Analysis of non ambiguous BOC signal acquisition performance Acquisition

The Binary Offset Carrier planned for future GNSS signal, including several GALILEO Signals as well as GPS M-code, presents a high degree of spectral separation from conventional signals. It also greatly improves positioning accuracy and enhances multipath rejection. However, with such a modulation, the acquisition process is made more complex. Specific techniques must be employed in order to avoid unacceptable errors. This paper assesses the performance of three method allowing to acquire and track BOC signal unambiguously : The Bump-jumping technique, The "BPSK-like" technique and the subcarrier Phase cancellation technique

Unambiguous Tracking Method Based on Combined Correlation Functions for sine/cosine-BOC CBOC and AltBOC Modulated Signals

Unambiguous tracking for Binary Offset Carrier (BOC) modulated signals is an important requirement of modern Global Navigation Satellite System (GNSS) receivers. An unambiguous tracking method based on combined correlation functions for even/odd order sine/cosine-BOC, Composite BOC(CBOC) and Alternate BOC(AltBOC) modulated signals is proposed. Firstly, a unitary mathematical formulation for all kinds of BOC modulations is introduced. Then an unambiguous tracking method is proposed based on the formulation and the idea of pseudo correlation function (PCF) method. Finally, the tracking loop based on the proposed method is designed. Simulation results indicate that the proposed method can remove side peaks while retaining the sharp main peak for all kinds of BOC modulations. The tracking performance for AltBOC is examined and the results show that the proposed method has better performance in thermal noise and long-delay multipath mitigation than the traditional unambiguous tracking methods

Galileo Signals Acquisition Using Enhanced Subcarrier Elimination Conversion and Faster Processing

To solve multipath and to enhance the localisation accuracy in a harsh environment, BOC modulation has been adopted in modern GNSS transmission, such as GPS-M-code and Galileo-OS-code signals. The designers of the BOC technique have pointed out that the correlation function becomes ambiguous when the received signal is correlated with the reference BOC signal at code phase resolutions of 0.5 Chip. This has motivated many contributions to resolving this ambiguity, for example, by processing each side of the BOC lobes as a BPSK signal. Our literature survey concluded that solutions claiming to have mitigated this ambiguity actually have resulted in a more complex receiver implementation. The Enhanced Subcarrier Elimination (ESCE) method detailed in this paper proposes combining the two side lobes into a single lobe centered at the main frequency, thus gaining 2dB more signal power as well as reducing the correlation requirements (signal’s mixing and transforming operations) to the half; i.e. accelerating the acquisition process. HaLo-430 platform generated signals used for testing the MATLAB model of ESCE proves that we outperform three of the most used unambiguous methods

Acquisition Performance of Galileo E5a Signal

The introduction of new modulations on the global navigation satellite systems brings potential improvements for ground positioning. Clever receiver designs taking advantage of the characteristics of the new signals will be able to achieve better accuracy, higher sensitivity, improved multipath mitigation and tracking robustness. In this context, this paper focuses on the Galileo E5a signal and study different acquisition architectures that can be applied on this signal. Their performances are discussed in terms of detection sensitivity and by a theoretical characterization of the false alarm and detection probabilities. The theoretical results are validated by measurements using a Spirent constellation simulator, a Fraunhofer triple band frontend and a non real time software receiver

Efficient Delay Tracking Methods with Sidelobes Cancellation for BOC-Modulated Signals

In positioning applications, where the line of sight (LOS) is needed with high accuracy, the accurate delay estimation is an important task. The new satellite-based positioning systems, such as Galileo and modernized GPS, will use a new modulation type, that is, the binary offset carrier (BOC) modulation. This type of modulation creates multiple peaks (ambiguities) in the envelope of the correlation function, and thus triggers new challenges in the delay-frequency acquisition and tracking stages. Moreover, the properties of BOC-modulated signals are yet not well studied in the context of fading multipath channels. In this paper, sidelobe cancellation techniques are applied with various tracking structures in order to remove or diminish the side peaks, while keeping a sharp and narrow main lobe, thus allowing a better tracking. Five sidelobe cancellation methods (SCM) are proposed and studied: SCM with interference cancellation (IC), SCM with narrow correlator, SCM with high-resolution correlator (HRC), SCM with differential correlation (DC), and SCM with threshold. Compared to other delay tracking methods, the proposed SCM approaches have the advantage that they can be applied to any sine or cosine BOC-modulated signal. We analyze the performances of various tracking techniques in the presence of fading multipath channels and we compare them with other methods existing in the literature. The SCM approaches bring improvement also in scenarios with closely-spaced paths, which are the most problematic from the accurate positioning point of view.</p

A METHOD OF SIDE-PEAK MITIGATION APPLIED TO BINARY OFFSET CARRIER MODULATED GNSS SIGNALS TRACKING APPLIED IN GNSS RECEIVERS

