Channel quality estimation and impairment mitigation in 802.11 networks

Wireless communication has been boosted by the adoption of 802.11 as standard de facto for WLAN transmission. Born as a niche technology for providing wireless connectivity in small office/enterprise environments, 802.11 has in fact become a common and cheap access solution to the Internet, thanks to the large availability of wireless gateways (home modems, public hot-spots, community networks, and so on). Nowdays, the trend towards increasingly dense 802.11 wireless deployments is creating a real need for effective approaches for channel allocation/hopping, power control, etc. for interference mitigation while new applications such mesh networks in outdoor contexts and media distribution within the home are creating new quality of service demands that require more sophisticated approaches to radio resource allocation. The new framework of WLAN deployments require a complete understanding of channel quality at PHY and MAC layer. Goal of this thesis is to assess the MAC/PHY channel quality and mitigate the different channel impairments in 802.11 networks, both in dense/controlled indoor scenarios and emerging outdoor contexts. More specifically, chapter 1 deals with the necessary background material and gives insight into the different channel impairments/quality it can be encountered in WLAN networks. Then the thesis pursues a down/top approach: chapter 2, 3 and 4 aim at affording impairments/quality at PHY level, while chapter 5 and 6 analyse channel impairments/quality from a MAC level perspective. An important contribution of this thesis is to undisclose that some PHY layer parameters, such as the transmission power, the antenna selection, and interference mitigation scheme, have a deep impact on network performance. Since the criteria for selecting these parameters is left to the vendor specific implementations, the performance spread of most experimental results about 802.11 WLAN could be affected by vendor proprietary schemes. Particularly, in chapter 2 we find that switching transmit diversity mechanisms implemented in off-the-shelf devices with two antenna connectors can dramatically affect both performance and link quality probing mechanisms in outdoor medium-range WLAN deployments, whenever one antenna deterministically works worse than the other one. A second physical algorithm with side-effects is shown in chapter 3. Particulary the chapter shows that interference mitigation algorithms may play havoc with the link-level testbeds, since they may erroneously lower the sensitivity threshold, and thus not detect the 802.11 transmit sources. Finally, once disabled the interference mitigation algorithm — as well as any switching diversity scheme described in the previous chapter — link-level experimental assessment concludes that, unlike 802.11b, which appears a robust technology in most of the operational conditions, 802.11g may lead to inefficiencies when employed in an outdoor scenario, due to the lower multi-path tolerance of 802.11g. Since multipath is hard to predict, a novel mechanism to improve the link-distance estimation accuracy — based on CPU clock information — is outlined in chapter 4. The proposed methodology can not only be applied in localization context, but also for estimating the multi-path profile. The second part of the thesis moves the perspective to the MAC point of view and its impairments. Particularly, chapter 5 provides the design of a MAC channel quality estimator to distinguish the different types of MAC impairments and gives separate quantitative measures of the severity of each one. Since the estimator takes advantage of the native characteristics of the 802.11 protocol, the approach is suited to implementation on commodity hardware and makes available new measures that can be of direct use for rate adaptation, channel allocation, etc. Then, chapter 6 introduces a previous unknown phenomenon, the Hidden ACK, that may cause frame losses into multiple WLAN networks when a node replies with an ACK frame. Again, a solution is provided without requiring any modification to the 802.11 protocol. Whenever possible, the quantitative analysis has been led through experimental assessments with implementation on commodity hardware. This was the adopted methodology in chapter 2, 3, 4 and 5. Particularly, this has required an accurate investigation of two brands of WLAN cards, particularly the Atheros and Intel cards, and their driver/firmware, respectively MADWiFi and IPW2200, which are currently the most adopted, respectively, by researchers and layman users

Joint multi-objective MEH selection and traffic path computation in 5G-MEC systems

Multi-access Edge Computing (MEC) is an emerging technology that allows to reduce the service latency and traffic congestion and to enable cloud offloading and context awareness. MEC consists in deploying computing devices, called MEC Hosts (MEHs), close to the user. Given the mobility of the user, several problems rise. The first problem is to select a MEH to run the service requested by the user. Another problem is to select the path to steer the traffic from the user to the selected MEH. The paper jointly addresses these two problems. First, the paper proposes a procedure to create a graph that is able to capture both network-layer and application-layer performance. Then, the proposed graph is used to apply the Multi-objective Dijkstra Algorithm (MDA), a technique used for multi-objective optimization problems, in order to find solutions to the addressed problems by simultaneously considering different performance metrics and constraints. To evaluate the performance of MDA, the paper implements a testbed based on AdvantEDGE and Kubernetes to migrate a VideoLAN application between two MEHs. A controller has been realized to integrate MDA with the 5G-MEC system in the testbed. The results show that MDA is able to perform the migration with a limited impact on the network performance and user experience. The lack of migration would instead lead to a severe reduction of the user experience.publishedVersio

