Search

Emerging vehicle-to-everything (V2X) services rely on the secure exchange of periodic messages between vehicles and between vehicles and infrastructure. However, transmission of false/incorrect data by malicious vehicles may pose important security perils. Therefore, it is essential to detect safety-threatening erroneous information and mitigate potentially detrimental effects on road users. In this paper, we assess the effectiveness of a reinforcement learning (RL) approach for misbehaviour detection in V2X scenarios using an open-source dataset. Considering the case of sudden-stop attacks, the performance of RL-based detection is evaluated over commonly used detection metrics. Our research outcomes reveal that misbehaving vehicles can be accurately detected by exploiting real-time position and speed patterns., Grant numbers : 2014 SGR 1551 - Grup de Tecnologies de Comunicacions and SPOT5G - Single Point of attachment communications heterogeneous mobile data networks (TEC2017-87456-P) projects.© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Vehicle-to-everything (V2X) communications enable real-time information exchange between vehicles and infrastructure, which extends the perception range of vehicles beyond the limits of on-board sensors and, thus, facilitating the realisation of cooperative, connected, and automated mobility (CCAM) services that will improve road safety and traffic efficiency. In the context of CCAM, the successful deployments of cooperative intelligent transport system (C-ITS) use cases, with the integration of advanced wireless communication technologies, are effectively leading to make transport safer and more efficient. However, the evaluation of multi-vendor and multi-protocol based CCAM service architectures can become challenging and complex. Additionally, conducting on-demand field trials of such architectures with real vehicles involved is prohibitively expensive and time-consuming. In order to overcome these obstacles, in this paper, we present the development of a standards-compliant experimental vehicular on-board unit (OBU) that supports the integration of multiple V2X protocols from different vendors to communicate with heterogeneous cloud-based services that are offered by several original equipment manufacturers (OEMs). We experimentally demonstrate the functionalities of the OBU in a real-world deployment of a cooperative collision avoidance service infrastructure that is based on edge and cloud servers. In addition, we measure end-to-end application-level latencies of multi-protocol supported V2X information flows to show the effectiveness of interoperability in V2X communications between different vehicle OEMs.

This demo presents the instantiation of a high level architecture proposed by INSPIRE-5Gplus to manage secured End-to-End (E2E) Network Slices. Network Slices are associated with Security Service Level Agreement (SSLA) to enhance the security on the virtual deployed resources, thus securing the created E2E Secure Network Slices. The proposed secured network slicing architecture is validated against a vehicular scenario, based on Anticipated Cooperative Collision Avoidance use case. In this scenario, we propose to detect false vehicular messages through a novel SSLA based on an Intrusion Detection System. The demo provides measurement of significant metrics such as mean time to detect, mean time to contain, and transaction speed.

Cross-border scenarios are of extreme importance in current research work on 5G networks for connected vehicles. Network services and applications for connected vehicles, which are in specific cases expected to run on Mobile Edge Computing (MEC) infrastructure, might experience problems through country borders due to inter-domain. Given that cross-border scenarios typically imply a change of network operator, deployed MEC services need to work in such environments and, where applicable, different entities need to synchronize their input/output vehicular messages and work seamlessly in such a multi-operator context. One of most significant MEC services is vehicular message brokering. It consists on the controlled publishing and notification mechanisms to create awareness to all subscribed vehicles concerning their position as well as other significant events that may arise, such as hazardous events. This paper presents an architecture and method for vehicular message exchange, based on current Intelligent Transport Systems (ITS) standards, and proposes a novel hierarchical message brokering approach with the purpose of solving cross-domain scenarios, which can be applied not only in the aforementioned cross-border case but also in other scenarios where there is no single domain (i.e., with multiple vendors). Message Queuing Telemetry Transport (MQTT) servers are used in a hierarchical approach (locating a parent MQTT broker in a public cloud) in order to demonstrate the feasibility of using them for cross-border scenarios. Latency results are obtained in order to evaluate the performance penalty of the proposed solution.

