Presents the table of contents for this issue of the publication.

I welcome you to the fourth issue of the IEEE Communications Surveys and Tutorials in 2019. This issue includes 25 papers covering different aspects of communication networks. In particular, these articles survey and tutor various issues in “Wireless and Cellular Communications,” “5G Communications,” “Vehicular and Sensor Communications,” “IoT and M2M,” “Internet Technologies,” and “Network Security.” A brief account for each of these papers is given below.

Low latency applications, such as multimedia communications, autonomous vehicles, and Tactile Internet are the emerging applications for next-generation wireless networks, such as 5th generation (5G) mobile networks. Existing physical-layer channel models, however, do not explicitly consider quality-of-service (QoS) aware related parameters under specific delay constraints. To investigate the performance of low-latency applications in future networks, a new mathematical framework is needed. Effective capacity (EC), which is a link-layer channel model with QoS-awareness, can be used to investigate the performance of wireless networks under certain statistical delay constraints. In this paper, we provide a comprehensive survey on existing works, that use the EC model in various wireless networks. We summarize the work related to EC for different networks, such as cognitive radio networks (CRNs), cellular networks, relay networks, adhoc networks, and mesh networks. We explore five case studies encompassing EC operation with different design and architectural requirements. We survey various delay-sensitive applications, such as voice and video with their EC analysis under certain delay constraints. We finally present the future research directions with open issues covering EC maximization.

In order to effectively provide ultra reliable low latency communications and pervasive connectivity for Internet of Things (IoT) devices, next-generation wireless networks can leverage intelligent, data-driven functions enabled by the integration of machine learning (ML) notions across the wireless core and edge infrastructure. In this context, this paper provides a comprehensive tutorial that overviews how artificial neural networks (ANNs)-based ML algorithms can be employed for solving various wireless networking problems. For this purpose, we first present a detailed overview of a number of key types of ANNs that include recurrent, spiking, and deep neural networks, that are pertinent to wireless networking applications. For each type of ANN, we present the basic architecture as well as specific examples that are particularly important and relevant wireless network design. Such ANN examples include echo state networks, liquid state machine, and long short term memory. Then, we provide an in-depth overview on the variety of wireless communication problems that can be addressed using ANNs, ranging from communication using unmanned aerial vehicles to virtual reality applications over wireless networks as well as edge computing and caching. For each individual application, we present the main motivation for using ANNs along with the associated challenges while we also provide a detailed example for a use case scenario and outline future works that can be addressed using ANNs. In a nutshell, this paper constitutes the first holistic tutorial on the development of ANN-based ML techniques tailored to the needs of future wireless networks.

As a key technique for enabling artificial intelligence, machine learning (ML) is capable of solving complex problems without explicit programming. Motivated by its successful applications to many practical tasks like image recognition, both industry and the research community have advocated the applications of ML in wireless communication. This paper comprehensively surveys the recent advances of the applications of ML in wireless communication, which are classified as: resource management in the MAC layer, networking and mobility management in the network layer, and localization in the application layer. The applications in resource management further include power control, spectrum management, backhaul management, cache management, and beamformer design and computation resource management, while ML-based networking focuses on the applications in clustering, base station switching control, user association, and routing. Moreover, literatures in each aspect is organized according to the adopted ML techniques. In addition, several conditions for applying ML to wireless communication are identified to help readers decide whether to use ML and which kind of ML techniques to use. Traditional approaches are also summarized together with their performance comparison with ML-based approaches, based on which the motivations of surveyed literatures to adopt ML are clarified. Given the extensiveness of the research area, challenges and unresolved issues are presented to facilitate future studies. Specifically, ML-based network slicing, infrastructure update to support ML-based paradigms, open data sets and platforms for researchers, theoretical guidance for ML implementation, and so on are discussed.

Massive multiple-input multiple-output (MIMO) is a key technology to meet the user demands in performance and quality of services (QoS) for next generation communication systems. Due to a large number of antennas and radio frequency (RF) chains, complexity of the symbol detectors increased rapidly in a massive MIMO uplink receiver. Thus, the research to find the perfect massive MIMO detection algorithm with optimal performance and low complexity has gained a lot of attention during the past decade. A plethora of massive MIMO detection algorithms has been proposed in the literature. The aim of this paper is to provide insights on such algorithms to a generalist of wireless communications. We garner the massive MIMO detection algorithms and classify them so that a reader can find a distinction between different algorithms from a wider range of solutions. We present optimal and near-optimal detection principles specifically designed for the massive MIMO system such as detectors based on a local search, belief propagation and box detection. In addition, we cover detectors based on approximate inversion, which has gained popularity among the VLSI signal processing community due to their deterministic dataflow and low complexity. We also briefly explore several nonlinear small-scale MIMO (2-4 antenna receivers) detectors and their applicability in the massive MIMO context. In addition, we present recent advances of detection algorithms which are mostly based on machine learning or sparsity based algorithms. In each section, we also mention the related implementations of the detectors. A discussion of the pros and cons of each detector is provided.

This paper presents a comprehensive literature review on applications of deep reinforcement learning (DRL) in communications and networking. Modern networks, e.g., Internet of Things (IoT) and unmanned aerial vehicle (UAV) networks, become more decentralized and autonomous. In such networks, network entities need to make decisions locally to maximize the network performance under uncertainty of network environment. Reinforcement learning has been efficiently used to enable the network entities to obtain the optimal policy including, e.g., decisions or actions, given their states when the state and action spaces are small. However, in complex and large-scale networks, the state and action spaces are usually large, and the reinforcement learning may not be able to find the optimal policy in reasonable time. Therefore, DRL, a combination of reinforcement learning with deep learning, has been developed to overcome the shortcomings. In this survey, we first give a tutorial of DRL from fundamental concepts to advanced models. Then, we review DRL approaches proposed to address emerging issues in communications and networking. The issues include dynamic network access, data rate control, wireless caching, data offloading, network security, and connectivity preservation which are all important to next generation networks, such as 5G and beyond. Furthermore, we present applications of DRL for traffic routing, resource sharing, and data collection. Finally, we highlight important challenges, open issues, and future research directions of applying DRL.

