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International audience; The growing need for localization has created an array of alternative approaches to GNSS, based on Wi-Fi, Bluetooth, Ultra-Wideband, etc. Long Range Wide Area Network (LoRaWAN) is one such technology that has garnered tremendous attention due to its low power and long-range capabilities. Many attempts to achieve localization using LoRaWAN have been made till now, based on a variety of techniques such as Angle of Arrival (AoA), Time Difference of Arrival (TDoA), Received Signal Strength Index (RSSI). In this paper, we present a novel, standalone localization approach by developing a collaborative, TDoA-based methodology using LoRaWAN. The server determines the target node location by means of TDoA measurements from the target node to the gateways. The introduction of an additional stationary node allows the synchronization of the gateways without utilizing GNSS, either inbuilt or external. The cooperation between target node, synchronization node and server, is the innovative feature which makes this approach attractive for GNSS-free localization. Further, we explore the effects of timing resolution, time-on-air, and duty cycle constraints on the localization error. Finally, the distribution of error in a triangle of gateways situated approximately 8.6 kilometers apart is simulated in ideal Line of Sight (LoS) conditions, showing the maximum error to be around 23 meters.

International audience; Stand-alone GNSS positioning is challenged to meet the applications’ demanded accuracy and reliability in urban environments. In order to obtain an optimal and reliable position estimate using GNSS, it is necessary to have an accurate model of the pseudorange and pseudorange-rate error terms’ distributions. Previous research contributions addressed the statistical characterization of the pseudorange measurements’ multipath and noise error components in an urban environment by proposing a methodology to isolate the multipath error and the thermal noise component from the pseudorange measurement. The proposed methodology was adapted to include dual constellation measurements in the L1 band, GPS L1 C/A and Galileo E1 OS signal measurements. Moreover, a reliable classification of the signal reception conditions, Lion-of-Sight (LOS) and Non LOS (NLOS), was addressed. The work conducted in this article consists first in further adaptingthe methodology proposed in the previous work to the pseduorange rate (Doppler frequency) measurement and second, in inspecting the benefits of the derived pseudorange and pseudorange-rate measurements’ error component characterizations when applied on the PVT navigation solution. Finally, the analysis of the PVT estimation performance based on satellite measurement selection principle is presented.

International audience; An increasing number of new applications require an accurate positioning even in urban environments; however, in such environments, especially in urban canyons, GNSS positioning is challenged to meet the applications’ demanded accuracy and reliability. In fact, in order to obtain an optimal and reliable position estimate using GNSS, it is necessary to have an accurate model of the pseudorange and pseudorange rate error terms’ distributions. This work focuses thus its attention on the statistical characterization of the pseudorange measurements’ multipath error component by proposing a methodology to obtain such characterization: isolation of the multipath error component from the use of a reference station, to eliminate ionospheric error terms, and from a filtering process, to eliminate the receiver clock bias. The proposed methodology has been adapted to include dual constellation measurementsin the L1 band, GPS L1 C/A and Galileo E1 OS signal measurements, as an evolution to the previous method presented by the authors in [1]. Moreover, in order to obtain a reliable classification of the signal reception conditions, Lion-of-Sight (LOS) and Non LOS (NLOS), which will allow a finer characterization of the multipath error component, this work introduces the use of an upward looking camera with a wide Field-of-View (FOV), a fisheye camera: the satellites are projected on the pictures taken by the camera allowing to observe which satellites are obstructed by the scenario obstacles (buildings, trees, etc). The proposed methodology is applied to real measurements obtained from a data campaign conducted in Toulouse urban area with a U-Blox receiver with its antenna and a fisheye camera mounted on the roof of a car. The pseudorange measurements are classified by the signal ??/??0 and by the elevation angle between the satellites and the receiver, which are common signal characteristics influencing the multipath error component impact on the pseudorange measurement. Additionally, the performance assessment of each parameter in terms of signal reception conditions classification between LOS and NLOS has determined the upper hand of the ??/??0 parameter.

