bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacteriophages in Engineered Bioreactors
Authors: Islam Md Imdadul , Goel Ramesh
Published: December 2019

Bacteriophages, viruses that infect bacteria, coexist with their prokaryotic hosts in activated sludge reactors. They are among the most diverse biological entities in aquatic and terrestrial ecosystems, surviving through predation and horizontal gene transfer and have profound effects on microbial ecosystems everywhere. As microbial ecology is an integral part of any environmental biotechnology process, it is important to understand the factors that affect the microbial ecology composition. Little attention has been paid to the diversity of phages in engineered bioreactors, such as in activated sludge processes (ASPs). Phage treatments have the potential to control environmental wastewater process problems including, but not limited to, foaming in activated sludge plants, sludge dewaterability and digestibility; pathogenic bacteria; and to reduce competition between nuisance bacteria and functionally important microbial populations. These problems affect the treatment process and deteriorate the quality of effluent and sludge. Understanding phage–bacterial dynamics is important for successful application of phage therapy to wastewater problems. In this article, we present some important features of bacteriophages and then summarize the current state of knowledge related to the presence of bacteriophages in engineered bioreactors. Finally, we conclude this article with some future recommendations related to the need to study phages in engineered bioreactors.
Microbial Interactions in Anaerobic Wastewater Treatment
Authors: Wang Yongfeng , He Qiang
Published: December 2019

Anaerobic treatment technology, represented by anaerobic digestion, is an important microbial process for wastewater treatment. Anaerobic treatment is superior to aerobic processes with reduced energy demand, lower excess sludge production, and the generation of methane as a source of renewable energy. In anaerobic treatment, organic waste is converted into methane and carbon dioxide via four successive steps – hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The interactions between microbial populations have major impacts on the performance of anaerobic treatment processes. The competition between populations ofFirmicutesandBacteroidetesis closely correlated to process stability. Similarly, the competition between two acetoclastic methanogens with distinct kinetics characteristics, i.e.MethanosaetaandMethanosarcina, is linked to changes in the level of acetate as a metabolic intermediate associated with process perturbations. Further, syntrophic interactions between theBacteriaandArchaeaplay central roles in maintaining process balance. Indeed, syntrophic interactions are required for the conversion of diverse intermediates and substrates, including organic acids, alcohols, and aromatics, in anaerobic treatment. The microbial interactions underlying anaerobic treatment are critical to process performance. The availability of new tools, such as high‐throughput sequencing technologies, makes it possible to gain further understanding of population interactions at the microbiome level in order to develop more robust anaerobic treatment processes for broader applications as sustainable alternatives.
Energy Use in Water Distribution Systems: A Life Cycle Perspective
Authors: Karunathilake Hirushie , Prabatha Tharindu , Khan Shahnawaz , Hewage Kasun
Published: December 2019

Water distribution systems (WDSs) serve to deliver water from the source to intended consumers or endpoint applications, with the requisite quality and quantity. While these systems are a critically needed aspect of modern civilizations and their infrastructure, they also consume significant amounts of energy during their life cycle. The environmental impacts related to energy use have received global attention in recent times, with increasing concerns about anthropogenic climate change. Efforts are being made at all levels to reduce energy use in order to achieve the climate action targets set at regional, federal, and global levels. Water pumping to end users causes the highest energy use impacts in a WDS. The flow distances, component sizing and facility locations, flow rates, and other parameters need to be carefully managed in designing water distribution networks to minimize energy use and economic impacts. In attempting to develop more energy efficient WDSs, their energy use and impacts need to be contemplated from a holistic life cycle perspective.
Hofmeister Effects
Authors: Parsons Drew F. , Boström Mathias , Kunz Werner , Ninham Barry W.
Published: December 2019

Hofmeister effects, also known as specific ion effects, are variations in interactions between particles and surfaces or other particles in salt solutions that depend on the specific identity of the ions comprising the salt. Na
+
is the dominant cation in physiological fluids, Li
+
is used to treat bipolar disorder, K
+
is used in lethal injections. The differences matter, and yet these ions are identical if considered solely as simple point charges. Hofmeister effects are ubiquitous, observed in protein aggregation, surface tension, bubble coalescence, pH. The origin of specific ion effects can be understood as a consequence of electron structure, both in ion size and in polarizability of the electron cloud. Not only the intrinsic size of the ion but also recent theoretical developments suggest the formation of the cavity in the solvent, in which the ion resides, plays a key role in determining these effects, alongside ionic van der Waals interactions driven by ion polarisability.
Canopy‐Forming Ecosystem Engineers in Aquatic Ecosystems
Authors: Hendriks Iris E. , van Duren Luca A. , Ackerman Josef D.
Published: December 2019

Aquatic vegetation can form dense beds, spanning a range of scales, from forestlike canopies of tens of meters high created by giant kelps to small meter‐ or decimeter‐scale canopies of seaweeds and aquatic plants. These canopies interact with the flowing water in the overlying water column and have a profound effect on biogeochemical, biological, and ecological processes. In near‐bottom environments these organisms contribute substantially to bottom roughness as they form flexible canopies, which modify hydrodynamic properties in the near bed region with concomitant effects on sediment and ecological processes. In this article, we describe the environment aquatic macrophytes live in and then consider the fundamental biological and ecological processes including mass transport of dissolved material, such as nutrients, carbon, and oxygen, and their uptake by the vegetation and transport of particulate matter, such as sediment and organic matter, which has implications for carbon sequestration and sediment accretion.

