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Even though achieving global connectivity represents one of the main goals of 5G and beyond wireless networks, exurban areas are still suffering frequent outages because of the lack of proper telecom infrastructures, which are often available only in urban areas. Indeed, cellular network design is usually capacity driven, and thus the densities of base stations (BSs) follow mostly population and especially revenue densities. Contextually, we focus on one of the most promising solutions to provide sufficient and reliable coverage in far-flung areas: aerial base stations (ABSs), which consist of unmanned aerial vehicles (UAVs) carrying cellular BS equipment. In this article, we extensively discuss the problem of bridging what is called the urban–rural digital divide (i.e., the connectivity gap between urban and rural areas) from various perspectives. First, we showcase various alternative solutions and compare conventional terrestrial networks with aerial networks from a techno-economic point of view. Then, we highlight the topological aspects of rural environments and explain how they can affect the actual design of cellular networks. In addition, we investigate both the coverage probability and the reliability of the communication links via simulations, proving that the integration of ABSs can be quite promising in a 6G perspective. Finally, we propose two original extensions of our case study as open problems. [ABSTRACT FROM AUTHOR]

5G network slicing is promising in prioritizing time‐critical protection communication in wireless networks of smart grids. However, network slicing offered by telecommunication providers encompasses all smart grid applications, lacking granularity. Smart grid automation standards provide recommendations on prioritization of protection communication to improve reliability but only for wired connections. Therefore, this paper investigates hierarchical token bucket (HTB) traffic shaping and uplink (UL) bitrate adaptation of a live video stream for prioritizing protection communication within a 5G slice. An experimental setup combines controller‐hardware‐in‐the‐loop (CHIL) with a quality of service (QoS) measurement system for validation. The system under test consists of commercial 5G networks, intelligent electronic devices (IEDs), and merging units for validation with three smart grid applications: fault location, line differential, and intertrip protection. HTB traffic shaping improves protected faults by 47.57% in congested and 1.16% in non‐congested scenarios. UL bitrate of the video stream adaptation by 2 Mbps increases protected faults by 3.69%. HTB traffic shaping even improves prioritization with a wired connection without introducing additional delays. HTB traffic shaping must be deployed in routers to maintain good QoS for critical applications. Collaboration between utilities and telecommunication providers is essential to effectively deploy 5G network slicing on smart grids. [ABSTRACT FROM AUTHOR]

Abstract 5G network slicing is promising in prioritizing time‐critical protection communication in wireless networks of smart grids. However, network slicing offered by telecommunication providers encompasses all smart grid applications, lacking granularity. Smart grid automation standards provide recommendations on prioritization of protection communication to improve reliability but only for wired connections. Therefore, this paper investigates hierarchical token bucket (HTB) traffic shaping and uplink (UL) bitrate adaptation of a live video stream for prioritizing protection communication within a 5G slice. An experimental setup combines controller‐hardware‐in‐the‐loop (CHIL) with a quality of service (QoS) measurement system for validation. The system under test consists of commercial 5G networks, intelligent electronic devices (IEDs), and merging units for validation with three smart grid applications: fault location, line differential, and intertrip protection. HTB traffic shaping improves protected faults by 47.57% in congested and 1.16% in non‐congested scenarios. UL bitrate of the video stream adaptation by 2 Mbps increases protected faults by 3.69%. HTB traffic shaping even improves prioritization with a wired connection without introducing additional delays. HTB traffic shaping must be deployed in routers to maintain good QoS for critical applications. Collaboration between utilities and telecommunication providers is essential to effectively deploy 5G network slicing on smart grids.

The research community’s attention has been attracted to the reliability of networks exposed to large-scale disasters and this has become a critical concern in network studies during the last decade. Earthquakes are high on the list of those showing the most significant impacts on communication networks, and simultaneously, they are the least predictable events. This study uses the Probabilistic Seismic Hazard Analysis method to estimate the network element state after an earthquake. The approach considers a seismic source model and ground prediction equations to assess the intensity measure for each element according to its location. In the simulation, nodes fail according to the building’s fragility curves. Similarly, links fail according to a failure rate depending on the intensity measure and the cable’s characteristics. We use the source-terminal, and the diameter constrained reliability metrics. The approach goes beyond the graph representation of the network and incorporates the terrain characteristics and the component’s robustness into the network performance analysis at an affordable computational cost. We study the method on a network in a seismic region with almost 9000 km of optical fiber. We observed that for source-terminal that are less than 500 km apart the improvements are marginals while for those that are more than 1000 km apart, reliability improves near a 30% in the enhanced designs. We also showed that these results depend heavily on the robustness/fragility of the infrastructure, showing that performance measures based only the network topology are not enough to evaluate new designs.

Knowledge about the reliability of a wireless sensor network is important in industry. Indeed, in holonic manufacturing, it is convenient to ensure that decisions are made with reliable data. However, experimental evaluation in a real environment is a task that consumes time and financial resources, it also depends on several factors such as the technical characteristics of the transceiver and the location of the nodes. Thus, the use of simulation and calculation software in Industry 4.0 can potentially reduce costs and implementation time significantly, nonetheless some simulators deal with power consumption and network reliability with theoretical models that have limitations for commercial devices. This paper presents the sWSN3 tool that, through an intuitive graphical interface allows placing sensor nodes on the virtual environment of a plant layout and calculates the reliability of a wireless sensor network using parameters such as signal to noise ratio, received packet rate, and battery life time. Results show that sWSN3 can accurately estimate the reliability of a virtual WSN.

