Galileo AltBOC receivers - Analysis of receiver architectures, acquisition strategies and multipath mitigation techniques for the E5 AltBOC signal

Master of Science Thesi

Advanced Signal Processing in Multi-mode Multi-frequency Receivers for Positioning Applications

The demands for positioning services are increasing steadily since the first Global Navigation Satellite Systems (GNSS), NAVSTAR Global Positioning System, also known as GPS was introduced in the early 80s. The increasing demands for positioning services have accelerated the advent of other satellite-based systems, such as the Russian GLONASS, the European Galileo and the Chinese Compass/Beidou-2 system. However, the GNSS fail to provide accurate positioning solution indoors, which is one of the demanding environments. Therefore developing indoor positioning techniques has become a very important topic, mainly in terms of continuity of services and seamless localization. This has led to many theoretical and experimental studies in this field using a wide range of techniques, from purely GNSS approach to methods employing networks of physical sensors or Wireless Local Area Networks (WLAN). These systems, together with satellite­ based ones, all have their advantages, but they also face different challenges. Most of these are related to the physical channel containing various error sources that affect the quality of the received signal and degrade the receiver's positioning performance. The users will benefit from having multiple systems with more satellites and different positioning methods available. In this way, the positioning performance against the errors and challenges will be superior to having only a single system. This can be realized by the multi-mode multi-frequency receiver, which is able to process jointly the new signals, modulations and frequencies introduced in modem positioning systems. The work presented in this thesis focuses on the signal processing part for research and development of such a receiver and outlines the potential capability of the future receivers for positioning applications. More specifically, this thesis studies the narrowband interference effects on the future GNSS signals in both single-frequency and multi­ frequency receivers, makes a performance analysis of dual-frequency ionosphere delay estimation methods under strong multipath errors and presents an optimized multi­ correlator based multipath mitigation technique for future GNSS signals. In addition, the performance of four multipath mitigation techniques under time-varying, measurement­ based channel models is compared. Finally, a new Non-Line-of-Sight identification based on non-GNSS signal is proposed for improving the path-loss modeling based indoor positioning in multi-mode multi-frequency receivers. This thesis consists of an introductory part with live chapters and a compendium of six original publications ([I] - [VI]), attached as appendices

Modes dégradés résultant de l'utilisation multi constellation du GNSS

Actuellement, on constate dans le domaine de la navigation, un besoin croissant de localisation par satellites. Apres une course a l'amelioration de la precision (maintenant proche de quelques centimetres grace a des techniques de lever d'ambiguite sur des mesures de phase), la releve du nouveau defi de l'amelioration de l'integrite du GNSS (GPS, Galileo) est a present engagee. L'integrite represente le degre de confiance que l'on peut placer dans l'exactitude des informations fournies par le systeme, ainsi que la capacite a avertir l'utilisateur d'un dysfonctionnement du GNSS dans un delai raisonnable. Le concept d'integrite du GNSS multi-constellation necessite une coordination au niveau de l'architecture des futurs recepteurs combines (GPS-Galileo). Le fonctionnement d'un tel recepteur dans le cas de passage du systeme multi-constellation en mode degrade est un probleme tres important pour l'integrite de navigation. Cette these se focalise sur les problemes lies a la navigation aeronautique multiconstellation et multi-systeme GNSS. En particulier, les conditions de fourniture de solution de navigation integre sont evaluees durant la phase d'approche APV I (avec guidage vertical). En disposant du GPS existant, du systeme Galileo et d'un systeme complementaire geostationnaire (SBAS), dont les satellites emettent sur des frequences aeronautiques en bande ARNS, la question fondamentale est comment tirer tous les benefices d'un tel systeme multi-constellation pour un recepteur embarque a bord d'un avion civil. En particulier, la question du maintien du niveau de performance durant cette phase de vol APV, en termes de precision, continuite, integrite et disponibilite, lorsque l'une des composantes du systeme est degradee ou perdu, doit etre resolue. L'objectif de ce travail de these est donc d'etudier la capacite d'un recepteur combine avionique d'effectuer la tache de reconfiguration de l'algorithme de traitement apres l'apparition de pannes ou d'interferences dans une partie du systeme GNSS multiconstellation et d'emettre un signal d'alarme dans le cas ou les performances de la partie du systeme non contaminee ne sont pas suffisantes pour continuer l'operation en cours en respectant les exigences de l'aviation civile. Egalement, l'objectif de ce travail est d'etudier les methodes associees a l'execution de cette reconfiguration pour garantir l'utilisation de la partie du systeme GNSS multi-constellation non contaminee dans les meilleures conditions. Cette etude a donc un interet pour les constructeurs des futurs recepteurs avioniques multiconstellation. ABSTRACT : The International Civil Aviation Organization (ICAO) has defined the concept of Global Navigation Satellite System (GNSS), which corresponds to the set of systems allowing to perform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system which constitutes one of the components of the GNSS. Currently, this system broadcasts a civil signal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPS is being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) and L5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNS band: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band and Galileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that of GPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operational benefits for civil aviation use. However, civil aviation requirements are very stringent and up to now, the bare systems alone cannot be used as a means of navigation. For instance, the GPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms of accuracy, integrity, continuity of service and availability, ICAO standards define different systems/algorithms to augment the basic constellations. GPS, Galileo and the augmentation systems could be combined to comply with the ICAO requirements and complete the lack of GPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service level required by the ICAO, the architecture of future combined GNSS receivers must be standardized. The European Organization for Civil Aviation Equipment (EUROCAE) Working Group 62, which is in charge of Galileo standardization for civil aviation in Europe, proposes new combined receivers architectures, in coordination with the Radio Technical Commission for Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 by providing inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of the combined receivers' architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet a phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. That is why future combined receivers must be capable of detecting the impact of perturbations that may lead to the loss of one GNSS component, in order to be able to initiate a switch. These perturbations are mainly atmospheric disturbances, interferences and multipath. In this thesis we focus on the particular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain open issues and may affect pseudorange measurements accuracy, as well as integrity, continuity and availability of these measurements. In literature, many different interference detection algorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in this thesis, we address the problem of interference detection at the correlators outputs. The particular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signals processing is proposed. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS or GALILEO navigation signals processing at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO E1 and E5 signals will bring their contribution. However, if affected by a Radio Frequency Interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate the ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multi constellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. This problem is identified for instance in [NATS, 2003]. Consequently, in this thesis, we investigate techniques to maintain dual frequency performances when a frequency is lost (L1 C/A or E1 OS for instance) after an interference occurrence