These processes, aptly called ecosystem services, are important for human societies and attract the interest of researchers who will add to our understanding of the fundamental processes that are due to the interaction of fluid dynamics and macrophytes in a changing climate. This will facilitate transformational thinking and ultimately innovative solutions required for the future of humanity.
Nonlinear Wave Interactions over Coastal Muds
Authors: Tahvildari Navid , Sharifineyestani Elham
Published: December 2019

Many coasts around the world are fully or partially muddy. Surface waves sustain attenuation and modulation over mud, and bottom mud is fluidized and suspended in response to surface forcing. Surface wave–mud interaction has been studied numerically, theoretically, and in the field. In this study, we outline some recent theoretical and numerical work on the subject. Particularly, we discuss phase‐resolved numerical simulation of surface wave evolution over viscoelastic mud in the presence of currents and highlight the significance of mud elasticity on the process. Ignoring mud elasticity, which is the case in operational models, questions their application to a wide range of wave conditions where mud exhibits solid‐like behavior. We also discuss analytical models, developed using perturbation theory, to study generation of interfacial waves by a surface wave in a two‐fluid system as a feedback from the mud layer to surface forcing. Comparison between a second‐ and third‐order model shows that while the second‐order model is sufficient to study the generation process, it substantially overestimates long‐term amplitude of interface oscillations. Impacts of important parameters on dynamics of interfacial wave generation, namely relative thickness of mud layer, ratio of density and viscosity of mud to water, and surface wave properties are investigated.
Methane in Groundwater: Pathways
Authors: Martini Anna , Osborn Stephen , McIntosh Jennifer
Published: December 2019

Groundwater can contain measurable quantities of methane associated with
in situ
processes of methanogenesis and desorption from geologic materials, and also from external migration from deeper gas‐bearing units. It may also contain “fugitive gas” due to leakage from exploration and production of hydrocarbons or from the microbial breakdown of organic contaminants introduced to the aquifer. More recently, natural gas production via high volume hydraulic fracturing of tight formations has been implicated as a route for both methane and other fluids to enter groundwater resources. While distinguishing the source of the gas is often critical, secondary processes such as mixing and aerobic and anaerobic oxidation make these identifications difficult. Important to these determinations is an understanding of the hydrology, geology, and history of development in the watershed, coupled with detailed geochemical and isotopic analysis.
Low‐Flow Groundwater Purging and Sampling
Authors: Vance David B. , Jacobs James A.
Published: December 2019

Low‐flow groundwater sampling was developed in the 1990s as a way to obtain accurate, representative, and reproducible groundwater samples in a manner which generated less sampling‐derived liquids requiring disposal. Groundwater monitor wells are installed primarily as tools to measure the dissolved concentrations of contaminants in groundwater in and around facilities where the release of contaminants has occurred or where the potential exists for such a release. Although they are widely used, there are still questions about how best to collect samples from groundwater monitoring wells in such a way as to generate representative results. Installation of a well always results in some disturbance of the local environment around the well. Moreover, water in a well can become stagnant and often does not reflect the surrounding groundwater conditions. Traditional methods of purging can be problematic. Thus, low flow groundwater purging is an important method to be used prior to sampling. This article discusses methods of low flow purging for groundwater monitoring wells
Microbes and Inorganic Colloids in Particulate Transport in Groundwater
Authors: Vance David B. , Jacobs James A.
Published: December 2019

Enhanced bioremediation via bioaugmentation requires understanding of groundwater flow of both colloids and microbes. Groundwater microbes not only include primarily bacteria but also may include archaea, fungi, protists, viruses, and other microscopic organisms. Bacteria, the largest portion by mass or population of groundwater microbes, are single‐celled organisms that lack a true nucleus and normally have a cell wall. There may be from 100 million to 1 billion bacteria per gram of dry soil in the shallow soil near plant roots. There may be as many as 10–100 million bacteria per gram in groundwater, depending on depth, nutrients, carbon sources, and redox conditions. Evaluation of mass transport of entrained material in groundwater flow systems is typically focused on two primary areas, dissolved organic or inorganic species, and flowing free phase liquids. However, although generally not as dominant overall, the movement of small particles in groundwater can cause problems at the low concentrations required by regulatory limits. In addition, the proponents of
in situ
bioaugmentation, through injection of bacteria, must rely on successful particulate mass transport through the saturated soil matrix.
Natural Attenuation and Enhanced Bioremediation of Petroleum Hydrocarbons Geochemical Factors in Groundwater Remediation
Authors: Jacobs James A. , Vance David B.
Published: December 2019