International audience

International audience; In global navigation satellite system (GNSS) receivers, the first signal processing stage is the acquisition, which consists of detecting the received GNSS signals and determining the associated code delay and Doppler frequency by means of correlations with a code and carrier replicas. These codes, as part of the GNSS signal, were chosen to have very good correlation properties without considering the effect of a potential received Doppler frequency. In the literature, it is often admitted that the maximum GPS L1 C/A code cross-correlation is about -24 dB. We show that this maximum can be as high as -19.2 dB when considering a Doppler frequency in a typical range of [-5, 5] kHz. We also show the positive impact of the coherent integration time on the cross-correlation and that even a satellite with Doppler outside the frequency search space of a receiver impacts the cross correlation. In addition, the expression of the correlation is often provided in the continuous time domain, while its implementation is typically made in the discrete domain. It is then legitimate to ask the validity of this approximation. Therefore, the purpose of this research is twofold: First, we discuss typical approximations and evaluate their regions of validity, and second, we provide characteristic values such as maximums and quantiles of the auto- and cross correlation of the GPS L1 C/A and Galileo E1 OS codes in the presence of Doppler, for frequency ranges up to 50 kHz and for different integration times.

International audience; In global navigation satellite system (GNSS) receivers, the acquisition process is the first stage of the signal processing module. It consists of assessing the presence of GNSS signals and providing a rough estimation of the incoming signal parameters: the Doppler frequency and the code delay. However, the presence of bit sign transitions affects receiver performance in signal acquisition detection. This article focuses on the bit transition and its impact on the acquisition performance by providing a general mathematical study and an illustration for two GNSS signals: the global positioning system legacy civil signal (GPS L1 C/A) and Galileo E1 open service (OS). This study is applicable to a terrestrial user in a constraint environment. Furthermore, the presented results are mathematical models of the probability of detection in the presence of bit sign transitions (only one potential bit sign transition per integration interval), and potential uncertainties on the Doppler frequency and code delay. These do not result from empirical acquisition of real signals.

Since the development of the GPS, the global navigation satellite systems (GNSS) have been widely diversified: maintenance, modernization and deployment of new systems such as the European Galileo. In addition, the number of GNSS signals applications, based on the use of GNSS signals, is increasing. To meet these new challenges and requirements, GNSS receivers are constantly evolving. A new trend is the development of software receiver which processes the GNSS signal in a software way unlike hardware receiver, equipping our vehicles, smartphones, for example. This thesis is part of a common project between a laboratory and a company, consisting of the development of a software receiver tracking GPS L1 C/A and Galileo E1 OS. The more specific aim of the thesis is to study the acquisition, first signal processing which provides a rough estimation of the incoming signal parameters. This work focuses particularly the low power signals, an acquisition threshold is set at 27 dB-Hz considered as a representative of urban or degraded environments. It is important to note that the success of the acquisition of such signals should be at least 9 times out of 10, without any aid or knowledge of almanac or ephemeris. Initially, a solid theoretical study of the acquisition performance and sources of degradation is conducted. One of them is the bit transitions due to the presence of the navigation message and the secondary code on pilot component of the new signals. It is thus highlighted the need to use a Transition-Insensitive acquisition method. Secondly, an innovative method, the Double-Block Zero-Padding Transition- Insensitive (DBZPTI) is developed to permit efficiently the acquisition of Galileo E1 OS signal. It takes part in the development of the global acquisition strategy, which should provide an estimate of the Doppler frequency and code delay, fine and reliable, for a satisfactory signal tracking., Depuis le développement du GPS, les systèmes de navigation par satellites (GNSS) se sont largement diversifiés : maintenance, modernisation et déploiement de nouveaux systèmes, comme l’européen Galileo. De plus, le nombre d’applications basées sur l’utilisation de signaux GNSS ne cesse d’augmenter. Pour répondre à ces nouveaux challenges et besoins, les récepteurs GNSS ne cessent d’évoluer. Un nouvel axe est le développement du récepteur logiciel qui présente la particularité d’un traitement logiciel des signaux contrairement au récepteur matériel, équipant nos véhicules, smartphones par exemple. Cette thèse de doctorat s’inscrit dans le projet commun d’un laboratoire et d’une PME consistant au développement d’un récepteur logiciel poursuivant les signaux GPS L1 C/A et Galileo E1 OS. L’objectif plus spécifique de la thèse est d’étudier l’acquisition, première étape du traitement du signal GNSS qui doit fournir une estimation grossière des paramètres du signal entrant. Ce travail vise particulièrement les signaux à faible puissance, un seuil d’acquisition est fixé à 27 dB-Hz pouvant s’apparenter à l’acquisition en milieu urbain ou dégradé. Il est important de noter qu’une des contraintes est de réussir l’acquisition de tels signaux au moins 9 fois sur 10, sans aucune aide extérieure ou connaissance des almanachs ou éphémérides. Dans un premier temps, une solide étude théorique portant sur les performances de l’acquisition et les sources de dégradations est menée. Parmi elles, peuvent être citées, les transitions de bits dues à la présence du message de navigation et du code secondaire sur la voie pilote des nouveaux signaux. Est ainsi mis en lumière la nécessité d’avoir recours à une méthode d’acquisition insensible aux inversions de signe du message de navigation. Dans un deuxième temps, une méthode innovante, le Double-Block Zero-Padding Transition-Insensitive (DBZPTI), est donc développée pour permettre l’acquisition du signal Galileo E1 OS de façon efficiente. Elle prend part au développement de la stratégie globale d’acquisition dont l’objectif est d’avoir en sortie une estimation de la fréquence Doppler et du retard de code du signal entrant, assez fine et fiable pour une satisfaisante poursuite du signal