5G Multi-access Edge Computing: Security, Dependability, and Performance

The main innovation of the Fifth Generation (5G) of mobile networks is the ability to provide novel services with new and stricter requirements. One of the technologies that enable the new 5G services is the Multi-access Edge Computing (MEC). MEC is a system composed of multiple devices with computing and storage capabilities that are deployed at the edge of the network, i.e., close to the end users. MEC reduces latency and enables contextual information and real-time awareness of the local environment. MEC also allows cloud offloading and the reduction of traffic congestion. Performance is not the only requirement that the new 5G services have. New mission-critical applications also require high security and dependability. These three aspects (security, dependability, and performance) are rarely addressed together. This survey fills this gap and presents 5G MEC by addressing all these three aspects. First, we overview the background knowledge on MEC by referring to the current standardization efforts. Second, we individually present each aspect by introducing the related taxonomy (important for the not expert on the aspect), the state of the art, and the challenges on 5G MEC. Finally, we discuss the challenges of jointly addressing the three aspects.Comment: 33 pages, 11 figures, 15 tables. This paper is under review at IEEE Communications Surveys & Tutorials. Copyright IEEE 202

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

FROM SMALL-WORLDS TO BIG DATA:TEMPORAL AND MULTIDIMENSIONAL ASPECTS OF HUMAN NETWORKS

In this thesis we address the close interplay among mobility, offline relationships and online interactions and the related human networks at different dimensional scales and temporal granularities. By generally adopting a data-driven approach, we move from small datasets about physical interactions mediated by human-carried devices, describing small social realities, to large-scale graphs that evolve over time, as well as from human mobility trajectories to face-to-face contacts occurring in different geographical contexts. We explore in depth the relation between human mobility and the social structure induced by the overlapping of different people's trajectories on GPS traces collected in urban and metropolitan areas. We define the notions of geo-location and geo-community which are operational in describing in a unique framework both spatial and social aspects of human behavior. Through the concept of geo-community we model the human mobility adopting a bipartite graph. Thanks to this graph representation we can generate a social structure that is plausible w.r.t. the real interactions. In general the modeling approach have the merit for reporting the mobility in a graph-theoretic framework making the study of the interplay mobility/sociality more affordable and intuitive. Our modeling approach also results in a mobility model, Geo-CoMM, which lies on and exploits the idea of geo-community. The model represents a particular instance of a general framework we provide. A framework where the social structure behind the preferred-location based mobility models emerges. We validate Geo-CoMM on spatial, temporal, pairwise connectivity and social features showing that it reproduces the main statistical properties observed in real traces. As concerns the offline/online interplay we provide a complete overview of the close connection between online and offline sociality. To reach our goal we gather data about offline contacts and social interactions on Facebook of a group of students and we propose a multidimensional network analysis which allows us to deeply understand how the characteristics of users in the distinct networks impact each other. Results show how offline and Facebook friends are different. This way we confirm and worsen the general intuition that online social networks have shifted away from their original goal to mirror the offline sociality of individuals. As for the role and the social importance, it becomes apparent that social features such as user popularity or community structure do not transfer along social dimensions, as confirmed by our correlation analysis of the network layers and by the comparison among the communities. In the last chapters we analyze the evolution of the online social network from a physical time perspective, i.e. considering the graph evolution as a graph time-series and not as a function of the network basic properties (number of nodes or links). As for the physical time in a user-centric viewpoint, we investigate the bursty nature of the link creation process in online social network. We prove not only that it is a highly inhomogeneous process, but also identify patterns of burstiness common to all nodes. Then we focus on the dynamic formation of two fundamental network building components: dyads and triads. We propose two new metrics to aid the temporal analysis on physical time: link creation delay and triangle closure delay. These two metrics enable us to study the dynamic creation of dyads and triads, and to highlight network behavior that would otherwise remain hidden. In our analysis, we find that link delays are generally very low in absolute time and are largely independent of the dates people join the network. To highlight the social nature of this metric, we introduce the term \textit{peerness} to quantify how well linked users overlap in lifetimes. As for triadic closure delay we first introduce an algorithm to extract of temporal triangle which enables us to monitor the triangle formation process, and to detect sudden changes in the triangle formation behavior, possibly related to external events. In particular, we show that the introduction of new service functionalities had a disruptive impact on the triangle creation process in the network