Cooperative, connected and automated mobility(CCAM) services along different countries require cross-bordersolutions to support seamless delivery of services in a multi-operator, multi-telco-vendor, and multi-car-manufacturer sce-nario. The H2020 5GCroCo project will trial 5G technologies inthe European cross-border corridor along France, Germany andLuxembourg, as well as in five small-scale trial sites. 5GCroCoanalyses three cross-border use cases: tele-operated driving, high-definition map generation and distribution for autonomous vehi-cles, and anticipated cooperative collision avoidance (ACCA). Thispaper presents the infrastructure, control architecture, backendsoftware, and end-to-end service orchestration of the cross-borderACCA use case deployed in the Barcelona small-scale trial site., Grant numbers : AURORAS - Autonomic and disaggregated optical networks leveraging edge computing and photonic technologies (RTI2018-099178-B-I00).

Future 5G systems have set a goal to support mission-critical Vehicle-to-Everything (V2X) communications and they contribute to an important step towards connected and automated driving. To achieve this goal, the communication technologies should be designed based on a solid understanding of the new V2X applications and the related requirements and challenges. In this regard, we provide a description of the main V2X application categories and their representative use cases selected based on an analysis of the future needs of cooperative and automated driving. We also present a methodology on how to derive the network related requirements from the automotive specific requirements. The methodology can be used to analyze the key requirements of both existing and future V2X use cases.

Massive machine-type communication (mMTC) is expected to revolutionize the fifth-generation (5G) and beyond-5G systems by enabling connectivity for a high number of low-rate low-power devices with sporadic activity patterns. To realize the full potential of mMTC, radical enhancements are required for the radio access design and the architecture of current cellular systems. In this paper, we discuss the mMTC peculiarities in the context of emerging energy and automotive use cases. We identify key mMTC challenges that hinder efficient and scalable connectivity in the smart grid and in vehicular communication. Representative technical enablers are then proposed aiming to tackle the massive connectivity limitations in various scenarios. The performance assessment of the presented approaches reveals the superior performance compared to the benchmark schemes while useful insights can be drawn for the design principles of future mMTC protocols. Finally, we discuss some key technology trends relevant to mMTC that are expected to provide a roadmap for the design of novel solutions to evolve Dost-5G connectivity.

The vision of cooperative, connected and automated mobility (CCAM) across Europe can only be realized when harmonized solutions that support cross-border traffic exist. The possibility of providing CCAM services along different countries when vehicles drive across various national borders has a huge innovative business potential. However, the seamless provision of connectivity and the uninterrupted delivery of services along borders also poses interesting technical challenges. The situation is particularly innovative given the multi-country, multi-operator, multi-telco-vendor, and multi-car-manufacturer scenario of any cross-border layout. This paper introduces the challenges associated to a cross-border deployment of communication technologies through the analysis of three use cases: tele-operated driving, high-definition map generation and distribution for autonomous vehicles, and anticipated cooperative collision avoidance. Furthermore, a set of 5G solutions have been identified to ensure that CCAM services can be supported efficiently in cross-border scenarios. Faster handover of a data connection from one operator to another, generalized inter-mobile edge computing (MEC) coordination, and quality of service (QoS) prediction are some of the solutions that have been introduced to reduce the uncertainties of a real 5G cross-border deployment.

Even before 5G is rolled out, Mobile Edge Computing (MEC) can be considered as a key driver towards the deployment of vehicular use cases, which pose stringent latency and bandwidth requirements to the underlying Vehicle-to-Everything (V2X) communication infrastructure. In this paper, we present a MEC-enabled cooperative Collision AVoidance (CAV) service designed to anticipate the detection and localization of road hazards by extending vehicles’ perception range beyond the capabilities of their own sensors. The CAV service is a software application that runs on MEC servers allocated at the roadside and at Mobile Network Operators’ (MNO) infrastructures. The CAV service receives ETSI ITS-G5 standard-compliant messages transmitted by vehicles: periodic Cooperative Awareness Messages (CAM), which include the position, velocity and direction of the vehicle; and event-triggered Decentralized Environmental Notification Messages (DENM), which include the position of detected road hazards. The CAV service creates a distributed dynamic map using all the received information, and sends unicast messages to each vehicle with the relevant information within its collision risk area. We have implemented and validated the operation of the CAV service using vehicles’ On-Board Units (OBU) based on OpenC2X, an open-source experimental platform supporting the ETSI ITS-G5 standard.

