Inertial measurement units (IMUs) are key components of various applications including navigation, robotics, aerospace, and automotive systems. IMU sensor characteristics have a significant impact on the accuracy and reliability of these applications. In particular, noise characteristics and bias stability are critical for proper filter settings to perform a combined GNSS/IMU solution. This paper presents an analysis based on the Allan deviation of different IMU sensors that correspond to different grades of micro-electromechanical systems (MEMS)-type IMUs in order to evaluate their accuracy and stability over time. The study covers three IMU sensors of different grades (ascending order): Rokubun Argonaut navigator sensor (InvenSense TDK MPU9250), Samsung Galaxy Note10 phone sensor (STMicroelectronics LSM6DSR), and NovAtel PwrPak7 sensor (Epson EG320N). The noise components of the sensors are computed using overlapped Allan deviation analysis on data collected over the course of a week in a static position. The focus of the analysis is to characterize the random walk noise and bias stability, which are the most critical for combined GNSS/IMU navigation and may differ or may not be listed in manufacturers’ specifications. Noise characteristics are calculated for the studied sensors and examples of their use in loosely coupled GNSS/IMU processing are assessed. This work proposes a structured and reproducible approach for working with sensors for their use in navigation tasks in combination with GNSS, and can be used for sensors of different levels to supplement missing or incorrect sensor manufacturers’ data.

The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter–receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ΔVTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude.

In urban contexts, the increasing density of electronic devices equipped with Global Navigation Satellite System (GNSS) receivers and complementary positioning technologies is attracting research and development efforts devoted to an improvement of the quality of life towards the smart city paradigm. Vehicular and pedestrian positioning and navigation capabilities are among the major drivers for innovation in this process. Ultra-low-cost electronics such as smartphones and Internet of Things (IoT) sensors aim at providing accurate and reliable positioning solutions through a set of promising solutions. Among these, snapshot positioning allows to remotely perform the post-processing of GNSS signals in IoT sensor networks while Wi-Fi™ ranging and cooperative positioning provide auxiliary anchors of opportunity to enhance indoor/outdoor positioning capabilities. This paper presents an innovative platform to perform a centralised testing and assessment of such positioning and navigation technologies along with a set of results obtained in the context of the European project HANSEL, by relying on current network technologies and infrastructures (i.e., Wi-Fi™ and cellular connectivity).

WiFi Round Trip Time (RTT) unlocks meter level accuracies in user terminal positions where no other navigation systems, such as Global Navigation Satellite Systems (GNSS), are able to (e.g., indoors). However, little has been done so far to obtain a scalable and automated system that computes the position of the WiFi Access Points (WAP) using RTT and that is able to estimate, in addition to the position, the hardware biases that offset the WiFi ranging measurements. These biases have a direct impact on the ultimate position accuracy of the terminals. This work proposes a method in which the computation of the WiFi Access Points positions and hardware biases (i.e., products) can be estimated based on the ranges and position fixes provided by user terminals (i.e., inverse positioning) and details how this can be improved if raw GNSS measurements (pseudoranges and carrier phase) are also available in the terminal. The data setup used to obtain a performance assessment was configured in a benign scenario (open sky with no obstructions) in order to obtain an upper boundary on the positioning error that can be achieved with the proposed method. Under these conditions, accuracies better than 1.5 m were achieved for the WAP position and hardware bias. The proposed method is suitable to be implemented in an automated manner, without having to rely on dedicated campaigns to survey 802.11mc-compliant WAPs. This paper offers a technique to automatically estimate both mild-indoor WAP products (where terminals have both Wi-Fi RTT and GNSS coverage) and deep-indoor WAP (with no GNSS coverage where the terminals obtain their position exclusively from previously estimated mild-indoor WAPs).

The emergence of Low Earth Orbit (LEO) satellite constellations dedicated to positioning applications holds the promise of improving the capabilities of existing Global Navigation Satellite Systems (GNSS). However, the absence of operational systems necessitates a qualitative assessment of potential improvements through simulation. This paper introduces a methodology to convert Two Line Element (TLE) orbital parameters, abundantly available for LEO constellations for communication and Earth Observation, into the widely used RINEX 4 format employed by GNSS. The primary goal is to establish a comprehensive database of LEO constellation orbits directly compatible with the orbit propagation algorithms utilized in GNSS systems like the Global Positioning System (GPS). This approach enables seamless integration into simulation tools with minimal adjustments. While TLE parameters are optimized for the SGP4 propagation model and cautioned against use in classical Kepler orbit propagation scenarios requiring precision, the obtained discrepancies, within a few tens of kilometers, suggest that these representations are realistic for simulation purposes, as demonstrated with the Spire LEMUR LEO constellation. As a practical application, the paper conducts a visibility analysis using the Starlink constellation. Results affirm expectations, showcasing that the combination of GNSS with a LEO mega-constellation significantly enhances satellite coverage and reduces Dilution of Precision. This work contributes to the ongoing discourse on the potential benefits and practicality of integrating emerging LEO constellations with established GNSS systems, offering insights into improved navigation and timing capabilities through simulation-based assessments.

The Radio Occultation instrument at the upcoming EUMETSAT Polar System – Second Generation (EPS-SG) mission will be devoted primarily to monitor the neutral atmosphere through this payload, consisting of a GNSS receiver and occultation antennae pointing slightly below the Earth's limb. The resulting data will be processed by EUMETSAT (primarily for L1B data) and by the ROMSAF's Radio Occultation Processing Package (ROPP) software to obtain the vertical profiles of temperature, pressure and other relevant level 2 parameters of the neutral atmosphere. Newer versions of this software might include a feature by which empirical models of the ionosphere (i.e. vertical profiles of electron density) can be included in the processing in order to increase the accuracy of the inverted bending angle profiles. In order to test this new feature, this work includes the efforts that have been made in order to provide an empirical model of the ionosphere purely based on vertical profiles of electron density inverted from data of previous radio occultation (RO) missions (i.e. COSMIC/FORMOSAT-3). The methodology used in this work is based on using the separability hypothesis, to overcome the spherical symmetry assumption of the Abel inversion as well as a new mechanization of the inversion process, based on a joint processing of all the occultation data via a linear mean square filter, rather than adopting the classical peel onion approach. Additionally, with the development of this empirical model, efforts have been made to construct a proxy index for scintillation monitoring based on the inverted profiles (Occultation Scintillation Proxy Index or OSPI), which shows reasonable correlation with the amplitude scintillation index S₄.