Time, polarization, and wavelength multiplexing schemes have been used to satisfy the growing need of transmission capacity. Using space as a new dimension for communication systems has been recently suggested as a versatile technique to address future bandwidth issues. We review the potentials of harnessing the space as an additional degree of freedom for communication applications including free space optics, optical fiber installation, underwater wireless optical links, on-chip interconnects, data center indoor connections, radio frequency, and acoustic communications. We focus on the orbital angular momentum (OAM) modes and equally identify the challenges related to each of the applications of spatial modes and the particular OAM modes in communication. We further discuss the perspectives of this emerging technology. Finally, we provide the open research directions and discuss the practical deployment of OAM communication links for different applications.

During the last decade, the exponential growth of mobile devices and wireless services created a huge demand for radio frequency-based technologies. Meanwhile, the lighting industry has been revolutionized due to the popularization of LED light bulbs, which are more economical and efficient. In that context, visible light communication (VLC) is a disruptive technology based on LEDs that offers a free spectrum and high data rate, which can potentially serve as a complementary technology to the current radio frequency standards. In this paper, we present a comprehensive state-of-the-art survey of VLC, as well as the main concepts and challenges related to this emergent area. We overview VLC technology, from its physical aspects and communication architecture to its main applications and research challenges. Finally, we present the main research platforms available today, along with a deep analysis of the system design and future directions in the field.

Full dimension (FD) multiple-input multiple-output (MIMO) technology has attracted substantial research attention from both wireless industry and academia in the last few years as a promising technique for next-generation wireless communication networks. FD-MIMO scenarios utilize a planar 2-D active antenna system (AAS) that not only allows a large number of antenna elements to be placed within feasible base station (BS) form factors, but also provides the ability of adaptive electronic beam control over both the elevation and the traditional azimuth dimensions. This paper presents a tutorial on elevation beamforming analysis for cellular networks utilizing FD massive MIMO antenna arrays. In contrast to existing works that focus on the standardization of FD-MIMO in the 3rd generation partnership project (3GPP), this tutorial is distinguished by its depth with respect to the theoretical aspects of antenna array and 3-D channel modeling. In an attempt to bridge the gap between industry and academia, this preliminary tutorial introduces the relevant array and transceiver architecture designs proposed in the 3GPP Release 13 that enable elevation beamforming. Then it presents and compares two different 3-D channel modeling approaches that can be utilized for the performance analysis of elevation beamforming techniques. The spatial correlation in FD-MIMO arrays is characterized and compared based on both channel modeling approaches and some insights into the impact of different channel and array parameters on the correlation are drawn. All these aspects are put together to provide a mathematical framework for the design of elevation beamforming schemes in single-cell and multi-cell scenarios. Simulation examples associated with comparisons and discussions are also presented. To this end, this paper highlights the state-of-the-art research and points out future research directions.

Future Internet (FI) scenarios envisage ubiquitous broadband coverage and seamless mobility, enabling the availability of personalized network connectivity at all places and with a high quality of service (QoS). In such a heterogeneous and complex environment, vertical handover (VHO) management is key for achieving the connectivity objectives, but also presents several challenges. In surveying this topic, this paper takes a direction that extends the state-of-the-art: By incorporating concepts of autonomic network management (ANM), in particular the self-management and cognitive functionalities therein, to VHO management, this paper sheds new light to VHO operations from an ANM point of view, encompassing FI environments and the emerging fifth generation networks. In doing so, the survey identifies the main concepts and provides a taxonomy of relevant architectural components. Based on this taxonomy, a number of important autonomic features are identified, each one promoting the system’s self-optimization along a certain direction toward the overall enhancement of the VHO operations. Another contribution of this paper is the consideration of robustness in VHO decision making (i.e., achieving stable decisions under uncertainty) and a discussion of the relation between robustness factors and the autonomic features previously introduced. The general concepts developed in this paper are applied to representative state-of-the-art handover management solutions with autonomic characteristics. These specific solutions are presented, analyzed, and correlated according to the proposed taxonomy and criteria, culminating to conclusions that provide useful insights toward future, further enhanced solutions.

This paper presents a comprehensive literature review on applications of economic and pricing theory for resource management in the evolving fifth generation (5G) wireless networks. The 5G wireless networks are envisioned to overcome existing limitations of cellular networks in terms of data rate, capacity, latency, energy efficiency, spectrum efficiency, coverage, reliability, and cost per information transfer. To achieve the goals, the 5G systems will adopt emerging technologies such as massive multiple-input multiple-output, mmWave communications, and dense heterogeneous networks. However, 5G involves multiple entities and stakeholders that may have different objectives, e.g., high data rate, low latency, utility maximization, and revenue/profit maximization. This poses a number of challenges to resource management designs of 5G. While the traditional solutions may neither efficient nor applicable, economic and pricing models have been recently developed and adopted as useful tools to achieve the objectives. In this paper, we review economic and pricing approaches proposed to address resource management issues in the 5G wireless networks including user association, spectrum allocation, and interference and power management. Furthermore, we present applications of economic and pricing models for wireless caching and mobile data offloading. Finally, we highlight important challenges, open issues and future research directions of applying economic and pricing models to the 5G wireless networks.

Unmanned aerial vehicles (UAVs) have recently rapidly grown to facilitate a wide range of innovative applications that can fundamentally change the way cyber-physical systems (CPSs) are designed. CPSs are a modern generation of systems with synergic cooperation between computational and physical potentials that can interact with humans through several new mechanisms. The main advantages of using UAVs in CPS application is their exceptional features, including their mobility, dynamism, effortless deployment, adaptive altitude, agility, adjustability, and effective appraisal of real-world functions anytime and anywhere. Furthermore, from the technology perspective, UAVs are predicted to be a vital element of the development of advanced CPSs. Therefore, in this survey, we aim to pinpoint the most fundamental and important design challenges of multi-UAV systems for CPS applications. We highlight key and versatile aspects that span the coverage and tracking of targets and infrastructure objects, energy-efficient navigation, and image analysis using machine learning for fine-grained CPS applications. Key prototypes and testbeds are also investigated to show how these practical technologies can facilitate CPS applications. We present and propose state-of-the-art algorithms to address design challenges with both quantitative and qualitative methods and map these challenges with important CPS applications to draw insightful conclusions on the challenges of each application. Finally, we summarize potential new directions and ideas that could shape future research in these areas.