Network Function Virtualization (NFV) migrates the carrier-grade LTE Evolved Packet Core (EPC) that runs on commodity boxes to the public cloud. In the new virtualized environment, LTE EPC must offer high availability to its mobile users upon failures. Achieving high service availability is challenging because failover procedure must keep the latency-sensitive control-plane procedures intact during failures. Through our empirical study, we show that existing recovery mechanisms on the cloud and standardized LTE solutions are coarse-grained, thus unable to quickly recover from failures. They incur LTE service outage, lost network connectivity, and slow recovery. To address these issues, we describe a new design for fault-tolerant LTE EPC. It provides quick failure detection and timely recovery from failed operations. To reduce failure detection time, it leverages frequent retransmission of LTE control-plane signaling within EPC as an indication of failure. To recover from failure, it adopts a checkpointing based rollback recovery approach in the LTE context and addresses the shortcomings known in the classic checkpointing approach. Our design is LTE standard-compliant and works as a plug-and-play without modifying existing LTE implementations. Our results show that this approach can recover from the failure in 2.6 seconds and only incurs tens of milliseconds of overhead. [ABSTRACT FROM AUTHOR]

Abstract The authors proposed a fusion protocol using multilevel clustering (FPMC), which is completely dependent on the increased coverage and wireless sensor network (WSN) reliability‐clustering framework to eliminate duplication. Therefore, a static sensor for a point of interest is allocated where possible so that the particular area can be protected. Furthermore, FPMC ensures that only one sensor node is allocated to cover a specific point of interest. The network coverage, energy usage, mean movement of WSNs nodes and sensor nodes are active in each loop due to which efficiency of the proposed protocol was assessed under various densities, and its performance was also analysed. Evaluations have shown that with restricted active nodes and sensor nodes, the FPMC can increase the networking coverage. The FPMC should be stressed as reducing the overlap level. The proposed protocol is based on the fusion protocol using multi‐level clustering for improving coverage and connectivity WSNs.

Data center networks (DCNs) always strive to ensure high reliability and fault tolerance when Big Data processing and cloud computing are carried out. One effective method is to conduct the fault diagnosis based on subsystem structures (establish the subsystem-based reliability), which can be transformed into solving the problem of the probability that there exists at least one fault-free subnetwork in one network. In this article, we establish the subsystem-based reliability of BCube, which is the first time that fault diagnosis is carried out in the subsystem structures of the DCN. More specifically, we compute the upper and lower bounds on the subsystem-based reliability of BCube and determine the approximation on the subsystem-based reliability of BCube. Furthermore, we conduct some numerical simulations to validate the established analytical formulation. Our results show that the precise value of subsystem-based reliability of BCube can be basically represented by the approximation value of subsystem-based reliability of BCube, which means that it is much easier to evaluate the reliability of the network even when the network scale is sufficient large. Although the analysis is done for a particular network (BCube), the outcome can serve as a useful reference, and can shed light on the effectiveness of the fault diagnosis for other DCNs. [ABSTRACT FROM AUTHOR]

Software-Defined Networking (SDN) has aggressively grown in data center networks, telecommunication providers, and enterprises by virtue of its programmable and extensible control plane. Also, there have been many kinds of research on the security of SDN components along with the growth of SDN. Some of them have inspected network policy inconsistency problems that can severely cause network reliability and security issues in SDN. However, they do not consider whether a single network policy itself is corrupted during processing inside and between SDN components. In this paper, we thus focus on the question of how to automatically identify cases in which the SDN stack fails to prevent policy inconsistencies from arising among those components. We then present AudiSDN, an automated fuzz-testing framework designed to formulate test cases in which policy inconsistencies can arise in OpenFlow networks, the most prevalent SDN protocol. To prove its feasibility, we applied AudiSDN to two widely used SDN controllers, Floodlight and ONOS, and uncovered three separate CVEs (Common Vulnerabilities and Exposures) that cause the network policy inconsistencies among SDN components. Furthermore, we investigate the design flaws that cause the inconsistencies in modern SDN components, suggesting specific validations to address such a serious but understudied pragmatic concern. [ABSTRACT FROM AUTHOR]

The monumental growth in the frequency and sophistication of connected moving objects has led to a plethora of solutions to enable continuous, seamless, and reliable connectivity and service delivery. Connected, autonomous, and artificial intelligence (AI)-enabled Internet of Things (IoT) moving devices are playing a significant role in the establishment of reliable wireless connectivity infrastructures for Beyond 5G (B5G) telecommunication networks. The advancements in ad hoc communication and moving platforms are now being recognized as alternative solutions toward connectivity in many complex environments for applications, such as autonomous transportation and robotics. Today’s availability of AI-enabled moving devices, incorporating advanced processing and communication capabilities, together with advanced decentralization-enabling technologies, such as intelligent blockchain, provide alternatives to autonomy for moving platforms in smart cities. In this article, we discuss recent advances in moving IoT devices, such as unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs), that adapt intelligent connectivity support, data collection, decision making, and blockchain technology to facilitate autonomous configurability and service provisioning for IoT networks. [ABSTRACT FROM AUTHOR]

The concept of fixed infrastructures capable of fulfilling the requirements of moving devices in terms of connectivity and reliability has been the optimal solution for the past few decades. Today, such a solution is no longer feasible in the Internet of Things (IoT) era. All things are now connected, and a significant number of them are mobile, hence leading to connectivity and reliability issues. Connected and autonomous vehicles, in addition to more contemporary flying and moving devices such as unmanned aerial vehicles (UAVs) and IoT devices, will play a significant role in next-generation networks (NGNs). Node-to-node communication will also play a key role in NGNs and will provide alternative solutions toward connectivity in many complex environments for applications such as smart transportation. With that said, today's wide availability of smart moving devices provides a wider set of alternatives to autonomy for NGNs. In this article, we discuss some of the existing solutions that use connected vehicles, UAVs, and other moving intelligent devices to not only provide connectivity support, but also perform on-location data collection, anal-ysis, and decision making to enable the management of moving NGNs for intelligent services and applications. We envision a solution that is capa-ble of adapting generalized and decentralized learning on mobile devices, such as federated learning, with the advances in deep learning to support the autonomy and configurability aspects of moving NGNs. [ABSTRACT FROM AUTHOR]