There are several use cases that claim the need for a connected car. Among them there is the need for connectivity between vehicles and information sources, or V2V and V2X exchanges for accident prevention. In order to cope with the need for novel applications running on top of an interconnected network, the concept of fog computing appears as a realistic solution for both intra-car and inter-car data processing and decision making. This paper describes the proposed architecture and experimental evaluation of an innovative proof-of-concept (PoC) for a connected car, modeled with YANG, which can be remotely controlled using SDN/NFV and fog computing technologies. As an example, the remote control of the car might be based on a service application running on a fog node, which can be located close to a road side unit (RSU). We also propose a fog architecture in order to enable cooperative perception between connected cars. Finally, the performance evaluation uses a RESTCONF server installed in a Raspberry Pi aboard of a small car. This server is responsible for the sensors and actuators of the car and allows for its remote control from a user terminal (e.g., a smartphone, tablet, or laptop) and through the fog node, running a control application as a service.

The realization of advanced electrical grid functionalities, e.g., phasor measurement unit (PMU) information acquisition in wide-area monitoring systems (WAMS), requires a scalable and reliable underlying communication technology. Cellular networks, e.g., LTE/LTE-A systems, appear as a promising option to facilitate the smart grid evolution. However, the effect of LTE communication constraints on power system state estimation (SE) has not been thoroughly addressed in the literature. In this paper, we investigate the impact of the LTE random access channel (RACH) reliability on the transmitted PMU measurements and, consequently, on the SE accuracy. In particular, we assess the SE performance based on the achieved reliability per PMU attained with i) increasing number of contending devices in the system, i.e., smart meters and PMUs, and ii) varying cell coverage range. Numerical results demonstrate that, under different network and traffic configurations, SE accuracy can be significantly affected by the RACH reliability levels. Useful insights can thus be drawn for a reliability-aware design of a power system state estimator in LTE-based WAMS.

This paper evaluates the performance of a burst transmission mechanism using microsleep operation to support high energy efficiency in IEEE 802.11 Wireless Local Area Networks (WLANs). This mechanism is an implementation of the IEEE 802.11ac Transmission Opportunity Power Save Mode (TXOP PSM). A device using the TXOP PSM-based mechanism can switch to a low-power sleep state for the time that another device transmits a burst of data frames to a third one. This operation is called microsleep and its feasibility strongly depends on the time and energy consumption that a device incurs in the transitions from and to the sleep state. This paper accounts for the impact of these transitions in the derivation of an analytical model to calculate the energy efficiency of the TXOP PSM-based mechanism under network saturation. Results obtained show that the impact of the transition requirements on the feasibility of microsleep operation can be significant depending on the selected system parameters, although it can be reduced by using burst transmissions. When microsleep operation is feasible, the TXOP PSM-based mechanism can improve the energy efficiency of other legacy mechanisms by up to 424% under high traffic loads.

This paper provides a view to Peer-to-Peer (P2P) approach for smart grid operation adopted in P2P-SmarTest project. It provides an overview on solutions proposed for distributed P2P energy trading, P2P grid control and wireless communication enabling the proposed P2P operation. The paper proposes some business models that can be adopted in a P2P setting. We also outline the barriers and enablers against and for adopting local or regional P2P based electricity operations.

Recent standardization efforts on low-power wireless communication technologies, including time-slotted channel hopping (TSCH) and DASH7 Alliance Mode (D7AM), are starting to change industrial sensing applications, enabling networks to scale up to thousands of nodes whilst achieving high reliability. Past technologies, such as ZigBee, rooted in IEEE 802.15.4, and ISO 18000-7, rooted in frame-slotted ALOHA (FSA), are based on contention medium access control (MAC) layers and have very poor performance in dense networks, thus preventing the Internet of Things (IoT) paradigm from really taking off. Industrial sensing applications, such as those being deployed in oil refineries, have stringent requirements on data reliability and are being built using new standards. Despite the benefits of these new technologies, industrial shifts are not happening due to the enormous technology development and adoption costs and the fact that new standards are not well-known and completely understood. In this article, we provide a deep analysis of TSCH and D7AM, outlining operational and implementation details with the aim of facilitating the adoption of these technologies to sensor application developers. info:eu-repo/semantics/publishedVersion

The demand for safe and secure journeys over roads and highways has been growing at a tremendous pace over recent decades. At the same time, the smart city paradigm has emerged to improve citizens' quality of life by developing the smart mobility concept. Vehicular Ad hoc NETworks (VANETs) are widely recognized to be instrumental in realizing such concept, by enabling appealing safety and infotainment services. Such networks come with their own set of challenges, which range from managing high node mobility to securing data and user privacy. The Software Defined Networking (SDN) paradigm has been identified as a suitable solution for dealing with the dynamic network environment, the increased number of connected devices, and the heterogeneity of applications. While some preliminary investigations have been already conducted to check the applicability of the SDN paradigm to VANETs, and its presumed benefits for managing resources and mobility, it is still unclear what impact SDN will have on security and privacy. Security is a relevant issue in VANETs, because of the impact that threats can have on drivers' behavior and quality of life. This paper opens a discussion on the security threats that future SDN-enabled VANETs will have to face, and investigates how SDN could be beneficial in building new countermeasures. The analysis is conducted in real use cases (smart parking, smart grid of electric vehicles, platooning, and emergency services), which are expected to be among the vehicular applications that will most benefit from introducing an SDN architecture. La demanda de viajes seguros y protegidos por carreteras y autopistas ha estado creciendo a un ritmo tremendo en las últimas décadas. Al mismo tiempo, el paradigma de la ciudad inteligente surgió para mejorar la calidad de vida de los ciudadanos mediante el desarrollo del concepto de movilidad inteligente. Las redes vehiculares ad hoc (VANETs, por sus siglas en inglés) son ampliamente reconocidas como instrumentales en la realización de dicho concepto, al permitir servicios atractivos de seguridad y de infoentretenimiento. Dichas redes vienen con su propio conjunto de desafíos, que van desde la gestión de la movilidad de los nodos hasta la seguridad de los datos y la privacidad del usuario. El paradigma de redes definidas por software (SDN) se ha identificado como una solución adecuada para tratar con el entorno de red dinámico, el mayor número de dispositivos conectados y la heterogeneidad de las aplicaciones. Si bien ya se han llevado a cabo algunas investigaciones preliminares para verificar la aplicabilidad del paradigma SDN a las VANETs, y sus supuestos beneficios para la gestión de los recursos y la movilidad, aún no está claro qué impacto tendrán las SDN en la seguridad y la privacidad. La seguridad es un tema relevante en las VANETs, debido al impacto que las amenazas pueden tener en el comportamiento y la calidad de vida de los conductores. Este documento abre una discusión sobre las amenazas a la seguridad que las futuras VANETs habilitadas para las SDN tendrán que enfrentar, e investiga cómo las SDN podrían ser beneficiosas en la construcción de nuevas contramedidas. El análisis se lleva a cabo en casos de uso real (estacionamiento inteligente, red inteligente de vehículos eléctricos, platooning y servicios de emergencia), que se espera que estén entre las aplicaciones vehiculares que se beneficiarán más al introducir una arquitectura SDN. La demanda de viatges segurs i protegits per carreteres i autopistes ha estat creixent a un ritme enorme en les últimes dècades. Alhora, el paradigma de la ciutat intel·ligent va sorgir per millorar la qualitat de vida dels ciutadans mitjançant el desenvolupament del concepte de mobilitat intel·ligent. Les xarxes vehiculars ad hoc (VANETs, per les sigles en anglès) són àmpliament reconegudes com instrumentals en la realització d'aquest concepte, en permetre serveis atractius de seguretat i d'infoentreteniment. Aquestes xarxes vénen amb el seu propi conjunt de desafiaments, que van des de la gestió de la mobilitat dels nodes fins a la seguretat de les dades i la privacitat de l'usuari. El paradigma de xarxes definides per programari (SDN) s'ha identificat com una solució adequada per tractar amb l'entorn de xarxa dinàmic, el major nombre de dispositius connectats i l'heterogeneïtat de les aplicacions. Si bé ja s'han dut a terme algunes investigacions preliminars per verificar l'aplicabilitat del paradigma SDN a les VANETs, i els seus suposats beneficis per a la gestió dels recursos i la mobilitat, encara no està clar quin impacte tindran les SDN en la seguretat i la privacitat. La seguretat és un tema rellevant en les VANETs, a causa de l'impacte que les amenaces poden tenir en el comportament i la qualitat de vida dels conductors. Aquest document obre una discussió sobre les amenaces a la seguretat que les futures VANETs habilitades per a les SDN s'hauran d'enfrontar, i investiga com les SDN podrien ser beneficioses en la construcció de noves contramesures. L'anàlisi es porta a terme en casos d'ús real (estacionament intel·ligent, xarxa intel·ligent de vehicles elèctrics, platooning i serveis d'emergència), que s'espera que estiguin entre les aplicacions vehiculars que es beneficiaran més en introduir una arquitectura SDN.