Unmanned aerial vehicles (UAVs) can be deployed as wireless relays or aerial base stations to improve network connectivity and coverage in cellular networks. UAVs can also be used to significantly enhance the performance of mobile ad-hoc networks and wireless sensor networks. In the future, UAVs are expected to become an integral part of the fifth generation wireless networks as well as key enablers of the coming massive Internet of Things. However, there are still many challenging issues in designing architectures and deployment of UAV-based networks. To address the issues, game theory has recently been adopted as an effective tool for modeling and analyzing problems in UAV-aided networks. In this paper, we survey the applications of game theory in solving various UAV-assisted networks challenges. We first provide a brief introduction to wireless communications with UAVs and then introduce basic game theory concepts and their relation to wireless networks. We further present the classification and brief introduction to the games applied to solve problems in UAV-aided networks. We then provide a comprehensive literature review on game-theoretic techniques utilized in dealing with challenges in the UAV-based wireless networks. Finally, we introduce advanced distributed schemes for interference management in large UAV-assisted communication networks. This paper aims to provide readers with an understanding of UAV-aided networks in terms of their architecture, benefits, challenges, and various game theoretical solutions applied to these communications networks.

The rapid growth of consumer unmanned aerial vehicles (UAVs) is creating promising new business opportunities for cellular operators. On the one hand, UAVs can be connected to cellular networks as new types of user equipment, therefore generating significant revenues for the operators that can guarantee their stringent service requirements. On the other hand, UAVs offer the unprecedented opportunity to realize UAV-mounted flying base stations (BSs) that can dynamically reposition themselves to boost coverage, spectral efficiency, and user quality of experience. Indeed, the standardization bodies are currently exploring possibilities for serving commercial UAVs with cellular networks. Industries are beginning to trial early prototypes of flying BSs or user equipments, while academia is in full swing researching mathematical and algorithmic solutions to address interesting new problems arising from flying nodes in cellular networks. In this paper, we provide a comprehensive survey of all of these developments promoting smooth integration of UAVs into cellular networks. Specifically, we survey: 1) the types of consumer UAVs currently available off-the-shelf; 2) the interference issues and potential solutions addressed by standardization bodies for serving aerial users with the existing terrestrial BSs; 3) the challenges and opportunities for assisting cellular communications with UAV-based flying relays and BSs; 4) the ongoing prototyping and test bed activities; 5) the new regulations being developed to manage the commercial use of UAVs; and 6) the cyber-physical security of UAV-assisted cellular communications.

This paper provides recent advances in the area of Internet of Underground Things (IoUT) with emphasis on enabling communication technologies, networking issues, and localization techniques. IoUT is enabled by underground things (sensors), communication technology, and networking protocols. This new paradigm of IoUT facilitates the integration of sensing and communication in the underground environment for various industries, such as oil and gas, agriculture, seismic mapping, and border monitoring. These applications require to gather relevant information from the deployed underground things. However, the harsh underground propagation environment including sand, rock, and watersheds do not allow the use of single communication technology for information transfer between the surface and the underground things. Therefore, various wireless and wired communication technologies are used for underground communication. The wireless technologies are based on acoustic waves, electromagnetic waves, magnetic induction and visible light communication while the wired technologies use coaxial cable and optical fibers. In this paper, state-of-art communication technologies are surveyed, and the respective networking and localization techniques for IoUT are presented. Moreover, the advances and applications of IoUT are also reported. Also, new research challenges for the design and implementation of IoUT are identified.

A new industrial revolution is undergoing, based on a number of technological paradigms. The will to foster and guide this phenomenon has been summarized in the expression “Industry 4.0” (I4.0). Initiatives under this term share the vision that many key technologies underlying Cyber-Physical Systems and Big Data Analytics are converging to a new distributed, highly automated, and highly dynamic production network , and that this process needs regulatory and cultural advancements to effectively and timely develop. In this work, we focus on the technological aspect only, highlighting the unprecedented complexity of I4.0 emerging from the scientific literature. While previous works have focused on one or up to four related enablers, we consider ten technological enablers, including besides the most cited Big Data, Internet of Things, and Cloud Computing, also others more rarely considered as Fog and Mobile Computing, Artificial Intelligence, Human-Computer Interaction, Robotics, down to the often overlooked, very recent, or taken for granted Open-Source Software, Blockchain, and the Internet. For each we explore the main characteristics in relation to I4.0 and its interdependencies with other enablers. Finally we provide a detailed analysis of challenges in leveraging each of the enablers in I4.0, evidencing possible roadblocks to be overcome and pointing at possible future directions of research. Our goal is to provide a reference for the experts in some of the technological fields involved, for a reconnaissance of integration and hybridization possibilities with other fields in the endeavor of I4.0, as well as for the laymen, for a high-level grasp of the variety (and often deep history) of the scientific research backing I4.0.

Transport layer security (TLS) is becoming the de facto standard to provide end-to-end security in the current Internet. IoT and M2M scenarios are not an exception since TLS is also being adopted there. The ability of TLS for negotiating any security parameter, its flexibility and extensibility are responsible for its wide adoption but also for several attacks. Moreover, as it relies on public key infrastructure (PKI) for authentication, it is also affected by PKI problems. Considering the advent of IoT/M2M scenarios and their particularities, it is necessary to have a closer look at TLS history to evaluate the potential challenges of using TLS and PKI in these scenarios. According to this, this paper provides a deep revision of several security aspects of TLS and PKI, with a particular focus on current certificate pinning solutions in order to illustrate the potential problems that should be addressed.

