PERFORMANCE EVALUATION OF LOW-COST PRECISION POSITIONING METHODS FOR FUTURE PORT APPLICATIONS

In recent times, a lot of research has been conducted to improve the accuracy of various positioning systems. The motivation behind this trend is to ensure high quality GNSS services for various applications. In particular, emphasis has been placed on improving the level of accuracy of consumer grade GNSS receivers. Significant improvements in the quality of signal reception of these receivers would enable low-cost solutions for asset management in for example, harbor areas. Research in Receiver Autonomous Integrity Monitoring - Fault Detection and Exclusion (RAIM-FDE) algorithms give users the ability to exclude satellites with degraded signals, hereby improving the performance of the GNSS solution. This research investigates and evaluates the performance of various customer grade GNSS positioning systems intended for port applications. Various high precision techniques such as Precise Point Positioning and Real-Time Kinematic were conducted and accuracy levels were noted on Multi-band receivers, Single frequency receivers, and GNSS-enabled smartphone. Our final conclusion suggests optimal low-cost GNSS solutions for asset monitoring and management

Methods for Improving Performance in Consumer Grade GNSS Receivers

Viimeisten kolmen vuosikymmenen aikana satelliittinavigointi on kehittynyt ammatti ja sotilaskäyttäjien tekniikasta kaikkien saatavilla olevaksi tekniikaksi. Varsinkin viimeisen 15 vuoden aikana, kun vastaanottimet alkoivat pienentyä ja halpenivat, on lisääntynyt määrä yrityksiä, jotka toimittavat GPS-laitteita satoihin erilaisiin sovelluksiin. Kaikille moderneille tekniikoille on myös tyypillistä, että tutkimukseen ja siihen liittyvään vastaanottimien kehittämiseen on käytetty valtavasti rahaa, mikä on johtanut huomattavaan parantumiseen vastaanottimen suorituskyvyssä. GPS-vastaanottimien kehitystyön lisäksi uusien maailmanlaajuisten satelliittinavigointijärjestelmien, kuten venäläisen GLONASS, kiinalaisen BeiDou- ja eurooppalaisen Galileo-järjestelmien käyttöönotto tarjoaa entistä enemmän mahdollisuuksia suorituskyvyn parantamiseen. Sekä GPS että nämä uudet järjestelmät ovat myös ottaneet käyttöön uudentyyppisiä signaalirakenteita, jotka voivat tarjota parempilaatuisia havaintoja ja siten parantaa kaikkien vastaanottimien suorituskykyä. Lopuksi menetelmät, kuten PPP ja RTK, jotka aiemmin olivat varattu ammattikäyttäjille, ovat tulleet kuluttajamarkkinoille mahdollistaen ennennäkemättömän suorituskyvyn jokaiselle satelliittinavigointivastaanottimien käyttäjälle. Tässä opinnäytetyössä arvioidaan tämän kehityksen vaikutusta sekä suorituskykyyn että vastaanottimen arkkitehtuuriin. Työssä esitellään yksityiskohtaisesti FGI:ssä kehitetyn ohjelmistopohjaisen vastaanottimen, FGI-GSRx:n. Tämän vastaanottimen avulla on työssä arvioitu miten sekä uudet konstellaatiot että uudet nykyaikaiset signaalit ja niitten seurantamenetelmät vaikuttavat suorituskykyyn ja vastaanotin arkkitehtuuriin. Tämän lisäksi on arvioitu PPP- ja RTK-tarkkuuspaikannusmenetelmien vaikutus FinnRefCORS-verkkoa käyttäen useiden erityyppisten vastaanottimien kanssa, mukaan lukien kuluttajalaatuiset vastaanottimet. Tulokset osoittavat, että enemmän konstellaatioita ja signaaleja käytettäessä paikannusratkaisun tarkkuus paranee 3 metristä 1,4 metriin hyvissä olosuhteissa ja yli 10-kertaiseksi tiheästi rakennetuissa kaupungeissa, jossa käytettävissä olevien signaalien määrä kasvaa kertoimella 2 käytettäessä kolmea konstellaatiota. Uusia moderneja modulaatiotekniikoita, kuten BOC-modulaatiota, käytettäessä tulokset osoittavat Galileo-ratkaisun tarkkuuden paranevan lähes 25%:lla ja esitelty uusi signaalinkäsittelymenetelmä lisää tällaisen tarkkuuden saatavuutta 50%:sta lähes 100%:iin. Lopuksi tarkkuuspaikannusmenetelmien tulokset osoittavat, että 15 cm:n tarkkuus on saavutettavissa, mikä on merkittävä parannus verrattuna 1,4 metrin tarkkuuteen. Näiden parannusten saavuttamiseksi on olennaista, että itse vastaanotin on mukautettu hyödyntämään näitä uusia signaaleja ja konstellaatioita. Tämä tarkoittaa, että nykyaikaisten kuluttajamarkkinoiden vastaanottimien suunnittelu on haastavaa ja monissa tapauksissa ohjelmistopohjainen vastaanotin olisi parempi ja halvempi valinta kuin uusien mikropiirien kehittäminen.For the last three decades, satellite navigation has evolved from being a technology for professional