Software Simulator and Signal Analysis for Galileo E5 band Signals

Galileo is the European Global Navigation Satellite System (GNSS) that aims at providing high availability, increased accuracy, and various location services under the civilian control. Four in-orbit validation satellites have already been launched till date and the system is estimated to be fully deployed by the year 2020. The Galileo navigation signals are transmitted at four frequency bands, which are named E5a, E5b, E6, and E1 bands. The signal of interest in this thesis is Galileo E5a band and Galileo E5b band signals. Signal acquisition and signal tracking are the main functions in a GNSS receiver. Acquisition identifies all the visible satellites and estimates the coarse values of carrier frequency and code phase estimates of the satellite signal. Tracking refines the coarse carrier frequency and code phase estimates, and keeps track of the satellite. The objective of this thesis has been to design and implement Galileo E5a and E5b signals receiver which can acquire all the visible E5a and E5b signals and which gives coarse estimate of carrier frequency and code phase. Such a receiver has been successfully designed in Matlab starting from the Matlab initial files provided by the Finnish Geodetic Institute (FGI) provided tool. In this thesis, two different software implementations are analyzed: 1) The acquisition and tracking of simulated Galileo E5a signals generated in the Matlab Simulink E1-E5 model; and 2) The acquisition of real-time Galileo E5b signals received from the satellite provided by Finnish Geodetic Institute (FGI), Masala, Finland. In the Simulink implementation, the whole E5 signal is generated and propagated through different channel profiles. The received signals are tested with acquisition and tracking and the results are compared for different channel profile and Carrier-to-Noise density ratio. Similarly, the real-time Galileo signals from four satellites now available on sky from the Galileo constellation were received and performed acquisition. In both implementations, a sharp triangular peak was observed at the rough frequency and code phase estimates, proving that the Galileo E5a/b signals can be indeed acquired correctly with the implemented simulator

Precise positioning in real-time using GPS-RTK signal for visually impaired people navigation system

