Considering the inertial measurement unit (IMU) faults risk of an unmanned aerial vehicle (UAV), this paper provides an analysis of the error overboundings of position estimation in a tightly coupled IMU/global navigation satellite system (GNSS) integrated architecture under the IMU fault conditions using an error-state EKF-based approach and provides a comparison to a recently published EKF-based full state method. Simulation results show that both the error overboundings of the error-state and full-state EKFs can fit the state error against the IMU faults, but the error-state EKF is more suitable for UAV navigation system integrity assurance due to its higher calculation eciency. This study will be extended to the integrity monitoring of multisensor systems.

Raw TiO₂ nanoparticles were prepared using the hydrolysis of TiCl₄. The nanoparticles were subjected to a surface treatment in diluted sulphuric acid and, subsequently, calcined at different temperatures. Then, a type of super solid acid (SO₄²⁻/TiO₂) with particle sizes of 20∼30 nm was fabricated. The catalysis of SO₄²-/TiO₂ on the thermolysis of ammonium nitrate (AN) was probed using thermal analysis. For SO₄²⁻/TiO₂ (AN doped with 3%SO₄²⁻/TiO₂), the onset temperature decreased by 19°C and the peak temperature decreased by 15.8°C. For TiO₂ (AN doped with 3%TiO₂), the peak temperature decreased by only 0.5°C. Using the DSC-IR technology, the gas products of the decomposition of 3%SO₄²-/TiO₂-doped AN were detected. We found that the products were mainly N₂O (g) and a small amount of H₂O (g), and that no NH₃ (g) or HNO₃ (g) was detected, which ascertained the decomposition reaction of NH₄NO₃→N₂O(g)+H₂O(g). In addition, the catalysis mechanism of SO₄²-/TiO₂ on the AN decomposition was discussed in detail.

Signal-In-Space User Range Errors (SIS UREs) are assumed to be overbounded by a normal distribution with a standard deviation represented by the User Range Accuracy (URA). The BeiDou Navigation Satellite System (BDS) broadcast URA is not compatible with the historical SIS URE performance that affects the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) False Alert Probability (Pfa) and availability evaluation. This study compares the BDS broadcast and precise ephemeris from 1 March 2013 to 1 March 2017 to obtain SIS UREs. Through analyzing the statistical characteristics of the SIS UREs, we obtain the standard deviation σ_URE for the accuracy and continuity and σ_URA used for the integrity of the SIS UREs. The results show that the broadcast σ_URA of 2 m cannot completely overbound SIS UREs for all BDS satellites, but the σ_URA of 2.4 m can. Then, we use the σ_URA of 2.4 m to evaluate the ARAIM Pfa and availability. The results show that the Pfa may increase to 2 × 10⁻⁵ and exceed its limit by an order of magnitude. We also consider the differences between the SIS UREs of Geostationary Earth Orbit (GEO), Inclined Geo-Synchronous Orbit (IGSO), and Medium Earth Orbit (MEO). The results indicate that all Pfa values calculated by the computed σ_URE are less than the Pfa in the Integrity Support Message (ISM) for the worst-performing GEO satellite. The approximately 55% Pfa calculated by the computed σ_URE is less than the Pfa in ISM for the worst-performing IGSO satellite. Most Pfa values calculated by the computed σ_URE is less than the Pfa in the ISM for the worst-performing MEO satellite. For BDS satellites, the Pfa is mainly affected by σ_URE. When the σ_URA of 2.4 m is used to evaluate the availability, the computed availability is lower than the availability calculated by the broadcast σ_URA/σ_URE and the greatest degradation can reach 25%.

Receiver Autonomous Integrity Monitoring (RAIM) method is an effective means to provide integrity monitoring for users in time. In order to solve the misjudgment caused by the interference of gross error to the least squares algorithm, this paper proposes a RAIM method based on M-estimation for multiconstellation GNSS. Based on five programs, BDS, GPS/BDS, and GPS/BDS/GLONASS at the current stage, the future Beidou Global Navigation Satellite System, and the future GPS/BDS/GLONASS/Galileo system, the new RAIM method is compared with the traditional least squares method by simulation. The simulation results show that, with the increase of constellations, RAIM availability, fault detection probability, and fault identification probability will be improved. Under the same simulation conditions, the fault detection and identification probabilities based on M-estimation are higher than those based on least squares estimation, and M-estimation is more sensitive to minor deviation than least squares estimation.