Global Navigation Satellite Systems (GNSSs) remain the principal mean of positioning in many applications and systems, but in several types of environment, the performance of standalone receivers is degraded. Although many works show the benefits of the integration between GNSS and Inertial Navigation Systems (INSs), tightly-coupled architectures are mainly implemented in professional devices and are based on high-grade Inertial Measurement Units (IMUs). This paper investigates the performance improvements enabled by the tight integration, using low-cost sensors and a mass-market GNSS receiver. Performance is assessed through a series of tests carried out in real urban scenarios and is compared against commercial modules, operating in standalone mode or featuring loosely-coupled integrations. The paper describes the developed tight-integration algorithms with a terse mathematical model and assesses their efficacy from a practical perspective.

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Precision Agriculture (PA) refers to applications asking for reliable and highly available precise positions, at centimeter level, in most of operational scenarios. Machinery guidance, automatic steering and controlled traffic farming enable machinery to move along repeatable tracks on the field, minimizing pass-to-pass errors and overlaps. In the recent years, satellite-based navigation has also opened the door to (semi) autonomous machineries for some specific farming scenarios and operations. Farming industry is now looking to use small robots to bring efficiencies and benefits to farms, capable of complex tasks that have not been possible with traditional large-scale agricultural machinery. Even though the state-of-the-art Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) receivers usually match the requirements posed by PA applications in open fields, propagation effects degrade the performance under foliage or with surrounding obstacles. This paper presents an experimental testbed and methodology suitable to assess the real performance of RTK GNSS-based devices in operational environments. Such testbed and methodology were effective to compare different devices, which resulted to be equivalent in open-sky conditions, but with significant differences in other types of environments. The paper also discusses opportunities and current limits of GNSS for emerging PA applications based on small robots and artificial intelligence. INDEX TERMS Global navigation satellite system (GNSS), real time kinematic (RTK), horizontal position accuracy, positions availability.

Global Navigation Satellite Systems (GNSS) broadcast signals for positioning and navigation, which can be also employed for remote sensing applications. Indeed, the satellites of any GNSS can be seen as synchronized sources of electromagnetic radiation, and specific processing of the signals reflected back from the ground can be used to estimate the geophysical properties of the Earth’s surface. Several experiments have successfully demonstrated GNSS-reflectometry (GNSS-R), whereas new applications are continuously emerging and are presently under development, either from static or dynamic platforms. GNSS-R can be implemented at a low cost, primarily if small devices are mounted on-board unmanned aerial vehicles (UAVs), which today can be equipped with several types of sensors for environmental monitoring. So far, many instruments for GNSS-R have followed the GNSS bistatic radar architecture and consisted of custom GNSS receivers, often requiring a personal computer and bulky systems to store large amounts of data. This paper presents the development of a GNSS-based sensor for UAVs and small manned aircraft, used to classify lands according to their soil water content. The paper provides details on the design of the major hardware and software components, as well as the description of the results obtained through field tests.

The objective of the work is the evaluation of the impact of new modulation strategies foreseen for the Galileo Signal In Space (SIS) on the carrier tracking operation within the Global Navigation Satellite Systems (GNSS) receiver (namely Frequency Locked Loop (FLL)/Phase Locke Loop (PLL)) in presence of multipath. Although multipath has more relevant effects in term of measurement errors on the code tracking, its consequences on the carrier tracking can not be neglected in high accuracy applications that rely on the carrier phase measurement such as, for example, Real Time Kinematics (RTK) survey. Particular attention is addressed to the Multiplexed Binary Offset Carrier (MBOC) signals and the Alternate BOC (AltBOC) signals. The investigation is conducted considering a two ray model with the aim of producing an error diagram showing the multipath effect in the carrier tracking: the Delay Locked Loop (DLL) PLL interaction is considered in a static -low dynamic environment. Closed loop simulations are conducted by means of specific software tools based on the GNSS fully software receiver developed by the NavSAS group. Performance verification is done for a noisy environment. Results show loops performance in a multipath affected environment and the effects of noise in the carrier tracking operations. The PLL performance evaluation under multipath conditions, considering as input MBOC and AltBOC modulated signals, is important to understand the behavior of the new modulations especially in case of carrier tracking based applications that are the more demanding in terms of final positioning performance (i.e. geodetic applications).

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Signals from global navigation satellite systems (GNSS) can be utilized as signals of opportunity in remote sensing applications. Geophysical properties of the earth surface can be detected and monitored by processing the back-scattered GNSS signals from the ground. In the literature, several airborne GNSS-based passive radar experiments have been successfully demonstrated. With the advancements in small unmanned aerial vehicles (UAVs) and their applications for environmental monitoring, we want to investigate whether GNSS-based passive radar can provide valuable geospatial information from such platforms. Low-cost GNSS reflectometry sensors, developed using commercial of the shelf components, can be mounted onboard UAVs and flown to sense environmental parameters. This paper presents the results of a preliminary study to investigate the feasibility of utilizing data collected by UAV-based GNSS-R sensors to detect surface water for a potential application in supporting flood monitoring operations. The study was conducted in the area surrounding the Avigliana lakes in Northern Italy. The results show the possibility of detecting small water surfaces with few tens of meters resolution, and estimating the area of the lake surface with 92% accuracy. Furthermore, it is proved through simulations that the use of multi-GNSS increases this accuracy to about 99%.

The greater part of modern low-cost GNSS receivers are able to guarantee a fair positioning performance almost everywhere: difficult environments as indoor and urban canyons are also considered. The aim of this work is to investigate the effective potentialities of this kind of receivers, in particular in static and kinematic positioning using post-processing techniques. The high number of GPS permanent stations and the continuous increase of the number of GNSS multi-constellation permanent stations, will give a good opportunity to improve accuracy and precision levels. Several GPS mass-market chipsets have been used considering different scenarios. The benefits of the DGPS service made available by the test GPS network of the Politecnico di Torino have been taken into account.This research permits to measure the advantages provided by the use of low cost receivers with post-processing techniques and DGPS corrections. This was done comparing the results with the solutions obtained with a geodetic dual frequency receiver. The raw data collection has been performed thanks to the SAT-SURF & SAT-SURFER suite. SAT-SURFER is a software (developed by the NAVSAS group) allowing data collection (including differential ones from Virtual Reference Stations) in different formats. SAT-SURF is the hardware part of the suite: a flexible platform able to host different kinds of GPS chipsets.During the test the receivers were used in a unconventional way, not only because they were used with a GNSS Network, but also because of the realization of an ad hoc logging architecture.The tests bring to have interesting results, in particular about the level of accuracy in post-processing and in real time, where the contribution of the GNSS network is less appreciable. The level of accuracy is sufficient for some applications such as the thickening of the cartographic and cadastral network. The analysis of the results obtained from the real tests shows that it is possible to state that low cost receivers are suitable for applications requiring a good quasi real time positioning such as navigation and topographic applications.