Abstract Wireless sensor networks (WSNs) are becoming more popular in recent times due to the availability of low cost, the short transmission range of sensor nodes and their easy deployment in different application areas; however, security is crucial for WSNs due to the nature of data they transmit in most cases in their locations. Sensor nodes transmit through an open medium and due to the short communication range of each sensor node, a node may need to transmit through many hops to a final destination. Denial‐of‐service (DoS) is one of the attacks that can be launched against WSNs to prevent legitimate nodes from transmitting/receiving data packets. Developing an attack detection and countermeasure system to mitigate the effect of DoS is not an easy task. This work proposes lightweight models for DoS attack detection in WSNs. We developed different lightweight models and algorithms for the detection and elimination of DoS in WSNs and experimented the same. The performance of data delivery ratio, delay, detection rate, energy consumption, and false‐positive was carried out. The experimental results show that the proposed scheme achieved a high true‐positive detection rate, low false‐positive detection rate, energy‐efficient, and high data reliability. Numerical examples are presented to further validate the effectiveness of the proposed scheme.

Abstract Recently, the area coverage problem has emerged in the directional sensor network (DSN), where the sensor's sensed area depends on its working direction and viewing angle. This study has proposed a new algorithm based on the Voronoi diagram, called prioritized geometric area coverage (PGAC), to increase DSN's covered area. In a Voronoi diagram, all internal points of a convex polygon (cell) formed around a sensor are closer to the sensor than any other sensor. Therefore, the best sensor for covering a Voronoi cell area is the corresponding sensor of the cell. In contrast to similar approaches, PGAC considers the relation between the cell area and the sensor's covered area when selecting a sensor's working direction. It categorizes Voronoi cells, based on their geometric sizes, into three categories. In each category, PGAC adjusts the sensor's working direction to maximize the covered area and minimize the overlapping between adjacent cells. It also turns off redundant sensors for extending the network lifetime. Our simulation results showed that PGAC increases the covered area and decreases the number of active sensors compared to similar methods.

Abstract With the advent of the new decade, unmanned aerial vehicles (UAVs) will increasingly play an active role mainly as broadband transmission relays for broadcast applications. In the present study, we consider a feasible network where a transmitter, mounted on a hill, is connected through an optical wireless link with a UAV, hovering at a certain height above the earth. The UAV provides coverage over a circular geographic area and communicates through a radio frequency (RF) link with a ground user who is randomly located inside the circular region. In this context, a mixed optical/RF link is established where the performance is thoroughly investigated in terms of the outage probability. We assume that the optical wireless link is affected by a plethora of deteriorating factors, including the presence of fog, or the atmospheric scintillation, while the RF link is subject to small‐scale fading. Depending on the appearance of fog or turbulence, two different problems occur with a different mathematical formulation. For both cases, we extract closed‐form expressions for the signal‐to‐noise ratio statistics, which are the critical component towards determining the outage probability. Then, the impact of the impairments for some typical parameter values is properly depicted in appropriate graphs.

Abstract Internet of Things (IoTs) as a new network pattern for the intelligent world usually uses wireless sensor networks (WSNs) as a perception layer which consisted of numerous number of sensor nodes scattered in the environment to gather intended information. The selected information then is sent to a base station (BS) to be sent to cloud server for further processing. Since the energy of sensor nodes is limited, the most significant challenge in these networks is reducing the energy consumption of the network. It is proved that dividing the network to clusters can significantly reduce the energy consumption. One of the most popular clustering protocols in WSNs is the Low‐Energy Adaptive Clustering Hierarchy (LEACH). In this protocol, cluster heads (CHs) are selected randomly which results in poor performance in real scenarios. In this article, a new energy aware CH selection algorithm is proposed which selects CHs based on the residual energy, the position and centrality of nodes. It uses a variable range upon which the centrality and the number of neighbours of each node are calculated. Simulation results show that the proposed algorithm outperforms LEACH, Multi‐hope Routing with LEACH (MR‐LEACH) and Enhanced Multi‐hop LEACH (EM‐LEACH) in terms of reducing energy consumption, increasing network lifetime and improving network reliability.

With the development of complex networks and with increasing service demands, service use is becoming more complex and the composition of services is becoming more complicated. In the XaaS (X as a Service) environment, users only care about the QoE of a service and do not care about the composition process of the service. Therefore, it is important to evaluate the reliability of the entire service. In this article, we use Petri Net as a basis for modeling the composition of services. In addition, we consider the problems of shared resources and common cause faults. Both of these problems can cause network congestion and regional failures. We use distance to assess the effects of regional faults and queuing theory to simulate the network congestion process. Moreover, in the simulation, we verify the impacts of regional failures and network congestion on service reliability. We choose the Tree-Based Search algorithm and the Semi-Markov Model as comparison algorithms. The results of our algorithm are related to service time. Our algorithm can timely reflect the impact of regional failure or network congestion, and it can feedback different evaluation results according to environmental changes. Therefore, our algorithm is more comprehensive and has better performance. [ABSTRACT FROM AUTHOR]