International audience; This article focuses on the analysis of several FLL schemes for different GNSS signals in order to success the acquisition-to-tracking transition at low received C/N0. In a first part, a discussion on different FLL discriminators is lead by comparing frequency error response, linear region, data bit transition insensitivity... Then, based on Monte-Carlo simulations, for each signal, the choices of FLL scheme parameters as the discriminator, loop bandwidth, correlator outputs combination technique are studied in order to highlight the FFL schemes which provide the best performance in terms of probability to get locked.

International audience; This article focuses on the bit sign transition and its impact on the acquisition performance in terms of probability of detection. To do so, a theoretical study on the correlation process considering bit sign transition is done leading to the expression of the probability of detection, expressed in function of the bit transition location. Based on this, Monte-Carlo simulations were run to determine the acquisition performance degradations in terms of sensitivity losses and probability of detection for several GNSS civil signals. This allows determining the optimal acquisition parameters when bit sign transitions are considered during the acquisition process.

International audience; The number of transmitted GNSS signals has increased significantly with Galileo, Compass and QZSS constellations' ongoing deployment, GLONASS constellation maintenance and the introduction of new GPS signals. The choice of new properties and features integrated in the corresponding new signal was driven by the need for compatibility and interoperability between signals and to provide better performance to the user. However, some aspects, which can be ignored with the old signals, should be discussed for these signals. For example, the code Doppler, caused by the satellite motion on the code frequency can be important for BOC modulation signals or signals with high code frequency. This plays a major impact on the performance of the acquisition and the tracking of GNSS signals and in particular weak signals. The acquisition is the first signal processing step in a GNSS receiver. It consists in giving a rough estimation of the incoming signals parameters (Doppler frequency and code delay). In the literature, many acquisition performance studies are derived assuming that there is no code Doppler on the received signal. However, the code Doppler leads to a change in the period of the spreading code that can lead to: * A drift between the received and local PRN codes even if they were synchronized at the beginning of the correlation process (correlation loss) * A possible drift of the correct acquisition bin over time. This can create missed acquisitions A positive Doppler shift causes the spreading code duration to shrink while a negative Doppler shift causes the spreading code duration to expand with respect to a reference that would not consider code Doppler. For example, for an incoming Doppler frequency of 10 kHz, for the GPS L1 C/A signal, it translates into a drift of 1 chip in 154 ms. For the same Doppler frequency, it translates into a drift of 1 chip every 12 ms for GPS L5. This result can cause a serious problem for acquisition of weak signals because long correlations (100, 200, 300 ms or more) can be required. The presence of a strong uncompensated code Doppler could thus create acquisition performance degradations because the autocorrelation function is degraded: the maximum amplitude is lower than the desired one and the correct code delay keeps drifted during the acquisition process. Besides, it is interesting to understand that for the same dwell time spent analyzing a specific acquisition bin, the impact on the acquisition depends on the acquisition technique and the choice of the coherent integration duration or the number of non-coherent summations. The detailed analysis of these effects is the topic of this paper. It encompasses: * An analytically analysis of the effect of code Doppler on the acquisition process and performance as a function of the signal characteristics and the acquisition parameters, highlighting the need to take this effect into account * Provide some techniques permitting to reduce the performance loss This paper specifically targets the new GNSS signals (Galileo E1 OS and GPS L5) which have different signal properties in terms of: code frequency (1.023 MHz and 10.23 MHz), modulation (BPSK, CBOC), carrier frequency (L1, L5)... The paper organization is the following: * The first section proposes a mathematical model of the correlation between the received signal (with Doppler shift) and the locally generated signal (assumed with no Doppler shift). The analysis of the mathematical model allows understanding the degradations in terms of acquisition performance. * The second section gives a specific study for several GNSS signals (GPS L1 C/A, Galileo E1 OS, GPS L5). This highlights practical values for the acquisition of these signals in terms of degradations and validity of the assumptions. For example, it is senseless to acquire non-coherently during 100 ms the GPS L5 signal because there are at least 8 chips shift. * To tackle this problem, several methods have been proposed in the literature and are reminded in the last section. For each method, a study of the solution against the code Doppler shift is done allowing understanding in which cases it is the most appropriate.

