Snapshot Estimation Algorithms for GNSS Mass-Market Receivers

This 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 consumption

Installation and configuration of an ionospheric scintillation monitoring station based on GNSS SDR receivers in Brazil

The use of Global Navigation Satellite Systems (GNSSs) is nowadays very popular, and the positioning service that they provide is becoming the basis of several applications. Due to their wide coverage, GNSS signals can be used at no cost as probing signals to retrieve parameters to characterize the atmosphere, such as ionospheric scintillation indexes. GNSS receivers coupled to the specific algorithm are indeed a valid alternative to large and expensive ad hoc equipment such as ionosondes. In particular, Software Defined Radio (SDR) receivers are characterized by a higher level of flexibility and configurability when compared to commercial receivers, which fits for the purposes of ionospheric monitoring and enable the study of advanced and innovative algorithms, both for scientific purposes (ionospheric monitoring, space weather), and for technological development (robust GNSS receivers design). A GNSS-based ionosphere monitoring station, including an SDR-based receiver and a professional receiver, was installed in the CRAAM laboratory at Mackenzie Presbyterian University (São Paulo, Brazil) on May 2017. Details of the installation and the new approaches for the storage, processing, and transfer of GNSS data, including raw Intermediate Frequency (IF) samples, are described, along with preliminary results related to ionospheric events captured during the first months of its operation

Evaluation of the Multipath-induced Error Probability on the Estimation of Code-based Pseudoranges

Quantification 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

Installation and configuration of an Ionospheric Scintillation Monitoring Station based on GNSS receivers in Antarctica

Global Navigation Satellite Systems (GNSSs), such as the US Global Positioning System (GPS), The Russian GLONASS or the European Galileo, are space-based navigation systems. GNSSs enable a generic user located anywhere on the Earth to determine in real time his Position, Velocity and Time (PVT), by means of a Radio Frequency (RF) electro-magnetic signal, the Signal-In-Space (SIS), transmitted by a constellation of satellites orbiting around Earth. Uninterrupted Positioning, Navigation, and Timing (PNT) solution is determined by GNSS receivers, which continuously process the SIS from the satellites in view. GNSS receivers are part of the GNSSs ground segment. They are a suboptimal implementation of a maximum likelihood estimator of the SIS propagation time. The PNT solution is indeed based on the computation of the SIS Time Of Arrival (TOA), according to the satellite and receiver local clocks. This is achieved thanks to the presence of a different Pseudo Random Noise (PRN) spreading code in the modulated SIS broadcast by each satellite. In the GNSS receiver, the incoming signal is correlated with a local replica of signal code, obtaining the time difference information. The time difference is then transformed into a range information by multiplying it by the speed of light in the vacuum. However, since the receiver clock is not synchronized with the transmitters clock, this measure suffers of time bias, which is considered as an additional unknown in the navigation solution. Finally, the user position is determined on an Earth centred reference system with a process denoted trilateration, by exploiting the range information computed by the receiver and the information contained in the SIS navigation message, such as satellite ephemeris [Kaplan et al., 2005].Published1-252A. Fisica dell'alta atmosferaN/A or not JC

Code and Frequency Estimation in Galileo Mass Market Receivers

Mass 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

Assistance requirements definition for GNSS receivers in hostile environments

Increasing 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

Interference and Spoofing: New Challenges for Satellite Navigation Receivers

This chapter deals with one of the major concerns for reliable use of Global Navigation Satellite Systems (GNSS), providing a description of intentional and unintentional threats, such as interference, jamming, and spoofing. 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 GNSS. However, a wide range of recent civil applications related to user 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 embed in the receiver an interference reporting capability so that they can monitor and possibly mitigate interference event

Benefits of GNSS software receivers for ionospheric monitoring at high latitudes

Ionospheric propagation is harmful for the electromagnetic signals broadcast by Global Navigation Satellite System (GNSS) satellites, mainly because of the presence of electron density anomalies. GNSS receivers are indeed of primary importance in scintillation and Total Electron Content (TEC) monitoring, especially at low and high latitudes, where scintillations are more frequent. Professional dual frequency custom hardware Global Positioning System (GPS) receivers have been successfully exploited since years as measurement tools able to provide post-correlation data that are then used for modeling the atmospheric phenomena. Recent trends in scientific GPS receivers implementation consider Software Defined Radio (SDR) as a valuable technology that enables access to intermediate and low level receiver processing stages. With respect to commercial hardware tools, they provide a larger subset of observables related to the signal processing stages, as well as a high grade of flexibility and re-configurability, depending on the user needs. Such features enable the design and test of innovative ionosphere monitoring technique