This study deals with the performance analysis of adaptive combining‐based hybrid free‐space optics (FSO)/radio‐frequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal‐ratio‐combining (MRC) of RF and FSO links is performed at the destination. The small‐scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami‐m and Gamma–Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal‐to‐noise of the RF link, and the pointing errors parameter. [ABSTRACT FROM AUTHOR]

Research on underwater acoustic sensor networks has become a compelling field in recent years since resources on land are being depleted. Therefore, robust and efficient routing protocols are needed to ensure the reliability of message gathering and transmitting in underwater sensor networks. In the process of biological foraging in nature, creatures such as insects can find paths while adapting to dynamic environmental conditions through group cooperation, which provides a new perspective for research on routing protocols. In this study, the authors proposed an ant colony algorithm‐based routing protocol (ACAR). In ACAR, the pheromone with a novel physical meaning and concentration changing mechanism is utilised to guide ants (path establishing packets) to the sink node. In addition, node depth information is used to decrease redundancy in the underwater environment. The routing process can be summarised in three parts: pheromone list setup, routing decision and damaged path repair. Simulation results, carried out on an underwater simulator based on NS‐2, showed that ACAR outperforms other schemes with regards to network lifetime with a relatively better delivery ratio and latency in the proposed network scenarios. [ABSTRACT FROM AUTHOR]

Aerial computing is a key enabling technique to provide seamless telecommunication and IT services for emerging computation-craving applications. As a drone employed in an aerial computing platform is limited in computation, caching, communication, and control capabilities, researchers have utilized multiple drones for efficient multi-modal multi-task processes, which also bring great challenges in massive data transmission and dynamic network management. Motivated by recent advancement of device-to-device communication and software defined networking technologies, we propose an air-ground integrated aerial computing framework where a cloudlet server and multiple mobile edge servers are mounted on drones to provide reliable and efficient edge computing services for ground devices. The joint implementation of computation offloading and trajectory design for the proposed framework is investigated. Extensive numerical results demonstrate that our aerial computing framework achieves better performance in terms of average task completion time than traditional ones. [ABSTRACT FROM AUTHOR]

In this article, two new techniques of approximation of the reliability of a two-terminal network are developed based on the constructive theory of functions and related methods. Two methods of generating an approximation cubic spline are used: Lagrange-type interpolation procedures and Bernstein approximation operator. A possibility of minimizing the total error of approximation, based on keeping some properties invariant, is described in case of a large class of pairs of dual two-terminal networks. Simulations are included, showing that the error of approximation is negligible in case of some special initial data. [ABSTRACT FROM AUTHOR]

This article presents an improved state space decomposition (SSD) method for reliability evaluation of multistate networks. We observe that the decomposition process of the existing SSD is a sequential decomposition process. However, the SSD has the basis of parallel operations, as the decomposition process from each unspecified state is independent of each other. In addition, the existing SSD methods applied heuristic to select a proper minimal path vector (d-MP). When there is a tie during the process, the tie is broken arbitrarily. However, we find that different d-MPs with same function value of the current heuristic affect the efficiency of the decomposition procedure. Based on these observations, an improved SSD method is developed for reliability evaluation of multistate networks. First, a parallel mechanism is proposed and incorporated into the SSD algorithm. Second, several improved heuristics, namely R1, R2, R3, and R4, are developed to select a proper d-MP. The experimental results show that the proposed SSD method can improve the efficiency for reliability evaluation of multistate networks, which provides the reliability engineers and facility managers a more powerful tool for the design and maintenance of more complex multistate networks. [ABSTRACT FROM AUTHOR]

In this article, we evaluate the performance of a LoRaWAN network in industrial scenarios where different Industrial Internet of Things (IIoT) end nodes communicate to a central controller in order to provide monitoring and sensing information to optimize the efficiency of industrial processes and reduce costs. In particular, we consider confirmed and unconfirmed traffic, multigateway deployments, the usage of different classes of devices, and a nonstandard channel plan. Furthermore, we analyze the higher-layer impact of different models of LoRa PHY layer with industrial channel models. We show that, with proper configuration, LoRaWAN is able to serve IIoT sensing applications with a packet success rate over 90%, providing at the same time limited communication delays. [ABSTRACT FROM AUTHOR]

Fifth generation (5G) technologies have become the center of attention in managing and monitoring high-speed transportation system effectively with the intelligent and self-adaptive sensing capabilities. Besides, the boom in portable devices has witnessed a huge breakthrough in the data driven vehicular platform. However, sensor-based Internet of Things (IoT) devices are playing the major role as edge nodes in the intelligent transportation system (ITS). Thus, due to high mobility/speed of vehicles and resource-constrained nature of edge nodes more data packets will be lost with high power drain and shorter battery life. Thus, this research significantly contributes in three ways. First, 5G-based self-adaptive green (i.e., energy efficient) algorithm is proposed. Second, a novel 5G-driven reliable algorithm is proposed. Proposed joint energy efficient and reliable approach contains four layers, i.e., application, physical, networks, and medium access control. Third, a novel joint energy efficient and reliable framework is proposed for ITS. Moreover, the energy and reliability in terms of received signal strength (RSSI) and hence packet loss ratio (PLR) optimization is performed under the constraint that all transmitted packets must utilize minimum transmission power with high reliability under particular active time slot. Experimental results reveal that the proposed approach (with Cross Layer) significantly obtains the green (55%) and reliable (41%) ITS platform unlike the Baseline (without Cross Layer) for aging society. [ABSTRACT FROM AUTHOR]

