Innovative Signal Processing Solutions for Next-Generation Satellite Navigation Systems

L'abstract è presente nell'allegato / the abstract is in the attachmen

Modelling and Experimental Assessment of Inter-Personal Distancing Based on Shared GNSS Observables

In the last few years, all countries worldwide have fought the spread of SARS-CoV-2 (COVID-19) by exploiting Information and Communication Technologies (ICT) to perform contact tracing. In parallel, the pandemic has highlighted the relevance of mobility and social distancing among citizens. The monitoring of such aspects appeared prominent for reactive decision-making and the effective tracking of the infection chain. In parallel to the proximity sensing among people, indeed, the concept of social distancing has captured the attention to signal processing algorithms enabling short-to-medium range distance estimation to provide behavioral models in the emergency. By exploiting the availability of smart devices, the synergy between mobile network connectivity and Global Navigation Satellite Systems (GNSS), cooperative ranging approaches allow computing inter-personal distance measurements in outdoor environments through the exchange of light-weight navigation data among interconnected users. In this paper, a model for Inter-Agent Ranging (IAR) is provided and experimentally assessed to offer a naive collaborative distancing technique that leverages these features. Although the technique provides distance information, it does not imply the disclosure of the user’s locations being intrinsically prone to protect sensitive user data. A statistical error model is presented and validated through synthetic simulations and real, on-field experiments to support implementation in GNSS-equipped mobile devices. Accuracy and precision of IAR measurements are compared to other consolidated GNSS-based techniques showing comparable performance at lower complexity and computational effort

Impact of non-idealities on GNSS meta-signals processing

This paper deals with the concept of GNSS meta-signal processing, defined as the coherent process of two GNSS signals, broadcast on different carriers, and treated as a single wideband signal. The purpose of the paper is twofold: to analyse the effects on non-idealities on the meta-signal components and to investigate alternative schemes for the actual implementation inside the receiver

GNSS-only Collaborative Positioning Among Connected Vehicles

Cooperative positioning is considered a key strategy for the improvement of localization and navigation performance in harsh contexts such as urban areas. Modern communication paradigms can support the exchange of inter-vehicle ranges measured from on-board sensors or obtained through Global Satellite Navigation System (GNSS) measurements. The paper presents an overview of the GNSS-only collaborative localization in the context of cooperative connected cars. It provides an experimental example along with new results about the tight integration of collaboratively-generated inter-vehicle relative measurements collected by a target vehicle by means of a double differentiation w.r.t. to a set of five aiding vehicles. An average improvement of the positioning accuracy of about 11% motivates the research effort towards multi-agent connected positioning systems

Contact Plan Design for GNSS Constellations: A Case Study with Optical Inter-Satellite Links

Optical Inter-Satellite Links (OISLs) are being considered for future Global Navigation Satellite System (GNSS) constellations. Thanks to OISLs, the constellation incorporates improved clock synchronization and precise ranging among the satellites, which are essential features to achieve accurate time and orbit determination. High data rate communications within the space segment also reduce ground segment dependency, by means of decentralized access to information. However, the dual optimization of data and navigation performance metrics requires a careful assignment of OISLs to the available laser communication terminals on-board. To this end, we present a Contact Plan Design (CPD) scheme based on a Degree Constrained Minimum Spanning Tree heuristic applied to such OISL-enabled GNSS (O-GNSS) constellations. Results on the Kepler system, a novel GNSS proposal, show that a fair distribution of connectivity among the constellation can be ensured while optimizing its range-based position estimation capabilities (PDOP). A PDOP improvement of 85 % is reached on average by the optimized contact plan with respect to a generic scheduler that disregards the geometrical distribution of the chosen links

Empowering the Tracking Performance of LEO PNT by Means of Meta-Signals

Global Navigation Satellite Systems (GNSSs) are by far the most widespread technology for Position Navigation and Timing (PNT). They have been traditionally deployed exploiting Medium Earth Orbit (MEO) or Geostationary Earth Orbit (GEO) satellite constellations. To meet future demands and overcome MEO and GEO limitations, GNSSs based on Low Earth Orbit (LEO) constellations have been investigated as a radical system change. Although characterized by a higher Doppler effect, a PNT service supplied by means of LEO satellites can provide received signals that are about 30 dB stronger. Moreover, existing LEO constellations and the forthcoming mega-constellations, which are designed for broadband internet coverage, can be exploited to provide a piggybacked PNT service. With this cost-effective solution, a secondary PNT service might be subject to an economical use of resources, which may result in substantial bandwidth limitations. At the same time, the introduction of meta-signals in the GNSS literature has brought a new receiver signal processing strategy, particularly effective in terms of available bandwidth exploitation. It allows to increase the positioning accuracy exploiting a wideband processing approach, which might be challenging under severe Doppler conditions. A narrowband implementation of the meta-signal concept, namely Virtual Wideband (VWB) can tolerate harsh Doppler conditions while also reducing the processed bandwidth. It is thus more effective when addressing a secondary PNT service, where a limited frequency occupation might be an essential requirement. The aim of this work is to show the applicability of a VWB receiver architecture on signals provided by a piggybacked PNT service, hosted on a broadband LEO constellation. We demonstrate the capability of this implementation to bear high Doppler conditions while empowering the potential of LEO PNT

Optimized design of next-generation multiplexing schemes for GNSSs

Multilevel and multicarrier component signals are now common in many Global Navigation Satellite Systems challenging the employed multiplexing method that needs to be more flexible and powerful. In this work, we demonstrate how, by acting on two parameters of the digital baseband representation of component signals (the sampling frequency and the central frequency of the baseband complex envelope), it is possible to optimize the performance of the multiplexer, while still obtaining a composite signal that fulfills the required system constraints

Analysis of GNSS data at the Moon for the LuGRE project

The Lunar GNSS Receiver Experiment (LuGRE) aims at testing positioning and navigation at the Moon by using Earth Global Navigation Satellite Systems. Within this framework, to support the scientific mission definition and to process on-ground the data that will be collected, a proper GNSS software receiver is needed, implementing advanced signal processing algorithms that enable it to work in the Moon scenario. This paper discusses the issues and potentialities, presenting the preliminary results of the simulation of the Moon environment, as far as the navigation tasks are concerned

A Human-Derived Monoclonal Antibody Targeting Extracellular Connexin Domain Selectively Modulates Hemichannel Function

Connexin hemichannels, which are plasma membrane hexameric channels (connexons) composed of connexin protein protomers, have been implicated in a host of physiological processes and pathological conditions. A number of single point pathological mutations impart a "leaky" character to the affected hemichannels, i.e., make them more active or hyperactive, suggesting that normal physiological condition could be recovered using selective hemichannel inhibitors. Recently, a human-derived monoclonal antibody named abEC1.1 has been shown to inhibit both wild type and hyperactive hemichannels composed of human (h) connexin 26 (hCx26) subunits. The aims of this work were (1) to characterize further the ability of abEC1.1 to selectively modulate connexin hemichannel function and (2) to assess its in vitro stability in view of future translational applications. In silico analysis of abEC1.1 interaction with the hCx26 hemichannel identified critically important extracellular domain amino acids that are conserved in connexin 30 (hCx30) and connexin 32 (hCx32). Patch clamp experiments performed in HeLa DH cells confirmed the inhibition efficiency of abEC1.1 was comparable for hCx26, hCx30 and hCx32 hemichannels. Of note, even a single amino acid difference in the putative binding region reduced drastically the inhibitory effects of the antibody on all the other tested hemichannels, namely hCx30.2/31.3, hCx30.3, hCx31, hCx31.1, hCx37, hCx43 and hCx45. Plasma membrane channels composed of pannexin 1 were not affected by abEC1.1. Finally, size exclusion chromatography assays showed the antibody does not aggregate appreciably in vitro. Altogether, these results indicate abEC1.1 is a promising tool for further translational studies