and military users to a technology available for everyone. Especially during the last 15 years, since the receivers started getting smaller and cheaper, there has been an increasing number of companies delivering Global Positioning System (GPS) enabled devices for hundreds of different kind of applications. Typical for any modern technology, there has also been an enormous amount of money spent on research and accompanied receiver development resulting in an immense increase in receiver performance. In addition to the development efforts on GPS receivers the introduction of new global navigation satellite systems such as the Russian Globalnaja Navigatsionnaja Sputnikovaja Sistema (GLONASS), the Chinese BeiDou, and the European Galileo systems offers even more opportunities for improved performance. Both GPS and these new systems have also introduced new types of signal structures that can provide better quality observations and even further improve the performance of all receivers. Finally, methods like Precise Point Positioning (PPP) and Real Time Kinematic (RTK) that earlier were reserved for professional users have entered into the consumer market enabling never before seen performance for every user of satellite navigation receivers. This thesis will assess the impact of this development on both performance as well as on receiver architecture. The design of the software defined receiver developed at FGI, the FGI-GSRx, is presented in detail in this thesis. This receiver has then been used to assess the impact of using multiple constellations as well as new novel signal processing methods for modern signals. To evaluate the impact of PPP and RTK methods the FinnRef Continuously Operating Reference Station (CORS) network has been used together with several different types of receivers including consumer grade off the shelf receivers. The results show that when using more constellations and signals the accuracy of the positioning solution improves from3 meters to 1.4 meters in open sky conditions and by more than a factor 10 in severe urban canyons. For severe urban canyons the available also increases by a factor 2 when using three constellations. When using new modern modulation techniques like high order BOC results show an accuracy improvement for a Galileo solution of almost 25 % and the presented new signal processing method increase the availability of such an accuracy from 50 % to almost 100 %. Finally, results from precise point positioning methods show that an accuracy of 15 cm is achievable, which is a significant improvement compared to an accuracy of 1.4 m for a standalone multi constellation solution. To achieve these improvements, it is essential that the receiver itself is adapted to make use of these new signals and constellations. This means that the design of modern consumer market receivers is challenging and in many cases a software define receiver would be a better and cheaper choice than developing new Application Specific Integrated Circuit (ASIC)’s

Feasibility of Consumer Grade GNSS Receivers for the Integration in Multi-Sensor-Systems

Various GNSS applications require low-cost, small-scale, lightweight and power-saving GNSS devices and require high precision in terms of low noise for carrier phase and code observations. Applications vary from navigation approaches to positioning in geo-monitoring units up to integration in multi-sensor-systems. For highest precision, only GNSS receivers are suitable that provide access to raw data such as carrier phase, code ranges, Doppler and signal strength. A system integration is only possible if the overall noise level is known and quantified at the level of the original observations. A benchmark analysis based on a zero baseline is proposed to quantify the stochastic properties. The performance of the consumer grade GNSS receiver is determined and evaluated against geodetic GNSS receivers to better understand the utilization of consumer grade receivers. Results indicate high similarity to the geodetic receiver, even though technical limitations are present. Various stochastic techniques report normally distributed carrier-phase noise of 2mm and code-range noise of 0.5-0.8m. This is confirmed by studying the modified Allan standard deviation and code-minus-carrier combinations. Derived parameters serve as important indicators for the integration of GNSS receivers into multi-sensor-systems

