Advanced signal processing techniques for interference removal in Satellite Navigation Systems

This thesis investigates the use of innovative interference detection and mitigation techniques for GNSS based applications. The main purpose of this thesis is the development of advanced signal processing techniques outperforming current interference mitigation algorithms already implemented in off-the-shelf GNSS receivers. State-of-the-art interference countermeasures already investigated in literature, which process the signal at the ADC output, provide interference components suppression in the time domain or in the frequency domain, thus leading to a significant signal degradation in harmful interference scenarios where the GNSS signals spectra at the receiver antenna is completely jammed by external intentional or unintentional RFI sources. The proposed advanced interference countermeasures overcome such a limit, since they are based on particular signal processing techniques which manipulate the received samples at the ADC output, providing a representation in new domains where interference component can be better detected and separated from the rest of the signal, minimizing the useful signal distortion even in presence of multiple interference sources. At the cost of an increased computational complexity, such techniques can be optimized for increasing the sensitivity and the robustness of GNSS receiver merged in harmful environments. The work of this thesis addresses the design of such techniques by means of theoretical analyses, their performance assessment by means of simulation and their validation by means of synthetic and real GNSS data. Furthermore performance comparison with more traditional interference countermeasures is also presented considering a variety of harmful interference scenarios. In addition to the investigation of such new interference countermeasures, part of the thesis deals with the limit of current interference suppression technique, such as the pulse blanking, and its impact on the data demodulation performance. A very general investigation of the pulse blanking impact on the data demodulation performance for un-coded BPSK DSSS is provided. Then, the analysis focuses on the assessment of the navigation data demodulation performance for the current SBAS, then providing a proposal for system improvements, in terms of robustness and data rate increase, in future SBAS generation. Among the different interference scenarios considered, the thesis focuses on the potential interference environment expected in aviation context, since the Galileo E5 and GPS L5 bands, where the future GNSS based aviation services will be broadcast, are shared with other ARNS broadcasting strong pulsed interfering signals, which may seriously threat the on-board GNSS receiver operations . For such scenarios, simulation and analytic models are discussed and used as benchmark cases for assessing the mitigation techniques, in terms of SNR gain and data demodulation capability. The presence of interference (mitigated or not) causes a loss in the carrier to noise density ratio CN0 value for the received signal. For this reason, in order to reliably deal with such signals, the GNSS receiver must be able to feature high-sensitivity algorithms at the acquisition and tracking stages. For this reason the last part of the thesis investigates HS acquisition schemes for very weak GNSS signal detection. In particular, the purpose of this part of the work is to present a theoretical methodology for the design of an acquisition scheme capable of detecting signal down to 5 dB-Hz. The analysis carried out assuming the presence of assistance information which allows the receiver employing long coherent integration time (order of seconds). The particular scenario of the GNSS space environment is taken into consideration and the analysis is also focused on the definition of the requirements on the accuracy for potential Doppler aiding sources at the receiver level. The theoretical analysis is also supported by fully software simulatio

Retrieval-, Distributed-, and Interleaved Practice in the Classroom:A Systematic Review

Three of the most effective learning strategies identified are retrieval practice, distributed practice, and interleaved practice, also referred to as desirable difficulties. However, it is yet unknown to what extent these three practices foster learning in primary and secondary education classrooms (as opposed to the laboratory and/or tertiary education classrooms, where most research is conducted) and whether these strategies affect different students differently. To address these gaps, we conducted a systematic review. Initial and detailed screening of 869 documents found in a threefold search resulted in a pool of 29 journal articles published from 2006 through June 2020. Seventy-five effect sizes nested in 47 experiments nested in 29 documents were included in the review. Retrieval- and interleaved practice appeared to benefit students’ learning outcomes quite consistently; distributed practice less so. Furthermore, only cognitive Student*Task characteristics (i.e., features of the student’s cognition regarding the task, such as initial success) appeared to be significant moderators. We conclude that future research further conceptualising and operationalising initial effort is required, as is a differentiated approach to implementing desirable difficulties

[¹⁸F]fluorination of biorelevant arylboronic acid pinacol ester scaffolds synthesized by convergence techniques

Aim: The development of small molecules through convergent multicomponent reactions (MCR) has been boosted during the last decade due to the ability to synthesize, virtually without any side-products, numerous small drug-like molecules with several degrees of structural diversity.(1) The association of positron emission tomography (PET) labeling techniques in line with the “one-pot” development of biologically active compounds has the potential to become relevant not only for the evaluation and characterization of those MCR products through molecular imaging, but also to increase the library of radiotracers available. Therefore, since the [18F]fluorination of arylboronic acid pinacol ester derivatives tolerates electron-poor and electro-rich arenes and various functional groups,(2) the main goal of this research work was to achieve the 18F-radiolabeling of several different molecules synthesized through MCR. Materials and Methods: [18F]Fluorination of boronic acid pinacol esters was first extensively optimized using a benzaldehyde derivative in relation to the ideal amount of Cu(II) catalyst and precursor to be used, as well as the reaction solvent. Radiochemical conversion (RCC) yields were assessed by TLC-SG. The optimized radiolabeling conditions were subsequently applied to several structurally different MCR scaffolds comprising biologically relevant pharmacophores (e.g. β-lactam, morpholine, tetrazole, oxazole) that were synthesized to specifically contain a boronic acid pinacol ester group. Results: Radiolabeling with fluorine-18 was achieved with volumes (800 μl) and activities (≤ 2 GBq) compatible with most radiochemistry techniques and modules. In summary, an increase in the quantities of precursor or Cu(II) catalyst lead to higher conversion yields. An optimal amount of precursor (0.06 mmol) and Cu(OTf)2(py)4 (0.04 mmol) was defined for further reactions, with DMA being a preferential solvent over DMF. RCC yields from 15% to 76%, depending on the scaffold, were reproducibly achieved. Interestingly, it was noticed that the structure of the scaffolds, beyond the arylboronic acid, exerts some influence in the final RCC, with electron-withdrawing groups in the para position apparently enhancing the radiolabeling yield. Conclusion: The developed method with high RCC and reproducibility has the potential to be applied in line with MCR and also has a possibility to be incorporated in a later stage of this convergent “one-pot” synthesis strategy. Further studies are currently ongoing to apply this radiolabeling concept to fluorine-containing approved drugs whose boronic acid pinacol ester precursors can be synthesized through MCR (e.g. atorvastatin)

Exploring the Relationship between Tourism and Economic Growth in Small Island Economies: A Study of Fiji

This study examines the effect of tourism, measured by visitor arrivals) on the economic growth of Fiji, a small island economy, over the period 1975 to 2015. We use a neoclassical framework and regression analysis to examine the short-run and the long-run effects of tourism whilst accounting for structural breaks. We confirm the presence of a long-run association using the two-step procedure of Engle and Granger (1987) and the ARDL bounds test of Pesaran, Shin and Smith (2001). From the long-run results, we note that a 1% increase in visitor arrivals contribute about 0.22% to the GDP per capita. The short run elasticity is noted to be 0.19%. The study finds evidence of a unidirectional causality from economic growth to tourism, and mutually reinforcing effect between capital investment and tourism. Thus, we can expect greater impact of tourism on the economic growth through tourism related investment activities such as improvements in airports, roads, transportation, financial sector and telecommunications, and parks and beaches