Triple-frequency GNSS models for PPP with float ambiguity estimation: performance comparison using GPS

This contribution proposes two new precise point positioning (PPP) models that use triple-frequency data, designed to accelerate convergence of carrier-phase float ambiguities. The first model uses a triple-frequency ionosphere-free linear combination that has minimum noise propagation and geometry-preserving properties. The second model uses a mixed code and carrier-phase linear combination with the same properties. A third model was also implemented, which uses individual uncombined triple-frequency measurements. The three models were validated using triple-frequency GPS data and their performance was compared to the traditional dual-frequency model in terms of the convergence time taken to achieve and maintain a uniform three-dimensional accuracy of 5 cm. Testing includes PPP processing of 1-h measurement blocks using 1–8 days of data from three locations in Australia. It was shown that all the three triple-frequency models had improved solution convergence time compared to the traditional PPP dual-frequency model although they gave almost similar accuracy and precision. The convergence time, when using the triple-frequency ionosphere-free model improved, by 10%, the improvement was 9% when using the mixed code-phase model, whereas the individual uncombined model resulted in 8% improvement

Precise Point Positioning Augmentation for Various Grades of Global Navigation Satellite System Hardware

The next generation of low-cost, dual-frequency, multi-constellation GNSS receivers, boards, chips and antennas are now quickly entering the market, offering to disrupt portions of the precise GNSS positioning industry with much lower cost hardware and promising to provide precise positioning to a wide range of consumers. The presented work provides a timely, novel and thorough investigation into the positioning performance promise. A systematic and rigorous set of experiments has been carried-out, collecting measurements from a wide array of low-cost, dual-frequency, multi-constellation GNSS boards, chips and antennas introduced in late 2018 and early 2019. These sensors range from dual-frequency, multi-constellation chips in smartphones to stand-alone chips and boards. In order to be comprehensive and realistic, these experiments were conducted in a number of static and kinematic benign, typical, suburban and urban environments. In terms of processing raw measurements from these sensors, the Precise Point Positioning (PPP) GNSS measurement processing mode was used. PPP has become the defacto GNSS positioning and navigation technique for scientific and engineering applications that require dm- to cm-level positioning in remote areas with few obstructions and provides for very efficient worldwide, wide-array augmentation corrections. To enhance solution accuracy, novel contributions were made through atmospheric constraints and the use of dual- and triple-frequency measurements to significantly reduce PPP convergence period. Applying PPP correction augmentations to smartphones and recently released low-cost equipment, novel analyses were made with significantly improved solution accuracy. Significant customization to the York-PPP GNSS measurement processing engine was necessary, especially in the quality control and residual analysis functions, in order to successfully process these datasets. Results for new smartphone sensors show positioning performance is typically at the few dm-level with a convergence period of approximately 40 minutes, which is 1 to 2 orders of magnitude better than standard point positioning. The GNSS chips and boards combined with higher-quality antennas produce positioning performance approaching geodetic quality. Under ideal conditions, carrier-phase ambiguities are resolvable. The results presented show a novel perspective and are very promising for the use of PPP (as well as RTK) in next-generation GNSS sensors for various application in smartphones, autonomous vehicles, Internet of things (IoT), etc

Advanced receiver autonomous integrity monitoring using triple frequency data with a focus on treatment of biases

Most current Advanced Receiver Autonomous Integrity Monitoring (ARAIM) methods are designed to use dual-frequency ionosphere-free observations. These methods assume that receiver bias is absorbed in the common receiver clock offset and bound satellite biases by nominal values. However, most multi-constellation Global Navigation Satellite Systems (GNSS) can offer triple frequency data that can be used for civilian applications in the future, which can improve observation redundancy, solution precision and detection of faults. In this contribution, we explore the use of this type of observations from GPS, Galileo and BeiDou in ARAIM. Nevertheless, the use of triple frequency data introduces receiver differential biases that have to be taken into consideration. To demonstrate the significance of these additional biases we first present a method to quantify them at stations of known coordinates and using available products from the International GNSS service (IGS). To deal with the additional receiver biases, we use a between-satellite single difference (BSSD) observation model that eliminates their effect. A pilot test was performed to evaluate ARAIM availability for Localizer Performance with Vertical guidance down to 200. feet (LPV-200) when using the triple-frequency observations. Real data were collected for one month at stations of known coordinates located in regions of different satellite coverage characteristics. The BSSD triple-frequency model was evaluated to give early indication about its feasibility, where the implementation phase still requires further comprehensive studies. The vertical position error was always found to be bounded by the protection level proven initial validity of the proposed integrity model. © 2017 COSPAR