The “Smart World” envisioned by technology will be achieved by the penetration of intelligence into ubiquitous things, including physical objects, cyber-entities, social-elements or individuals, and human thinking. The development of Smart World is enabled by diverse applications of wireless sensor networks (WSNs) into those components identified as things. Such a smart-world will have features controlled significantly by the location information. Control and Policy information of Smart World services, often addressed as location-based services (LBSs), are governed by location data. Localization thus becomes the key enabling technology for Smart World facilities. It is generally classified as active and passive techniques in nature. Active localization is a widely adopted localization scheme where the target is detected and tracked carries a tag or attached device. The other category, Passive methods, defines targets to be localized as free of carrying a tag or device, hence also referred to as device-free localization (DFL) or sensor-less localization. The passive approach is a well suited for the development of diverse smart world applications with ubiquitous localization. DFL schemes fall into a wide range of application scenarios within the Smart World ecosystem. A few notable examples are occupancy detection, identity definition, positioning, gesture detection, activity monitoring, pedestrian and vehicle-traffic flow surveillance, security safeguarding, ambient intelligence-based systems, emergency rescue operations, smart work-spaces and patient or elderly monitoring. In this paper, the revolution of DFL technologies have been reviewed and classified comprehensively. Further, the emergence of the Smart World paradigm is analyzed in the context of DFL principles. Moreover, the inherent challenges within the application domains have been extensively discussed and improvement strategies for multi-target localization and counting approach are discussed. Finally, current trends and future research directions have been presented.

Current and future wireless applications strongly rely on precise real-time localization. A number of applications, such as smart cities, Internet of Things (IoT), medical services, automotive industry, underwater exploration, public safety, and military systems require reliable and accurate localization techniques. Generally, the most popular localization/positioning system is the global positioning system (GPS). GPS works well for outdoor environments but fails in indoor and harsh environments. Therefore, a number of other wireless local localization techniques are developed based on terrestrial wireless networks, wireless sensor networks (WSNs), and wireless local area networks (WLANs). Also, there exist localization techniques which fuse two or more technologies to find out the location of the user, also called signal of opportunity-based localization. Most of the localization techniques require ranging measurements, such as time of arrival (ToA), time difference of arrival (TDoA), direction of arrival (DoA), and received signal strength (RSS). There are also range-free localization techniques which consider the proximity information and do not require the actual ranging measurements. Dimensionality reduction techniques are famous among the range free localization schemes. Multidimensional scaling (MDS) is one of the dimensionality reduction technique which has been used extensively in the recent past for wireless networks localization. In this paper, a comprehensive survey is presented for MDS and MDS-based localization techniques in WSNs, IoT, cognitive radio networks, and 5G networks.

Over the years, the Internet has been enriched with new available communication technologies, for both fixed and mobile networks and devices, exhibiting an impressive growth in terms of performance, with steadily increasing available data rates. The Internet research community has kept trying to evolve the transport layer protocols to match the capabilities of modern networks, in order to fully reap the benefits of the new communication technologies. This paper surveys the main novelties related to transport protocols that have been recently proposed, identifying three main research trends: (i) the evolution of congestion control algorithms, to target optimal performance in challenging scenarios, possibly with the application of machine learning techniques; (ii) the proposal of brand new transport protocols, alternative to the Transmission Control Protocol (TCP) and implemented in the user-space; and (iii) the introduction of multipath capabilities at the transport layer.

Congestion control (CC) has a significant influence on the performance of transmission control protocol (TCP) connections. Over the last three decades, many researchers have extensively studied and proposed a multitude of enhancements to standard TCP CC. However, this topic still inspires both academic and industrial research communities due to the change in Internet application requirements and the evolution of Internet technologies. The standard TCP CC infers network congestion based on packet loss events which leads to long queuing delay when bottleneck buffer size is large. A promising solution to this problem is to use the delay signal (RTT or one-way delay measurements) to infer congestion earlier and react to the congestion before the queuing delay reaches a high value. In this survey paper, we describe the delay signal and the algorithms that completely or partially utilize this type of signal. Additionally, we illustrate standard CC and modern active queue management (AQM) principles and discus the interaction between AQM and the delay signal.

Nowadays, network technologies are essential for transferring and storing various information of users, companies, and industries. However, the growth of the information transfer rate expands the attack surface, offering a rich environment to intruders. Intrusion detection systems (IDSs) are widespread systems able to passively or actively control intrusive activities in a defined host and network perimeter. Recently, different IDSs have been proposed by integrating various detection techniques, generic or adapted to a specific domain and to the nature of attacks operating on. The cybersecurity landscape deals with tremendous diverse event streams that exponentially increase the attack vectors. Event stream processing (ESP) methods appear to be solutions that leverage event streams to provide actionable insights and faster detection. In this paper, we briefly describe domains (as well as their vulnerabilities) on which recent papers were-based. We also survey standards for vulnerability assessment and attack classification. Afterwards, we carry out a classification of IDSs, evaluation metrics, and datasets. Next, we provide the technical details and an evaluation of the most recent work on IDS techniques and ESP approaches covering different dimensions (axes): domains, architectures, and local communication technologies. Finally, we discuss challenges and strategies to improve IDS in terms of accuracy, performance, and robustness.

The development of the fifth generation (5G) wireless networks is gaining momentum to connect almost all aspects of life through the network with much higher speed, very low latency and ubiquitous connectivity. Due to its crucial role in our lives, the network must secure its users, components, and services. The security threat landscape of 5G has grown enormously due to the unprecedented increase in types of services and in the number of devices. Therefore, security solutions if not developed yet must be envisioned already to cope with diverse threats on various services, novel technologies, and increased user information accessible by the network. This paper outlines the 5G network threat landscape, the security vulnerabilities in the new technological concepts that will be adopted by 5G, and provides either solutions to those threats or future directions to cope with those security challenges. We also provide a brief outline of the post-5G cellular technologies and their security vulnerabilities which is referred to as future generations (XG) in this paper. In brief, this paper highlights the present and future security challenges in wireless networks, mainly in 5G, and future directions to secure wireless networks beyond 5G.

Over the last few years, healthcare administrations have been digitizing their provision of care that led to an increased number of networked medical devices and medical telemetry. Due to such digitization, medical devices have made phenomenal strides in the course of the last half-century. These networked medical devices have enhanced the quality and accessibility of health treatments by achieving pervasive healthcare vision. Moreover, these devices have transformed the canvas of medical treatments and improved the lives of the masses. Such innovation, as a result, assisted in paving the way for reliable healthcare facilities through the introduction of new areas of therapeutic and diagnostic treatments. Medical devices, nowadays, are portable, networked, and capable enough to facilitate human lives. The refined quality and variety of these devices put forward a promising future. However, on the other hand, the healthcare sector is experiencing the greatest amount of security breaches due to the presence of security flaws in medical devices. As these devices are no longer standalone systems and are network-connected, the attack surface has increased profoundly. Actually, devices in practice were designed, developed, and disseminated long ago. Therefore, they were not developed from the ground up with security as a vital design constraint. The flaws present in these devices have acquired the consideration of researchers from both industry and academia. In this paper, we studied security vulnerabilities present in state-of-the-art medical devices by studying security tests and the attacks demonstrated by the researchers on more than a hundred devices. Finally, some state-of-the-art solutions and countermeasures along with applicable regulations in literature were also studied and analyzed. Since these devices are life-critical and can even cause the death of a patient, therefore, this survey is significant as it can assist researchers to get an overview of loopholes present in medical devices and existing countermeasures. We concluded this survey paper with some open research areas that should be properly considered in order to secure these life-critical medical devices.

The salient features of cloud computing (such as on-demand self-service, resource pooling, broad network access, rapid elasticity, and measured service) are being exploited by attackers to launch the severe Distributed Denial of Service (DDoS) attack. Generally, the DDoS attacks in such an environment have been implemented by flooding a huge volume (high-rate) of malicious traffic to exhaust the victim servers’ resources. Due to this huge volume of malicious traffic, such attacks can be easily detected. Thus, attackers are getting attracted towards the low-rate DDoS attacks, slowly. Low-rate DDoS attacks are difficult to detect due to their stealthy and low-rate traffic. In the recent years, many efforts have been devoted to defend against the low-rate DDoS attacks. By utilizing the salient features of cloud computing, it becomes easy for an attacker to launch sophisticated low-rate DDoS attacks. Thus, the study of various DDoS attacks and their corresponding defense approaches becomes essential to protect the cloud infrastructure from fatal effects of DDoS attacks. This paper presents a comprehensive taxonomy of all the possible variants of cloud DDoS attacks solutions with detailed insight into the characterization, prevention, detection, and mitigation mechanisms. The paper provides a detailed discussion on essential performance metrics to evaluate various defense solutions and their behavior in a cloud environment. The purpose of this survey paper is to excite the cloud security researchers to develop effective defense solutions against the various DDoS attacks. The research gaps and challenges are found, and described in the paper while future research directions are outlined.

Blockchain is a technology making the shared registry concept from distributed systems a reality for a number of application domains, from the cryptocurrency one to potentially any industrial system requiring decentralized, robust, trusted, and automated decision making in a multi-stakeholder situation. Nevertheless, the actual advantages in using blockchain instead of any other traditional solution (such as centralized databases) are not completely understood to date, or at least there is a strong need for a vademecum guiding designers toward the right decision about when to adopt blockchain or not, which kind of blockchain better meets use-case requirements, and how to use it. In this paper, we aim at providing the community with such a vademecum, while giving a general presentation of blockchain that goes beyond its usage in Bitcoin and surveying a selection of the vast literature that emerged in the last few years. We draw the key requirements and their evolution when passing from permissionless to permissioned blockchains, presenting the differences between proposed and experimented consensus mechanisms, and describing existing blockchain platforms.

The Internet interdomain routing protocol (border gateway protocol) exhibits slow convergence. Many Internet applications suffer from the effects of its high convergence delay. In this paper, we provide an overview of the state-of-the-art methods on efforts to improve interdomain routing performance. We classified these efforts into five kinds of approaches: 1) speeding up updates; 2) limiting path exploration; 3) efficient policy configuration; 4) multipath; and 5) centralized control of the network. We detailed how each approach addresses the slow convergence problem. The goal of this paper is to provide the researchers a deep understanding on what has been done to improve Internet convergence time. We also discuss why, despite the existence of these efforts, the issue remains open.

I welcome you to the first issue of the IEEE Communications Surveys and Tutorials in 2019. This issue includes 35 papers covering different aspects of communication networks. In particular, these articles survey and tutor various issues in “5G Networks,” “Wireless and Cellular Communications,” “Software Defined Networks and NFV,” “Internet Technologies and Multimedia Communications,” “Network Security: Classic Networks,” “Network Security: Emerging Networks” and “Miscellaneous.” There are three papers in the miscellaneous category that survey the issues in Power Line Communications, Network Verification and Testing, and Quantum Computing. A brief account for each of these papers is given below.

The aim of this special issue was to collect from academic and industrial players, tutorials and surveys related to the latest smart grid and energy related technologies and architectures. Contributions on major developments and updates on smart grid systems are considered. We received a total of 15 submissions from which five were finally accepted for this special issue. The papers span from smart grid communications to building energy efficiency, smart metering, information management, and co-simulation of power and communication systems. Each of the five article is briefly summarized.

I WELCOME you to the first issue of ComST in 2014. This issue includes twenty six articles covering different aspects of communication networks. In particular, these articles cover various issues in wireless communications and networking, devices, networks, and applications for energy-efficient communications, security in communication networks, mobile cloud computing and context-aware computing, and networking protocols. A brief account for each of these articles is given below.

