Dottorato in INFRASTRUTTURE E TRASPORTI

Titolo della tesi: GNSS Point Positioning and Variometric Solutions Integration to Support and Improve Real-Time Navigation

Nowadays, Global Navigation Satellite Systems (GNSS) technology is pervasive in the civilian daily life. Among all the possible application elds, satellite navigation systems play a major role in kinematic applications ranging from pedestrian or vehicle navigation to people and goods tracking. Furthermore, the recent developments, in both satellite and user segments, are pushing forward the development of innovative and more accurate dynamic applications also on mass-market GNSS receivers as Android smartphones. In this variety of possible applications, dierent GNSSbased algorithms can be considered depending on the targeted requirements. The main aim of this thesis is to introduce and validate GNSS POWER, a standalone positioning algorithm developed as a trade-o between traditional code-based and phase-based approaches. GNSS POWER relies on both pseuodorange and carrier-phase observations. The algorithm is based on a loosely coupling strategy between a robust SPP and the variometric velocities estimated leveraging on variometric phase observations and kinematic Variometric Approach for Displacements Analysis Stand-alone Engine (kin-VADASE). The use of variometric phase measurements allows to estimate instantaneous 3D velocity with accuracy of few mm/s. However, considering the contribute of pseudorange observations analysed using an SPP algorithm, GNSS POWER can target absolute accuracy of few decimetres and epochby- epoch displacements with few centimetres uncertainty. The methodology is validated in both static and kinematic conditions with dierent GNSS receivers using Global Positioning System (GPS) and Galileo L1/E1 observations. The results in static scenario demonstrates mean accuracy around 0.5 m for the horizontal components and around 1.0 m in the height using one week of GNSS measurements from a Continuous Operating Reference Stations (CORS) receiver. In order to target the same accuracy level on poorer observations, a cycle slip detector, based on variometric phase measurements, and two methodologies for robust adjustment - i.e. LOOCV and recursive Huber function - are introduced and validated on data from a u-blox ZED F9P and a Xiaomi Mi 8. Furthermore, the tests in kinematic scenarios in open sky conditions demonstrate comparable results with geodetic receivers. Horizontal submeter accuracy can be achieved using Android smartphones as well. A marked improvement with respect to the traditional SPP is also observed in vehicle navigation scenario for both high-end receiver and Android smartphones. Additionally, a real-time GNSS POWER tool is introduced and described in the thesis with the main purpose to exploit orbits, clocks and code biases SSR corrections to increase the overall accuracy. As demonstrated from static tests, the availability of real-time SSR corrections streamed in Radio Technical Commission for Maritime Services (RTCM) format further enhances the accuracy of GNSS POWER solutions. A comparison on one week of GNSS measurements from a CORS station highlights a mean improvement of 0.05 m, 0.10 m and 0.04 m in the East, North and Up Root Mean Square Error (RMSE) with respect to the use of only broadcast information. The test in kinematic scenario, carried out on a shorter time interval - i.e. 25 minutes -, conrms the importance of applying SSR corrections not only on geodetic receivers but also on Android smartphones. For instance, the enhancement with respect to the solution based on broadcast navigation message in the horizontal R50 and R95 can reach the 18%. For all the kinematic datasets in analysis, the epoch-by-epoch accuracy of GNSS POWER is in the range of few centimetres demonstrating high-precision in retrieving tracks geometry. Based on the results disccused in this thesis, GNSS POWER is now becoming a key GNSS algorithm in different research and commercial projects with focus on topographic, mHealth and precision agriculture applications. In conclusion, this thesis introduces and validates a realtime standalone GNSS algorithm able to support instantaneous, stable and reliable Position, Velocity and Time (PVT) solutions with absolute accuracy of few decimetres and epoch-by-epoch displacements of few centimetres.