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

Master of Science Thesi

Analyzing Code Tracking Algorithms for Galileo Open Service Signal

The ever-increasing public interest on location and positioning services has originated a demand for higher performance Global Navigation Satellite Systems (GNSSs). Galileo Open Service (OS) signal, part of the European contribution to future GNSS, was designed to respond to the above demand. In all GNSSs, the estimation with high accuracy of the Line-Of-Sight (LOS) delay is a prerequisite. The Delay Lock Loops (DLLs) and their enhanced variants (i.e., feed-back code tracking loops) are the structures of choice for the commercial GNSS receivers, but their performance in severe multipath scenarios is still rather limited. In addition, the new satellite positioning system proposals specify the use of a new modulation, the Binary Offset Carrier (BOC) modulation, which triggers a new challenge in the code tracking stage. Therefore, in order to meet this emerging challenge and to improve the accuracy of the delay estimation in severe multipath scenarios, this thesis analyzes feed-back as well as feed-forward code tracking algorithms and proposes a novel algorithm, namely Peak Tracking (PT), which is a combination of both feed-back and feed-forward structures and utilizes the advantages inherent in these structures. In this thesis, the code tracking algorithms are studied and analyzed for Sine BOC (SinBOC) modulated Galileo OS signal for various multipath profiles in Rayleigh fading channel model. The performance of the analyzed algorithms are measured in terms of various well-known criteria such as Root-Mean-Square-Error (RMSE), Mean-Time-to-Lose Lock (MTLL), delay error variance and Multipath Error Envelopes (MEEs). The simulation results show that the proposed PT algorithm outperforms all other analyzed algorithms in various multipath profiles in good Carrier-to-Noise-Ratios (CNRs). The simulation results are compared with the theoretical Cramer-Rao Bound (CRB) and the comparison shows that the delay error variance for PT algorithm approaches the theoretical limit with the increase in CNR. Therefore, the proposed algorithm can be considered as an excellent candidate for implementation in future Galileo receivers, especially when tracking accuracy is a concern. /Kir1

Multipath Propagation, Mitigation and Monitoring in the Light of Galileo and the Modernized GPS

