In this paper we present initial results on the use of new signals, namely GPS L5 and Galileo E1b and E5a, for scintillation monitoring at a base station in Antarctica. Our results show that Galileo signals can be exploited and easily integrated with GPS measurements. Furthermore, by taking advantage of the flexibility and configurability of software receivers, new Galileo signals provide a substantial update of the monitoring capability of already deployed GPS hardware
Monitoring Ionosphere over Antarctica by means of a GNSS Signal Acquisition System and a Software Radio Receiver
No full textThe Earth's upper atmosphere presents a region particularly rich of free electrons, the ionosphere. Such high concentration makes the ionosphere the major natural contributor to the degraded quality of the GNSS signals received at ground. In polar regions, such as in Antarctica, this degradation can be stronger, creating serious problems in using GNSS devices for logistic and scientific purposes. An ionosphere monitoring station, based on a GNSS signal acquisition system and on a software radio receiver, has been installed in two research stations in Antarctica, in the frame of the DemoGRAPE project. The full system is not only able to monitor TEC and scintillation activity in GPS L1 C/A and L2C signals, but also to grab and store raw unprocessed samples for post-processing analysis by means of software radio techniques. This paper presents the description of the setup and of the installation of the system as well as a report of the first results obtained by processing the data acquired during the first week of operation
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