The European Marie Curie Project ADVANTAGE (Advanced Communications and Information processing in smart grid systems) was launched in 2014. It represents a major inter-disciplinary research project into the topic of Smart Grid technology. A key aspect of the project is to bring together and train 13 early stage researchers from the traditionally separate fields of power systems and communications engineering research. This chapter describes some of the initial research results that have arisen from the project and to highlight some of the key advances and developments that are being studied in the project. The major research focus of the ADVANTAGE project is on advancing technologies for the smart grid, providing architectural solutions and developing innovative information and communications technology (ICT) solutions to support its operation.

Fifth Generation (5G) wireless systems are expected to connect an avalanche of "smart" objects disseminated from the largest "Smart City" to the smallest "Smart Home". In this vision, Long Term Evolution-Advanced (LTE-A) is deemed to play a fundamental role in the Internet of Things (IoT) arena providing a large coherent infrastructure and a wide wireless connectivity to the devices. However, since LTE-A was originally designed to support high data rates and large data size, novel solutions are required to enable an efficient use of radio resources to convey small data packets typically exchanged by IoT applications in "smart" environments. On the other hand, the typically high energy consumption required by cellular communications is a serious obstacle to large scale IoT deployments under cellular connectivity as in the case of Smart City scenarios. Network-assisted Device-to-Device (D2D) communications are considered as a viable solution to reduce the energy consumption for the devices. The particular approach presented in this paper consists in appointing one of the IoT smart devices as a collector of all data from a cluster of objects using D2D links, thus acting as an aggregator toward the eNodeB. By smartly adapting the Modulation and Coding Scheme (MCS) on the communication links, we will show it is possible to maximize the radio resource utilization as a function of the total amount of data to be sent. A further benefit that we will highlight is the possibility to reduce the transmission power when a more robust MCS is adopted. A comprehensive performance evaluation in a wide set of scenarios will testify the achievable gains in terms of energy efficiency and resource utilization in the envisaged D2D-based IoT data collection.

The Energy Harvesting-aware Contention Treebased Access (EH-CTA) protocol is presented in this paper as a novel Medium Access Control (MAC) protocol for wireless Machine-to-Machine (M2M) networks where enddevices are equipped with energy harvesters. The protocol is theoretically modeled to analyze its performance. A performance comparison with an EH-aware Dynamic Frame Slotted-ALOHA (EH-DFSA) shows its superior performance. While EH-DFSA requires an estimation of the number of contenders per frame in order to dynamically adjust the frame length, EH-CTA uses short and fixed frame lengths. This ensures scalability and facilitates synchronization in highly dense M2M networks.