This issue includes 27 articles covering different aspects of communication networks. In particular, these articles cover various issues in wireless networks, energy efficiency and health issues in wireless networks, vehicular, ad hoc, and sensor networks, Internet, security, and programmable networks, and video and multimedia.

The Editor-in-Chief welcomes you to the first issue of ComST in 2012. This issue includes 10 articles. A brief account for each of the articles included in this issue is provided.

2 Welcome to the first issue of the year 2008 of the IEEE Communications Surveys and Tutorials (ComST). Papers in this issue survey the research effort in several areas such as security, traffic engineering, mesh networks and cross layer design. The assessment of the security of a system determines its capability to resist to attacks which involves searching for known vulnerabilities. Moreover, the assessment process can be improved by understanding the nature of known vulnerabilities. The knowledge gained can be organized into a suitable taxonomy, which can then be used as a framework for systematically examining new system for similar and yet unknown vulnerabilities. In this line, there have been many attempts to produce taxonomies in the past years. In “Taxonomies of Attacks and Vulnerabilities in Computer Systems,” Vinay M. Igure and Ronald D. Williams provide a comprehensive survey of the work done on taxonomies of attacks and vulnerabilities in computer systems from 1974 to 2006. The authors discuss the effectiveness of different schemes used in security assessment processes as well as the main characteristics of various taxonomies so that a framework for organizing information on known attacks and vulnerabilities can be construct. The self-duplicating, self-propagating malicious codes, known as computer worms, spread themselves without any human interaction and launch destructive attacks against computer networks. At the same time, being fully automated makes their behavior predictable. In “A Survey of Internet Worm Detection and Containment Pele Li, Mehdi Salour, and Xiao Su present a survey on Internet worm detection and containment schemes. Worm characteristics are identified by their behavior. A classification and a comparison of worm detection algorithms complement the description of the main schemes proposed. Moreover, the locations to implement worm detection as well as current methods used to slow down and to stop the spread of worms are described in great detail. Finally, the authors point out directions for future research on the topic. Traffic Engineering (TE) is an important tool for the operation of Internet Network Providers (INPs) seeking to optimize network performance at a low cost. Routing optimization plays a key role in traffic engineering in finding efficient routes to achieve the target goals. In “An Overview of Routing Optimization for Internet Traffic Engineering,” Ning Wang, Kin Hon Ho, George Pavlou and Michael Howarth describe routing optimization solutions for Internet traffic engineering and challenges associated to TE operation. The authors provide taxonomy of existing routing algorithms, dating from the advent of the TE concept in the late 1990s, including a classification of algorithms on the basis of their main characteristics. Moreover, issues such as robustness, TE interactions and interoperability with overlay selfish routing are addressed in this paper. While revisiting existing solutions, important questions still open in traffic engineering are suggested. In “Meshed High Data Rate Personal Area Networks” S. A. Mahmud, Kumarendra Sivarajah, S. Khan, H. AlRaweshidy provide a tutorial on meshed Personal Area Networks (PANs), the proposed solutions for meshing high data rate PANs and the main drivers behind meshing PANs. The authors introduce PAN architectures and the operation in mesh configuration. The added functionality of routing in meshed PANs, optimizations oriented to multi-interface/multichannel communication, improved dynamic channel selection, transmitted power control procedures, security aspects and other issues such as the hidden node/exposed node in mesh S U R V E Y S I E E E C O M M U N I C A T I O N S

FOR RESEARCHERS and practitioners, IEEE Communications Surveys and Tutorials (ComST) has now become the premier source of in-depth survey and tutorial articles covering all aspects of the communications and networking field. At the 14 year of its publication (since 1998), ComST has placed itself at the 3rd position (with an impact factor of 3.692 reported by Thomson Reuters, and the five year impact factor of 8.462) among all publications in the Telecommunications area. Thanks to the great efforts of Nelson Fonseca, the immediate past Editor-in-Chief, ComST has been recognized as an official IEEE journal. ComST is now indexed in ISI Thomson Reuters SCI (Scientific Citation Index). ComST papers are constantly among the most downloaded papers from IEEE Xplore and ComSoc Digital Library. The flexibility in manuscript submission, fast average review turn-around time along with high-quality reviews, and above all, selection of excellent-quality papers for publication, have resulted in the very high reputation of ComST. For the first time in the IEEE Communications Society, ComST has implemented the fastposting procedure for the accepted articles. Access to this journal is available to non-members as well as members of the IEEE Communications Society. ComST has, therefore, become a venue of choice by the authors for publishing their impactful technical work, and consequently, the number of submissions is growing rapidly. Amidst the above achievements and recognitions of ComST, I feel very privileged to have the challenging opportunity to shepherd this premier publication of the IEEE Communications Society for the next two years. I look forward to working with all the stakeholders — the authors, the Editors, the readers, and their support to take ComST to the next higher level of excellence. To provide better services to our authors and readers from both academia and industry, among others, I will explore the possibilities of special sections or even entire issues dedicated for articles related to emerging areas and research trends in communications and networking technology, services, and applications. I will appreciate any suggestion and comment in this regard. To this end, I welcome you to the first issue of ComST in 2012. This issue includes 10 articles. A brief account for each of the articles included in this issue is given below. Carbon footprint reduction has been one of the major challenges for modern communications system. Hence, reduction of unnecessary energy consumption is becoming a major concern because of the potential economical benefits

I WELCOME you to the second issue of ComST in 2014. This issue includes twenty six articles covering different aspects of communication networks. In particular, these articles cover various issues in wireless communications, radio resource techniques for wireless networks and mobility management for data networks, wireless sensor networks, security in communication networks, and future Internet. A brief account for each of these articles is given below.