In situ
monitored natural attenuation (MNA) and enhanced bioremediation of petroleum hydrocarbons released into the environment are affected by a variety of limiting factors, including the availability of a terminal electron acceptor (TEA), macronutrients (nitrogen and phosphate), as well as an energy source (carbon). The TEA for aerobic degradation is limited to oxygen. For anaerobic degradation, TEA processes include denitrification using nitrate (NO
3
−
), manganese reduction using manganese dioxide (MnO
2
), iron reduction using bioavailable iron that includes the hydroxide form (Fe(OH)
3
), sulfate reduction using the sulfate ion (SO
4
2−
), and methanogenesis using carbon dioxide (CO
2
). Of this list, dissolved oxygen is usually the limiting factor. Other factors that limit or inhibit microbial growth include toxic concentrations of naturally occurring or anthropogenic metals or other contaminants.

Macronutrients are measured in the laboratory as nitrogen in the form of ammonia or nitrate and orthophosphate. Nutrients, although important, are not as critical as depletion of the TEA. The energy source is the carbon in the hydrocarbons or chlorinated solvents that act as food for the microbes.

MNA occurs when these processes are believed to be occurring on their own without additives. Natural attenuation frequently starts on many hydrocarbon sites, but the aerobic degradation process frequently stops or slows down considerably because of the limiting factors of oxygen and nutrient depletion.
Benzene in Groundwater: Chemical Behavior and Treatment
Authors: Jacobs James A.
Published: December 2019

Benzene (C
6
H
6
) is a clear, colorless, highly flammable aromatic hydrocarbon liquid. As an important ingredient for making plastics, rubber, resins, and synthetic fabrics like nylon and polyester, benzene is one of the most commonly used industrial chemicals in the world. It is also used as a solvent in printing, paints, and dry cleaning. It is also a major component of gasoline. The wide ranging industrial applications of benzene make it widely distributed, particularly in the case of petroleum products, of which it is a primary constituent. Benzene is highly toxic to humans and the environment. Because of its severe toxic effects, both in the short and long term, benzene use has been under strict regulations for many years. Nonetheless, widespread contamination of benzene has occurred in the environment, and, therefore, significant regulatory efforts in the United States and other nations are being enacted to limit or eliminate potential impacts.
Organic Compounds Present at Minute Concentrations in the Hydrologic System
Authors: Jacobs James A.
Published: December 2019

Laboratory analytical methods have continuously improved during the past few decades with much lower detection levels enabling some interesting studies of human impact on the condition of the hydrologic system. Certain organic contaminants are present at extremely low concentrations in surface and groundwaters throughout the nation, even in remote wilderness areas. This article focuses on some organic contaminants frequently found at extremely low levels. Such compounds include organic wastewater contaminants (OWCs) such as steroids, nonprescription drugs, insect repellent, detergent metabolites, disinfectants, plasticizers, and fire retardants. The gasoline additive methyl
tert
‐butyl ether (M
t
BE) and certain chlorinated solvents can also be found at very low levels in some public supply wells. This article provides a brief overview of some key organic contaminants that occur at very low levels in waters in the United States and many other parts of the world. Their occurrence and distribution are starting to be better understood as more waters are sampled and surveyed using low‐detection‐limit methods of organic analysis.
Nitrate in Groundwater: Chemical Behavior and Treatment
Authors: Jacobs James A.
Published: December 2019

Nitrate (NO3) is a naturally occurring substance, which is an essential nutrient for the growth of plants. Nitrates from animal manure such as cattle and oxen have long been used as a natural fertilizer in fields. Early commercial sources of nitrates were guano, the accumulated excrement of seabirds and bats, rich in nitrogen, phosphate, and potassium. With the development of the Haber–Bosch process, an industrial‐scale manufacturing of nitrate fertilizers was possible in 1910. This breakthrough in chemistry has allowed farmers the availability of low‐cost artificial nitrate fertilizers for over the past 100 years. Excessive nitrate fertilizer use combined with runoff from fertilized farmer fields, gardens, golf courses, lawns, and other facilities, has, over time, allowed for nitrate impacts to ground and surface waters. Today, nitrates are sourced from nitrate fertilizers, the storage or use of animal manure, leaky septic systems, leaky sanitary sewer pipelines, and improper disposal of treated wastewater containing high nitrate levels. Through storm runoff and leaching processes, nitrates have become dissolved in stormwater runoff or infiltration waters. These sources of dissolved nitrates have created significant impacts on worldwide surface water and groundwater resources. The impacts may vary with the season, where nitrate‐rich stormwater is commonly associated with spring storms and runoff. The excess nutrients in rivers, lakes, bays, and marine waters create ecological dead zones. Dead zones exist where dissolved oxygen concentration are low and fish and other aquatic life cannot survive and suffocate. Dead zones are biological desserts where healthy and diverse marine life are absent and only jellyfish and organisms capable of surviving hypoxic marine conditions can survive.