Aproximación formal para la gestión y evaluación de Living Labs

La participación de los usuarios en el proceso de innovación ha favorecido el desarrollo de productos y servicios tecnológicos más acorde con sus necesidades, y a través de la apertura de la innovación gestionada por las organizaciones se ha favorecido la creación de nuevas formas de gestionar el conocimiento. Los Living Labs constituyen una aproximación integrada a la innovación abierta dirigida por los usuarios en el cual se crea un entorno real para la cocreación y experimentación con la activa participación de los usuarios desde tempranas etapas del ciclo de innovación. La configuración y ejecución de estos entornos de innovación ha significado la aparición de diversos desafíos y problemas, y con el fin de abordarlos se desarrollaron varias y dispersas aproximaciones. A pesar de las diversas aportaciones encontradas en la literatura, una necesidad aún no resuelta integralmente y satisfactoriamente es cómo llevar a cabo la evaluación y mejora de los Living Labs de tal manera que sea posible determinar la madurez de la organización como entorno de innovación y determinar la potencialidad e impacto de las innovaciones generadas. Ello permitiría conocer el nivel de desempeño del Living Lab y la efectividad de las innovaciones generadas tanto para los usuarios como para el entorno local y regional con la finalidad de establecer posteriormente, en base a los resultados conseguidos, planes de mejora. Con la finalidad de proporcionar una solución formalizada e integral, esta tesis doctoral se centra en describir los mecanismos para obtener el nivel de desempeño del Living Lab como entorno real de innovación abierta dirigida por el usuario, y en determinar la efectividad y el impacto de los productos y servicios tecnológicos desarrollados por medio de la elaboración de un Modelo de Evaluación y Mejora definiendo un conjunto de buenas prácticas agrupadas por procesos para la gestión de la innovación, y especificando una serie de actividades para la realización de la evaluación. El Modelo de Evaluación y Mejora incluye además información acerca de los roles y responsabilidades considerados para la configuración del personal de evaluación. Los resultados obtenidos a partir de la validación del Modelo de Evaluación y Mejora propuesto en esta tesis estuvieron orientados a determinar la representatividad de las prácticas para la gestión y desarrollo de los Living Labs, la adecuada caracterización de la evolución y mejora de estos entornos de innovación, la aceptable declaración de aspectos de evaluación acerca de los resultados e impactos generados, y la especificación de apropiados mecanimos para llevar a cabo el proceso de evaluación. --------------------------------------------------------------------------------------------------------------------------------------------------------------------Users’ involvement in the innovation process has favored the development of technology products and services most suitable to their needs, and through the open innovation managed by organizations has led to the creation of new ways of managing knowledge. Living Labs are an integrated approach to user-driven open innovation, and it creates a real environment for co-creation and experimentation with active user participation from early stages of innovation. Some challenges and problems came out by configuring and implementing these innovation environments, and in order to address them several and sparse approaches were developed. Despite the various contributions found in the literature, a need still unresolved is how to fully and satisfactorily perform evaluation and improvement of Living Labs in such a way that is possible to determine the maturity of these organizations as innovation environments and determine the added value and impact of innovations generated. This would determine the Living Lab’s performance level and the effectiveness from innovations generated for both users and territorial environment in order to establish later improvement plans based on the results achieved. In order to provide a formalized and holistic solution, this thesis focuses on describing the mechanisms to get the Living Lab’s performance level as real environment of user-driven open innovation, and determining the effectiveness and impact of technological products and services developed through the development of a model which defines a set of best practices grouped by process areas aimed at innovation management, and specifying a range of activities for conducting an evaluation process. The model also includes information about roles and responsibilities for configuring staff assessment. The results obtained from validating the proposed model were aimed at determining the representativeness of practices for managing and developing Living Labs, getting a suitable characterization about the evolution and improvement of these innovation environments, an acceptable statement of evaluation aspects about results and impacts, and an appropriate specification of mechanisms to carry out the evaluation process