Survey on Signal Processing for GNSS under Ionospheric Scintillation: Detection, Monitoring, and Mitigation

Ionospheric scintillation is the physical phenomena affecting radio waves coming from the space through the ionosphere. Such disturbance is caused by ionospheric electron density irregularities and is a major threat in Global Navigation Satellite Systems (GNSS). From a signal processing perspective, scintillation is one of the most challenging propagation scenarios, particularly affecting high-precision GNSS receivers and safety critical applications where accuracy, availability, continuity and integrity are mandatory. Under scintillation, GNSS signals are affected by amplitude and phase variations, which mainly compromise the synchronization stage of the receiver. To counteract these effects, one must resort to advanced signal processing techniques such as adaptive/robust methods, machine learning or parameter estimation. This contribution reviews the signal processing landscape in GNSS receivers, with emphasis on different detection, monitoring and mitigation problems. New results using real data are provided to support the discussion. To conclude, future perspectives of interest to the GNSS community are discussed

Low-cost GNSS software receiver performance assessment

The Software-Defined Receiver (SDR) is a rapidly evolving technology which is a useful tool for researchers and allows users an extreme level customization. The main aim of this work is the assessment of the performance of the combination consisting of the Global Navigation Satellite Systems software receiver (GNSS-SDR), developed by CTTC (Centre Tecnològic de Telecomunicacions de la Catalunya), and a low-cost front-end. GNSS signals were acquired by a Nuand bladeRF x-40 front-end fed by the TOPCON PG-A1 antenna. Particular attention was paid to the study of the clock-steering mechanism due to the low-cost characteristics of the bladeRF x-40 clock. Two different tests were carried out: In the first test, the clock-steering algorithm was activated, while in the second, it was deactivated. The tests were conducted in a highly degraded scenario where the receiver was surrounded by tall buildings. Single-Point and Code Differential positioning were computed. The achieved results show that the steering function guarantees the availability of more solutions, but the DRMS is quite the same in the two tests

The Efficacy of Implementing a Small, Low-Cost, Real Time Kinematic GPS System into a Small Unmanned Aerial System Architecture

Along with the growing uses for small unmanned aerial systems (UAS) within the Department of Defense (DoD), is the utility of small UAS within the civilian market is also increasing. This has led to significant research and development on small UAS subsystems by the commercial market. The focus of this research is characterizing and investigating the application considerations of a small, low-cost real time kinematic (RTK) GPS receiver system. Work was also accomplished to characterize the accuracy and precision of the commonly used GPS receiver subsystem in small UAS to show the increased utility of the RTK GPS system. The results show that in a static environment, the RTK GPS system outperforms the commonly used standalone GPS receiver by a factor of 100 in two- and three-dimensional precision. However, the results from the tests involving a moving platform exposed several limitations which can degrade the precision of the RTK GPS system to precision values achievable by a standalone GPS receiver. These limitations do not inhibit the RTK GPS system’s ability to perform its primary intended purpose, and can be mitigated through proper integration and application selection of the system. It is recommended that the Air Force Institute of Technology continue to use the investigated RTK GPS system as a ground truth source while proving other navigation technologies for UAS flight

Low-cost GPS/GLONASS Precise Positioning Algorithm in Constrained Environment

Le GNSS (Global Navigation Satellite System), et en particulier sa composante actuelle le système américain GPS et le système russe GLONASS, sont aujourd'hui utilisés pour des applications géodésiques afin d'obtenir un positionnement précis, de l'ordre du centimètre. Cela nécessite un certain nombre de traitements complexes, des équipements coûteux et éventuellement des compléments au sol des systèmes GPS et GLONASS. Ces applications sont aujourd'hui principalement réalisées en environnement « ouvert » et ne peuvent fonctionner en environnement plus contraint. L'augmentation croissante de l'utilisation du GNSS dans des domaines variés va voir émerger de nombreuses applications où le positionnement précis sera requis (par exemple des applications de transport/guidage automatique ou d'aide à la conduite nécessitant des performances importantes en terme de précision mais aussi en terme de confiance dans la position –l'intégrité- et de robustesse et disponibilité). D'autre part, l'arrivée sur le marché de récepteurs bas-coûts (inférieur à 100 euros) capables de poursuivre les signaux provenant de plusieurs constellations et d'en délivrer les mesures brutes laisse entrevoir des avancées importantes en termes de performance et de démocratisation de ces techniques de positionnement précis. Dans le cadre d'un utilisateur routier, l'un des enjeux du positionnement précis pour les années à venir est ainsi d'assurer sa disponibilité en tout terrain, c'est-à-dire dans le plus grand nombre d'environnements possibles, dont les environnements dégradés (végétation dense, environnement urbain, etc.) Dans ce contexte, l'objectif de la thèse a été d'élaborer et d'optimiser des algorithmes de positionnement précis (typiquement basés sur la poursuite de la phase de porteuse des signaux GNSS) afin de prendre en compte les contraintes liées à l'utilisation d'un récepteur bas coût et à l'environnement. En particulier, un logiciel de positionnement précis (RTK) capable de résoudre les ambiguïtés des mesures de phase GPS et GLONASS a été développé. La structure particulière des signaux GLONASS (FDMA) requiert notamment un traitement spécifiques des mesures de phase décrit dans la thèse afin de pouvoir isoler les ambiguïtés de phase en tant qu'entiers. Ce traitement est compliqué par l'utilisation de mesures provenant d'un récepteur bas coût dont les canaux GLONASS ne sont pas calibrés. L'utilisation d'une méthode de calibration des mesures de code et de phase décrite dans la thèse permet de réduire les biais affectant les différentes mesures GLONASS. Il est ainsi démontré que la résolution entière des ambiguïtés de phase GLONASS est possible avec un récepteur bas coût après calibration de celui-ci. La faible qualité des mesures, du fait de l'utilisation d'un récepteur bas coût en milieu dégradé est prise en compte dans le logiciel de positionnement précis en adoptant une pondération des mesures spécifique et des paramètres de validation de l'ambiguïté dépendant de l'environnement. Enfin, une méthode de résolution des sauts de cycle innovante est présentée dans la thèse, afin d'améliorer la continuité de l'estimation des ambiguïtés de phase. Les résultats de 2 campagnes de mesures effectuées sur le périphérique Toulousain et dans le centre-ville de Toulouse ont montré une précision de 1.5m 68% du temps et de 3.5m 95% du temps dans un environnement de type urbain. En milieu semi-urbain type périphérique, cette précision atteint 10cm 68% du temps et 75cm 95% du temps. Finalement, cette thèse démontre la faisabilité d'un système de positionnement précis bas-coût pour un utilisateur routier. ABSTRACT : GNSS and particularly GPS and GLONASS systems are currently used in some geodetic applications to obtain a centimeter-level precise position. Such a level of accuracy is obtained by performing complex processing on expensive high-end receivers and antennas, and by using precise corrections. Moreover, these applications are typically performed in clear-sky environments and cannot be applied in constrained environments. The constant improvement in GNSS availability and accuracy should allow the development of various applications in which precise positioning is required, such as automatic people transportation or advanced driver assistance systems. Moreover, the recent release on the market of low-cost receivers capable of delivering raw data from multiple constellations gives a glimpse of the potential improvement and the collapse in prices of precise positioning techniques. However, one of the challenge of road user precise positioning techniques is their availability in all types of environments potentially encountered, notably constrained environments (dense tree canopy, urban environments…). This difficulty is amplified by the use of low-cost receivers and antennas, which potentially deliver lower quality measurements. In this context the goal of this PhD study was to develop a precise positioning algorithm based on code, Doppler and carrier phase measurements from a low-cost receiver, potentially in a constrained environment. In particular, a precise positioning software based on RTK algorithm is described in this PhD study. It is demonstrated that GPS and GLONASS measurements from a low-cost receivers can be used to estimate carrier phase ambiguities as integers. The lower quality of measurements is handled by appropriately weighting and masking measurements, as well as performing an efficient outlier exclusion technique. Finally, an innovative cycle slip resolution technique is proposed. Two measurements campaigns were performed to assess the performance of the proposed algorithm. A horizontal position error 95th percentile of less than 70 centimeters is reached in a beltway environment in both campaigns, whereas a 95th percentile of less than 3.5 meters is reached in urban environment. Therefore, this study demonstrates the possibility of precisely estimating the position of a road user using low-cost hardware

