Grid-based Hybrid 3DMA GNSS and Terrestrial Positioning

The paper discusses the increasing use of hybridized sensor information for GNSS-based localization and navigation, including the use of 3D map-aided GNSS positioning and terrestrial systems based on different geometric measurement principles. However, both GNSS and terrestrial systems are subject to negative impacts from the propagation environment, which can violate the assumptions of conventionally applied parametric state estimators. Furthermore, dynamic parametric state estimation does not account for multi-modalities within the state space leading to an information loss within the prediction step. In addition, the synchronization of non-deterministic multi-rate measurement systems needs to be accounted. In order to address these challenges, the paper proposes the use of a non-parametric filtering method, specifically a 3DMA multi-epoch Grid Filter, for the tight integration of GNSS and terrestrial signals. Specifically, the fusion of GNSS, Ultra-wide Band (UWB) and vehicle motion data is introduced based on a discrete state representation. Algorithmic challenges, including the use of different measurement models and time synchronization, are addressed. In order to evaluate the proposed method, real-world tests were conducted on an urban automotive testbed in both static and dynamic scenarios. We empirically show that we achieve sub-meter accuracy in the static scenario by averaging a positioning error of $0.64$ m, whereas in the dynamic scenario the average positioning error amounts to $1.62$ m. The paper provides a proof-of-concept of the introduced method and shows the feasibility of the inclusion of terrestrial signals in a 3DMA positioning framework in order to further enhance localization in GNSS-degraded environments

Potentials of Deterministic Radio Propagation Simulation for AI-Enabled Localization and Sensing

Machine leaning (ML) and artificial intelligence (AI) enable new methods for localization and sensing in next-generation networks to fulfill a wide range of use cases. These approaches rely on learning approaches that require large amounts of training and validation data. This paper addresses the data generation bottleneck to develop and validate such methods by proposing an integrated toolchain based on deterministic channel modeling and radio propagation simulation. The toolchain is demonstrated exemplary for scenario classification to obtain localization-related channel parameters within an aircraft cabin environment

An Empirical Study on V2X Enhanced Low-Cost GNSS Cooperative Positioning in Urban Environments

High-precision and lane selective position estimation is of fundamental importance for prospective advanced driver assistance systems (ADAS) and automated driving functions, as well as for traffic information and management processes in intelligent transportation systems (ITS). User and vehicle positioning is usually based on Global Navigation Satellite System (GNSS), which, as stand-alone positioning, does not meet the necessary requirements in terms of accuracy. Furthermore, the rise of connected driving offers various possibilities to enhance GNSS positioning by applying cooperative positioning (CP) methods. Utilizing only low-cost sensors, especially in urban environments, GNSS CP faces several demanding challenges. Therefore, this contribution presents an empirical study on how Vehicle-to-Everything (V2X) technologies can aid GNSS position estimation in urban environments, with the focus being solely on positioning performance instead of multi-sensor data fusion. The performance of CP utilizing common positioning approaches as well as CP integration in state-of-the-art Vehicular Ad-hoc Networks (VANET) is displayed and discussed. Additionally, a measurement campaign, providing a representational foundation for validating multiple CP methods using only consumer level and low-cost GNSS receivers, as well as commercially available IEEE 802.11p V2X communication modules in a typical urban environment is presented. Evaluating the algorithm&rsquo s performance, it is shown that CP approaches are less accurate compared to single positioning in the given environment. In order to investigate error influences, a skyview modelling seeking to identify non-line-of-sight (NLoS) effects using a 3D building model was performed. We found the position estimates to be less accurate in areas which are affected by NLoS effects such as multipath reception. Due to covariance propagation, the accuracy of CP approaches is decreased, calling for strategies for multipath detection and mitigation. In summary, this contribution will provide insights on integration, implementation strategies and accuracy performances, as well as drawbacks for local area, low-cost GNSS CP in urban environments. Document type: Articl

Visible-to-telecom quantum frequency conversion of light from a single quantum emitter

Quantum frequency conversion (QFC), a nonlinear optical process in which the frequency of a quantum light field is altered while conserving its non-classical correlations, was first demonstrated 20 years ago. Meanwhile, it is considered an essential tool for the implementation of quantum repeaters since it allows for interfacing quantum memories with telecom-wavelength photons as quantum information carriers. Here we demonstrate efficient (>30%) QFC of visible single photons (711 nm) emitted by a quantum dot (QD) to a telecom wavelength (1,313 nm). Analysis of the first and second-order coherence before and after wavelength conversion clearly proves that important properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with QFC as a promising technique for quantum repeater schemes.Comment: 11 pages, 4 figure

Four-wave mixing in coupled semiconductor quantum dots

We present a theoretical analysis of four-wave mixing in coupled quantum dots subject to inhomogeneous broadening. For the biexciton transitions a clear signature of interdot-coupling appears in the spectra. The possibility of experimental observation is discussed

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with arXiv:0904.369

Surface atomic relaxation and magnetism on hydrogen-adsorbed Fe(110) surfaces from first principles

We have computed adsorption energies, vibrational frequencies, surface relaxation and buckling for hydrogen adsorbed on a body-centred-cubic Fe(110) surface as a function of the degree of H coverage. This adsorption system is important in a variety of technological processes such as the hydrogen embrittlement in ferritic steels, which motivated this work, and the Haber–Bosch process. We employed spin-polarised density functional theory to optimise geometries of a six-layer Fe slab, followed by frozen mode finite displacement phonon calculations to compute Fe–H vibrational frequencies. We have found that the quasi-threefold (3f) site is the most stable adsorption site, with adsorption energies of ∼3.0 eV/H for all coverages studied. The long-bridge (lb) site, which is close in energy to the 3f site, is actually a transition state leading to the stable 3f site. The calculated harmonic vibrational frequencies collectively span from 730 to 1220 cm−1, for a range of coverages. The increased first-to-second layer spacing in the presence of adsorbed hydrogen, and the pronounced buckling observed in the Fe surface layer, may facilitate the diffusion of hydrogen atoms into the bulk, and therefore impact the early stages of hydrogen embrittlement in steels

How Integrated are the Local U.S. Markets for Natural Gas?—New Evidence Using Rolling Cointegration

In this paper we investigate the degree of market integration for natural gas in the USA. We perform a rolling cointegration estimation of the city gate gas price and the overall gas price in the USA. The long run adjustment coefficients of all states are reported over a rolling window of 60 month from 1989 to 2013. We can identify eight distinct clusters. Clusters are characterized by a different level adjustment on average. Estimates suggest half-life times ranging from 3 weeks to 6 month. Several regulatory actions in order to liberalize the market of natural gas have an effect in terms of the level relationship. These effects are limited. However, we cannot find these structural breaks in all states. The latest change in exploration technologies, hydraulic fracturing and horizontal drilling, does not yet seem to play an important role to explain price dynamics and market integration. JEL Classification: Q4

Evaluation of Technology-Supported Distance Measuring to Ensure Safe Aircraft Boarding during COVID-19 Pandemic

With the rise of COVID-19, the sustainability of air transport is a major challenge, as there is limited space in aircraft cabins, resulting in a higher risk of virus transmission. In order to detect possible chains of infection, technology-supported apps are used for social distancing. These COVID-19 applications are based on the display of the received signal strength for distance estimation, which is strongly influenced by the spreading environment due to the signal multipath reception. Therefore, we evaluate the applicability of technology-based social distancing methods in an aircraft cabin environment using a radio propagation simulation based on a three-dimensional aircraft model. We demonstrate the susceptibility to errors of the conventional COVID-19 distance estimation, which can lead to large errors in the determination of distances and to the impracticability of traditional tracing approaches during passenger boarding/deboarding. In the context of the future connected cabin, a robust distance measurement must be implemented to ensure safe travel. Finally, our results can be transferred to similar fields of application, e.g., trains or public transport