Processed 5G Signals Mathematical Models for Positioning considering a Non-Constant Propagation Channel

International audienceThe objective of this paper is to determine the ranging performance of the upcoming fifth generation (5G) signal. In order to do so, it is required to define 5G correlator outputs mathematical models. 5G systems will use OFDM (Orthogonal Frequency Division Multiplexing) signals; in the literature, mathematical models of OFDM signals are developed at the different receiver signal processing stages. These models assumed that the propagation channel is constant over an OFDM symbol; nevertheless, an in-depth study of QuaDRiGa, a 5G compliant propagation channel simulator, invalidates this hypothesis. Therefore, in this paper, mathematical models are developed that take into account the channel evolution. The focus is given on correlator outputs and results are applied to the computation of 5G based pseudo range accuracy

Asymptotically efficient GNSS trilateration

Localization based on the reception of radio-frequency waveforms is a crucial problem in many civilian or military applications. It is also the main objective of all Global Navigation Satellite System (GNSS). Given delayed and Doppler shifted replicas of the satellites transmitted signals, the most widespread approach consists in a suboptimal two-step procedure. First, estimate the delays and Dopplers from each satellite independently, then estimate the user position and speed thanks to a Least Square (LS) minimization. More accurate and robust techniques, such as a direct Maximum Likelihood (ML) maximization, that exploit the links in between the different channels exist but suffer from an heavy computational burden that prevent their use in real time applications. Two-steps procedures with an appropriate Weighted LS (WLS) minimization are shown to be asymptotically equivalent to the ML procedure. In this paper, we develop a closed-form expression of this WLS asymptotically efficient solution. We show that this simple expression is the sum of two terms. The first one, depending on the pseudo-ranges is the widespread used WLS solution. The second one is a Doppler-aided corrective term that should be taken into account to improve the position estimation when the observation time increases

Effects of cyanobacteria soil crusts on surface roughness and splash erosion

Soil surface roughness (SSR) modifies interactions and feedback processes between terrestrial and atmospheric systems driven by both the abiotic and biotic components of soils. This paper compares SSR response to a low intensity multi‐day rainfall event for soils with and without early successional stage cyanobacteria‐dominated biological soil crusts (CBCs). A rainfall simulator was used to apply 2 mm, 5 mm and 2 mm of rain separated by a 24‐hour period over 3 days at an intensity of 60 mm hr‐1. Changes in SSR were quantified using geostatistically‐derived indicators calculated from semivariogram analysis of high resolution laser scans. The CBCs were stronger and splash erosion substantially less than from the physical soil crusts. Prior to rainfall treatment soils with CBCs had greater SSR than those without. The rainfall treatments caused the physical crusted soils to increase SSR and spatial patterning due to the translocation of particles, soil loss and the development of raindrop impact craters. Rainfall caused swelling of cyanobacterial filaments but only a slight increase in SSR, and raindrop impact cratering and splash loss were low on the soils with CBCs. There is no relationship between random roughness and splash erosion, but an increase in splash loss was associated with an increase in topographic roughness and small‐scale spatial patterning. A comparison of this study with other research indicates that for rainfall events up to 100 mm the effectiveness of CBCs in reducing soil loss is >80% regardless of the rainfall amount and intensity which highlights their importance for landscape stabilization

Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78 μm (0.078 mm) and a vertical resolution of 12 μm (0.012 mm). Application of 2 mm, 5 mm and 2 mm of rainfall each separated by a 24 h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied

Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78 μm (0.078 mm) and a vertical resolution of 12 μm (0.012 mm). Application of 2 mm, 5 mm and 2 mm of rainfall each separated by a 24 h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied

Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78 μm (0.078 mm) and a vertical resolution of 12 μm (0.012 mm). Application of 2 mm, 5 mm and 2 mm of rainfall each separated by a 24 h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied

A New GNSS Integrity Monitoring Based on Channels Joint Characterization

Many GNSS (Global Navigation Satellites System) applications need high integrity performances. Receiver Autonomous Integrity Monitoring (RAIM), or similar method, is commonly used. Initially developed for aeronautics, RAIM techniques may not be fully adapted for terrestrial navigation, especially in urban environments. Those techniques use basically the pseudoranges to derive an integrity criterion. In this paper, we introduce a new integrity criterion based on the correlation quality of each channel. This quality assessment is computed from the correlation levels for each channel, all based on a single position and speed. Hence, as the so-called Direct Position Estimation (DPE), we exploit the joint behaviour of all channels to detect any incoherence at an upstream step of the processing. This Direct RAIM (D-RAIM) allows detecting possible integrity problems before it can be seen on a classical RAIM scheme that only exploits the outputs of each channel

The effects of wind-induced inclination on the dynamics of semi-submersible floating wind turbines in the time domain

This study focusses on the coupling effects arising from the changes in the hydrodynamic behaviour of a semi-submersible floating wind turbine when it undergoes large inclinations under wind loading. By means of a range of time-domain simulations, it is shown that both the hull geometric nonlinearity effect and the alteration of viscous hydrodynamic forces can significantly affect the dynamics of a typical floating wind turbine operating in waves at rated conditions. The consequences of said effects for both aligned and misaligned wind and waves are explored. In general terms inclinations are found to increase motions, where the modes that are more affected depend on the relative direction between incident wind and waves. Understanding the sources of aero-hydrodynamic coupling is key to providing sound design and modelling guidelines for the coming generation of floating wind turbines

Etat des connaissances sur la fiabilité des retouches effectuées en clinique sur les éléments céramiques

RENNES1-BU Santé (352382103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF