Design of pilot channel tracking loop Systems for high sensitivity Galileo receivers

Global Navigation Satellite Systems (GNSS) have been in the center stage of the recent technological upheaval that has been initiated by the rise of smartphones in the last decade. This is clearly reflected in the development of many applications based on GNSS technology as well as the emergence of multi-constellation GNSS with the launch of the first Galileo satellites at the end of the year 2011. GNSS does not only guarantee global positioning, navigation and timing services but also extends to applications in banking, agriculture, mapping, surveying, archaeology, seismology, commerce, ionosphere scintillation monitoring, remote sensing (soil moisture, ocean salinity, type of surface), wind speed monitoring, ocean surface monitoring, altimetry and many others. In the last decade, Location Based Services (LBS) have increased significant market demand where GNSS has been coupled with technologies based on terrestrial communication links in order to meet strict positioning accuracy requirements. In these conditions, relying on GNSS technology alone, raises a few challenges for signal synchronization even before positioning attempts and are mainly due to a considerable signal attenuation as it propagates through construction material and into indoor environments. Ionosphere scintillation induces a similar challenge where in addition to amplitude fading, the carrier phase and frequency suffer from indeterministic fluctuations. This research activity is devoted to explore and design the elements constituting pilot channel scalar tracking loop systems, specifically tailored to Galileo signals. It is expected that running such systems with extended integration intervals offers robust synchronization of the incoming signal which is heavily affected by external indeterministic fluctuations. In some conditions, it is desired to follow these fluctuations as in ionosphere scintillation monitoring while in other instances it is mainly desired to filter them out as noise to guarantee positioning capabilities. This is the objective of this research study which applies for both indoor environments and ionosphere scintillation affected signals. Towards this endeavor, a comprehensive theoretical study of the carrier and code tracking loops elements is undertaken, and particular attention is directed to the following aspects: • carrier frequency and phase discriminators and the relative optimum integration time • Galileo specific code discriminators and code tracking architecture especially tailored to Composite Binary Offset Carrier (CBOC) modulated signals. • optimum loop filters designed in the digital domain for different types of phase input signals • local signal generation using a numerically controlled oscillator and loop filter estimates • front-end filter bandlimiting effects on the tracking performance. This design is further tested with simulated Galileo signals with and without ionosphere scintillation as well as raw Galileo signals in an equatorial region during March 2013. Tracking performance comparison is carried out between the customized Galileo receiver developed in this research activity and an ionosphere scintillation dedicated professional GNSS receiver, the Septentrio PolaRxS PRO R receiver

Extending Integration Time for Galileo Tracking Robustness Under Ionosphere Scintillation

As a wide array of services and applications are becoming more reliant on Global Navigation Satellite System (GNSS) technology, its continuity requirements are naturally becoming more stringent. The ionosphere scintillation phenomenon is one of the major concerns that threaten these continuity requirements. It results in amplitude, phase and frequency fluctuations of Radio Frequency (RF) signals traveling through space and piercing the ionosphere, hundreds of Km of altitude, where turbulent ionized gases or plasma that stem from solar winds modify the characteristics of electromagnetic signals. The objective of this paper is to study the impact of extending the coherent integration interval used in GNSS scalar tracking loops, in terms of maintaining tracking or synchronization of the European GNSS Galileo E1 Open Service (OS) signals. For that end, a first order optimum loop filter is designed in the digital domain, optimal in minimizing both transient energy and thermal noise tracking jitter. Moreover, a theoretical study of its stability and degree of stability is carried out through root locus and Bode plots. Its performance is also compared to that of traditional analog loop filters often used in literature. Carrier and code tracking loops using this optimum digital loop filter are tested on simulated weak Galileo signals as well as simulated scintillation affected signals. Fast and slow amplitude, phase scintillation are first considered separately to understand the mechanisms of each variable (amplitude/phase), and then both fluctuations are incorporated onto the simulated Galileo signal

Mean acquisition time of GNSS peer-to-peer networks

The acquisition engine is the most critical block within a Global Navigation Satellite Systems (GNSS) receiver as all subsequent blocks in the receiver chain depend on it. To that end, an innovative Peer to Peer (P2P) architecture is studied in this paper, where special acquisition engines are expected to perform better in terms of Mean Acquisition Time (MAT). This is due to peers nearby which share GNSS aiding information in terms of code delay, Doppler frequency and Carrier-to-Noise Ratio (CNR). It is thus expected to reduce the search space over which the Cross-Ambiguity Function (CAF) is evaluated as well as to initialize the correct integration time a-priori. The performance improvement in terms of MAT as a result of the P2P setting is tested against the standard acquisition engine in a comprehensive way. Indeed, the MAT of a standard acquisition engine is compared to that of a P2P engine with a thorough investigation of several search strategies where the best strategy yielding the optimum MAT is chosen for each acquisition engine

Technique for MAT analysis and performance assessment of P2P Acquisition Engines

The first processing block within a Global Navigation Satellite Systems (GNSS) receiver is the acquisition engine. As it may represent a bottleneck for subsequent blocks in the receiver chain, it is essential to tune the acquisition engine to have any chance in designing an efficient receiver. Peer to Peer (P2P) networks present the opportunity to do so, by exchanging GNSS aiding information among nodes of the network to reduce the acquisition search space. Moreover, the Mean Acquisition Time (MAT) is often used as a performance metric and usually derived using probability generating functions and flow graph diagrams based on Markov processes. In this paper, an intuitive technique based on acquisition time and MAT diagrams is presented and used to derive an expression of the MAT as well as to analyze its constitutive terms. The MAT of a standard acquisition engine is compared to that of a P2P engine with a thorough investigation of a Gaussian search order and zig-zag search strategy to assess the performance improvement brought about by P2P networks

Augmented GNSS Differential Corrections Minimum Mean Square Error Estimation Sensitivity to Spatial Correlation Modeling Errors

Railway signaling is a safety system that has evolved over the last couple of centuries towards autonomous functionality. Recently, great effort is being devoted in this field, towards the use and exploitation of Global Navigation Satellite System (GNSS) signals and GNSS augmentation systems in view of lower railway track equipments and maintenance costs, that is a priority to sustain the investments for modernizing the local and regional lines most of which lack automatic train protection systems and are still manually operated. The objective of this paper is to assess the sensitivity of the Linear Minimum Mean Square Error (LMMSE) algorithm to modeling errors in the spatial correlation function that characterizes true pseudorange Differential Corrections (DCs). This study is inspired by the railway application; however, it applies to all transportation systems, including the road sector, that need to be complemented by an augmentation system in order to deliver accurate and reliable positioning with integrity specifications. A vector of noisy pseudorange DC measurements are simulated, assuming a Gauss-Markov model with a decay rate parameter inversely proportional to the correlation distance that exists between two points of a certain environment. The LMMSE algorithm is applied on this vector to estimate the true DC, and the estimation error is compared to the noise added during simulation. The results show that for large enough correlation distance to Reference Stations (RSs) distance separation ratio values, the LMMSE brings considerable advantage in terms of estimation error accuracy and precision. Conversely, the LMMSE algorithm may deteriorate the quality of the DC measurements whenever the ratio falls below a certain threshold

First Joint GPS/IOV-PFM Galileo PVT estimation using carrier phase measurements

The advent of the first two satellites of the final Galileo constellation launched by Soyuz from Europe's spaceport in French Guiana on October 21st is a major milestone for the European as well as global satellite navigation field. In fact, these two satellites pave the way for a much awaited set of experiments testing the benefits brought about by an additional constellation in orbit, Galileo. The European constellation formed by last generation satellites carrying very precise hydrogen maser clocks, and transmitting sophisticated navigation payloads, is expected to increase positioning availability and improve satellite geometry so far as to decrease positioning errors with respect to the use of GPS satellites exclusively. In this paper, signal acquisition, tracking and demodulation of the signal broadcast by the first Galileo satellite (the so-called IOV-PFM Galileo satellite) in the E1 bandwidth is performed. Starting to monitor this satellite from December 2011, we were able to observe a valid ephemeris data on December 21 and December 22 in 2011, respectively. Thus, a valid satellite orbit information has been obtained and used to compute pseudoranges in the Galileo system. Furthermore, precise carrier-phase positioning is carried out combining GPS L1 with Galileo E1 carrier phase measurements to reach a cm level accuracy positioning. The joint GPS and Galileo PVT strategy is then compared to the standalone GPS PV

Deliverable D4.2 - Technical Specification of Survey Toolset. ERSAT GGC. ERTMS on SATELLITE Galileo Game Changer

This document is the deliverable D4.2-Technical Specification of the Survey Toolset where the outcome of the work performed in WP4.2 of the ERSAT GGC project is described. This document follows up the work performed in WP4.1 and reported in the deliverable D4.1, extending the ongoing general definition of the track area classification process. The goal of WP4.2 is the specification and development of the toolset for the survey and classification of track areas, giving the system overview and providing the different interacting blocks as the measurement hardware system, the processing software toolbox and the final classification data. Regarding this D4.2, the functional and technical specifications of the toolset are here provided with the description of the interfaces between the different detection techniques and decision logic blocks. Outcome of D4.3 will be the prototype implementation and installation. The document also includes the specification of the measurement system and hardware to be used in the survey process so that the necessary data for the classification techniques can be collected in the railway scenario. Finally, the specification of the output data - the track area classification results - is also analysed and provided. The specification of the survey measurement system and software toolset addressed in the current document will support the next project activities related to the development of the software tools for the classification of track areas in WP4.2 and the execution of measurement campaigns in WP4.3