ABSTRACT In this study, a new method of signal tracking technique in Global Navigation Satellite System (GNSS) is proposed. It is based on a combination of the autocorrelation function (ACF) with another cross correlation function in order to eliminate or reduce the power of the side peaks in ACF of Binary Offset Carrier (BOC) modulated signals. These types of modulated signals are adopted by both GNSSs like the modernized Global Positioning System (GPS) and Galileo. Moreover, this method still keep the sharp of main peak of ACF in order to maintain the advantage of BOC(n,n) signals in code tracking and multipath mitigation. In the proposed method, the output of the discriminator in delay tracking loop has no false lock point. The performance of multipath mitigation of the proposed method is better than Narrow Correlator method. The good performance of the proposed scheme in multipath mitigation has been tested using simulation results

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

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

Physical Layer Challenges and Solutions in Seamless Positioning via GNSS, Cellular and WLAN Systems

As different positioning applications have started to be a common part of our lives, positioning methods have to cope with increasing demands. Global Navigation Satellite System (GNSS) can offer accurate location estimate outdoors, but achieving seamless large-scale indoor localization remains still a challenging topic. The requirements for simple and cost-effective indoor positioning system have led to the utilization of wireless systems already available, such as cellular networks and Wireless Local Area Network (WLAN). One common approach with the advantage of a large-scale standard-independent implementation is based on the Received Signal Strength (RSS) measurements.This thesis addresses both GNSS and non-GNSS positioning algorithms and aims to offer a compact overview of the wireless localization issues, concentrating on some of the major challenges and solutions in GNSS and RSS-based positioning. The GNSS-related challenges addressed here refer to the channel modelling part for indoor GNSS and to the acquisition part in High Sensitivity (HS)-GNSS. The RSSrelated challenges addressed here refer to the data collection and calibration, channel effects such as path loss and shadowing, and three-dimensional indoor positioning estimation.This thesis presents a measurement-based analysis of indoor channel models for GNSS signals and of path loss and shadowing models for WLAN and cellular signals. Novel low-complexity acquisition algorithms are developed for HS-GNSS. In addition, a solution to transmitter topology evaluation and database reduction solutions for large-scale mobile-centric RSS-based positioning are proposed. This thesis also studies the effect of RSS offsets in the calibration phase and various floor estimators, and offers an extensive comparison of different RSS-based positioning algorithms

