In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, wide availability, and relative ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail, relative to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios.

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

Cellular systems evolved from a dedicated mobile communication system to an almost omnipresent system with unlimited coverage anywhere and anytime for any device. The growing ubiquity of the network stirred expectations to determine the location of the mobile devices themselves. Since the beginning of standardization, each cellular mobile radio generation has been designed for communication services, and satellite navigation systems, such as Global Positioning System (GPS), have provided precise localization as an add-on service to the mobile terminal. Self-contained localization services relying on the mobile network elements have offered only rough position estimates. Moreover, satellite-based technologies suffer a severe degradation of their localization performance in indoors and urban areas. Therefore, only in subsequent cellular standard releases, more accurate cellular-based location methods have been considered to accommodate more challenging localization services. This survey provides an overview of the evolution of the various localization methods that were standardized from the first to the fourth generation of cellular mobile radio, and looks over what can be expected with the new radio and network aspects for the upcoming generation of fifth generation.

Survey of Cellular Mobile Radio Localization Methods: From 1G to 5G

The chloroplast genome encodes proteins required for photosynthesis, gene expression, and other essential organellar functions. Derived from a cyanobacterial ancestor, the chloroplast combines prokaryotic and eukaryotic features of gene expression and is regulated by many nucleus-encoded proteins. This review covers four major chloroplast posttranscriptional processes: RNA processing, editing, splicing, and turnover. RNA processing includes the generation of transcript 5' and 3' termini, as well as the cleavage of polycistronic transcripts. Editing converts specific C residues to U and often changes the amino acid that is specified by the edited codon. Chloroplasts feature introns of groups I and II, which undergo protein-facilitated cis- or trans-splicing in vivo. Each of these RNA-based processes involves proteins of the pentatricopeptide motif-containing family, which does not occur in prokaryotes. Plant-specific RNA-binding proteins may underpin the adaptation of the chloroplast to the eukaryotic context.

Chloroplast RNA metabolism.

The appearance of cars has raised materialistic civilization and living standard to an unprecedented level. Today, it is hard to imagine how we human beings can live without cars. Yet, motor vehicles can cause a great number of deaths and injuries as well as considerable economic losses, which have constituted the global burden. Understanding of the occurrence and development of road traffic injuries will contribute to the prevention and control of crash and to the implementation of "everybody has the right to enjoy health" proposed by WHO.

Road traffic injuries.

Location information for events, assets, and individuals, mostly focusing on two dimensions so far, has triggered a multitude of applications across different verticals, such as consumer, networking, industrial, health care, public safety, and emergency response use cases. To fully exploit the potential of location awareness and enable new advanced location-based services, localization algorithms need to be combined with complementary technologies including accurate height estimation, i.e., three dimensional location, reliable user mobility classification, and efficient indoor mapping solutions. This survey provides a comprehensive review of such enabling technologies. In particular, we present cellular localization systems including recent results on 5G localization, and solutions based on wireless local area networks, highlighting those that are capable of computing 3D location in multi-floor indoor environments. We overview range-free localization schemes, which have been traditionally explored in wireless sensor networks and are nowadays gaining attention for several envisioned Internet of Things applications. We also present user mobility estimation techniques, particularly those applicable in cellular networks, that can improve localization and tracking accuracy. Regarding the mapping of physical space inside buildings for aiding tracking and navigation applications, we study recent advances and focus on smartphone-based indoor simultaneous localization and mapping approaches. The survey concludes with service availability and system scalability considerations, as well as security and privacy concerns in location architectures, discusses the technology roadmap, and identifies future research directions.

A Survey of Enabling Technologies for Network Localization, Tracking, and Navigation

The exoribonuclease polynucleotide phosphorylase (PNPase) has been implicated in mRNA processing and degradation in bacteria as well as in chloroplasts of higher plants. Here, we report the first comprehensive in vivo study of chloroplast PNPase function. Modulation of PNPase activity in Arabidopsis chloroplasts by a reverse genetic approach revealed that, although this enzyme is essential for efficient 3′-end processing of mRNAs, it is insufficient to mediate transcript degradation. Surprisingly, we identified PNPase as also being indispensable for 3′-end maturation of 23S rRNA transcripts. Analysis of tRNA amounts in transgenic Arabidopsis plants suggests a direct correlation of PNPase activity and tRNA levels, indicating an additional function of this exoribo nuclease in tRNA decay. Moreover, the extent of polyadenylated mRNAs in chloroplasts is negatively correlated with PNPase activity. Together, our results attribute novel functions to PNPase in the metabolism of all major classes of plastid RNAs and suggest an unexpectedly complex role for PNPase in RNA processing and decay.

