1,720,991 research outputs found
Snapshot Estimation Algorithms for GNSS Mass-Market Receivers
Full text linkThis thesis resumes the PhD program carried out in the signal processing, satellite positioning and telecommunication fields, within the Navigation, Signal Analysis and Simulation (NavSAS) group, Department of Electronics and Telecommunications (DET) of Politecnico di Torino, in the period going from January 2012 to December 2014. The main topic of the PhD activity is represented by Global Navigation Satellite System (GNSS) receivers core technologies. In particular, it deals with the design, development, test and performance assessment of innovative architectures, techniques, and algorithms for Global Positioning System (GPS) and Galileo receivers, both professional high performance and commercial mass-market. GPS, and in general GNSSs are radio-communication infrastructures, aimed to enable a generic user to compute Position, Velocity and Time (PVT). The signals transmitted by a constellation of satellites are processed by an electronic device, performing trilateration with respect to the satellites, taken as reference points. At least 4 satellites are required to be in Line of Sight (LOS) with the receiver, so as to obtain 4 different signals and to solve the 4 navigation unknowns: latitude, longitude, height and time. Since their first appearance, in the early seventies, GNSS chipsets and devices are gaining a fundamental role in most applications of everyday life, and their global market continues to grow rapidly. In 25 years, GNSS receivers became extremely used worldwide, not only for positioning and navigation purposes, but also for time synchronization, thus spanning an unlimited range of applications, from commercial to scientific, from military to recreational. GNSS mass-market receivers are extremely widespread, produced in very high volume—hundreds of millions just for smartphones and tablets—and sold at a limited price. This variety of applications and possibilities represents the main reason of the continuous growth of the GNSS field: in fact, new systems are emerging beside GPS, such as GLONASS, currently operational and in expansion, Galileo and Beidou. With the latest trends of multi-constellation receivers, the positioning accuracy can greatly improve, as well as its robustness, availability, reliability, but at the expense of a greater complexity and power consumptio
Galileo/GPS Mass Market Receivers: Tracking Algorithms Analysis and Performance
No full textThe scope of the work is the development and demonstration of the main GNSS algorithms currently used in GNSS mass-market receivers, with a particular interest toward Galileo signals. An exhaustive survey on existing commercial receivers signal processing techniques has been carried out and the most promising state-of-the-art algorithms for GPS signals have been analyzed and extended to E1B and E1C Galileo signals. The selected techniques have then been implemented in a software receiver, able to process raw GPS and Galileo samples. First the accuracy of the techniques is analyzed, both in terms of code delay and Doppler frequency estimates accuracy, proving the functionality of the multicorrelator processing unit. Second, some tests on robustness sensitivity have been carried out with a simulated LMS channel, proving the benefits of open loop strategies. Finally some tests on power consumption, representing one of the key drivers for the mobile consumer devices design, are carried out. The analysis of the results provides an early assessment on the suitability of these techniques, improving the attractiveness of Galileo to the massmarket community
Doppler Frequency Estimation in GNSS Receivers Based on Double FFT
No full textThis work presents an innovative Doppler frequency estimation technique, particularly suited for GNSS receivers operating in vehicular scenarios. Mass-market and commercial navigation devices are more and more exploited for in-car navigation and for vehicular applications based on positioning. However, the low computational burden affordable by such devices requires the implementation of low complexity algorithms, allowing real-time and on-demand processing. This is the case for instance of open-loop architectures and of MLE-based techniques, which estimate the frequency component of the GNSS signal through a discrete Fourier transform. A state-of-the-art of such methods is first carried out, outlining their benefits, regarding robustness and stability, and their limitations, mainly concerning the accuracy. Successively an innovative refinement technique is introduced, based on the computation of a frequency correction term. Further enhancements are then proposed to solve particular issues, as the estimation of the sign of the correction term and the impact of the initial frequency error. In particular, zero-forcing and a double FFT - which represent the main contribution of this work - are proposed to increase the accuracy without increasing the computational load. A complete analytical derivation and theoretical description is provided, along with a detailed performance assessment. Finally a performance comparison with existing techniques and with the Cramer-Rao lower bound for frequency estimation is given, confirming the excellent behavior of the proposed algorithm for the signal conditions and strengths typical of a vehicular scenario and in the presence of frequent interruption
Evaluation of the Multipath-induced Error Probability on the Estimation of Code-based Pseudoranges