Nitrate is an integral part of the nitrogen cycle, especially at the microbial level. A microbial process called nitrification is performed by nitrifying bacteria. Although ammonia can be used by some plants as an essential nutrient, most nitrogen taken up by plants is processed by nitrifying bacteria to convert ammonium (NH4+) into nitrite (NO2–), and then into nitrate (NO3–) where it can be used by the plant. At an even smaller scale, at the molecular level, nitrate is used in the respiratory electron transport chain in the absence of oxygen. For subsurface remediation in the absence of oxygen, anaerobic microbes in the groundwater can use available nitrate for cellular respiration, making nitrate one of four alternate terminal electron acceptors.
Uranium in Groundwater: Chemical Behavior and Treatment
Authors: Jacobs James A.
Published: December 2019

Uranium can occur naturally in groundwater or it can be present as a result of processing for nuclear reactors, nuclear weapons, and other uses. Uranium can occur in nature in four oxidation states, and environmental redox conditions can affect uranium fate and transport in groundwater. Although uranium is radioactive and can cause cancer, its primary toxic effect when consumed in water is that of a heavy metal. This article outlines the occurrence, distribution, redox chemistry, and fate and transport of uranium in groundwater. The article also introduces a variety of methods for uranium groundwater remediation.
Arsenic in Groundwater: Chemical Behavior and Treatment
Authors: Vance David B. , Jacobs James A.
Published: December 2019

Arsenic (As) is a naturally occurring metalloid element with atomic number 33. Although widely distributed in the Earth's crust, Arsenic is only the 52nd element in terms of crustal abundance. Because arsenic is toxic and can cause various forms of cancer, it must be removed from drinking water. A variety of different removal treatments and technologies are discussed in this article.
Groundwater Remediation and Horizontal Wells
Authors: Jacobs James A. , Vance David B.
Published: December 2019

Horizontal wells have been used in an increasing number of groundwater remediation projects. In addition to chemical and biological reactive barriers, horizontal borings can be used for groundwater extraction and control, air sparging, bioremediation, groundwater injection, for vadose zone soil vapor extraction or bioventing systems, and free product recovery. This article provides an introduction to horizontal well technology and its use in groundwater remediation.
Groundwater Remediation by Injection
Authors: Vance David B. , Jacobs James A.
Published: December 2019

With few exceptions, groundwater remediation requires either an
in situ
injection of reactive chemicals or groundwater recovery, treatment, and disposal. The reinjection of treated water or the placement of chemicals in the subsurface used to treat contaminants can cause unintended subsurface geochemical conditions that may create new contamination issues or impact
in situ
transport properties. This article discusses methods for preventing subsurface challenges related to water injection during groundwater remediation or water disposal.
Remediation of Metals in Groundwater
Authors: Jacobs James A. , Vance David B.
Published: December 2019

Many ground waters and soils around the world are plagued by metals contamination, which can pose substantial ecosystem and human health risks. Given the widespread problem and the paucity of innovative approaches to remediation, it is clear that metal contamination represents a serious environmental concern as well as a significant market opportunity for environmental service companies. This article provides some general background on metals chemistry and insight into potential groundwater remediation strategies.
Vibrio Bacteria in Aquatic Ecosystems: Effects of Climate Change on Antibiotic Resistance
Authors: Scott Cecile Hart , Horton Cassie , Brett Catherine , Palmer Emily , Pipes Shannon , Tufford Dan , Sandifer Paul A. , DeLorenzo Marie , Pennington Paul L. , Porter Dwayne E. , Ek Christina , Norman Sean , Scott Geoffrey I.
Published: December 2019

Water is essential for all life as we know it, but it can also be the source of dangerous and even fatal diseases, such as those associated with certain Vibrio bacteria. This article focuses on several Vibrio bacteria that are known to cause severe and potentially fatal illnesses, the most high profile of which is cholera. The article begins by discussing how Dr. John Snow first recognized that cholera was a waterborne disease, using data he collected in Victorian Age London. Three prominent disease‐causing Vibrio species:V. cholerae,V. parahaemolyticus, andV. vulnificusare then discussed in some detail in terms of how they cause illness, primarily from seafood consumption, wound infections, and waterborne illness as well as the role climate change may play in terms of impacting the rapid spread of Vibrio illness observed globally the past 25 years. Today environmental scientists and epidemiologist are faced with the same dilemma with climate change and Vibrio bacteria that Sir John Snow was faced with cholera and urbanization in the nineteenth century. Since climate change may be affecting the occurrence, distribution, and even the virulence of these pathogenic organisms, we conclude by discussing how interdisciplinary teams of scientists are developing complex epidemiological tools and forecast models to better inform the public and prevent future Vibrio‐associated illnesses just as Sir John Snow did with cholera.
Settlement and Recruitment of Pelagic Larvae to Benthic Habitats
Authors: Nishizaki Michael T. , Ackerman Josef D.
Published: December 2019