Low-Cost GNSS Software Receiver Performance Assessment

The Software-Defined Receiver (SDR) is a rapidly evolving technology which is a useful tool for researchers and allows users an extreme level customization. The main aim of this work is the assessment of the performance of the combination consisting of the Global Navigation Satellite Systems Software-Defined Receiver (GNSS-SDR), developed by CTTC (Centre Tecnològic de Telecomunicacions de la Catalunya), and a low-cost front-end. GNSS signals were acquired by a Nuand bladeRF x-40 front-end fed by the TOPCON PG-A1 antenna. Particular attention was paid to the study of the clock-steering mechanism due to the low-cost characteristics of the bladeRF x-40 clock. Two different tests were carried out: In the first test, the clock-steering algorithm was activated, while in the second, it was deactivated. The tests were conducted in a highly degraded scenario where the receiver was surrounded by tall buildings. Single-Point and Code Differential positioning were computed. The achieved results show that the steering function guarantees the availability of more solutions, but the DRMS is quite the same in the two tests

Contributions to high accuracy snapshot GNSS positioning

(English) Snapshot positioning is the technique to determine the position of a Global Navigation Satellite System (GNSS) receiver using only a very brief interval of the received satellite signal. In recent years, this technique has received a great amount of attention thanks to its unique advantages in power efficiency, Time To First Fix (TTFF) and economic costs for deployment. However, the state of the art algorithms regarding snapshot positioning were based on code measurements only, which unavoidably limited the positioning accuracy to meter level. The present PhD research aims at achieving high-accuracy (centimetre level) snapshot positioning by properly utilizing carrier phase measurements. Two technical challenges should be tackled before such level of accuracy can be achieved, namely, satellite transmission time inaccuracy and the so-called Data Bit Ambiguity (DBA) issue. The first challenge is essentially originated from the lack of absolute timing accuracy in the receiver, as only the coarse time information is available from an external assistance module and its error can be up to a few seconds. Applying a conventional Coarse Time Filter (CTF) can increase this timing accuracy to millisecond level. However, this is still not enough for carrier-phase based positioning since the satellite position errors introduced by such timing errors range up to one meter, which certainly impedes the carrier phase Integer Ambiguity Resolution (IAR). A method is proposed to set a global time tag and correspondingly construct the pseudoranges with full period corrections. The second challenge is caused by the fact that snapshot measurements are generated based on the results of the correlation between the received signal and the local replicas. Multiple replicas are typically produced in snapshot positioning following the Multi Hypothesis (MH) acquisition architecture. It may happen that more than one local replica (i.e. hypothesis) result in the maximum correlation energy. Hence, we need to identify the actual secondary codes or data bit symbols encoded in the received signal, i.e. to resolve the DBA. Particularly, when the local replica is generated with exactly opposite symbols to the actual ones, the resulting carrier phase measurement contains a Half Cycle Error (HCE) and impedes also the IAR step. A method has been proposed in this PhD to resolve the DBA issue for pilot signals with encoded secondary codes. This method attempts to form a consensus among all satellites regarding their secondary codes under the assistance of their flight time differences. A different approach has been developed for data signals. It amends the carrier phase HCEs one after another by an iterative satellite inclusion procedure. This approach uses the Real Time Kinematics (RTK) LAMBDA Ratio Factor (LRF) as an indicator to evaluate the potential existence of the HCEs. The present PhD focuses on implementing the so-called Snapshot RTK (SRTK) technique. As in the classic RTK technique, SRTK cancels most of the measurement errors through the Double-Differenced (DD) process. The workflow details of SRTK are explained incorporating the aforementioned new algorithms. Several experiments were performed based on real world signal recordings and the results confirm the feasibility of obtaining SRTK fix solutions. The performance of SRTK is numerically demonstrated under different parameters of signal bandwidth, integration time and baseline distance. The SRTK fix rates can reach more than 90% in most of the scenarios, with centimetre-level positioning errors observed in the fixed solutions. It can be concluded that upon the implementation of the global time tag method, high accuracy snapshot positioning becomes feasible with the SRTK technique and its performance varies depending on the SRTK configuration. The algorithms developed for the DBA issue and carrier phase HCEs also prove to effectively improve the performance of SRTK.