No full textQuantification of the multipath-induced error in GNSS code-based range measurements is usually entrusted to curves as the multipath error envelope (MEE). Although very useful for comparative evaluations, these metrics do not include any realistic information on the propagation channel statistical characterization and consequently cannot be used to quantify the multipath error in an absolute way. A modification of the MEE is therefore proposed, including semi-analytic realizations of the channel statistics, in the form of the power-delay profile and the delays distribution. In addition, the multipath error distribution and the multipath error probability are derived, leading to a realistic evaluation of the performance of different discriminator architectures in different scenario
Performance analysis of duty-cycle power saving techniques in GNSS mass-market receivers
No full textThe 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
A mass-market Galileo receiver: Its algorithms and performance
Full text linkThe two main GNSS receiver market segments, professional high-precision receivers and mass market/consumer receivers, have very different structure, objectives, features, architecture, and cost. The code-delay estimation is performed in the software receiver by a parallel correlation unit, giving as output a multi-correlation with certain chip spacing. This approach presents some advantages, mostly the fact that the number of correlation values that can be provided is thousands of times greater, compared to a standard receiver channel. Use of multiple correlators increases multipath-rejection capabilities, essential features in mass-market receivers, especially for positioning in urban scenarios. The TTFF was estimated with about 50 tests, in hot, warm, and cold start, first using both GPS and Galileo satellites, and then using only one constellation. In the second case only the 2D fix is considered, since, according to the scenario described, at maximum three satellites are in view
An Insight on Mass Market Receivers Algorithms and their Performance with Galileo OS
No full textThe scope of the work is the development and demonstration of the main GNSS algorithms currently used in mass-market GNSS receivers, by focusing on a GPS and Galileo consumer receiver. Indeed, the global market for commercial GNSS chipsets continue to rapidly grow. In the next future. when more constellations are available, the constellations selection may be driven by particular signal characteristics that can result helpful features. Thanks to the release of the Galileo ICD in 2010, Galileo capable chips have been developed well in advance and at present there are several consumer devices ready to process Galileo signals with just a firmware update, for example the STM Teseo 2.
An exhaustive survey on existing mass-market signal processing techniques has been carried out; the most promising state-of-the-art algorithms for GPS signals have been analyzed, implemented in a software receiver and extended to E1BC Galileo signals. The performance of these techniques in terms of code delay and Doppler frequency estimates has been verified with simulated GNSS data.
At the same time, three main mass-market design drivers have been identified, studied with the software receiver and tested with the Teseo 2. First the TTFF for different C/N0, for hot, warm and cold start, and for different constellation combinations has been computed. Then some tests on the sensitivity in harsh environments have been carried out, exploiting a simulated LMS channel and different user dynamics. Finally, power consumption strategies, in particular duty cycle tracking, were considered.
The testing activity has been conducted in the ESTEC Navigation Lab and, on-field, using a mobile test-bed vehicle. The analysis of the results spots the performance differences between the same algorithms applied to different constellation signals and provides an early assessment on the suitability of their characteristics, hereby improving the attractiveness of Galileo to the mass-market community
Code and Frequency Estimation in Galileo Mass Market Receivers
No full textMass market receivers feature particular signal processing techniques, to comply with mobile and consumer devices resources and requirements. Delay and frequency estimation algorithms have then been redefined or adapted, in particular to cope with the new Galileo OS signals. The scope of the work is the analysis, development and performance examination of some of the main GNSS acquisition and tracking algorithms currently used in mass market receivers. The feasibility of such techniques is proved by means of semi-analytical and Monte Carlo simulations, outlining the estimators sensitivity and accuracy, and by tests on real Galileo IOV signal
Recent Trends in Interference Mitigation and Spoofing Detection
No full textThis paper gives a classification of intentional and unintentional threats, such as interference, jamming and spoofing, and discusses some of the recent trends concerning techniques for their detection and mitigation. Despite the fact that these phenomena have been studied since the early stages of Global Positioning System (GPS), they were mainly addressed for military applications of Global Navigation Satellite Systems (GNSS). However, a wide range of recent civil applications related to user’s safety or featuring financial implications would be deeply affected by interfering or spoofing signals intentionally created. For such a reason, added value processing algorithms are being studied and designed, in order to improve accuracy and robustness of the receiver and to assure the reliability of the estimated position and time solution
Assistance requirements definition for GNSS receivers in hostile environments
No full textIncreasing sensitivity and robustness of navigation receivers in hostile environments has become a central topic for the GNSS community. The paper investigates the use of assistance information allowing GNSS receivers' operations even in denied environments, characterized by high dynamics and low C/N0. The main assistance information will be discussed and, for each of them, a set of requirements definition will be presented, allowing weak GNSS signal acquisition and trackin
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