International audience; The low power and spread spectrum nature of GNSS signals make their detection and acquisition a key, but challenging aspect of receiver processing designs. A team of researchers investigated the performance of four new GNSS signals and the legacy GPS L1 C/A code, comparing their probability of detection at a specific level of received signal strength. Factors of particular interest included the bit sign transition, acquisition bin size, and uncompensated code Doppler.

International audience; The number of transmitted GNSS (Global Navigation Satellite Systems) signals has increased significantly with Galileo, Compass and QZSS constellations' ongoing deployment, GLONASS constellation maintenance and the introduction of new GPS signals. All the future GNSS civil signals are composed of two components: one being the pilot component which contains known secondary codes. In order to avoid fully exploit secondary code properties and the bit transition problem on the pilot component allowing long coherent integration for a better tracking, it is necessary to acquire the secondary code. This paper presents a mathematical model that determines the probability of correct acquisition of the secondary code once the spreading code has been acquired. The second point of the paper is the presentation of experimental results which provides some interesting results in terms of secondary code acquisition. The first one is the probability of secondary code acquisition when it is only read once. The second one corresponds to the required time to acquire the secondary code with a high probability for a given C/N0. These results, provided for four GNSS signals (GPS L1C, GPS L5, Galileo E1 OS and Galileo E5a/b) permit to compare the U.S GNSS with the European GNSS for several L band frequencies (L1 and L5).

International audience; Acquisition is the first process of a GNSS receiver and is also the process which needs the most resources. Moreover, acquiring of weak Galileo E1 OS signals is a real challenge due to the presence of frequent (potentially at each spreading code period) bit transitions (data bit on the data component and secondary code chip on the pilot component). After a study of the effects of data modulation, two acquisition strategies, one bit transition insensitive and the other not, are developed and brought face to face on performance criteria such as: execution time, probability of detection, probability of false alarm...

International audience; The deployment of the European global navigation satellite system, Galileo, with its specific signal structure, encourages the development of new signal processing methods at the receiver level. In particular, the structure and characteristics of the Galileo E1 OS signal make its acquisition not easy and require optimization to reduce computation time and complexity. The present article proposes a novel Galileo E1 OS signal acquisition method. The background technique to do so is taken from an existing GPS L1 signal acquisition method, the Double Block Zero Padding (DBZP). This paper provides the detailed description (including the mathematical model) of the DBZP and shows its theoretical performance in terms of probability of detection and number of operations. Based on this analysis, the paper proposes an improvement of the DBZP for signals, like Galileo E1 OS, that include frequent bit transitions. This technique is compared with a reference acquisition method, and shows very good and interesting results demonstrating the potential of this innovative Galileo E1 OS signal acquisition method.