Machine-to-Machine (M2M) area networks aim at connecting an M2M gateway with a large number of energy-constrained devices that must operate autonomously for years. Therefore, attaining high energy efficiency is essential in the deployment of M2M networks. In this paper, we consider a dense M2M area network composed of hundreds or thousands of devices that periodically transmit data upon request from a gateway or coordinator. We theoretically analyse the devices’ energy consumption using two Medium Access Control (MAC) protocols which are based on a tree-splitting algorithm to resolve collisions among devices: the Contention Tree Algorithm (CTA) and the Distributed Queuing (DQ) access. We have carried out computer-based simulations to validate the accuracy of the theoretical models and to compare the energy performance using DQ, CTA, and Frame Slotted-ALOHA (FSA) in M2M area networks with devices in compliance with the IEEE 802.15.4 physical layer. Results show that the performance of DQ is totally independent of the number of contending devices, and it can reduce the energy consumed per device in more than 35% with respect to CTA and in more than 80% with respect to FSA.

The capacity limits of the Random Access Channel (RACH) of Long Term Evolution (LTE) for highly dense Machine-to-Machine communications are studied in this paper. We consider the case study when a high number of devices attempt to transmit information to the same base station in a very short period of time. Simulations have been performed considering several parameter configurations related to the random access procedure of LTE. The energy consumption is used as a primordial metric to compare any improvement regarding the random access procedure in future releases, in order to evaluate the impact on the battery lifetime of autonomous devices.

Data collection is a key scenario for the Internet of Things because it enables gathering sensor data from distributed nodes that use low-power and long-range wireless technologies to communicate in a single-hop approach. In this kind of scenario, the network is composed of one coordinator that covers a particular area and a large number of nodes, typically hundreds or thousands, that transmit data to the coordinator upon request. Considering this scenario, in this paper we experimentally validate the energy consumption of two Medium Access Control (MAC) protocols, Frame Slotted ALOHA (FSA) and Distributed Queuing (DQ). We model both protocols as a state machine and conduct experiments to measure the average energy consumption in each state and the average number of times that a node has to be in each state in order to transmit a data packet to the coordinator. The results show that FSA is more energy efficient than DQ if the number of nodes is known a priori because the number of slots per frame can be adjusted accordingly. However, in such scenarios the number of nodes cannot be easily anticipated, leading to additional packet collisions and a higher energy consumption due to retransmissions. Contrarily, DQ does not require to know the number of nodes in advance because it is able to efficiently construct an ad hoc network schedule for each collection round. This kind of a schedule ensures that there are no packet collisions during data transmission, thus leading to an energy consumption reduction above 10% compared to FSA.

The focus of this study is the optimal configuration of a wireless low-power duty-cycled network with respect to the minimal energy consumption. Precisely, the energy consumption of a truncated-ARQ scheme in realistic shadowing environments is examined for the reference IEEE 802.15.4e standard protocol and for its cooperative extension that is presented in the paper. We show how to choose between the direct or multihop forwarding and the cooperative version of the two. We determine the optimal forwarding strategy for both loose and strict reliability requirements. Low-power links are parametrised by the interdevice distance and the corresponding outage probability, for the fixed output transmission power. It is shown that significant amounts of energy can be saved when the most adequate scheme of the three is applied. All analytical results are validated in the network simulator ns-3.

In the evolution of communication networks, there has always been a need to increase the capacity to cope with the continuous growing demand for data transmission. However, with the arrival of the Internet-of-Things and the commoditization of broadband access through smartphones, tablets, smart-watches, and all types of connecting devices, future networks must be capable of providing higher bandwidth and Quality of Experience, as wellas operating in dense networks with a massive number of simultaneous connections. This high number of connections will be very heterogeneous, spanning from highly-demanding data rate applications to low-complexity and high energy-efficient Machine-to-Machine communications. In such a dense and complex scenario, a more flexible use of spectrum resources is deemed to be the way to meet the growing requirements for data transmission. In particular, this article focuses on Device-to-Device communications and small cell deployments as emerging facilitators of such a demanding and heterogeneous scenario. The pros and cons of both complementary strategies are identified from both a technical and a business point of view, and main standardization activities are discussed. The aim of this article is to identify and describe open challenges and to inspire new areas for research that make viable the next generation of dense networks. QC 20220627