Communications Surveys and Tutorials. Paper in this issue survey the research effort in several areas such mobility in Wimax, mobility models in VANET, handoff in cellular networks, admission control in MANETS, physical impairments in optical networks, physical layer issues in the 802.11n standard as well as jamming in wireless sensor networks Despite the challenges faced when transmitting data through varying wireless channels, broadband metropolitan area wireless systems are becoming a reality, partly thanks to the increasingly sophisticated designs that are being employed. Such designs have been made possible by theoretical advances and also by improvements in technology that have led to faster and cheaper implementations compared to older systems. Currently, the focus is on developing 4G systems in the framework of IMT-Advanced, an ITU platform on which the next generation of wireless systems will be built. In “A Survey on Next Generation Mobile WiMAX Networks: Objectives, features and technical Challenges,” Ioannis Papapanagiotou, , Dimitris Toumpakaris, Jungwon Lee, Michael Devetsikiotis survey some of the state-of-the-art characteristics of the physical (PHY) and medium access control (MAC) layers of 802.16m. The concepts and algorithms that are implemented in 802.16m will very likely be used in IMT-Advanced systems, either as they will appear in the 802.16m standard or in similar, and possibly more sophisticated versions. Therefore, it is of interest not only to present these concepts and the ways that they address the needs of future systems, but also to identify technical challenges that will have to be tackled in order for Next Generation Wireless Systems to meet the objectives set by IMT-Advanced. Vehicular Ad-hoc Networks (VANETs) represent a rapidly emerging, particularly challenging class of Mobile Ad Hoc Networks (MANETs). VANETs are distributed, self-organizing communication networks built up from moving vehicles, and are thus characterized by very high speeds and limited degrees of freedom in nodes movement patterns. Such particular features often make standard networking protocols inefficient or unusable in VANETs. The current major objective of protocols developed for VANET is to benefit from the messages exchanged between cars to alter traffic, either for safety issues with advanced safety messages, or for traffic management in order to avoid traffic jams. In both cases, a strong interaction has been defined between the network protocol and vehicular mobility. In the standard approach, data traffic is altered by mobility. Yet in VANETs, mobility may also be influenced by data traffic. There is therefore a specific bidirectional relationship between mobility and wireless communication in VANETs. When considering the huge impact that the deployment of VANET technologies could have on the automotive market, the growing effort in the development of communication protocols and mobility models specific to vehicular networks is easily understandable. In “Mobility Models for Vehicular Ad Hoc Networks: A Survey and Taxonomy,” Jerome Harriy Fethi Filali and Christian Bonnet introduce a framework for the generation of vehicular mobility models. They illustrate the different approaches proposed for the development of vehicular mobility models and their interactions with network simulators. Finally, an overview and taxonomy of a large range of mobility models available for vehicular ad hoc networks is introduced. Mobile ad hoc networks (MANETs) promise unique communication opportunities. The IEEE 802.11 standard has allowed affordable MANETs to be realised. However, providing Quality of Service (QoS) assurances to MANET applications is difficult due to the unreliable wireless channel, the lack of centralized control, contention for channel access and node mobility. One of the most crucial components of a system for providing QoS assurances is admission control which estimates the state of the network’s resources and thereby decide which application data sessions can be admitted without promising more resources than are available and thus violating previously made guarantees. Due to the aforementioned difficulties, estimating the network resources and maintaining QoS guarantees, are non-trivial tasks. In “Admission Control Schemes for 802.11-based Multi-hop Mobile Ad hoc Networks: a Survey,” Lajos Hanzo-II. and Rahim Tafazolli, give a comprehensive survey of the salient unicast admission control schemes designed for IEEE 802.11-based multi-hop MANETs. The relevant considerations for the design of such protocols are discussed and several methods of classifying the schemes found in the literature are proposed. An outline of the operation, reaction to route failures, as well as the strengths and weaknesses of each protocol is given. Cellular radio is the fastest growing and most demanding area in the telecommunications industry. New generation cellular mobile radio systems offering practicality and versatility and new mobile handsets supporting a range of innovative services and access to the mobile users are the objectives and the main interests not only of the telecommunication companies, operators and providers, but also of the research community. Handoff is a key element in the wireless cellular networks to provide Quality of Service (QoS) to the users and to support users’ mobility. Handoff failure will result in the forced termination of an ongoing call. From the user’s point of view, the service of a handoff request is more important, as the forced IEEE COMMUNICATIONS SURVEYS AND TUTORIALS, VOL. 11, NO. 4, FOURTH QUARTER 2009 1

I Welcome you to the fourth issue of the IEEE Communications Surveys and Tutorials in 2017. This issue includes 35 papers covering different aspects of communication networks. In particular, these articles survey and tutor various issues in “Wireless, Sensor, and Cognitive Radio Networks,” “Software-Defined Networking, Mobile Edge Computing, and Intelligent Networks,” “Internet of Things and Vehicular Networks,” “Security, High-Performance Computing, Positioning, and Localization Techniques,” and “Internet, Multimedia, Social Network, Molecular Network, and Optical Communication.” A brief account for each of these papers is given below.

I Welcome you to the third issue of IEEE Communications Surveys and Tutorials (ComST) in 2016. I am pleased to let you know that according to the latest JCR published by Thomson Reuters (JCR 2015), the impact factor of IEEE ComST is 9.22. This is the highest among all journals in the telecommunications and electrical engineering area. This is truly significant. I gratefully acknowledge the support from our authors, readers, and the Editors toward this outstanding achievement of our journal.

An efficient resource discovery mechanism is one of the fundamental requirements for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involves searching for the appropriate resource types that match the user's application requirements. Various kinds of solutions to grid resource discovery have been suggested, including centralized and hierarchical information server approaches. However, both of these approaches have serious limitations in regard to scalability, fault tolerance, and network congestion. To overcome these limitations, indexing resource information using a decentralized (e.g., peer-to-peer (P2P)) network model has been actively proposed in the past few years. This article investigates various decentralized resource discovery techniques primarily driven by the P2P network model. To summarize, this article presents a: summary of the current state of the art in grid resource discovery, resource taxonomy with focus on the computational grid paradigm, P2P taxonomy with a focus on extending the current structured systems (e.g., distributed hash tables) for indexing d-dimensional grid resource queries,1 a detailed survey of existing work that can support rf-dimensional grid resource queries, and classification of the surveyed approaches based on the proposed P2P taxonomy. We believe that this taxonomy and its mapping to relevant systems would be useful for academic and industry-based researchers who are engaged in the design of scalable grid and P2P systems.

