Tightly-Coupled Opportunistic Navigation for Deep Urban and Indoor Positioning

A strategy is presented for exploiting the frequency stability, transmit location, and timing information of ambient radio-frequency “signals of opportunity” for the purpose of navigating in deep urban and indoor environments. The strategy, referred to as tightly-coupled opportunistic navigation (TCON), involves a receiver continually searching for signals from which to extract navigation and timing information. The receiver begins by characterizing these signals, whether downloading characterizations from a collaborative online database or performing characterizations on-the-fly. Signal observables are subsequently combined within a central estimator to produce an optimal estimate of position and time. A simple demonstration of the TCON strategy focused on timing shows that a TCONenabled receiver can characterize and use CDMA cellular signals to correct its local clock variations, allowing it to coherently integrate GNSS signals beyond 100 seconds.Aerospace Engineering and Engineering Mechanic

Timing Experiments with Global Navigation Satellite System Clocks

The science of timekeeping is crucial in many dierent applications around the world. One of the most signicative applications in which time and frequency metrology has an essential role are Global Navigation Satellite Systems (GNSS). Any satellite navigation system indeed, is based on the transmission of signals from a constellation of satellites: processing these signals it is possible to estimate the position of a user, provided that the time of transmission is indicated with extremely high accuracy. In fact, being the distance measured from a time, any error in the measure of time will be directly mapped into an error in the user position, which has to be kept below its specied limits. The positioning accuracy is widely determined by the clocks quality. It is why all the satellites need to y very accurate atomic clocks: fundamental for their excellent stability. An agreement between the European Community and the European Space Agency (ESA) gave rise to a new European satellite system: Galileo. The Istituto Nazionale di Ricerca Metrologica (INRiM) is deeply involved in the Galileo project, mainly concerning the activities related to the experimental phases, such as the generation of an experimental reference time scale for the system and the metrological characterization of atomic clocks employed onboard satellites. This thesis will describe the timing experiments carried out in these years of doctorate with GNSS clocks, both with space and ground clocks, within the experimental phases of the Galileo project

Characterization of a 450-km Baseline GPS Carrier-Phase Link using an Optical Fiber Link

A GPS carrier-phase frequency transfer link along a baseline of 450 km has been established and is characterized by comparing it to a phase-stabilized optical fiber link of 920 km length, established between the two endpoints, the Max-Planck-Institut f\"ur Quantenoptik in Garching and the Physikalisch-Technische Bundesanstalt in Braunschweig. The characterization is accomplished by comparing two active hydrogen masers operated at both institutes. The masers serve as local oscillators and cancel out when the double differences are calculated, such that they do not constitute a limitation for the GPS link characterization. We achieve a frequency instability of 3 x 10^(-13) in 30 s and 5 x 10^(-16) for long averaging times. Frequency comparison results obtained via both links show no deviation larger than the statistical uncertainty of 6 x 10^(-16). These results can be interpreted as a successful cross-check of the measurement uncertainty of a truly remote end fiber link.Comment: 14 pages, 6 figure

Robustness of circadian clocks to daylight fluctuations: hints from the picoeucaryote Ostreococcus tauri

The development of systemic approaches in biology has put emphasis on identifying genetic modules whose behavior can be modeled accurately so as to gain insight into their structure and function. However most gene circuits in a cell are under control of external signals and thus quantitative agreement between experimental data and a mathematical model is difficult. Circadian biology has been one notable exception: quantitative models of the internal clock that orchestrates biological processes over the 24-hour diurnal cycle have been constructed for a few organisms, from cyanobacteria to plants and mammals. In most cases, a complex architecture with interlocked feedback loops has been evidenced. Here we present first modeling results for the circadian clock of the green unicellular alga Ostreococcus tauri. Two plant-like clock genes have been shown to play a central role in Ostreococcus clock. We find that their expression time profiles can be accurately reproduced by a minimal model of a two-gene transcriptional feedback loop. Remarkably, best adjustment of data recorded under light/dark alternation is obtained when assuming that the oscillator is not coupled to the diurnal cycle. This suggests that coupling to light is confined to specific time intervals and has no dynamical effect when the oscillator is entrained by the diurnal cycle. This intringuing property may reflect a strategy to minimize the impact of fluctuations in daylight intensity on the core circadian oscillator, a type of perturbation that has been rarely considered when assessing the robustness of circadian clocks

Ultra-Precise Optical and Microwave Synthesis With an Er/Yb:Glass Frequency Comb

This thesis focuses on the development of an optical frequency comb based on an Er/Yb:glass modelocked laser, and its application to precision optical and microwave metrology of atomic clocks. Frequency combs can be used for wideband generation of phase-coherent signals that span both the microwave and optical domains. This capability vastly expands the utility and application of optical atomic clocks, which are currently 100 times more accurate and stable than the current definition of the SI second, based on microwave 133Cs fountain clocks. Within national metrology labs like the National Institute of Standards and Technology (NIST), optical frequency combs are central to the characterization of atomic clocks and the realization of all-optical time scales, which rely on frequency combs to generate optical and microwave timing signals from ensembles of high-stability references.&nbsp; In this work, I detail the steps to design, build, and characterize a robust, low-noise and cost-effective frequency comb based on an Er/Yb:glass free-space modelocked laser. I developed such a comb and demonstrated its capability in a number of applications: 1) calibration of the NIST microwave time scale via optical frequency division of the 171Yb optical lattice clock, 2) generation of the highest spectral purity 10 GHz signals using a highly robust transfer oscillator technique, and 3) using the frequency comb to phase-coherently link NIST&rsquo;s 27Al+ single-ion clock and 177Yb optical-lattice clock in the first demonstration of differential spectroscopy, a technique that has enabled the highest-stability inter-species clock comparison to date. This technique allows for higher accuracy frequency ratio measurements of optical clocks and more accurate contributions of single-ion clocks in an optical time scale, demonstrating an order-of-magnitude improvement in stability.&nbsp; Finally, I have begun developing the infrastructure needed to support the creation of an all-optical time scale at NIST. This work has involved investigating the limiting noise sources in time/frequency transfer over optical fiber links, to support the highest resolution comparison of next-generation optical clocks. I have also worked on transmission of high stability 10 GHz microwave signals via radio-over-fiber, needed to upgrade the microwave timing capabilities of research laboratories within NIST Boulder. Both techniques will be valuable in the dissemination of high-stability and high-accuracy signals derived from optical clocks and will enable the development of next-generation technology with stringent synchronization requirements.</p