Among the numerous potential sources of GNSS signal degradation, multipath takes on a prominent position. Unlike other errors like ionospheric or tropospheric path delays which can be modeled or significantly reduced by differential techniques, multipath influences cannot be mitigated by such approaches. Although a lot of multipath mitigation techniques have been proposed and developed in the past among them many receiver internal approaches using special signal processing algorithms multipath (especially multipath with small geometric path delays) still remains a major error source. This is why multipath has been a major design driver for the definition of the Galileo signal structure carried out in the past years and the subsequent signal optimization activities. This thesis tries to provide a broad and comprehensive insight into various aspects of multipath propagation, mitigation and monitoring (without claiming to be exhaustive). It contains an overview of the most important aspects of multipath propagation, including the discussion of different types of multipath signals (e.g. specular vs. diffuse multipath, satellite vs. receiver multipath or hardware-induced multipath), typical characteristics such as periodic signal variations whose frequency depends on the satellite-antenna-reflector geometry and the impact on the signal tracking process within a GNSS receiver. A large part of this thesis is dedicated to aspects of multipath mitigation, first providing a summary of the most common multipath mitigation techniques with a special focus on receiver-internal approaches such as the narrow correlation technique, double-delta correlator implementations, the Early-Late Slope (ELS) technique or Early/Early tracking implementations. However, other mitigation approaches such as using arrays of closely spaced antennas or multipath-limiting antennas are discussed as well. Some of these techniques are used for subsequent multipath performance analyses considering signals of the (modernized) GPS and Galileo. These analyses base on a new methodology to estimate typical and meaningful multipath errors making use of multipath error envelopes that are scaled in a suitable way to account for different multipath environments. It will be shown that typical (mean) multipath errors can be derived from these scaled envelopes by computation of the envelopes running average and that these mean multipath errors are of the same order as multipath errors obtained from complex statistical channel models. Another part of this thesis covers various aspects of multipath detection and monitoring. First, current techniques for multipath detection and monitoring are described and discussed with respect to their benefits and drawbacks or their real-time capability. Among the considered approaches are techniques like code minus carrier monitoring, SNR monitoring, the use of differenced observations or spectral and wavelet analysis. Following this introductory overview, a completely new approach for real-time multipath monitoring by processing multi-correlator observations will be introduced. Previously being used primarily for the detection of Evil Waveforms (signal failures that originate from a malfunction of the satellites signal generation and transmission hardware), the same basic observations (linear combinations of correlator outputs) can be used for the development of a multi-correlator-based real-time multipath monitoring system. The objective is to provide the user with instant information whether or not a signal is affected by multipath. The proposed monitoring scheme has been implemented in the form of a Matlab-based software called RTMM (Real-Time Multipath Monitor) which has been used to verify the monitoring approach and to determine its sensitivity.Die Qualität eines Satellitensignals wird durch eine Vielzahl potenzieller Fehlerquellen negativ beeinflusst. Neben atmosphärischen Einflüssen tragen Mehrwegeeinflüsse einen wesentlichen Anteil zum Gesamtfehlerbudget der Satellitennavigation bei. Während eine ganze Reihe von Fehlereinflüssen durch geeignete Modellierung oder differenzielle Verfahren deutlich reduziert werden können, ist dies durch die räumliche Dekorrelation der Mehrwegeeffekte nicht möglich. Obwohl in der Vergangenheit eine Vielzahl von Verfahren zur Mehrwegereduzierung vorgeschlagen und entwickelt wurden, stellen Mehrwegesignale noch immer eine wesentliche, stets zu berücksichtigende Fehlerquelle dar. Aus diesem Grund spielten die zu erwartenden Mehrwegefehler auch eine sehr wichtige Rolle im Zuge der Definition sowie der Optimierung der Galileo-Signalstruktur und können somit als wesentliches Design-Kriterium angesehen werden. Die vorliegende Arbeit gibt einen umfassenden Einblick in verschiedene Aspekte der Mehrwegeausbreitung, -reduzierung sowie der Detektion und der Überwachung auftretender Mehrwegeeffekte. Die Arbeit beschreibt zunächst die wichtigsten Aspekte der Mehrwegeausbreitung, wobei beispielsweise unterschiedliche Arten von Reflexionen oder unterschiedliche Entstehungsarten ebenso diskutiert werden wie typische Auswirkungen von Mehrwegesignalen wie die Entstehung periodischer Signalvariationen. Solche Signalvariationen sind in starkem Maße abhängig von der durch die Satellitenposition, dem Antennenstandpunkt und der Lage des Reflexionspunktes definierten Geometrie. Die Frequenz dieser Signalvariationen wird für unterschiedliche geometrische Verhältnisse berechnet. Zudem werden der Einfluss bzw. die Auswirkungen einer Mehrwegeausbreitung auf den Signalverarbeitungsprozess in einem GNSS Empfänger aufgezeigt. Einen weiteren Schwerpunkt dieser Arbeit bilden die derzeit gebräuchlichen Methoden zur Reduzierung von Mehrwegeeinflüssen. Dabei werden zunächst die wichtigsten empfängerinternen Ansätze vorgestellt. Aber auch Methoden wie die Verwendung von Antennenarrays oder spezieller Antennen bleiben nicht unberücksichtigt. Einige dieser Methoden bilden im Folgenden die Grundlage für die Bestimmung von typischen Mehrwegefehlern. Dazu wird eine neuartige Methodik vorgestellt, um aus Hüllkurven des Mehrwegefehlers aussagekräftige mittlere Mehrwegefehler zu bestimmen. Hierzu werden die Hüllkurven mit Hilfe einiger aus statistischen Kanalmodellen abgeleiteter Parameter in geeigneter Weise skaliert, um unterschiedlichen Mehrwegeumgebungen Rechnung zu tragen. Es wird gezeigt, dass die mit Hilfe dieser relativ einfachen und effizienten Methode ermittelten Mehrwegefehler in derselben Größenordnung liegen wie die aus komplexen statistischen Kanalmodellen ermittelten Fehler. Einen weiteren Themenkomplex stellen Methoden zur Detektion und zum Monitoring von Mehrwegeeinflüssen dar. Dabei werden zunächst derzeit verwendete Ansätze vorgestellt und hinsichtlich ihrer Vor- und Nachteile sowie hinsichtlich ihrer Echtzeitfähigkeit diskutiert. In Anschluss daran wird ein neuartiger Ansatz zur Detektion und zum Monitoring von Mehrwegesignalen in Echtzeit vorgestellt, der auf der Auswertung von Multikorrelatorbeobachtungen basiert. Ziel dieser Entwicklung ist es, einen potenziellen Nutzer sofort darüber informieren zu können, wenn ein Signal mit Mehrwegefehlern behaftet ist. Der vorgeschlagene Ansatz wurde in Form einer Matlab-basierten implementiert, welche im Folgenden zur Verifizierung und zur Bestimmung der Empfindlichkeit des Verfahrens verwendet wird