Public transport systems in a metropolitan area experiences several complex issues, like resource scarcity, resource allocation, congestion, resource reliability and so on, due to the dynamic arrivals of heterogeneous commuter and exceptional occurrence of unforeseen events. The progress of these issues may lead to economic losses, under-utilization of transport resources, and commuters’ queuing delay. In this paper, we propose a novel dynamic public transport vehicle allocation scheme based on Emergent Intelligence (EI) technique in a metropolitan area. In addition, we demonstrate the EI technique’s capability for solving public transport system problems. To do so, the EI technique maintains historical information, commuters’ arrival rates, resource avaialability, deficit resources and surplus resources of neighbor depots’s agent. In the proposed scheme, the EI technique is utilized to collect, analyze, share and optimally allocate transport resources effectively. The proposed EI technique provides reliable services (allocation and scheduling) by coordinating with a reliable neighborhood depot’s agent. We have build mathematical models for estimation of resources, utilization and reliability parameters. The proposed scheme is exhaustively tested by simulation and analyzed with varying commuters’ arrival rates, number of vehicles, number of requests, and different values of reliability parameters. The proposed scheme’s results (analytical, simulation and comparison) show the reliabiltiy, accuracy and real time deployability. [ABSTRACT FROM AUTHOR]

Attaining reliable communications traditionally relies on a closed-loop methodology but inevitably incurs a good amount of networking latency thanks to complicated feedback mechanism and signaling storm. Such a closed-loop methodology thus shackles the current cellular network with a tradeoff between high reliability and low latency. To completely avoid the latency induced by closed-loop communication, this article aims to study how to jointly employ open-loop communication and multi-cell association in a heterogeneous network (HetNet) so as to achieve ultra-reliable and low-latency communications. We first introduce how mobile users in a HetNet adopt the proposed proactive multi-cell association (PMCA) scheme to form their virtual cell that consists of multiple access points (APs) and then analyze the communication reliability and latency performances. We show that the communication reliability can be significantly improved by the PMCA scheme and maximized by optimizing the densities of the users and the APs. The analyses of the uplink and downlink delays are also accomplished, which show that extremely low latency can be fulfilled in the virtual cell of a single user if the PMCA scheme is adopted and the radio resources of each AP are appropriately allocated. [ABSTRACT FROM AUTHOR]

With the development of information technology, the network consists of various proprietary hardware devices, and the use of these devices brings problems. To solve problems, network function virtualization is proposed, which decouples the software and hardware in the network, and deploys the existing network function devices to a common physical platform. However, network virtualization needs will inevitably face reliability problems during resource virtualization and service function chain deployment. This article proposes a service function chain reliability evaluation method and reliability optimization algorithm. The composition relationship and reliability influencing factors of service function chain were analyzed, including resource preemption, common cause failure, fault recovery and redundant backup. The service function chain was modeled as a Petri net model, and reliability evaluation results related to execution time were obtained. Based on the reliability assessment results, a VNF migration strategy is designed, with reliability as the optimization goal while considering costs. Simulation results show that, compared with the reliability optimization strategy based on backup, our algorithm costs less and reduces the impact of resource preemption on service reliability. [ABSTRACT FROM AUTHOR]

In the network function virtualization (NFV) environment, network services are usually provided in the form of service function chains (SFCs), which defines the link order of virtual network functions required in service requests and are mapped to the physical network. Although NFV facilitates the flexible provision of network services, service interruptions may occur as a result of software and hardware failures. Current solutions mostly use the backup method to ensure the reliability of SFCs. However, these methods ignore the SFC construction phase that has an impact on reliability. Besides, the resource efficiency still requires improvement. To address these issues, reliability-oriented SFC construction and backup problems are investigated in this work. First, an instance-sharing and reliable construction algorithm (ISRCA) is proposed to aggregate multiple SFCs into a service function graph (SFG), and perform reliability screening for the SFG set. After mapping the SFG to the physical network, a node-ranking algorithm with centrality and reliability (NRCR) is proposed for backup node selection and backup instance deployment to improve the reliability of SFCs that have not met the requirements. Experimental results demonstrate that under the premise of ensuring reliability, the proposed backup method can reduce the consumption of bandwidth resources by about 11.7%, when combined with the proposed construction method, it can further reduce the backup resources by 13.9%. [ABSTRACT FROM AUTHOR]

$k$ -terminal network reliability is the probability that $k$ terminal vertices are connected given that edges in the network fail independently while vertices do not fail. It depends on the distribution of these terminal vertices as well as network topology. The problem of computing $k$ -terminal reliability is NP-hard. Previous literature mainly focus on designing efficient algorithms to compute it in different graphs, but are lacking in the analysis for optimal distribution of $k$ terminal vertices in sparse graphs, within which those with $n$ nodes and $m$ edges, where $m \leq n + 1$ , are most basic classes. Hence, it is of great significance to investigate the optimal distribution of terminal vertices in these classes of graphs before considering general cases. In this paper, we prove that $k$ -terminal network reliability obtains the maximum if $k$ terminal vertices induce a connected subgraph. Further, we give equations of maximum reliability for all possible graphs in the above classes. The experiments illlustrate the variation, with several parameters and according to our theoretical results, of maximal $k$ -terminal reliability, and provide observations for graphs with any number of edges. [ABSTRACT FROM AUTHOR]

This study deals with the performance analysis of adaptive combining‐based hybrid free‐space optics (FSO)/radio‐frequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal‐ratio‐combining (MRC) of RF and FSO links is performed at the destination. The small‐scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami‐m and Gamma–Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal‐to‐noise of the RF link, and the pointing errors parameter. [ABSTRACT FROM AUTHOR]

