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

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

Master of Science Thesi

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

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

Simulink-Based Acquisition Unit for Galileo E1 CBOC Modulated Signals

At the moment, Global Positioning System (GPS) is the only positioning system with global coverage. Currently, there are efforts to modernize GPS with the aim of improving its performance. Meanwhile, Europe is developing its own satellite positioning system, GALILEO. In order to provide interoperability with GPS and globally available navigational systems, new modulation techniques have been introduced. Multiplexed Binary-Offset-Carrier (MBOC) modulated signals are the main candidates for the future Galileo Open Services (OS) and modernized GPS L1C signals. Spreading waveforms corresponding to pilot and data components can be formed in a number of ways, including Composite Binary Offset Carrier (CBOC) and Time-Multiplexed Binary Offset Carrier (TMBOC). CBOC is considered here because CBOC has been selected for Galileo E1 OS signals in the most recent Galileo SIS-ICD of 2008. This new composition of E1 signal allows different techniques for acquiring the signal, i.e. data-only channel, pilot-only channel and joint data and pilot channel. The MBOC(6,1,1/11) power spectral density (PSD) has better performance than SinBOC(1,1) power spectral density because it is a mixture of BOC(1,1) spectrum and BOC(6,1) spectrum. MBOC modulation schemes also bring new challenges due to additional side lobes in the envelope of the Autocorrelation Function (ACF) compared with the traditional BPSK modulation used in the basic GPS signals, which make the signal acquisition process challenging. In order to deal with the side lobes, the steps ‘Δtbin’ for searching the time-bin search space should be chosen carefully. The goal of this thesis has been to develop an acquisition unit based on CBOC reference code and analyze the performance of new acquisition unit in terms of acquisition performance because MBOC signal has better power spectral density compared to SinBOC(1,1) signal. A brief study about the choice of the time-bin step ‘Δtbin’ for searching the time-frequency window has been studied. Three different strategies have been used to acquire the signal and results are presented for each approach. The switching architecture model has introduced in the transmitter part which operates at dual frequency are also addressed under the scope of this thesis. The simulations are carried out with an own developed Simulink model for Galileo OS E1 signals, based on the most recent Galileo Signal-in-Space Interface Control Documentation. Conclusions are drawn with respect to the performance deterioration of a reference SinBOC(1,1) receiver compared to a reference CBOC receiver, and also with respect to different techniques used for acquiring the signal. Comparisons between the infinite bandwidth (theoretical case, typically used in literature) and a limited front-end filter bandwidth of 3 MHz (double-sided bandwidth) are also made. The choice of significant detection threshold in order to detect the signal properly and the performance degradation of the CBOC reference receiver when using switching architecture model in terms of detection probability are also presented. /Kir1

Millimeter Communication Propagation Program First quarterly report, 1 Nov. 1964 - 1 Feb. 1965

Effects of propagation medium on millimeter-wave space-earth communication

Multi-GNSS signals acquisition techniques for software defines receivers

Any commercially viable wireless solution onboard Smartphones should resolve the technical issues as well as preserving the limited resources available such as processing and battery. Therefore, integrating/combining the process of more than one function will free up much needed resources that can be then reused to enhance these functions further. This thesis details my innovative solutions that integrate multi-GNSS signals of specific civilian transmission from GPS, Galileo and GLONASS systems, and process them in a single RF front-end channel (detection and acquisition), ideal for GNSS software receiver onboard Smartphones. During the course of my PhD study, the focus of my work was on improving the reception and processing of localisation techniques based on signals from multi-satellite systems. I have published seven papers on new acquisition solutions for single and multi-GNSS signals based on the bandpass sampling and the compressive sensing techniques. These solutions, when applied onboard Smartphones, shall not only enhance the performance of the GNSS localisation solution but also reduce the implementation complexity (size and processing requirements) and thus save valuable processing time and battery energy. Firstly, my research has exploited the bandpass sampling technique, if being a good candidate for processing multi-signals at the same time. This portion of the work has produced three methods. The first method is designed to detect the GPS, Galileo and GLONASS-CDMA signals’ presence at an early stage before the acquisition process. This is to avoid wasting processing resources that are normally spent on chasing signals not present/non-existent. The second focuses on overcoming the ambiguity when acquiring Galileo-OS signal at a code phase resolution equal to 0.5 Chip or higher and this achieved by multiplying the received signal with the generated sub-carrier frequency. This new conversion saves doing a complete correlation chain processing when compared to conventionally used methods. The third method simplifies the joining implementation of the Galileo-OS data-pilot signal acquisition by constructing an orthogonal signal so as to acquire them in a single correlation chain, yet offering the same performance as using two correlation chains. Secondly, the compressive sensing technique is used to acquire multi-GNSS signals to achieve computation complexity reduction over correlator based methods, like Matched Filter, while still maintaining acquisition integrity. As a result of this research work, four implementation methods were produced to handle single or multi-GNSS signals. The first of these methods is designed to change dynamically the number and the size of the required channels/correlators according to the received GPS signal-power during the acquisition process. This adaptive solution offers better fix capability when the GPS receiver is located in a harsh signal environment, or it will save valuable processing/decoding time when the receiver is outdoors. The second method enhances the sensing process of the compressive sensing framework by using a deterministic orthogonal waveform such as the Hadamard matrix, which enabled us to sample the signal at the information band and reconstruct it without information loss. This experience in compressive sensing led the research to manage more reduction in terms of computational complexity and memory requirements in the third method that decomposes the dictionary matrix (representing a bank of correlators), saving more than 80% in signal acquisition process without loss of the integration between the code and frequency, irrespective of the signal strength. The decomposition is realised by removing the generated Doppler shifts from the dictionary matrix, while keeping the carrier frequency fixed for all these generated shifted satellites codes. This novelty of the decomposed dictionary implementation enabled other GNSS signals to be combined with the GPS signal without large overhead if the two, or more, signals are folded or down-converted to the same intermediate frequency. The fourth method is, therefore, implemented for the first time, a novel compressive sensing software receiver that acquires both GPS and Galileo signals simultaneously. The performance of this method is as good as that of a Matched Filter implementation performance. However, this implementation achieves a saving of 50% in processing time and produces a fine frequency for the Doppler shift at resolution within 10Hz. Our experimental results, based on actual RF captured signals and other simulation environments, have proven that all above seven implementation methods produced by this thesis retain much valuable battery energy and processing resources onboard Smartphones

Millimeter communication propagation program, volume I Final report, 1 Nov. 1964 - 1 Nov. 1965

Millimeter wave propagation experiment design for space communicatio

ATS-5 trilateration support

The development of an L-band trilateration network capable of locating the ATS-5 satellite, determining the satellite's orbital elements, and predicting the satellite position was investigated. An automatic tone-code ranging transponder was used to compare ranging measurements and communications reliability for the VHF and L-band. The L-band transponder network, analytical techniques, and the determination of the Kepler orbit parameters are described along with the calibration procedures, operation procedures, and verification of trilateration position