Signal design and Theoretical bounds for Time-Of-Arrival estimation in GNSS applications

Positioning accuracy in satellite navigation systems depends on time-delay estimation (TDE) between satellite transmitted codes and local receiver replicas. This thesis is specifically focused on the problem of improving time delay estimation (TDE) accuracy of SS signals, focusing on the fundamental issue of estimation theory and on the properties of the transmitted signal. TDE fundamentals limits are deeply investigated, encompassing the Cram´er Rao Bound and the Ziv-Zakai Bound, and their modified versions to lighten their computation in presence of unknown parameters, in addiction to the time delay. The adoption of the ZZB as benchmark for both acquisition and tracking stage performance is addressed, analyzing innovative or standard signalling waveforms such as Galileo SIS. The main contributions of this thesis are dealt with the analysis of applicability of spread spectrum continuous phase-modulated (SS-CPM) and spread spectrum filtered multitone (SS-FMT) as ranging signals. A special subset of CPM, labeled as “Semi-integer MSK (SiMSK)” obtained by properly setting the modulation parameters, is revealed easily adaptable to the requirements on emissions, intrinsically constant envelope and spectral efficient, while still allowing good tracking performance. Besides, an ad hoc encoding of the SS-SiMSK enables the design of a constant envelope signal bearing two different rate services, without any approximation at the transmitter side. The analysis of the multicarrier (MC) signal revealed the high degree of freedom in its design, proposing the special Filtered Multitone (FMT) modulation as possible candidate for ranging signals. The strictly bandlimited property and the full spectral flexibility possessed by the FMT are exploited in some cases of study to adapt the system to channel conditions or in particular to emulate existing or innovative spectra. For both the SSCPM and SS-FMT modulation schemes investigated, some estimation algorithms are tested and their performance are compared to the correspondent theoretical bound

Resilient Peer-to-Peer Ranging using Narrowband High-Performance Software-Defined Radios for Mission-Critical Applications