Research on underwater acoustic sensor networks has become a compelling field in recent years since resources on land are being depleted. Therefore, robust and efficient routing protocols are needed to ensure the reliability of message gathering and transmitting in underwater sensor networks. In the process of biological foraging in nature, creatures such as insects can find paths while adapting to dynamic environmental conditions through group cooperation, which provides a new perspective for research on routing protocols. In this study, the authors proposed an ant colony algorithm‐based routing protocol (ACAR). In ACAR, the pheromone with a novel physical meaning and concentration changing mechanism is utilised to guide ants (path establishing packets) to the sink node. In addition, node depth information is used to decrease redundancy in the underwater environment. The routing process can be summarised in three parts: pheromone list setup, routing decision and damaged path repair. Simulation results, carried out on an underwater simulator based on NS‐2, showed that ACAR outperforms other schemes with regards to network lifetime with a relatively better delivery ratio and latency in the proposed network scenarios. [ABSTRACT FROM AUTHOR]

In this study, the performance of downlink simultaneous wireless information and power transfer (SWIPT) networks over Nakagami‐m fading is analysed. The SWIPT network is modelled as a two‐tier heterogeneous network, where one tier is the information transmission network and the other is the power transmission network. The seamless integration enables both data and energy to be transferred from access points to the users. Using the stochastic geometry theory, the expressions for outage probability at the information receiver are derived in decoupled and integrated SWIPT networks. Also, the average harvested energy at the power receiver is derived assuming a non‐linear energy harvesting model. Simulation results validate the analytical expressions and the impacts of various system parameters on the SWITP performance are investigated. [ABSTRACT FROM AUTHOR]

Fast session transfer (FST) is introduced by wireless gigabit (WiGig) standards to transfer the data communication session among wireless fidelity (Wi‐Fi) and WiGig channels based on the availability. In the conventional Wi‐Fi/WiGig FST decision‐making, the session of data transmission is transferred from Wi‐Fi to WiGig whenever it is possible regardless of the traffic loads on both bands and the expected WiGig blocking probability. Also, WiGig to Wi‐Fi FST occurs whenever the WiGig signal is lost even if the WiGig link is undergoing an instant path blocking. This results in Wi‐Fi/WiGig load imbalance as well as large average delay in user data delivery. In this study, a novel Wi‐Fi/WiGig FST decision‐making algorithm is proposed utilising fuzzy logic while considering the coverage probability of the WiGig link, the sizes of the users' remaining messages relative to the available data rates of both bands, and the probability of WiGig path blocking. Furthermore, a WiGig interruption‐classification methodology is proposed to detect the occurrence of the WiGig instant path blocking and then decide if it is better to wait for WiGig signal recovery or immediately transfer to Wi‐Fi. Simulation analysis demonstrates the effectiveness of the proposed Wi‐Fi/WiGig FST decision‐making algorithm, over the conventional one. [ABSTRACT FROM AUTHOR]

Ever since the idea of buffers was incorporated in wireless communications, buffer‐aided relaying has become an emerging breakthrough in the world of transmitting and receiving signals. Equipping the relays with buffers adds a new degree of freedom capable of enhancing numerous quality‐of‐service (QoS) metrics including throughput, outage probability, power efficiency and physical‐layer security. The QoS enhancement is achieved by compromising the end‐to‐end delay that is inflicted by storing the packets in the relays' buffers until a suitable source–relay or relay–destination link is selected. In this context, the selection of a relay for transmission/reception is important since it governs the QoS‐delay trade‐off that can be contemplated. In this survey, the authors review and analyse various link selection protocols in buffer‐aided relaying systems. These relaying strategies are categorised and contrasted according to their performance levels, limitations, applications, system model assumptions and complexity. Finally, they discuss current challenges, and highlight future research directions. [ABSTRACT FROM AUTHOR]

In this study, a simple two‐user multiple‐input multiple‐output (MIMO) relaying scenario is considered. To efficiently exploit the spectrum resources, a generalised singular value decomposition (GSVD) based precoding scheme with non‐orthogonal multiple access (NOMA) is proposed, which converts the multiple channels into several parallel single channels. The performance of the proposed GSVD‐MIMO relaying scheme is evaluated by using the distribution characteristics of squared generalised singular values of two users' channel matrices and the eigenvalues of the relay's channel matrix to obtain the expressions of the average data rate and outage probabilities. Both the asymptotic case and a practical scenario with nodes equipped with finite numbers of antennas are analysed because the distribution characteristics of squared generalised singular values in the two cases are different. Two special cases, single‐input multiple‐output and multiple‐input single‐output are considered. Simulation experiments are carried out to verify the effectiveness and accuracy of the obtained analytical results. [ABSTRACT FROM AUTHOR]

Securing wireless communication, being inherently vulnerable to eavesdropping and jamming attacks, becomes more challenging in resource‐constrained networks such as internet‐of‐things. Towards this, physical layer security (PLS) has gained significant attention due to its low complexity. The authors address the issue of random inter‐node distances in secrecy analysis and develop a comprehensive quality‐of‐service (QoS) aware PLS framework for the analysis of both eavesdropping and jamming capabilities of the attacker. The proposed solution covers the spatially stochastic deployment of nodes. The secrecy performance is characterised against both attacks using inter‐node distance‐based probabilistic distribution functions. The model takes into account the practical limits arising out of underlying QoS requirements, which include the maximum distance between legitimate users driven by transmit power and receiver sensitivity. A novel concept of eavesdropping zone is introduced, and the relative impact of jamming power is investigated. Closed‐form expressions for asymptotic secrecy outage probability are derived offering insights into the design of optimal system parameters for desired security level against the attacker's capability of both attacks. The analytical framework, validated by numerical results, establishes that the proposed solution offers a potentially accurate characterisation of the PLS performance and key design perspective from point‐of‐view of both legitimate user and attacker. [ABSTRACT FROM AUTHOR]