Many organism that live on the benthos (or bottom) of aquatic ecosystems have biphasic life histories because they reproduce by releasing eggs and sperm in the water column that develop into plankton larvae, which are dispersed by water currents. These populations are considered open systems because postlarval juveniles recruit in regions separate from the adult population. In this article, we present some of the diversity of larval types that have evolved in different organisms. We focus primarily on marine organisms, but include a few examples from freshwater as appropriate. We also discuss the processes that affect the recruitment of new individuals into benthic populations, which involve (i) larval supply, (ii) larval settlement, and (iii) post‐settlement. We note that these processes act over a variety of temporal and spatial scales and we identify the hypotheses that have been presented to explain how variations in these affect recruitment. A large number of processes and hypotheses have been proposed for the settlement and recruitment of pelagic larvae to benthic habitats, which is not surprising given the diversity of organisms involved.
Groundwater Remediation:In SituPassive Methods
Authors: Jacobs James A.
Published: December 2019

Groundwater remediation by passivein situremediation technologies uses a variety of physical, chemical, or biological processes that act without significant human intervention in the subsurface to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater. Passive and semi‐passive remedial methods use minimal or no power, have few or no moving parts, have few or no time constraints, and meet local and national regulatory guidelines. As for all forms ofin situremediation, proper assessment and hydrogeological characterization are the keys to success.
High‐Speed Train Channels
Authors: Guan Ke , Yi Haofan , He Danping , Ai Bo , Zhong Zhangdui
Published: December 2019

Since rail transportation has become a major transportation model, increasing demand for seamless high‐data‐rate wireless communication is required in high‐speed trains (HSTs) to improve the quality of services. This article introduces the Global System for Mobile Communication‐Railway (GSM‐R), which is currently widely utilized for train communication and control, and the Long‐Term Evolution‐Railway (LTE‐R), which is to replace GSM‐R for future high‐data transmission. Different HST propagation scenarios are detailed according to the typical geometries in reality. Path loss, shadow factor, RiceanK‐factor, root‐mean‐square (RMS) delay spread, and the angular spreads are the main characteristics to describe an HST channel. These analyzed channel characteristics provide the foundation for future work. Finally, key challenges and developing orientation in this area are outlined.
Energy‐Aware Heterogeneous Networks
Authors: Zhong Yi , Wang Gang
Published: December 2019

Cloud radio access network (C‐RAN) architecture is a cost‐ and energy‐efficient solution to increase the capacity of the cellular network. In order to adapt the traffic and reduce the system cost, we propose the complementary networking architecture for the C‐RAN, which takes advantages of both the C‐RAN and the traditional base stations (BSs). We propose to combine the Neyman–Scott cluster process and the Poisson hole process to model the architecture; then, the interference in the large‐scale network with cooperation is well characterized through the Poisson point process approximation. By mixing the two multiple association mechanisms, i.e. the RRH‐selection mode and the cooperation mode, we explore the trade‐offs among the area spectrum efficiency (ASE), the mean delay, and the system cost, both analytically and numerically. The results reveal that the mean delay is negatively correlated to the ASE for small ASE and is reversed for large ASE, while the cost is always positively correlated to the ASE. The cooperation mode increases the useful signal, and it also increases the interference which becomes dominant when the radius of the RRH cluster is large. The proportion of subframes operating in the two modes can be configured to trade off the ASE, the mean delay, and the cost.
Energy‐Efficient Radio Resource Management
Authors: Wei Zhiqiang , Cai Yuanxin , Ng Derrick W.K. , Yuan Jinhong
Published: December 2019

Energy‐efficient resource management is a promising solution to enable environment friendly and cost‐effective wireless communication networks. This article presents the basic principles of the energy‐efficient resource allocation design in wireless networks. Two types of energy‐efficiency (EE) definitions, system‐centric EE and user‐centric EE, are introduced, discussed, and analyzed. We reveal that when the circuit power consumption is not negligible, there is a nontrivial trade‐off between the EE and spectral efficiency, which should be taken into account for the optimal resource allocation algorithm design. In general, the system‐ and the user‐centric EE maximization can be classified as a single‐ratio problem and a sum‐of‐ratios problem, respectively, and they can be solved via various iterative parametric algorithms. As an illustrative example, we have also presented the energy‐efficient resource allocation design in an orthogonal frequency division multiple access (OFDMA) system.