Multi-GNSS integer ambiguity resolution enabled precise positioning

In this PhD thesis multi-Global Navigation Satellite System (GNSS) positioning results when combining the American Global Positioning System (GPS), Chinese BeiDou Navigation Satellite System (BDS), European Galileo and Japanese Quasi-Zenith Satellite System (QZSS) will be presented. The combined systems will be evaluated in comparison to the single-systems, for short (atmosphere-fixed) to long (atmosphere-present) baselines. It will be shown that the combined systems can provide for improved integer ambiguity resolution and positioning performance over the single-systems

GNSS Precise Point Positioning Using Low-Cost GNSS Receivers

There are positioning techniques available such as Real-Time Kinematic (RTK) which allow user to obtain few cm-level positioning, but require infrastructure cost, i.e., setting up local or regional networks of base stations to provide corrections. Precise Point Positioning (PPP) using dual-frequency receivers is a popular standalone technique to process GNSS data by applying precise satellite orbit and clock correction along with other corrections to produce cm to dm-level positioning. At the time of writing, almost all low-cost and ultra-low-cost (few $10s) GNSS units are single-frequency chips. Single-frequency PPP poses challenges in terms of effectively mitigating ionospheric delay and the multipath, as there is no second frequency to remove the ionospheric delay. The quality of measurements also deteriorates drastically from geodetic-grade to ultra-low-cost hardware. Given these challenges, this study attempts to improve the performance of single-frequency PPP using geodetic-grade hardware, and to capture the potential positioning performance of this new generation of low-cost and ultra-low-cost GNSS chips. Raw measurement analysis and post-fit residuals show that measurements from cellphones are more prone to multipath compared to signals from geodetic-grade and low-cost receivers. Horizontal accuracy of a few-centimetres is demonstrated with geodetic-grade hardware. Whereas accuracy of few-decimetres is observed from low-cost and ultra-low-cost GNSS hardware. With multi-constellation processing, improvements in accuracy and reductions in convergence time over initial 60 minutes period, are also demonstrated with three different set of GNSS hardware. Horizontal and vertical rms of 37 cm and 51 cm, respectively, is achieved using a cellphone

Analysis of ionospheric disruptions in GNSS signals from Tonga eruption

The Tonga volcano eruption at 04:15 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, causing very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. The released energy generates perturbations on the electronic density present on the atmosphere, known as Traveling Ionospheric Disturbances (TIDs), i.e., wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere. Geomagnetic and ionospheric phenomena affect communications, GNSS, and other systems on which our technological society depends. The present final master’s thesis aims to analyse some of the most relevant TIDs characteristics (such as propagation speed, time, etc.) as a function of the distance from the eruption in Global Navigation Satellite System (GNSS) signals. First, evaluate Receiver Independent Exchange Format (RINEX) files, i.e., a data interchange format for raw satellite navigation system data, and then, compute Prefit Residuals, i.e., the input data for the navigation equations. With this data, TIDs will be analysed with a series of indices that sample in post-process the disturbance of the ionosphere, developed by Research group of Astronomy and GEomatics of the Universitat Politecnica de Catalunya (gAGE).La erupción del volcán Tonga a las 04:15 UT del 15-01-2022 liberó enormes cantidades de energía a la atmósfera, desencadenando variaciones geofísicas muy significativas no solo en la proximidad inmediata del epicentro sino también a nivel mundial en toda la atmósfera. Estas variaciones se conocen como perturbaciones ionosféricas viajeras (TID, por sus si-glas en inglés), es decir, irregularidades de propagación en forma de onda que alteran el entorno de densidad de electrones y desempeñan un papel importante en la propagación de señales de radio que se propagan a través de la ionosfera. Los fenómenos geomagnéticos e ionosféricos afectan a las comunicaciones, GNSS y otros sistemas de los que depende nuestra sociedad tecnológica. La presente tesis final de máster tiene como objetivo analizar algunas de las características más relevantes de los TIDs (como la velocidad de propagación, el tiempo, etc.) en función de la distancia desde la erupción en las señales del Sistema Global de Navegación por Satélite (GNSS). Primero, evaluando los archivos de Receiver Independent Exchange Format (RINEX), es decir, un formato de intercambio de datos para los datos brutos del sistema de navegación por satélite, y luego, calculando los residuos de preajuste, es decir, los datos de entrada para las ecuaciones de navegación. Con estos datos, se analizarán las TIDs con una serie de índices que muestrean en postproceso la perturbación de la ionosfera, desarrollados por el grupo de investigación de Astronomía y GEomática de la Universitat Politecnica de Cata-lunya (gAGE).Incomin