(Español) El posicionamiento instantáneo es la técnica para determinar la posición de un receptor del Sistema Global de Navegación por Satélite (GNSS) utilizando solo un intervalo muy breve de la señal recibida. En los últimos años, esta técnica ha recibido una gran atención gracias a sus ventajas únicas en eficiencia energética, tiempo hasta la primera posición (TTFF) y reducidos costes económicos para la implementación. Sin embargo, el estado del arte de los algoritmos relacionados con el posicionamiento de señales instantáneas utilizaron solo medidas de código, lo que inevitablemente limitó la precisión del posicionamiento a al nivel del metro. La presente Tesis Doctoral tiene como objetivo lograr un posicionamiento instantáneo de alta precisión (nivel centimétrico) mediante las medidas de fase de la portadora. Para ello, deben abordarse dos desafíos técnicos antes de que se pueda alcanzar ese nivel de precisión: resolver la inexactitud del tiempo de transmisión del satélite y el llamado problema de ambigüedad de bit de datos (DBA). El primer desafío se origina esencialmente por la falta de precisión de tiempo absoluto en el receptor, ya que solo está disponible la información del tiempo aproximado desde un módulo de asistencia externo y su error puede ser de hasta unos segundos. Así, se propone un método para establecer una etiqueta de tiempo global y construir correspondientemente los pseudorangos con correcciones de período completo. El segundo desafío se debe al hecho de que las mediciones instantáneas se generan en función de los resultados de la correlación entre la señal recibida y las réplicas locales. Las múltiples réplicas generalmente se producen en el posicionamiento de instantáneas siguiendo la arquitectura de de adquisición de el Múltiples Hipótesis (MH). Por lo tanto, se necesita identificar los códigos secundarios reales o los símbolos de bits de datos codificados en la señal recibida, para resolver el DBA. En particular, cuando la réplica local se genera con símbolos exactamente opuestos a los reales, el resultado de la medición de la fase de la portadora contiene un error de medio ciclo (HCE) e impide también la resolución de ambigüedad entera (IAR). Se ha propuesto un método en esta Tesis Doctoral para resolver el problema de DBA para señales piloto con códigos secundarios. Este método intenta formar un consenso entre todos los satélites con respecto a sus códigos secundarios bajo la asistencia de sus diferencias de tiempo de vuelo. Un enfoque diferente ha sido desarrollado para señales que contienen datos del mensaje de navegación. Se modifica los HCE de la fase de portadora uno tras otro mediante un procedimiento iterativo de inclusión de satélites. Este método utiliza el factor de relación LAMBDA (LRF) utilizado en posicionamiento relativo en tiempo real (RTK) como indicador para evaluar la existencia potencial de los HCE. La presente tesis doctoral se centra en implementar la técnica denominada Snapshot RTK (SRTK). Se realizaron varios experimentos basados ?en ?señales del mundo real. Las grabaciones y los resultados confirman la viabilidad de obtener soluciones SRTK con IAR. El rendimiento de SRTK es numéricamente demostrado bajo diferentes parámetros tales como el ancho de banda de señal, tiempo de integración y distancia de línea de base. Las tasas de fijación IAR de SRTK pueden alcanzar más del 90% en la mayoría de los escenarios, observándose errores de posicionamiento centimétricos en las soluciones fijas. Se puede concluir que tras la implementación del método de etiqueta de tiempo global, que el posicionamiento de instantáneas de alta precisión se vuelve factible con la técnica SRTK y las prestaciones varían dependiendo de la configuración. Los algoritmos desarrollados para la resolución de DBA y los HCE de fase portadora también demuestran que mejoran efectivamente el rendimientoCiència i tecnologies aeroespacial