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University, 24/9/2010.This thesis presents the research carried out to investigate and achieve highly reliable and accurate navigation system of guidance for visually impaired pedestrians. The main aim with this PhD project has been to identify the limits and insufficiencies in utilising Network Real-Time Kinematic Global Navigation Satellite Systems (NRTK GNSS) and its augmentation techniques within the frame of pedestrian applications in a variety of environments and circumstances. Moreover, the system can be used in many other applications, including unmanned vehicles, military applications, police, etc. NRTK GNSS positioning is considered to be a superior solution in comparison to the conventional standalone Global Positioning System (GPS) technique whose accuracy is highly affected by the distance dependent errors such as satellite orbital and atmospheric biases. Nevertheless, NRTK GNSS positioning is particularly constrained by wireless data link coverage, delays of correction and transmission and completeness, GPS and GLONASS signal availability, etc., which could downgrade the positioning quality of the NRTK results. This research is based on the dual frequency NRTK GNSS (GPS and GLONASS). Additionally, it is incorporated into several positioning and communication methods responsible for data correction while providing the position solutions, in which all identified contextual factors and application requirements are accounted. The positioning model operates through client-server based architecture consisted of a Navigation Service Centre (NSC) and a Mobile Navigation Unit (MNU). Hybrid functional approaches were consisting of several processing procedures allowing the positioning model to operate in position determination modes. NRTK GNSS and augmentation service is used if enough navigation information was available at the MNU using its local positioning device (GPS/GLONASS receiver).The positioning model at MNU was experimentally evaluated and centimetric accuracy was generally attained during both static and kinematic tests in various environments (urban, suburban and rural). This high accuracy was merely affected by some level of unavailability mainly caused by GPS and GLONASS signal blockage. Additionally, the influence of the number of satellites in view, dilution of precision (DOP) and age corrections (AoC) over the accuracy and stability of the NRTK GNSS solution was also investigated during this research and presented in the thesis. This positioning performance has outperformed the existing GPS service. In addition, utilising a simulation evaluation facility the positioning model at MNU performance was quantified with reference to a hybrid positioning service that will be offered by future Galileo Open Service (OS) along with GPS. However, a significant difference in terms of the service availability for the advantage of the hybrid system was experienced in all remaining scenarios and environments more especially the urban areas due to surrounding obstacles and conditions. As an outcome of this research a new and precise positioning model was proposed. The adaptive framework is understood as approaching an integration of the available positioning technology into the context of surrounding wireless communication for a maintainable performance. The positioning model has the capability of delivering indeed accurate, precise and consistent position solutions, and thus is fulfilling the requirements of visually impaired people navigation application, as identified in the adaptive framework

Processing and integrity of DC/DF GBAS for CAT II/III operations

In Civil Aviation domain, to cope with the increasing traffic demand, research activities are pointed toward the optimization of the airspace capacity. Researches are thus ongoing on all Civil Aviation areas: Communication, Navigation, Surveillance (CNS) and Air Traffic Management (ATM). Focusing on the navigation aspect, the goals are expected to be met by improving performances of the existing services through the developments of new NAVigation AIDS (NAVAIDS) and the definition of new procedures based on these new systems. The Global Navigation Satellite System (GNSS) is recognized as a key technology in providing accurate navigation services with a worldwide coverage. The GNSS concept was defined by the International Civil Aviation Organization (ICAO). A symbol of its importance, in civil aviation, can be observed in the avionics of new civil aviation aircraft since a majority of them are now equipped with GNSS receivers. The GNSS concept includes the provision of an integrity monitoring function by an augmentation system in addition to the core constellations. This is needed to meet all the required performance metrics of accuracy, integrity, continuity and availability which cannot be met by the stand-alone constellations such as GPS. Three augmentation systems have been developed within civil aviation: the GBAS (Ground Based Augmentation System), the SBAS (Satellite Based Augmentation System) and the ABAS (Aircraft Based Augmentation System). GBAS, in particular, is currently standardized to provide precision approach navigation services down to Category I (CAT I) using GPS or Glonass constellations and L1 band signals. This service is known as GBAS Approach Service Type-C (GAST-C). In order to extend this concept down to CAT II/III service, research activities is ongoing to define the new service called a GAST-D. Among other challenges, the monitoring of the ionospheric threat is the area where the integrity requirement is not met. Thanks to the deployment of new constellations, Galileo and Beidou, and the modernization process of the existing ones, GPS and Glonass, the future of GNSS is envisaged to be Multi-Constellation (MC) and Multi-frequency (MF). In Europe, research activities have been focused on a Dual-Constellation (DC) GNSS and DC GBAS services based on GPS and Galileo constellations. Moreover, to overcome the problems experienced by Single-Frequency (SF) GBAS due to ionosphere anomalies, the use of two frequencies (Dual Frequency, DF) has been selected as a mean to improve ionosphere anomalies detection and to mitigate ionosphere residual errors. Advantages in using a DC/DF GBAS (GAST-F) system are, however, not only related to the integrity monitoring performance improvement. Benefits, brought by DC and DF, are also related to •the robustness of the entire system against unintentional interference thanks to the use of measurements in two protected frequency bands, •the robustness against a constellation failure, •the accuracy improvement by using new signals with improved performance, and more satellites. However, the use of new signals and a new constellation, does not bring only benefits. It also raises a series of challenges that have to be solved to fully benefit from the new concept. In this thesis, some challenges, related to DC/DF GBAS, have been investigated. One of them, rising from the use of new GNSS signals, is to determine the impact of error sources that are uncorrelated between the ground station and the aircraft and that induce an error on the estimated position. Using two frequencies, there is the possibility to form measurement combinations like Divergence-free (D-free) and Ionosphere-free (I-free) for which the errors impact has to be analyzed. In this thesis, the impact of the uncorrelated errors (noise and multipath as main sources) on ground measurements is analyzed. The aim is to compare the derived performances with the curve proposed in (RTCA,Inc DO-253C, 2008) for th