Attaining very high energy efficiency is one of the big challenges to implement Machine-to-Machine (M2M) networks whose lifetime (without human intervention) must be measured in years. In this paper, we consider a synchronized duty-cycled M2M network composed of a large number of devices that periodically wake up their radio interfaces to transmit data to a coordinator. We theoretically analyze the delay and energy efficiency of two contention-based Medium Access Control (MAC) protocols for this kind of networks. One protocol is based on Frame Slotted ALOHA, and the other is based on a tree-splitting contention resolution algorithm. Computer-based simulations have been carried out to ensure the accuracy of the theoretical models and to evaluate and compare the performance of the two alternatives for M2M applications based on low power Wi-Fi devices.

In this paper we show how a cooperative Medium Access Control (MAC) protocol can help extend the lifetime of Machine to Machine (M2M) networks. A comparison between non-cooperative Automatic Repeat reQuest (ARQ) schemes (retransmissions performed only from the source) and a cooperative retransmission scheme (all the stations in the network are spontaneous helpers and assist the destination during the communication) in energy-constrained networks is also presented in this work. The results shown in this paper are discussed in terms of the trade off between the network lifetime and the amount of data delivered, leading to the conditions where it is possible to optimize the lifetime of this kind of networks.

Over the last years, cooperative communications have been studied from both fundamental and practical points of view. However, most of the existing studies of cooperative communications rely on math or computer simulation. In this paper, we describe the implementation of a cooperative communication strategy for wireless networks in a testbed based on Click Modular Router. We describe the methodology we have followed to reprogram the drivers controlling the data layer functions of off-the-shelf commercial Wireless Network Interface Cards (NICs). More precisely, we have implemented a Cooperative Automatic Retransmission (C-ARQ) scheme to show that the performance of wireless communications can be boosted by using an intermediate relay when the wireless channel between the source and the destination is in bad conditions. The results presented in this paper are promising, as they show that previous theory and simulation results presented in the literature can become true in a real implementation.

The design of communications protocols that exploit the availability of both cellular and short-range radio access interfaces in a same terminal can be exploited to improve the energy efficiency of wireless communications networks. Devices equipped with a cellular radio interface can act as dynamic gateways to provide energy-constrained devices in its single-hop cluster with cellular connectivity. For this purpose, any device may discover its single-hop neighbourhood in order to select the appropriate gateway candidates. Conventional neighbour discovery algorithms have a great cost in terms of delay and energy consumption, and thus they are not the optimal approach for energy-constrained devices. This paper presents the energy consumption analysis of two distributed neighbour discovery algorithms based on frame slotted-ALOHA, and evaluates their performance in terms of energy consumption. In addition, it describes the conditions that minimize the energy consumption in the discovery process.

Mobile Machine-to-Machine (M2M) market is expected to grow dramatically in the upcoming years; predictions agree that the majority of wireless traffic will correspond to this type of communication. M2M devices deployed in proximity to each other might be handled as groups or clusters when sharing the same communication attributes and serving to achieve joint target. Moreover, devices that feature multiple radio interfaces are commonly used nowadays; they can be connected to a cellular access network, e.g., LTE, and simultaneously to a short-range network, also known as capillary network, among surrounding devices, e.g., Wi-Fi and ZigBee. For services such as over-the-air (OTA) firmware update, the same information shall be sent to all the group members over the cellular access network. A Multi-Radio Cooperative Retransmission Scheme for Reliable Multicast Services is presented as a solution to reliably manage reception errors occurred over the cellular network; by carrying out retransmissions over a short-range network it is possible to reduce both the traffic load over the cellular link and the energy consumption in error recovery. Ns-3 simulations were performed with LTE network models to analyze the scheme in terms of energy consumption and prove its usefulness in autonomous, battery driven, devices.

The IEEE 802.11p Task Group has recently released a new standard for wireless access in vehicular environments (WAVE). It constitutes an amendment to the 802.11 for Wireless Local Area Networks (WLANs) to meet the requirements of applications related to roadsafety involving interand intra-vehicle communications as well as communications from vehicle to the roadside infrastructure. Indeed, the importance of the targeted applications has forced authorities to allocate some dedicated bandwidth (nearby the 5.9GHz) to ensure the security of the communications. However, despite the suitability of this standard for use in high-speed vehicular communications, it is not possible to pass over the unprecedented market penetration of the popular 802.11 networks, the so-called WiFi networks. Before we can see a world where all the cars are equipped with 802.11p devices, current and nearfuture applications might probably run on the original 802.11. Moreover, interaction between humans and vehicles will probably be carried out by means of the 802.11, which is the standard that is flooding most of personal tech devices, such as laptops, mobile phones, gaming consoles, etc. Therefore, it is important to keep on working in the improvement of the 802.11 Standard for its use in, at least, some vehicular applications. This is the main motivation for this chapter, where we focus on the Medium Access Control (MAC) protocol of the 802.11 Standard, and we propose a simple mechanism to improve its performance in densely populated applications where it falls short to provide users with good service. Envisioned applications include those were a high number of vehicles and pedestrians coexist in a given area, such as for example, a crossing in a city where all the cars share information to coordinate the drive along the crossing and prevent accidents. Into more detail, the Distributed Coordination Function (DCF) is the mandatory access method defined in the widely spread IEEE 802.11 Standard for WLANs [1]. This access method is based on Carrier Sensing Multiple Access (CSMA), i.e., listen before transmit, in combination with a Binary Exponential Backoff (BEB) mechanism. An optional Collision Avoidance (CA) mechanism is also defined by which a handshake Request to Send (RTS) – Clear to Send (CTS) can be established between source and destination before the actual transmission of data. This CA mechanism aims at reducing the impact of the collisions of data packets and to combat the hidden terminal problem. The DCF can be executed in either ad hoc or infrastructure-based networks and is the only access method implemented in most commercial hardware. Despite the doubtless commercial success of the DCF, the simplicity

Cooperative Automatic Retransmission Request (C-ARQ) schemes allow those users which overhear a transmission to act as spontaneous relays when a packet has been received with errors at destination. When these users assist a source-destination pair in the retransmission process, the area exposed to the original transmission increases in comparison with non-cooperative ARQ schemes. In addition, the extension of the transmission time, due to the retransmissions, increases the vulnerability of a transmission to the hidden terminal problem. The paper provides a performance analysis of the hidden and exposed terminal effects in an 802.11-based wireless network where a C-ARQ scheme is executed at the Medium Access Control (MAC) layer. The presented analysis is supported by computer-based simulations.

We present in this paper the analysis of an IEEE 802.11 network in the presence of hidden and exposed terminals when a Cooperative ARQ (C-ARQ) scheme is executed at the MAC layer. When spontaneous helpers transmit to assist in a failed transmission, the area exposed to the original transmission increases in comparison to non-cooperative ARQ schemes. In this paper we quantify this effect and we evaluate the relevance of designing efficient protocols to combat the exposed terminal problem.

We present in this paper the analytical evaluation of a simple mechanism to reduce the average transmission delay of master stations in a network based on the Distributed Queuing MAC protocol for Ad hoc Networks (DQMAN). When DQMAN is executed, the network is self-organized into dynamic and spontaneous master-slave clusters. Within each cluster, a highperformance MAC protocol based on a tree-splitting collision resolution algorithm which uses access minislots is executed. By allowing temporary master stations to avoid contention to get access to the channel, their average packet transmission delay can be effectively reduced compared to that of slaves. This technique provides thus master stations with higher access priority to the channel and, indeed, could be used in any MAC protocol based on access minislots to provide a subset of users with higher priority.

The Distributed Queuing with Collision Avoidance (DQCA) Medium Access Control (MAC) protocol has been presented in the literature as a high-performance protocol for uplink traffic in WLANs. Previous works regarding DQCA are focused on the operation of a single cell, where no interaction with neighboring sites is considered. In this paper, we define specific handoff functions (channel sensing, discovery and reassociation functions) that enable the roaming of users in a scenario composed by a number of different DQCA access points deployed in a specific area using different channel frequencies.