It can be intuitively inferred that a high‐quality depth map can be used to quickly detect the salient region in stereo vision, implying that depth information plays an essential role in stereoscopic visual attention. However, existing methods generally use the depth map as an auxiliary cue to improve the saliency detection performance. In this study, the authors present an algorithm to directly detect the salient object from a high‐quality depth image. The proposed algorithm utilises a depth reliability indicator to assess the confidence of a depth image. Depth compactness, a novel feature that incorporates the depth reliability of the super‐pixels, is computed as a primary salient feature. Moreover, in order to enhance another salient feature (i.e. depth contrast), they develop a coarse background filtering method to suppress background interference. Experimental results demonstrate that the proposed method performs favourably against the popular depth‐aware saliency detection approaches at a lower computational cost. [ABSTRACT FROM AUTHOR]

Fifth generation (5G) mobile systems are expected to be integrated with different radio access methods such as satellite components to provide seamless connectivity and ubiquitous coverage for users worldwide. In this article, we first provide a brief review of current initiatives and system architecture for the convergence of satellite and 5G networks. Then, we investigate various approaches to improve reliability or security at the physical layer for the integrated 5G-satellite networks. An effective achievable rate is presented as the key performance indicator to measure the security and reliability trade-off, followed by the implementation of a proposed beamforming scheme. Finally, we present future trends and challenges in integrated 5G-satellite networks. [ABSTRACT FROM AUTHOR]

Wireless sensor network (WSN) comprises of numerous sensors deployed either directly or randomly in the region of interest. Due to the limited power of the sensors, these networks are energy‐constrained and thus need efficient power utilisation. Efficient clustering and cluster head (CH) selection ensures balanced energy distribution to the sensors within the WSN and hence prolong the network lifetime. This study proposes the method for evaluating the threshold for the CH selection after each round, which increases the network lifetime and throughput significantly. The threshold for CH selection is modified considering the normalised first‐order and second‐order statistical parameters, such as mean average low‐energy adaptive clustering hierarchy (AvgLEACH) and variance (VarLEACH) of the overall network energy. These methods have been formulated after studying the effect of the number of working nodes in each round on the threshold value selection. Apart from including energy parameter to the threshold equation, the methods of VarLEACH and AvgLEACH are augmented with a residual energy parameter that is local to the nodes and named as VarRLEACH and AvgRLEACH. The simulation results comparing all the methods suggest that the proposed method AvgRLEACH outperforms LEACH by a factor of 1.5 in delivering data to the base station and outlives the network driven by LEACH protocol by 30–40%. [ABSTRACT FROM AUTHOR]

This paper reports the results of experimental studies of six different wireless sensor nodes and networks under a radiation environment with a dose rate of 20 K Rad (Si)/h. The wireless nodes evaluated are ZigBee, WirelessHART, ISA 100.11a, LoRa, and 433/915 MHz point‐to‐point devices made from commercial off‐the‐shelf (COTS) components. The experiments were carried out using a 60Co gamma source, while the devices are at on‐power operating states, and their operating statuses have been continuously monitored to determine the first instance of failure and the rate of gradual degradation in terms of communication channel performance and quality of the wireless signals. Observations indicate that the different devices and networks exhibit varying levels of radiation tolerance. For example, some can only survive for less than one hour, but others are operating satisfactorily for several hours. Furthermore, before a device suffers a fatal hardware failure, the performance degradation progresses slowly. It is believed that this is the first time that such results are reported in the open literature. Their significance is that the results can provide some practical guidance to select the most suitable wireless devices for the design and construction of remote monitoring systems for high‐level radiation environments. [ABSTRACT FROM AUTHOR]

This Letter proposes a stochastic model of the wearable sensor nodes of a wireless body area network (WBAN) based on Markov decision process (MDP). The proposed technique tackles the problem of maximising the likelihood of data transmission while minimising the computational cost and energy. Suitable transmission strategies subject to the energy level of the nodes and channel conditions are needed to be investigated to strike a balance between network lifetime and packet delivery ratio. MDP formulation of the problem is solved offline to find out the optimal transmission strategies for the representative input conditions. The results of this offline computation approach can directly map to optimal transmission policies for intra-WBAN communications. The experimental results demonstrate the robustness of the proposed scheme in handling both favourable and unfavourable operating conditions. [ABSTRACT FROM AUTHOR]

A millimeter wave (mmWave) and sub-6 GHz (μ Wave) dual-mode network can take advantages of the signals over both bands. The user scheduling in the medium access layer and the transmit precoding in the physical layer are coupled and should be optimized jointly. This work investigates the joint cross-layer optimization problems for two dual-mode systems: the full dual transmission system in which each user equipment can be scheduled over both frequency bands and the half dual transmission system in which each user equipment can only be scheduled over one band. A concave expression is adopted to lower-bound the achievable rate of each user equipment with perfect and imperfect channel estimation. Based on the lower bound, effective algorithms are proposed to solve the joint cross-layer optimization problems. The proposed algorithms can also be used for other dual-mode networks. Simulations show superiority of joint transmit precoding for the two frequency bands signals. Moreover, the full dual transmission system outperforms the half dual transmission system in terms of the minimum rate. The rate degradation of the half dual transmission system is insignificant while its implementation complexity is much lower than the full dual transmission system. [ABSTRACT FROM AUTHOR]