/pdf/pnpase-activity-determines-the-efficiency-of-mrna-3-end-30go36pfrz.pdf

PNPase activity determines the efficiency of mRNA 3′-end processing, the degradation of tRNA and the extent of polyadenylation in chloroplasts

Novel joint delay Doppler probability density functions for vehicle-to-vehicle communications channels are introduced. Prior measurements of vehicle-to-vehicle channels have unveiled their nonstationarity; thus, the wide-sense stationary and also the uncorrelated scattering assumption for such channels is often violated, which makes their modeling challenging. In this work it is proposed to exploit geometry-based stochastic modeling to cope with the nonstationarity of vehicle-to-vehicle channels. To this end, delay-dependent Doppler pdfs are derived for arbitrary times. It is assumed that scatterers are randomly distributed on an ellipse with two moving vehicles being in its foci. The proposed approach allows reducing the dimensionality of the resulting problem. This in turn leads to a significantly simplified derivation of the delay-dependent Doppler pdfs for general vehicle-to-vehicle propagation environments; moreover, the resulting computations can be performed almost fully analytically. By combining the calculated Doppler pdf with a delay pdf, the joint pdf of delay and Doppler is obtained. The joint pdf then can be put into relation with the generalized local scattering function. The presented modeling approach is simple yet very scalable and accurate, which allows its application in different vehicular scenarios. The obtained modeling results correspond very well with measurement data reported in prior works.

Delay-Dependent Doppler Probability Density Functions for Vehicle-to-Vehicle Scatter Channels

Today's mobile radio systems deploy reference signals which can be used or which are even dedicated for signal propagation delay-based mobile terminal positioning. Usually, the signal power of such reference signals is uniformly distributed over the available spectrum. It is known from estimation theory that such a uniform power distribution of reference signals is not optimal for signal propagation delay estimation. In this paper we consider mobile terminal positioning based on signal propagation delay estimation in the uplink case. For positioning, we introduce a parametric waveform. This waveform provides a scalar parameter for controlling the distribution of the available signal power over the spectrum. Using this waveform parameter we aim to minimize the positioning error. For optimization, we require a functional dependency between the waveform parameter and the positioning error we can expect. For the derivation of this function we combine the approaches of the Cramer-Rao and Ziv-Zakai bounds for position and propagation delay estimation. As an exemplary environment we consider a mobile terminal located in an area surrounded by 3 base stations. For this environment we show that the optimized waveform spends a significant part of the available power at the spectrum edges, leading to a performance gain of 37.3% at the center of the area between the base stations.

/pdf/optimizing-waveforms-for-positioning-in-5g-avs35yrbnk.pdf

Optimizing waveforms for positioning in 5G

In the paper, we present results from flight trials conducted to investigate the characteristics of the L-band air-to-ground radio channel for positioning applications. We discuss the employed hardware setup, synchronization concept, calibration procedures, and investigated flight patterns. It is shown that the setup is suitable for investigating both multipath structure and absolute propagation time of the radio signals. The power delay and Doppler power profiles, as well as the time-of-arrival estimation accuracy, are presented. Manuscript

Measurement of the l-band air-to-ground channel for positioning applications

One deployment option for the future broadband L-band digital aeronautical communications system (L-DACS) is operating as an inlay system between two adjacent channels of the distance measuring equipment (DME) system. Investigations for the broadband aeronautical multi-carrier communications (B-AMC) [1] system, one candidate for the broadband L-DACS, have shown that interference originating from DME systems operating in adjacent channels has a strong impact on the B-AMC system. To enable the utilization of spectral gaps between two adjacent DME channels, two efficient methods for mitigating the impact of interference are proposed and investigated for the B-AMC system, namely pulse blanking and erasure based decoding. Simulations show that the impact of DME interference onto the L-DACS can be reduced considerably by choosing an appropriate coding scheme to make the transmit signal robust against interference. The impact of interference is mitigated by means of the proposed methods, resulting in a performance close to the performance in the interference-free case.

/pdf/interference-mitigation-for-broadband-l-dacs-458vbv0fqz.pdf

Michael Walter

Papers

PNPase activity determines the efficiency of mRNA 3′-end processing, the degradation of tRNA and the extent of polyadenylation in chloroplasts

Delay-Dependent Doppler Probability Density Functions for Vehicle-to-Vehicle Scatter Channels

Optimizing waveforms for positioning in 5G

Measurement of the l-band air-to-ground channel for positioning applications

Interference mitigation for broadband L-DACS