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NARDIN, ANDREA

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Doctoral DissertationDoctoral Program in Electrical, Electronics and Communications Engineering(35thcycle)Innovative Signal ProcessingSolutions for Next-GenerationSatellite Navigation SystemsByAndrea Nardin******Supervisor(s):Prof. Fabio Dovis, SupervisorDoctoral Examination Committee:Dr. Carles Fernández-Prades , Referee, Centre Tecnològic de Telecomunicacions deCatalunya (CTTC)Prof. Elena Simona Lohan, Referee, Tampere UniversityProf. Roberto Garello, Politecnico di TorinoDr. Christophe Macabiau, Ecole Nationale de l’Aviation Civile (ENAC)Prof. Gonzalo Seco Granados, Universitat Autònoma de Barcelona (UAB)Prof. Xin Chen, Shanghai Jiao Tong UniversityPolitecnico di Torino2023AbstractFrom the development of the first satellite navigation system during the late 1950s, wehave been observing a continuous modernization process. Global Navigation SatelliteSystems (GNSSs) are nowadays the most widespread technology for positioning,navigation and timing (PNT) and have been traditionally deployed exploiting mediumearth orbit (MEO). Although characterized by a stronger Doppler effect, PNT basedon low earth orbit (LEO) constellations has been investigated as a radical systemchange or as an enhancement for existing GNSSs, to provide better position, velocity,and time (PVT) estimation accuracy, signal robustness, and service availability.As constellations are growing, providing a reliable service becomes more diffi-cult. Indeed, timely information about orbit determination and system time needsto be provisioned to each satellite by a network of ground stations. However, con-tinuous radio visibility cannot be ensured for large constellations, such as LEOfleets; therefore, to foster space segment autonomy, the use of inter-satellite links(ISLs) has been foreseen in the last years as a natural system enhancement to grant adecentralized access to information. Moreover, the adoption of optical inter-satellitelinks (OISLs) has been proposed to achieve improved clock synchronization, preciseranging, and high data rate communications, resulting in an overall better accuracyand autonomy. However, given the limited number of simultaneous ISLs, the dual op-timization of data and navigation performance metrics requires a careful assignmentof connections to the available transponders.PNT services are available thanks to the simultaneous broadcasting of multiplesignals and signal design innovation has been often steered toward powerful multi-plexing schemes, to combine multiple signals into a single composite transmittedsignal. Indeed, modern signal multiplexing methods allow to seamlessly enhancethe existing signal-in-space with newer signals and to support frequent and rapidreconfigurations of the transmitted signal set, promptly adapting to system upgradesviand future needs. However, as the number of signals grows, efficient multiplexingbecomes more challenging, resulting in significant power loss.Nevertheless, GNSS receivers are also continuously evolving as a primary answerto user demands. Advanced algorithms and new processing strategies are thereforeexploited to improve PVT estimation performance, leveraging, for instance, multiplesignals or modern receivers’ connectivity (e.g. smartphones), but their applicabilityin new GNSS scenarios should be assessed.The aim of this dissertation is to explore innovative prospects for future satellitenavigation systems, proposing and analyzing several solutions at system, signals,and user level. The objective of this work has been therefore to seek for performanceimprovements, acting at various levels of the GNSS value chain, yet fulfilling possibleupcoming needs and constraints. In this context, this work focuses on improving theuse of resources, both upstream, to enhance signals and services, and downstream,by leveraging such signals for a better user performance. Specific research questionswere addressed for this purpose: how can ISLs be assigned while optimizing data andnavigation performance? Can multiple signals transmission be more efficient? Howcan we leverage signal multiplicity and receiver technologies to improve accuracyand robustness of the final PVT estimation?The first part is dedicated to the space segment evolution. The problem of opti-mizing the contact plan for a GNSS equipped with OISLs is specifically addressedand optimal range-based satellite positioning is achieved through the dedicateddesign of objective functions and satellite network modeling. A contact plan de-sign scheme is presented, based on a degree constrained minimum spanning tree(DCMST) heuristic. Results on the Kepler system, a novel GNSS proposal, show thata Position Dilution of Precision (PDOP) improvement of 85 % is reached on averageby the optimized contact plan with respect to a generic scheduler that disregards thegeometrical distribution of the chosen links.The second part is focused on multiplexing methods for future satellite navigationsystems. An input optimization method for multicarrier multiplexing algorithmsis presented, to improve the use of power resources in upcoming payloads. A badchoice of input configuration can, in fact, severely affect the multiplexing perfor-mance causing a power loss of more than 20%. Avoiding such poorly performingconfigurations motivates the proposed algorithm.viiThe third part is dedicated to user technologies and signal processing algorithms,focusing on those techniques that especially fit upcoming changes. The contributionof this dissertation to user-level advancements is therefore twofold: (i) the definitionand testing of a processing architecture, enabled by the higher complexity of modernreceivers, that leverages multiple signals to provide improved accuracy; (ii) theproposal of a crowdsourcing algorithm, enabled by the enhanced connectivity thatcharacterizes the current and upcoming user base, with the goal to hinder intentionalinterference threats.A generalized theory of the concept of meta-signal, extended to orthogonalsignals, is thus proposed, to address (i) and efficiently exploit band-limited signalswhile improving Doppler robustness. The method has been compared to a typicalmeta-signal implementation and its robustness has been tested against differentimpairments and scenario settings for next-generation GNSSs. This approach grantsaccurate signal tracking with an adjustable estimation accuracy. Such predominantflexibility, together with the Doppler robustness, make the investigated architecturesuitable to rapidly adapt to the fast-changing needs of future and alternative GNSSs.Enhanced connectivity was explored for collaborative approaches against jam-ming (ii), a serious threat for current and future GNSSs due to received signals’ lowpower. Congested areas are particularly sensitive to these kinds of attacks, but theyalso present an opportunity to leverage crowdsourced data for threat localization. Inthis framework, a jammer localization scheme based on a physics-based learningapproach is proposed. The interference localization method is based on a signalpropagation model, enhanced through the use of physics-based path loss modelingand an augmented, data-driven, component. This method proved to seamlessly adaptto very different propagation scenarios, without any prior information about thecharacteristics of the jammer.

Innovative Signal Processing Solutions for Next-Generation Satellite Navigation Systems

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Innovative Signal Processing Solutions for Next-Generation Satellite Navigation Systems

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