Delay Trackers for Galileo CBOC Modulated Signals and Their Simulink-based Implementations

Galileo will be the future European Global Navigation Satellite Systems (GNSSs), which is going to provide high availability, increased accuracy and various location services. This new satellite system proposes the use of a new modulation, namely the Composite Binary Offset Carrier (CBOC) modulation, which motivates the research on GNSS receiver with this new modulation. Code tracking is one of the main functions in a GNSS receiver and its task is to give an accurate estimation of the code delay. The accuracy of this code delay estimation is strictly connected with the accuracy of user position computation. One typical code tracking structure is the code tracking loop. The code tracking algorithms or delay trackers used in code tracking loop are the main aspect, which affects the performance of code tracking loop. Various typical delay trackers are studied in this thesis. Simulation is one important issue in the design and analysis of any communication system or navigation system. One method for testing delay trackers and effects from different tracking algorithms can be realized in the simulation tool, such as a software receiver. The simulation tool makes it convenient to test various algorithms used in the receiver and to investigate the receiver performance before the algorithms are built in the real devices. On the other hand, the implementation of delay trackers in a software receiver can be also helpful for further developing the simulation tool. The goal of this thesis has been to develop and analyze the implementations of various code delay trackers for Galileo systems via Simulink tool. The analysis has also helped to further develop the model in order to include realistic receiver constraints for mass-market application. The performance of the delay trackers is measured in terms of Root Mean Square Error (RMSE), tracking error variance and Multipath Error Envelopes (MEEs). /Kir1

Narrowband interference rejection studies for Galileo signals via Simulink

Four Global Navigation Satellite System (GNSS) are scheduled to be fully operational orbiting the Earth in the coming years. A considerably high number of signals, coming from each of the satellites that will constitute those constellations, will share the radio electric spectrum. Aeronautical Radio Navigation Systems (ARNS) share the E5 Galileo band. Examples of ARNS are Distance Measuring Equipment (DME) and Tactical Air Navigation system (TACAN). It should also be mentioned that electronic attacks (jamming or spoofing) have always been a latent threat for satellite services. All of this are important interference sources which can partially or completely disable a GNSS system. These interferences must be, and are currently being studied together with interference mitigation methods. The aim of the work presented in this thesis is to study the narrowband interference effects in Galileo E5 band and to assess three mitigation techniques against two types of narrowband interferences, Continuous Wave Interference (CWI) and DME signals. Cancellation techniques can be classified into two major groups: time-domain approaches and frequency-domain approaches. Methods that combine time and frequency together are also given in the literature (e.g. cyclostationarity-based methods) but their implementations are very costly with high sampling rates as those used for example in Galileo E5 signals. The mitigation techniques that are addressed in this thesis are zeroing, dynamic notch filtering and blanking pulse methods. All of them can be understood as filtering techniques that remove any signal above a certain threshold. This thesis shows that zeroing is more suitable for CWI and blanking is better against DME signals. These techniques have been developed within a Matlab-Simulink based simulator initiated in 2007 at Tampere University of Technology. The implemented simulator could be a great help tool for future research and development projects

GNSS Integrity Monitoring assisted by Signal Processing techniques in Harsh Environments