Advanced GPS signal processing techniques for LBS services

Par le passé, il était indispensable, pour le bon fonctionnement du GPS (Global Positioning System), que le signal soit en vision directe entre le satellite et le récepteur, et les signaux faibles n'étaient pas exploitables. Mais l'extension du GPS aux services LBS (Location Based Services) et à d'autres applications de navigation a changé ce paradigme. Par conséquent, on prévoit une augmentation considérable de techniques de localisation de plus en plus performantes, surtout dans des environnements du type indoor ou urbain. Les exigences de la localisation dans ce type d'environnements posent un véritable défi pour la conception des récepteurs GPS. Le but de la thèse est d'optimiser les techniques existantes de traitement du signal GPS pour la localisation dans des milieux contraints, dans le cadre de l'AGPS (Assisted GPS). Ce système suppose que le récepteur GPS est connecté ou introduit dans un téléphone portable. Ce genre de couplage permet de transférer au récepteur GPS des données d'assistance via le réseau GSM (Global System for Mobile communications). Ces données fournissent au récepteur GPS la liste des satellites visibles, mais aussi des valeurs estimées de leur Doppler et leur retard de code, réduisant ainsi la fenêtre de recherche de ces paramètres. Les travaux de la thèse consistent à explorer différentes techniques d'acquisition du signal GPS pour réduire le temps d'acquisition nécessaire ou TTFF (Time To First Fix), sans affecter la sensibilité du récepteur GPS. Ceci est réalisé après une étude du canal GPS radio. L'étude débute par une revue du GPS et de la structure du signal utilisé dans ce système. Le processus d'acquisition est ensuite décrit en détails: l'acquisition classique est décrite en premier pour mettre en évidence par la suite l'effet du milieu de propagation sur cette étape du traitement du signal. A cet effet, les milieux contraignants (Indoors et Urbains) seront modélisés et analysés. Cette analyse permettra de mettre en évidence les problèmes subits par les ondes radio se propageant dans ce type d'environnements. On notera que le canal urbain a été analysé en utilisant un modèle déjà existant élaboré par Alexander Steingass et Andreas Lehner du DLR (Centre Aérospatial Allemand) [Steingass et al., 2005]. D'autre part, un modèle statistique du canal indoor a été développé par l'ESA (European Space Agency) dans le cadre du projet intitulé “Navigation signal measurement campaign for critical environments” et présenté dans [Pérez-Fontán et al, 2004]. Mais ce modèle considère un canal statistique invariable dans le temps. Pour cela nous avons développé un modèle Indoor qui envisage plutôt un canal variant avec le temps, en prenant en compte les variations temporelles de certains paramètres du canal, comme le retard et la phase de la fonction de transfert. Les valeurs initiales de ces paramètres utilisés dans notre modèle sont toutefois basées sur les distributions statistiques fournies par le modèle de l'ESA. L'étude des canaux de propagation porte surtout sur les multitrajets, les inter-corrélations, et le masquage du signal. Les multitrajets sont particulièrement gênants dans le cas de milieux urbains, les intercorrélations et le masquage sont par contre plus gênants dans les milieux indoors. Ces phénomènes peuvent impliquer des erreurs dans la position calculée par le récepteur. Pour y remédier, une des solutions est d'augmenter la durée d'observation du signal pour améliorer le rapport signal sur bruit. Mais ceci conduit à des temps d'acquisition beaucoup plus longs. Par conséquent, la qualité commerciale du récepteur est mise en cause vues les contraintes sur le TTFF nécessaires pour fournir une première solution. Ces contraintes en termes de temps ii de traitements sont aussi importantes que les contraintes en termes de précision pour les utilisateurs du GPS. Mais ces deux contraintes vont en général l'une à l'encontre de l'autre. Par conséquent, une solution idéale consistera à réduire le temps d'acquisition sans pour autant affecter la sensibilité du récepteur. Ainsi, dans la suite de l'exposé des méthodes avancées de traitement du signal dans la phase d'acquisition seront présentées. La plupart de ces méthodes vise à réduire le temps total d'acquisition plutôt qu'à améliorer la sensibilité du récepteur: ceci permet de tolérer) le traitement de signaux plus longs - afin d'améliorer la sensibilité - sans augmenter la durée globale de traitement. Ces méthodes seront tout d'abord caractérisées en évaluant les avantages et les inconvénients de chacune d'elles. Une évaluation de performances de ces algorithmes, utilisant des signaux générés avec un Spirent STR4500 sera conduite dans une étape finale de cette étude. ABSTRACT : In the past, in order for GPS (Global Positioning System) to work accurately, the presence of an unobstructed LOS (Line-Of- ight) signal was necessary. Weak signals were not suitable for use because they may have large associated noise and other errors. The expansion of GPS to LBS (Location- ased Services) and other navigation applications all over the world, such as the E-911 and the E-112 mandates in the United States and Europe respectively, changed the paradigm. Consequently a dramatic increase in the need for more and more performant positioning techniques is expected, especially in urban and indoor environments. These rising localization requirements pose a particularly difficult challenge for GPS receivers design. The thesis objective is to evaluate and enhance existing GPS signal acquisition techniques for positioning goals in harsh environments, in the context of AGPS (Assisted GPS). The AGPS system assumes that the GPS receiver is connected to or introduced in a mobile phone. This allows for the transfer of AD (Assistance Data) to the GPS receiver via the GSM (Global System for Mobile communications) cellular network. Amongst others, the AD provides the GPS receiver with the list of visible satellites and estimates of their Dopplers and code delays, thus reducing the search window of these parameters. This work consists in exploring different GPS signal acquisition to reduce the acquisition time or TTFF (Time To First Fix), without affecting the receiver sensitivity. This is done after a prior study of the GPS radio channel. The study starts out with a revue of the GPS system and the GPS transmitted and received signal structure. The acquisition process is then described in details: the classical acquisition is first described in order to proceed afterwards with the impact of the propagation environment on this stage of the signal processing. For this purpose, harsh environments (urban and indoor) are modelled and analysed. This analysis enables to study the problems which encounter the radio frequency signal propagation through such environments. Note that the urban channel is studied using an existing statistical model developed by Alexander Steingass and Andreas Lehner at the DLR (German Aerospace Center) [Steingass et al., 2005]. On the other hand, an indoor channel model was developed by the ESA (European Space Agency) in the frame of a project entitled “Navigation signal measurement campaign for critical environments” and presented in [Pérez-Fontán et al, 2004]. But this model considers a time invariant statistical channel. Consequently, we developed an Indoor model which rather considers a time variant channel, by taking into account temporal variations of some channel parameters, like the transfer function delay and phase. The initial values are however based on the statistical distributions provided by the ESA model. The channels are analysed is terms of multipaths, cross-correlations and signal masking. The multipaths replicas are particularly disturbing in urban environments while the cross-correlations and masking effects are more disturbing in indoor environments. These phenomena may induce errors in the final solution calculated by the receiver. In order to avoid this error, one solution consists in increasing the signal observation duration in order to enhance the signal to noise ratio. But this generally implies longer acquisition time, thus affecting the receiver iv performance, commercially speaking. Indeed, the time requirements are as important as sensitivity requirements for GPS users. However, these two requirements are not generally compatible with each other. Consequently, an ideal solution consists in reducing the acquisition time without greatly affecting the receiver sensitivity. Accordingly, such advanced methods for acquisition signal processing are described next. Most of these methods aim at reducing the total acquisition time, rather than enhancing the receiver sensitivity. This means however that longer signal blocks can be processed (thus enhancing sensitivity) without affecting the global processing duration. At first, each of these methods is evaluated through the description of its advantages and drawbacks. A performance evaluation of these algorithms, using signals generated with a Spirent STR4500, ensues as a final step of this stud