The design is formulated as a nonconvex optimization problem. By exploiting the factional programming and dual decomposition, the globally optimal solution is obtained. Furthermore, our simulation results demonstrate the fast convergence and the superior EE achieved by our proposed resource allocation design. In addition, some future research extensions for realizing energy‐efficient wireless communication networks are identified and discussed.
Cloud Radio Access Networks
Authors: Peng Mugen , Yan Shi
Published: December 2019

Cloud radio access networks (C‐RANs) have been proposed as promising solutions to provide high spectral and reduce energy consumption. Based on the centralized baseband processing, the user‐centric objectives can be achieved through the adaptive technique and will relieve the high capital expenditure and operation expenditure. In this article, we first comprehensively summarize the recent advances of the C‐RAN architecture in both industries and academic community views. Then, the key features of C‐RAN performance enhancement technologies, fronthaul compression, and cooperative radio resource allocation are discussed. Meanwhile, the challenges and C‐RAN evolutions are discussed to provide research topics on the potential insights in the future.
Vehicular Networks
Authors: Liu Jiajia
Published: December 2019

With the development of modern automobile industry and the evergrowing demand for all kinds of advanced vehicular services, automobile ushered in its changing era. To achieve efficient and accident‐free transportation, both academia and industry have made positive efforts. However, as the basis of vehicle intelligence and security, sensors have intrinsic limitations and are sometimes susceptible to the external environment. At the same time, there is a huge market demand for providing high‐quality infotainment services for vehicle passengers. Therefore, to further enhance transportation safety and meet business trends, information sharing among vehicles is particularly important. Subsequently, the concept of vehicular networks is heating up, which can realize information sharing and cooperative control by establishing the connection between vehicles and external nodes through communication technology, thus greatly improving the efficiency, safety, and comfort of road transportation. The realization of vehicular networks depends on various vehicular communication technologies. In addition to the existing standardized automotive communication technologies, such as DSRC and LTE‐V, the research on the upcoming 5G vehicular networks is also in full swing, which is envisioned as a promising and diverse ecosystem that can provide customers with a variety of communication services. This article will take communication technology as the starting point to carry on the latest and comprehensive investigation to the vehicular networks.
Integrated Terrestrial–Satellite Networks
Authors: Jiang Chunxiao , Zhu Xiangming , Kuang Linling , Ge Ning , Lu Jianhua
Published: December 2019

Satellite networks are able to provide seamless services for ground users with the wide coverage, which is intrinsically suitable for providing broadcasting or multicasting services. While terrestrial networks have experienced rapid development in the past years, in the next‐generation communications, the architecture of integrated terrestrial–satellite networks is promising to enable users to seamlessly access all types of services. In this article, we investigate the problem of cooperative transmission in integrated terrestrial–satellite networks, where two cases of unicast transmission and multicast transmission are discussed separately. Overall, this article aims to provide a comprehensive discussion and also propose a general framework of cooperative transmission in future terrestrial–satellite networks.
Wireless Content Caching Networks
Authors: Song Jaeyoung , Choi Wan
Published: December 2019

To overcome the present challenges on wireless communication system, content caching, which uses memory as communication resource, emerges as one of the promising solutions in the aspects of its low cost and high efficiency. In this article, significant results on wireless content caching networks are introduced. In order to design efficient wireless content caching networks, various approaches and methods are studied. Mainly, content placement, transmission strategy, and resource allocations are investigated, and substantial works for each category are covered throughout this article. Content placement is the fundamental design factor which impacts the performance of caching system dominantly. Considering distinct properties of wireless communication, several unique features which content placement of wireless content caching networks shows are covered first in the main body of this article. Next, based on the given content placement, novel transmission scheme will be introduced in the point of utilizing memory as storage for side information. Lastly, optimal schemes, which allocate resources of the wireless content caching networks including memory, are presented.
Slicing and Radio Resource Management
Authors: Samdanis Konstantinos , Foukas Xenofon , Pateromichelakis Emmanouil , Ksentini Adlen
Published: December 2019

This article provides an overview of radio resource management (RRM) in the context of network slicing considering a range of different deployment options and practicalities. Initially, it elaborates the 3GPP radio access network (RAN) sharing in terms of business and architecture. Slice‐tailored RRM solutions are then considered for various base station deployments focusing on RRM principles and customization, which result in different paradigms of resource sharing including full isolation, sharing, and hybrid approaches. The concept of slice broker is also elaborated, which aims to allocate radio resources related to slice requests considering the desired service performance, highlighting the need of traffic and mobility forecasting. The notion of resource sharing is further analyzed, considering various RRM and scheduling schemes including multi‐objective and hierarchical RRM, slice‐aware flexible function split, TDD service‐oriented solutions, and joint radio and backhaul optimization and licensed assisted configurations.
Applicability of Network Function Virtualization in 5GNetwork
Authors: Trivisonno Riccardo
Published: December 2019

