Feature article: High sensitivity acquisition of GNSS signals with secondary code on FPGAs

The modern global navigation satellite systems (GNSS) signals, such as the Global Positioning System (GPS) L5 and L1C, and Galileo E5 and E1, have brought several innovations: the introduction of a pilot channel that does not contain any data to allow very long coherent integrations; the introduction of a secondary code to offer better cross-correlations, to facilitate the synchronization with the data, and to help interference mitigation; the introduction of new modulations to reduce the impact of multipath; and the use of higher chipping rates to have better accuracy and interference mitigatio

A New FFT-Based Algorithm for Secondary Code Acquisition for Galileo Signals

The innovative spreading codes used to modulate the new Galileo signals creates new challenges for receiver designers. It is well known in GNSS systems that longer integration times are needed to obtain a better sensitivity. However, the existence of the new tiered code concept that consists of the presence of a secondary code on top of the primary code to modulate the RF signal puts a limitation on the coherent integration time for pilot channels similarly to the effect of data bit ambiguity in data channels. Within this context, this paper tackles this issue by introducing a new algorithm for wiping off the secondary code and increase the coherent integration time. The algorithm is based on the combination of serial and parallel searches. The search for the primary code phase is performed serially within one primary code length, and the secondary code phase is searched in parallel over the entire length of the secondary code. Furthermore, the proposed algorithm improves the Doppler offset estimation and reduces the overall acquisition time. © 2011 IEEE

Fast Fourier transforms on energy-efficient application-specific processors

Many of the current applications used in battery powered devices are from digital signal processing, telecommunication, and multimedia domains. Traditionally application-specific fixed-function circuits have been used in these designs in form of application-specific integrated circuits (ASIC) to reach the required performance and energy-efficiency. The complexity of these applications has increased over the years, thus the design complexity has increased even faster, which implies increased design time. At the same time, there are more and more standards to be supported, thus using optimised fixed-function implementations for all the functions in all the standards is impractical. The non-recurring engineering costs for integrated circuits have also increased significantly, so manufacturers can only afford fewer chip iterations. Although tailoring the circuit for a specific application provides the best performance and/or energy-efficiency, such approach lacks flexibility. E.g., if an error is found after the manufacturing, an expensive chip iteration is required. In addition, new functionalities cannot be added afterwards to support evolution of standards. Flexibility can be obtained with software based implementation technologies. Unfortunately, general-purpose processors do not provide the energy-efficiency of the fixed-function circuit designs. A useful trade-off between flexibility and performance is implementation based on application-specific processors (ASP) where programmability provides the flexibility and computational resources customised for the given application provide the performance. In this Thesis, application-specific processors are considered by using fast Fourier transform as the representative algorithm. The architectural template used here is transport triggered architecture (TTA) which resembles very long instruction word machines but the operand execution resembles data flow machines rather than traditional operand triggering. The developed TTA processors exploit inherent parallelism of the application. In addition, several characteristics of the application have been identified and those are exploited by developing customised functional units for speeding up the execution. Several customisations are proposed for the data path of the processor but it is also important to match the memory bandwidth to the computation speed. This calls for a memory organisation supporting parallel memory accesses. The proposed optimisations have been used to improve the energy-efficiency of the processor and experiments show that a programmable solution can have energy-efficiency comparable to fixed-function ASIC designs

Performance Analysis of the Modernized GNSS Signal Acquisition

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

Performance Analysis of the Modernized GNSS Signal Acquisition

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 citée, 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. ABSTRACT : 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

Analyse des Performances de l’Acquisition des Nouveaux Signaux GNSS

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 signa