The Potency of the Modernized GNSS Signals for Real-Time Kinematic Positioning

GNSS positioning has become popular in the past decade as an efficient method of precise and real-time positioning. It is relatively low cost and ease-of-use. Up to now, several parameters were defined to characterize the performance of real-time positioning: availability, precision, accuracy. This article evaluates the performance of signal linear combinations for real-time positioning, both for static as well as the kinematic positioning. This article starts with the investigation of linear combinations (LC) rising from the carrier frequencies of the GNSS systems. Some Linear Combination shows potential benefits in carrier phase integer ambiguity resolution, particularly utilizing the Galileo and Beidou signal phase carrier. For each system, a set of combinations was studied, analyzed, and then selected during the development of GNSS positioning method utilizing the Least-squares Ambiguity Decorrelation Adjustment (LAMBDA). Special signal selection can affect the estimated position and its standard deviation. To further analyze, the results obtained from data processing are compared with respect to baselines and signals. The ambiguity fixing rate is correlated with the baseline length and the method as well as the signals that were used. The analysis of the measurement noise level was first conducted to set a baseline for the real-time GNSS positioning application. According to the results and to assess the data quality and positioning performance of GNSS in respect with GPS (Global Positioning System), an experimental test has established using MGEX data. This research investigates the satellite visibilities, multipath, Signal to Noise Ratio (SNR), and positioning performance. It is shown that in every epoch, at least 8 satellites are visible. The SNR’s are up to 60 dBHz, the code multipath residuals varies within ~1 m, while the phase residuals varies by about ~2 cm. hence the modernized GNSS signals have potencies to improves the RTK positioning

Carrier multipath mitigation in linear combinations of Global Navigation Satellite Systems measurements

Global Navigation Satellite Systems (GNSS) are the main systems that provide positioning, navigation and timing at a global level. They are being used in numerous applications in different sectors including transport, military, oil & gas, agriculture as well as location based services. A significant number of these applications require centimetre-level positioning accuracy, a challenging feat due to the many error sources that affect GNSS measurements. These include errors at the satellite, propagation medium, and receiver levels. Most of these errors can be mitigated by modeling, or by exploiting their spatial and temporal correlation characteristics. However, multipath errors, which result from the combination of the direct signal with reflected signals in the vicinity of the receiver antenna, are difficult to model and therefore, difficult to mitigate. Furthermore, high accuracy positioning applications typically rely on linear combinations of measurements at different frequencies (e.g. L1 and L2 in the case of the Global Positioning System) to mitigate frequency-dependent errors such as ionospheric errors (i.e. ionosphere free combination) or otherwise facilitate position calculation (e.g. Wide Lane observable). The multipath errors associated with such combinations are significantly larger than those of individual signals. The dependency of the multipath error on the environment and its low level in single frequency measurements (i.e. up to quarter of wavelength) makes modelling and mitigating it very difficult. Current techniques attempt to mitigate multipath errors for measurements at each individual frequency, independently of the error at other frequencies, even when linear combinations of measurements are used. The literature review carried out in this thesis has drawn three main conclusions regarding carrier multipath mitigation. Firstly, existing carrier multipath mitigation techniques are inaccurate, impractical or not effective. Secondly most of the practical techniques attempt to mitigate the error by de-weighting the measurements which are most prone to the multipath error (i.e measurement at low elevation). Thirdly, existing weighting techniques are oversimplified and do not reflect the error level accurately. In this research and for the first time, carrier multipath errors have been studied directly at the linear combination level. This is by exploiting the dispersive nature of multipath errors in order to model and correct them. New carrier multipath mitigation techniques applicable to linear combinations of measurements have been developed in this thesis on the basis of a new error model and a new observable referred to as the IFM (Inter-Frequency carrier Multipath). The IFM is computed from carrier phase measurements at two different frequencies, and corresponds to the combined multipath errors of those signals. In addition to multipath mitigation, this observable has various other applications. The well-defined relationship between the IFM and carrier multipath errors is used in this thesis to develop multipath mitigation techniques based on two approaches: multipath correction and measurement weighting. The new mitigation techniques are applicable to linear combinations of observations such as Wide Lane (WL) and Ionosphere Free (IF) carrier phase measurements in double differenced mode. The new multipath mitigation techniques have been validated using real data and the results compared with those obtained using the elevation weighting technique. The results show that the new methods developed in this thesis improve the mean error of horizontal position by up to 33% when using the IF combination. The results also show improvements of up to 78% in the time it takes to resolve ambiguities when using the WL combination.Open Acces