There has been a growing need for resilient positioning for numerous applications of the military and emergency services that routinely conduct operations that require an uninterrupted positioning service. However, the level of resilience required for these applications is difficult to achieve using the popular navigation and positioning systems available at the time of this writing. Most of these systems are dependent on existing infrastructure to function or have certain vulnerabilities that can be too easily exploited by hostile forces. Mobile ad-hoc networks can bypass some of these prevalent issues making them an auspicious topic for positioning and navigation research and development. Such networks consist of portable devices that collaborate to form wireless communication links with one another and collectively carry out vital network functions independent of any fixed centralized infrastructure. The purpose of the research presented in this thesis is to adapt the protocols of an existing narrowband mobile ad-hoc communications system provided by Terrafix to enable range measuring for positioning. This is done by extracting transmission and reception timestamps of signals exchanged between neighbouring radios in the network with the highest precision possible. However, many aspects of the radios forming this network are generally not conducive to precise ranging, so the ranging protocols implemented need to either maneuver around these shortcomings or compensate for loss of precision caused. In particular, the narrow bandwidth of the signals that drastically reduces the resolution of symbol timing. The objective is to determine what level of accuracy and precision is possible using this radio network and whether one can justify investment for further development. Early experiments have provided a simple ranging demonstration in a benign environment, using the existing synchronization protocols, by extracting time data. The experiments have then advanced to the radio’s signal processing to adjust the synchronization protocols for maximize symbol timing precision and correct for clock drift. By implementing innovative synchronization techniques to the radio network, ranging data collected under benign conditions can exhibit a standard deviation of less than 3m. The lowest standard deviation achieved using only the existing methods of synchronization was over two orders of magnitude greater. All this is achieved in spite of the very narrow 10−20kHz bandwidth of the radio signals, which makes producing range estimates with an error less than 10−100m much more challenging compared to wider bandwidth systems. However, this figure is beholden to the relative motion of neighbouring radios in the network and how frequently range estimates need to be made. This thesis demonstrates how such a precision may be obtained and how this figure is likely to hold up when applied in conditions that are not ideal

Infrared ranging in multipath environments for indoor localization of mobile targets

Esta tesis aborda el problema de la medida de diferencias de distancia mediante señales ópticas afectadas por multicamino, aplicada a la localización de agentes móviles en espacios interiores. Los avances en robótica, entornos inteligentes y vehículos autónomos han creado un campo de aplicación específico para la localización en interiores, cuyos requerimientos de precisión (en el rango de los cm) son muy superiores a los demandados por las aplicaciones de localización orientadas a personas, en cuyo contexto se han desarrollado la mayor parte de las alternativas tecnológicas. La investigación con métodos de geometría proyectiva basados en cámaras y de multilateración basados en medida de distancia con señales de radiofrecuencia de banda ancha, de ultrasonido y ópticas han demostrado un rendimiento potencial adecuado para cubrir estos requerimientos. Sin embargo, todas estas alternativas, aún en fase de investigación, presentan dificultades que limitan su aplicación práctica. En el caso de los sistemas ópticos, escasamente estudiados en este contexto, los trabajos previos se han basado en medidas de diferencia de fase de llegada de señales infrarrojas moduladas sinusoidalmente en intensidad. Una infraestructura centralizada computa medidas diferenciales, entre receptores fijos, de la señal emitida desde el móvil a posicionar, y calcula la posición del móvil mediante trilateración hiperbólica a partir de éstas. Estas investigaciones demostraron que se pueden alcanzar precisiones de pocos centímetros; sin embargo, las interferencias por multicamino debidas a la reflexión de la señal óptica en superficies del entorno pueden degradar esta precisión hasta las decenas de centímetros dependiendo de las características del espacio. Así pues, el efecto del multicamino es actualmente la principal fuente de error en esta tecnología, y por tanto, la principal barrera a superar para su implementación en situaciones reales. En esta tesis se propone y analiza un sistema de medida con señales ópticas que permite obtener estimaciones de diferencias de distancia precisas reduciendo el efecto crítico del multicamino. El sistema propuesto introduce una modulación con secuencias de ruido pseudoaleatorio sobre la modulación sinusoidal típicamente usada para medida de fase por onda continua, y aprovecha las propiedades de ensanchamiento en frecuencia de estas secuencias para reducir el efecto del multicamino. El sistema, que realiza una doble estimación de tiempo y fase de llegada, está compuesto por una etapa de sincronización que posibilita la demodulación parcialmente coherente de la señal recibida, seguida de un medidor diferencial de fase sobre las componentes desensanchadas tras la demodulación. Las condiciones de multicamino óptico típicas en espacios interiores, con una componente de camino directo claramente dominante, permiten que el proceso de demodulación recupere más potencia del camino directo que del resto de contribuciones, reduciendo el efecto del multicamino en la estimación final. Los resultados obtenidos demuestran que la aplicación del método propuesto permitiría realizar posicionamiento a partir de señales ópticas con el rendimiento adecuando para aplicaciones de robótica y guiado de vehículos en espacios interiores; además, el progresivo aumento de la potencia y el ancho de banda de los dispositivos optoelectrónicos disponibles permite esperar un incremento considerable de las prestaciones de la propuesta en los próximos años