Despite being a concept dating back to the sixties, virtualization technology has made its way into telecommunication systems only in recent times. In this paper, the genesis of virtualization has been revisited and its evolution, leading to significant impacts both on implementation and management of legacy networks as well as on the definition of the just born 5G system, has been analyzed. The paper elaborates on the benefits offered by the virtualization of flexible deployment and easier operations of 4G system, and shows how these potentials have been stretched into the design principles of 5G system architecture, natively enhancing its flexibility and programmability. The dissertation explores all components of 5G: the access network, the core network, and the management system. The excursus is studded with reference to relevant scientific papers and tightly coupled to the related industrial standardization activities, which have been running over the past decade. A few notable practical examples of virtualization‐related technologies and protocols, developed and tested over the past years, have also been briefly presented. The paper concludes with a short list of open issues to be addressed in the coming month for a successful application of virtualization on carrier grade telecommunication systems.
On the Support ofNFV: Available Tools and Solutions
Authors: Monserrat Jose F. , Vicente Javier , Bouchmal Faiza , Carrasco Oscar
Published: December 2019

Much has been written about the virtualization of mobile networks but very little about the practical aspects of this important paradigm shift. In this article, we address the practical aspects of creating an Infrastructure‐as‐a‐Service (IaaS). We first discuss some basic concepts and then focus on most promising technologies that allow the creation of such an infrastructure. Technologies such as OpenStack and Docker are discussed, and a practical implementation with libvirt deployed using Terraform solution is presented. Finally, we discuss specific aspects of Network Function Virtualization (NFV) and how a 5G network can really make use of an IaaS.
Techno‐Economic Analysis for Programmable Networks
Authors: Bouras Christos , Kollia Anastasia
Published: December 2019

The advent of the fifth generation (5G) of mobile networks will boost technology, as new solutions are needed to meet the growing 5G‐related demands identified both by scientists and telecommunication providers. Programmable logic solutions will be used, as they provide financial, performance, and environmental benefits. The programmable logic nowadays is represented by the combination of the software‐defined networking (SDN) technology with network function virtualization (NFV). This combination not only reduces hardware – as most network components are replaced by network functions or virtual machines (VMs) – but also offers better resource allocation and provides more bandwidth, CPU, etc., to the parts of the network that have become more congested.

Solutions, such as SDN, may concentrate fundamental advantages and profits, but they appear to face basic problems, therefore raising key questions concerning their cost and safety. One of these issues contains all the expenses for the acquisition of the technology and the adjustments that need to be incorporated into current infrastructure in order to cover SDN networks as well. This article analyzes a programmable model of SDN combined with NFVs. A sensitivity analysis (SA) is conducted to determine the factors that largely influence the pricing so as to propose ways to significantly reduce several types of costs and propose solutions or research directions to cut down on the expenses of these network factors.
Physical‐Layer Security for 5G and Beyond
Authors: Osorio Diana P.M. , Sánchez José D.V. , Alves Hirley
Published: December 2019

Recently, the physical layer has gained a more prominent role on the security context of wireless networks due to its potentiality on providing more effective solutions to safeguard confidentiality and privacy for 5G‐and‐beyond networks. Physical‐layer security (PLS) techniques are recognized to offer powerful features that can complement and enhance cryptography‐based mechanisms, by considering the unique properties of wireless channels. Even though physical‐layer security has been intensively studied in the past decade, novel scenarios expected for future networks impose big challenges for the full acceptance of PLS techniques as a component of the security solutions of 5G‐and‐beyond networks. This article provides a brief overview of the information theoretic fundamentals of secrecy and secrecy metrics. The most recognized PLS techniques are described, and the challenges and issues regarding some well‐known 5G technologies are also provided.
Multi‐RAT D2D Communication Paradigms: Potential Benefits and Challenging Issues
Authors: Atat Rachad , Ismail Muhammad
Published: December 2019

Device‐centric communications will constitute a key technology in the fifth‐generation (5G) networks, where mobile devices in near proximity participate in direct communications among each other bypassing the cellular base station. Such communication schemes are known as device‐to‐device (D2D) communications, which are anticipated to improve energy efficiency, decrease latency, improve spectrum utilization, and many other benefits. With the technological advancement in smartphones, multiple radio interfaces can be supported within the same mobile device. When these multi‐radio access technologies (RATs) are efficiently exploited, they give rise to a new emerging feature in device‐centric systems, such as devices‐to‐device (Ds2D) and devices‐to‐devices (Ds2Ds) communication modes. In this chapter, we highlight the different multi‐RAT D2D architectures, where we discuss the different criteria for switching between multi‐RAT D2D and cellular operation modes. The radio channel model and the different spectrum access techniques are also discussed. Then, the major benefits of multi‐RAT D2D such as energy efficiency and low latency are highlighted. Challenging issues that arise at different layers of the network protocol stack are discussed, with an emphasis on the medium access control, network, and transport layers. Finally, open research issues that require further investigations to get the most out of multi‐RAT D2D communications are discussed.
D2D and Game Theoretic Models
Authors: Wang Chih‐Yu
Published: December 2019