Sustainable operation of energy‐restrained wireless network services requires multiple objectives to be satisfied synchronously. Among these objectives, reduced spectrum outage, energy conservation, and minimal packet transmission failures considerably affect the energy harvesting operation of these networks. These three objectives are associated with disparate protocol layers incorporating the transport, medium access control, and physical layers of traditional networking architecture. The authors investigate energy harvesting wireless communications by formulating the multi‐objective optimisation problem comprising these global networking criteria, which are simultaneously optimised with the heuristic design procedure. For this, they employ a Pareto‐based evolutionary genetic algorithm technique built in the wireless network design and operation to find the optimal set of all non‐dominated solutions traversing the entire design search space. Besides, iterative implementation of the presented genetic optimisation model with distinct feasible integrations of crossover and mutation operations is performed to evaluate the proficiency of the proposed scheme for evaluating the Pareto‐optimal frontier set. The influence of different combinations of these operations is examined and adaptively applied with appropriate genetic parameters tuning for efficient meta‐heuristic search through the candidate solution space. Simulation results demonstrate that the proposed hybrid genetic mechanism outperforms the existing methods in terms of throughput, energy efficiency, and loss rate. [ABSTRACT FROM AUTHOR]

Network connectivity, i.e., the reachability of any network node from all other nodes, is often considered as the default network survivability metric against failures. However, in the case of a large-scale disaster disconnecting multiple network components, network connectivity may not be achievable. On the other hand, with the shifting service paradigm towards the cloud in today's networks, most services can still be provided as long as at least a content replica is available in all disconnected network partitions. As a result, the concept of content connectivity has been introduced as a new network survivability metric under a large-scale disaster. Content connectivity is defined as the reachability of content from every node in a network under a specific failure scenario. In this work, we investigate how to ensure content connectivity in optical metro networks. We derive necessary and sufficient conditions and develop what we believe to be a novel mathematical formulation to map a virtual network over a physical network such that content connectivity for the virtual network is ensured against multiple link failures in the physical network. In our numerical results, obtained under various network settings, we compare the performance of mapping with content connectivity and network connectivity and show that mapping with content connectivity can guarantee higher survivability, lower network bandwidth utilization, and significant improvement of service availability. [ABSTRACT FROM AUTHOR]

In this study, a dual‐hop cooperative communication system with radio frequency (RF) energy harvesting was investigated in two cases of linear and non‐linear energy harvesting models. In the proposed system, the signal is transmitted directly from a source node to a destination node or sent with support of selected relay nodes. While both the source node and the destination node are powered normally, the relay nodes are powered by harvesting technique. To choose the best relay node, a selection combination method was applied at the destination node in both cases of amplify‐and‐forward and decode‐and‐forward protocols. To evaluate the system performance, the outage probability of the cooperative communications over independent identically distributed Nakagami‐m was derived and analysed with arbitrary m parameter whereas this parameter was fixed to be integral value in previous research studies. Furthermore, the approximate and asymptotic operations are applied to simplify the outage probability expressions. The simulation program was developed based on the Monte Carlo method and MATLAB software with two aims of evaluating the system performance and verifying the theoretical results. The simulation results demonstrate that the analysis and evaluation of the study are considerably accurate. [ABSTRACT FROM AUTHOR]

This Letter investigates the impacts of hardware impairments (HIs) and channel estimation errors (CEEs) on the secrecy performance of satellite communication networks with one legitimate user and one eavesdropper. Particularly, the authors derive the closed‐form expression for the secrecy outage probability (SOP) of the considered secrecy satellite communication networks. Besides, in order to research the impact of the HIs and CEEs at high signal‐to‐noise ratios, they obtain the asymptotic expression for the SOP, which gives efficient and fast method to evaluate the effect of the considered system parameters on the secrecy system performance. At last, Monte Carlo computer results are given to verify the effects of HIs and CEEs on the secrecy system performance. [ABSTRACT FROM AUTHOR]

Ultrareliable and low-latency communications (uRLLC) is one of the most significant requirements for future wireless networks. The conventional terrestrial base stations cannot always provide the required uRLLC for emerging applications and scenarios, e.g., Tactile Internet services or when a large number of users get connected during an event. Therefore, multilayer airborne networks with low/medium/high altitude platforms can be deployed as an effective solution to offer capacity and coverage along with required latency and reliability for wireless networks. In this article, we propose three layers of the airborne network to support the uRLLC requirement in wireless networks. Optimized link selection schemes have been provided based on polychromatic sets (PSets) theory to focus on the uRLLC. With the optimized link selection algorithm, multiple properties of the airborne platforms are exploited, and the links are selected based on the multiconstrained requirements to support the desired performance of the airborne network. Moreover, two links distribution schemes have been proposed as distributed greedy scheme and centralized greedy scheme to demonstrate the deployment of the proposed airborne network. Numerical results show that both PSets-based links distribution schemes outperform the general distribution schemes on average latency and overall reliability also known as the unassociated ratio, which strongly supports the uRLLC in considered airborne networks. [ABSTRACT FROM AUTHOR]

Network sharing has already been adopted by mobile network operators as a reliable and effective countermeasure to the constantly increasing network cost. The introduction of 5G mobile communications is expected to revolutionize the telecommunications world. However, it also brings new challenges to network sharing, as new technologies (e.g., network virtualization, cloud architectures, and so on) and types of resources (e.g., computation and storage) come to the fore. Despite their inherent differences, the common characteristic of the emerging resources is that they are limited and, in many cases, insufficient to cover the rising traffic demands. In this article, we highlight the equivalence between the distribution of a limited number of resources and the bankruptcy problem, where the demands of different agents over a given commodity exceed its total quantity. In particular, i) we review the fundamentals and existing solutions of the bankruptcy problem; ii) we provide potential applications of this problem in mobile network sharing; and iii) we list challenges and open issues for the application of the bankruptcy game in the mobile communications domain. The main goal of our work is to identify new research lines that will foster 5G network sharing. [ABSTRACT FROM AUTHOR]