New Approach of Indoor and Outdoor Localization Systems

Accurate determination of the mobile position constitutes the basis of many new applications. This book provides a detailed account of wireless systems for positioning, signal processing, radio localization techniques (Time Difference Of Arrival), performances evaluation, and localization applications. The first section is dedicated to Satellite systems for positioning like GPS, GNSS. The second section addresses the localization applications using the wireless sensor networks. Some techniques are introduced for localization systems, especially for indoor positioning, such as Ultra Wide Band (UWB), WIFI. The last section is dedicated to Coupled GPS and other sensors. Some results of simulations, implementation and tests are given to help readers grasp the presented techniques. This is an ideal book for students, PhD students, academics and engineers in the field of Communication, localization & Signal Processing, especially in indoor and outdoor localization domains

Performance of Receiver Autonomous Integrity Monitoring (RAIM) for Maritime Operations

The use of GNSS in the context of maritime applications has evolved during the past. The International Maritime Organization (IMO) has defined and published requirements for those applications. Comparing the requirements on the one hand specified by ICAO and on the other hand by IMO, significant differences get obvious. A major focus is on the evaluation of the performance of the integrity algorithms. Also concept drivers are discussed

Waveform design and processing techniques in OFDM radar

Includes bibliographical referencesWith the advent of powerful digital hardware, software defined radio and radar have become an active area of research and development. This in turn has given rise to many new research directions in the radar community, which were previously not comprehensible. One such direction is the recently investigated OFDM radar, which uses OFDM waveforms instead of the classic linear frequency mod- ulated waveforms. Being a wideband signal, the OFDM symbol offers spectral efficiency along with improved range resolution, two enticing characteristics for radar. Historically a communication signal, OFDM is a special form of multi- carrier modulation, where a single data stream is transmitted over a number of lower rate carriers. The information is conveyed via sets of complex phase codes modulating the phase of the carriers. At the receiver, a demodulation stage estimates the transmitted phase codes and the information in the form of binary words is finally retrieved. In radar, the primary goal is to detect the presence of targets and possibly estimate some of their features through measurable quantities, e.g. range, Doppler, etc. Yet, being a young waveform in radar, more understanding is required to turn it into a standard radar waveform. Our goal, with this thesis, is to mature our comprehension of OFDM for radar and contribute to the realm of OFDM radar. First, we develop two processing alternatives for the case of a train of wideband OFDM pulses. In this, our first so-called time domain solution consists in applying a matched filter to compress the received echoes in the fast time before applying a fast Fourier transform in the slow time to form the range Doppler image. We motivate this approach after demonstrating that short OFDM pulses are Doppler tolerant. The merit of this approach is to conserve existing radar architectures while operating OFDM waveforms. The second so-called frequency domain solution that we propose is inspired from communication engineering research since the received echoes are tumbled in the frequency domain. After several manipulations, the range Doppler image is formed. We explain how this approach allows to retrieve an estimate of the unambiguous radial velocity, and propose two methods for that. The first method requires the use of identical sequence (IS) for the phase codes and is, as such, binding, while the other method works irrespective of the phase codes. Like the previous technique, this processing solution accommodates high Doppler frequencies and the degradation in the range Doppler image is negligible provided that the spacing between consecutive subcarriers is sufficient. Unfortunately, it suffers from the issue of intersymbol interference (ISI). After observing that both solutions provide the same processing gain, we clarify the constraints that shall apply to the OFDM signals in either of these solutions. In the first solution, special care has been employed to design OFDM pulses with low peak-to-mean power ratio (PMEPR) and low sidelobe level in the autocorrelation function. In the second solution, on the other hand, only the constraint of low PMEPR applies since the sidelobes of the scatterer characteristic function in the range Doppler image are Fourier based. Then, we develop a