The Global Navigation Satellite Systems (GNSS) applications are growing and more pervasive in the modern society. The presence of multi-constellation GNSS receivers able to use signals coming from different systems like the american Global Positioning System (GPS), the european Galileo, the Chinese Beidou and the russian GLONASS, permits to have more accuracy in position solution. All the receivers provide always more reliable solution but it is important to monitor the possible presence of problems in the position computation. These problems could be caused by the presence of impairments given by unintentional sources like multipath generated by the environment or intentional sources like spoofing attacks. In this thesis we focus on design algorithms at signal processing level used to assist Integrity operations in terms of Fault Detection and Exclusion (FDE). These are standalone algorithms all implemented in a software receiver without using external information. The first step was the creation of a detector for correlation distortion due to the multipath with his limitations. Once the detection is performed a quality index for the signal is computed and a decision about the exclusion of a specific Satellite Vehicle (SV) is taken. The exclusion could be not feasible so an alternative approach could be the inflation of the variance of the error models used in the position computation. The quality signal can be even used for spoofinng applications and a novel mitigation technique is developed and presented. In addition, the mitigation of the multipath can be reached at pseudoranges level by using new method to compute the position solution. The main contributions of this thesis are: the development of a multipath, or more in general, impairments detector at signal processing level; the creation of an index to measure the quality of a signal based on the detector’s output; the description of a novel signal processing method for detection and mitigation of spoofing effects, based on the use of linear regression algorithms; An alternative method to compute the Position Velocity and Time (PVT) solution by using different well known algorithms in order to mitigate the effects of the multipath on the position domain

Desarrollo de algoritmos para el tratamiento de datos GNSS : su aplicación a los escenarios GPS modernizado y Galileo

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Matemáticas, Sección Departamental de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología) (Astronomía y Geodesia), leída el 24-07-2012Nowadays, the major GNSS systems are the american GPS and the russian GLONASS, however, in a near future the european project Galileo and the chinesse system COMPASS will become part of the current GNSS scenario. These systems will transmit for the first time three different frequencies, giving place to a multi-system and multi-frequency scenario which will dramatically push the boundaries of the positioning techniques. Currently, one of the most studied positioning techniques is known as Precise Point Positioning (PPP), which is aimed at estimating precise receiver position from undifferenced GNSS code and carrier phase observations and precise satellite products. In this thesis, some new and original algorithms for static PPP have been developed, which are able to deal with the future multi-system and multifrequency GNSS observations. The new algorithms have been named MAP3. In the new approach, the least squares theory is applied twice to estimate the ionospheric delay, initial ambiguities and smoothed pseudodistances from undifferenced observations, which in turn are used to recover the receiver position and its clock offset. MAP3 provides position estimations with an accuracy of 2.5 cm after 2 hours observation and 7 mm in 1 day, being at the same level as other PPP programs and even better results are obtained with MAP3 in short observation periods. Moreover, MAP3 have provided some of the first results in positioning from GIOVE observations and GPC products. In addition, these algorithms have been applied in the analysis of the influence of ionospheric disturbances on the point positioning, concluding that the presence of a high ROT (Rate of TEC), observed at equatorial latitudes, reflects a significant degradation of the point positioning from dual-frequency observations.Actualmente, los únicos sistemas globales de navegación por satélites operativos son GPS y GLONASS, sin embargo, en un futuro cercano el proyecto europeo Galileo y el sistema chino COMPASS entrarán a formar parte del actual escenario GNSS. Estos sistemas emplearán por primera vez, tres frecuencias distintas, dando lugar a un escenario multi-frecuencia que revolucionará las técnicas de posicionamiento. Entre las técnicas actuales de posicionamiento con GNSS destaca el Posicionamiento Preciso Puntual (PPP), que consiste en determinar la posición de un receptor a partir de observaciones de código y fase no differenciadas y productos precisos. En este trabajo de tesis se han desarrollado unos nuevos y originales algoritmos para PPP estático, llamados MAP3, capaces de procesar observaciones GNSS multifrecuencia y multi-sistema del futuro escenario GNSS y determinar la posición de un receptor de forma precisa y exacta. Los algoritmos MAP3 se dividen en dos partes en las cuales se ha aplicado la teoría mínimos cuadrados y se han obtenido expresiones explícitas para estimar el retraso ionosférico, ambigüedades de fase inicial y pseudodistancias suavizadas, que se emplean para determinar la posición del receptor y el offset de su reloj. MAP3 proporciona una estimación de la posición con una exactitud de 2.5 cm tras 2 horas de observación y de 7 mm tras 24 h, resultados que mejoran los obtenidos hasta el momento con otros programas para PPP en periodos cortos de tiempo. Además, MAP3 han proporcionado los primeros resultados en el posicionamiento con observaciones GIOVE y productos del GPC. Por otro lado, estos algoritmos se han aplicado al análisis de los efectos de ciertas perturbaciones ionosféricas en el posicionamiento concluyendo que la presencia de un ROT (Rate of TEC) elevado, observado en latitudes ecuatoriales, refleja una degradación significativa del posicionamiento puntual con observaciones doble frecuencia.Unidad Deptal. de Astronomía y GeodesiaFac. de Ciencias MatemáticasTRUEunpu