D2D communications enable direct communications between devices in proximity. The unique local transmission property makes it especially vulnerable to selfish behaviors. Game theory is a trending approach to solve conflicts, competitions, and collaborations in D2D communications. With the help of game theory, we may predict selfish behaviors or configurations in D2D communications, which could cause system performance degradation. Such undesired behaviors can then be prevented through game‐theoretic mechanism designs, such as pricing, contract, auction, and matching. In addition, many game‐theoretic solutions are distributed in nature, which would be perfect choices of large‐scale D2D communications for self‐organization and self‐management In this article, we will first introduce the basic materials and concepts of game theory. Then, several technical problems in D2D communications, such as mode selection, QoS guarantee, resource allocation, and group formulation are presented. In each problem, we illustrate how to formulate the problem with proper game‐theoretic models, and how these formulations can help us to derive practical solutions to improve efficiency while regulating the undesired selfish behaviors. Finally, we point out potential research directions in this area.
IMT‐2020 Requirements and Realization
Authors: Romano Giovanni
Published: December 2019

The detailed specifications of the terrestrial radio interfaces of IMT‐2020 (International Mobile Telecommunications‐2020) are the end results of a process spanning several years. The main players, the time plan, and the relevant documentation are described in this article. The process can be subdivided in three phases: preparation; definition of requirements and process; and submission, evaluation of proposals, and finalization of a Recommendation on IMT‐2020. The first phase started in 2013 and provided the ITU‐R view on the overall process and timeline toward IMT‐2020. In particular, three main usage scenarios were identified: eMBB (enhanced mobile broadband); URLLC (ultra‐reliable and low‐latency communications); and mMTC, massive machine type communications. The second phase started in 2016 and defined the detailed time plan, the minimum requirements, and the evaluation criteria. The last phase started in October 2017 and encompasses the submission of the candidate proposals, their subsequent evaluation by independent evaluation groups, and the completion of a recommendation containing the technical specifications of the IMT‐2020 radio access technologies (anticipated to be finalized in the last quarter of 2020).
5
G
‐
NR
Spectrum Aspects
Authors: Zhou Xutao
Published: December 2019

In this article, detailed ITU‐R spectrum for IMT‐2020 system, 3GPP specifications for 5G‐NR frequency bands are introduced. In particularly, UE requirements of transmitting power, unwanted emission, and receiver sensitivity for both 3.5 GHz and mmWave bands have been presented in this article.
Design and Analysis of Millimeter‐Wave Antennas for the Fifth Generation Networks and Beyond
Authors: Jilani Syeda F. , Abbasi Qammer H. , Imran Muhammad A. , Alomainy Akram
Published: December 2019

Future 5G systems and beyond are anticipated to deploy compact, efficient, and versatile antennas in short‐range, ultradense millimeter‐wave (mmWave) wireless networks. This article emphasizes on the requirement of realizing antennas with wide bandwidth, high gain, adaptability, preferably conformal, and feasible and cost‐effective bulk manufacturing for the upcoming 5G networks.Ka‐band (26.5–40 GHz) is selected based on recent 5G standardization, and state‐of‐the‐art research contributions regarding antenna geometries are discussed on both rigid and flexible substrates by using advanced techniques of multiple‐input multiple‐output (MIMO), as well as wideband antennas and arrays to enhance the spectrum usability. mmWave wideband antennas have been developed for 5G networks, recommending that the spatial diversity at the antenna front ends could be significantly improved by deploying wideband antennas in a MIMO topology for simultaneous multiple‐channel communication. In addition, an efficient antenna front‐end solution is demonstrated, which integrates defected ground structures (DGS) for bandwidth improvement and integrated with MIMO technology. Flexible mmWave antenna is also suggested by using the DGS to implement wideband. Antenna gain is critically important for 5G systems to mitigate high propagation losses. Antenna design with both high gain and bandwidth is challenging as traditional wideband antennas are gain‐limited, while conventional arrays deliver high gain over a restricted bandwidth. Several attempts have been made to come up with such antenna designs, which provide reasonable gain performance over wide bandwidth at mmWave frequencies. These proposed 5G antennas are expected as potential contribution in the progress toward the realization of next generation of wireless networks.
The Ontological We as Prescription for Black Female Faculty Surviving and Thriving in the Academy
Authors: Merriweather Lisa R.
Published: December 2019

This chapter discusses and unpacks the ways in which gendered racism impacts African American female academics. An understanding of gendered racist realism exposes dominant racist ideologies in the academy, in general. Ontological beingness, specifically the ontological we, affords African American women the opportunity to confront and dismantle race combative discourses that attempt to circumscribe their beingness and identity. The ideological foundation of the ontological we is derived from DuBois’ double consciousness and womanism. It provides both perspective and a plan for addressing racist behavior experienced by African American female academics as part of their everyday reality in the academy.