waveform-processing concept for OFDM based stepped frequency waveforms. This approach is intended for high resolution radar with improved low probability of detection (LPD) characteristics, as we propose to employ a frequency hopping scheme from pulse to pulse other than the conventional linear one. In the same way we treated our second alternative earlier, we derive our high range resolution processing in matrix terms and assess the degradation caused by high Doppler on the range profile. We propose using a bank of range migration filters to retrieve the radial velocity of the scatterer and realise that the issue of classical ambiguity in Doppler can be alleviated provided that the relative bandwidth, i.e. the total bandwidth covered by the train of pulses divided by the carrier frequency, is chosen carefully. After discussing a deterministic artefact caused by frequency hopping and the means to reduce it at the waveform design or processing level, we discuss the benefit offered by our concept in comparison to other standard wideband methods and emphasize on its LPD characteristics at the waveform and pulse level. In our subsequent analysis, we investigate genetic algorithm (GA) based techniques to finetune OFDM pulses in terms of radar requirements viz., low PMEPR only or low PMEPR and low sidelobe level together, as evoked earlier. To motivate the use of genetic algorithms, we establish that existing techniques are not exible in terms of the OFDM structure (the assumption that all carriers are present is always made). Besides, the use of advanced objective functions suited to particular configurations (e.g. low sidelobe level in proximity of the main autocorrelation peak) as well as the combination of multiple objective functions can be done elegantly with GA based techniques. To justify that solely phase codes are used for our optimisation(s), we stress that the weights applied to the carriers composing the OFDM signal can be spared to cope with other radar related challenges and we give an example with a case of enhanced detection. Next, we develop a technique where we exploit the instantaneous wideband trans- mission to characterise the type of the canonical scatterers that compose a target. Our idea is based on the well-established results from the geometrical theory of diffraction (GTD), where the scattered energy varies with frequency. We present the problem related to ISI, stress the need to design the transmitted pulse so as to reduce this risk and suggest having prior knowledge over the scatterers relative positions. Subsequently, we develop a performance analysis to assess the behaviour of our technique in the presence of additive white Gaussian noise (AWGN). Then, we demonstrate the merit of integrating over several pulses to improve the characterisation rate of the scatterers. Because the scattering centres of a target resonate variably at different frequencies, frequency diversity is another enticing property which can be used to enhance the sensing performance. Here, we exploit this element of diversity to improve the classification function. We develop a technique where the classification takes place at the waveform design when few targets are present. In our case study, we have three simple targets. Each is composed of perfectly electrically conducting spheres for which we have exact models of the scattered field. We develop a GA based search to find optimal OFDM symbols that best discriminate one target against any other. Thereafter, the OFDM pulse used for probing the target in the scene is constructed by stacking the resulting symbols in time. After discussing the problem of finding the best frequency window to sense the target, we develop a performance analysis where our figure of merit is the overall probability of correct classification. Again, we prove the merit of integrating over several pulses to reach classification rates above 95%. In turn, this study opens onto new challenges in the realm of OFDM radar. We leave for future research the demonstration of the practical applicability of our novel concepts and mention manifold research axes, viz., a signal processing axis that would include methods to cope with inter symbol interference, range migration issues, methods to raise the ambiguity in Doppler when several echoes from distinct scatterers overlap in the case of our frequency domain processing solutions; an algorithmic axis that would concern the heuristic techniques employed in the design of our OFDM pulses. We foresee that further tuning might help speeding up our GA based algorithms and we expect that constrained multi- objective optimisation GA (MOO-GA) based techniques shall benefit the OFDM pulse design problem in radar. A system design axis that would account for the hardware components' behaviours, when possible, directly at the waveform design stage and would include implementation of the OFDM radar system