A wireless sensor network (WSN) is a network of spatially distributed autonomous sensor nodes that range in number from a few to several hundreds or even thousands. These sensors are deployed to monitor physical or environmental conditions, such as temperature, sound, pressure, etc., and to cooperatively pass their sensed data through the network to a processing location. Such networks are used in many industrial and consumer applications. Sensor devices should be inexpensive and small and have a long lifetime. Therefore, it is important to develop very efficient software and hardware solutions. For this reason, protocols for sensor networks should be carefully designed so as to make the most efficient use of the limited resources in the sensor devices in terms of energy, computation, and storage. In this context, the article titled “A Survey on Testbeds and Experimentation Environments for Wireless Sensor Networks” by Jens Horneber and Anton Hergenroder provides a survey on different methodologies followed to build testbeds and experimentation environments. The article reviews the emerging testbed requirements and outlines the state-of-the-art solutions. Moreover, it discusses common design decisions concerning architectures and experimentation support in current testbeds. In the same context of WSNs, the article titled “Congestion Control Protocols in Wireless Sensor Networks: A Survey” by Charalambos Sergiou, Pavlos Antoniou, and Vasos Vassiliou presents a survey on different algorithms for congestion control for reliable data delivery in WSNs. The article starts by studying congestion in WSNs and then outlines different schemes used for controlling congestion in WSNs. It reviews and classifies the state-of-the-art congestion control mechanisms. Also, it sheds light on possible future research topics. The article titled “Survey on the Characterization and Classification of Wireless Sensor Networks Applications” by Luis M. Borges, Fernando J. Velez, and Antonio S. Lebres puts together important information about the classification and characterization parameters of WSN applications. It starts by identifying some parameters known as “characterization

I WELCOME you to the third issue of ComST in 2015. At the outset, I would like to share with you the following piece of information. Based on the recent release of the 2014 Journal Citation Reports (JCR) by Thomson Reuters, IEEE COMMUNICATIONS SURVEYS AND TUTORIALS ranks the top among all IEEE publications in terms of the following three main indices: impact factor (2 yr): 6.806; impact factor (5 yr): 8.615; article influence factor: 3.910. This indicates the quality of this journal and the impact that it is making to our community. I would like to thank all the authors, reviewers, and editors who have contributed toward this achievement. This issue includes 25 articles covering different aspects of communication networks. In particular, these articles cover various issues in Wireless Networks, Ad-Hoc and Wireless Sensor Networks, Data Networks, Internet and Security, and Information Centric Networking. A brief account for each of these articles is given below.

I WELCOME you to the third issue of ComST in 2014. This issue includes twenty-seven articles covering different aspects of communications networks. These include twentytwo open call articles and five articles for the special section on “Energy and Smart Grid”. The open call articles cover various issues in “wireless communications”, “wireless sensor networks”, “Smart grid”, “Internet and security”, and “Body area networks”. A brief account for each of these articles is given below. There is a separate editorial from the Guest Editors discussing the articles for the special section in this issue.

I WELCOME you to the first issue of the IEEE Communications Surveys and Tutorials (ComST) in 2013. ComST continues to attract an increasing number of submissions. In 2012, there were 323 new submissions, which is about 40% higher than that in 2011. The average time for the first round of the review was 64 days and the average time between submission to final decision was 189 days. The acceptance rate was close to 18%. The impact factor of ComST is now 6.311 which makes ComST the world’s top periodical in communications technology and science for impact factor and citations. I believe all of these statistics are quite encouraging to the potential authors. I am confident that ComST will be increasingly popular among researchers in the telecommunications area and will continue to have a very high impact factor. This issue includes twenty-five articles covering different aspects of communication networks. In particular, issues related to the following are covered in these articles: smart power grids, power control in data centers, optical networking, mobility-aware medium access control (MAC) protocols, wireless sensor networks, energy management and efficiency in wireless communications, scheduling in wireless mesh networks and orthogonal frequency-division multiple access (OFDMA)-based systems, path-loss predictions and coverage mapping in wireless systems, network selection in heterogeneous wireless networks, interference management in femtocells, interference cancellation in OFDMA-based systems, self-organization in cellular networks, context-aware wireless networking, social based routing in delay-tolerant networks, mobile phone sensing systems, security threats in cognitive radio, mobile devices’ security, game theory for network security, and attacks and countermeasures for the IEEE 802.16 systems. A brief account for each of the articles included in this issue is given below.

Dynamic Spectrum Management (DSM) is an effective method for reducing the effect of crosstalk in Digital Subscriber Line (DSL) systems. This paper discusses various DSM algorithms, including Optimal Spectrum Balancing (OSB), Iterative Spectrum Balancing (ISB), Autonomous Spectrum Balancing (ASB), Iterative Water-Filling (IWF), Selective Iterative Water-filling (SIW), Successive Convex Approximation for Low complExity (SCALE), the Difference of Convex functions Algorithm (DCA), and Distributed Spectrum Balancing (DSB). They are compared in terms of performance (achievable data rate) and computational complexity.

This issue includes twenty five articles covering different aspects of communication networks. In particular, issues related to energy efficient multimedia transmission, interference coordination in cellular networks, resource allocation and reservation, game theoretic approaches for spectrum access via carrier sensing, cognitive networks, biologically inspired algorithms for computer networking, stochastic geometry modeling for cellular and cognitive wireless networks, human activity recognition via wearable sensors, intrusion detection in sensor networks, source location privacy in sensor networks, indoor inertial position systems, cloud computing for smart mobile devices, content delivery in mobile networks, power savings in data centers, mobile social networks, vehicular networks, protocol stack for the Internet of Things, transition from IPv4 to IPv6, active queue management, Ethernet security, and context provisioning. A brief account for each of the articles included in this issue is given.