Discovery and group communication for constrained Internet of Things devices using the Constrained Application Protocol

The ubiquitous Internet is rapidly spreading to new domains. This expansion of the Internet is comparable in scale to the spread of the Internet in the ’90s. The resulting Internet is now commonly referred to as the Internet of Things (IoT) and is expected to connect about 50 billion devices by the year 2020. This means that in just five years from the time of writing this PhD the number of interconnected devices will exceed the number of humans by sevenfold. It is further expected that the majority of these IoT devices will be resource constrained embedded devices such as sensors and actuators. Sensors collect information about the physical world and inject this information into the virtual world. Next processing and reasoning can occur and decisions can be taken to enact upon the physical world by injecting feedback to actuators. The integration of embedded devices into the Internet introduces new challenges, since many of the existing Internet technologies and protocols were not designed for this class of constrained devices. These devices are typically optimized for low cost and power consumption and thus have very limited power, memory, and processing resources and have long sleep periods. The networks formed by these embedded devices are also constrained and have different characteristics than those typical in todays Internet. These constrained networks have high packet loss, low throughput, frequent topology changes and small useful payload sizes. They are referred to as LLN. Therefore, it is in most cases unfeasible to run standard Internet protocols on this class of constrained devices and/or LLNs. New or adapted protocols that take into consideration the capabilities of the constrained devices and the characteristics of LLNs, are required. In the past few years, there were many efforts to enable the extension of the Internet technologies to constrained devices. Initially, most of these efforts were focusing on the networking layer. However, the expansion of the Internet in the 90s was not due to introducing new or better networking protocols. It was a result of introducing the World Wide Web (WWW), which made it easy to integrate services and applications. One of the essential technologies underpinning the WWW was the Hypertext Transfer Protocol (HTTP). Today, HTTP has become a key protocol in the realization of scalable web services building around the Representational State Transfer (REST) paradigm. The REST architectural style enables the realization of scalable and well-performing services using uniform and simple interfaces. The availability of an embedded counterpart of HTTP and the REST architecture could boost the uptake of the IoT. Therefore, more recently, work started to allow the integration of constrained devices in the Internet at the service level. The Internet Engineering Task Force (IETF) Constrained RESTful Environments (CoRE) working group has realized the REST architecture in a suitable form for the most constrained nodes and networks. To that end the Constrained Application Protocol (CoAP) was introduced, a specialized RESTful web transfer protocol for use with constrained networks and nodes. CoAP realizes a subset of the REST mechanisms offered by HTTP, but is optimized for Machine-to-Machine (M2M) applications. This PhD research builds upon CoAP to enable a better integration of constrained devices in the IoT and examines proposed CoAP solutions theoretically and experimentally proposing alternatives when appropriate. The first part of this PhD proposes a mechanism that facilitates the deployment of sensor networks and enables the discovery, end-to-end connectivity and service usage of newly deployed sensor nodes. The proposed approach makes use of CoAP and combines it with Domain Name System (DNS) in order to enable the use of userfriendly Fully Qualified Domain Names (FQDNs) for addressing sensor nodes. It includes the automatic discovery of sensors and sensor gateways and the translation of HTTP to CoAP, thus making the sensor resources globally discoverable and accessible from any Internet-connected client using either IPv6 addresses or DNS names both via HTTP or CoAP. As such, the proposed approach provides a feasible and flexible solution to achieve hierarchical self-organization with a minimum of pre-configuration. By doing so we minimize costly human interventions and eliminate the need for introducing new protocols dedicated for the discovery and organization of resources. This reduces both cost and the implementation footprint on the constrained devices. The second, larger, part of this PhD focuses on using CoAP to realize communication with groups of resources. In many IoT application domains, sensors or actuators need to be addressed as groups rather than individually, since individual resources might not be sufficient or useful. A simple example is that all lights in a room should go on or off as a result of the user toggling the light switch. As not all IoT applications may need group communication, the CoRE working group did not include it in the base CoAP specification. This way the base protocol is kept as efficient and as simple as possible so it would run on even the most constrained devices. Group communication and other features that might not be needed by all devices are standardized in a set of optional separate extensions. We first examined the proposed CoAP extension for group communication, which utilizes Internet Protocol version 6 (IPv6) multicasts. We highlight its strengths and weaknesses and propose our own complementary solution that uses unicast to realize group communication. Our solution offers capabilities beyond simple group communication. For example, we provide a validation mechanism that performs several checks on the group members, to make sure that combining them together is possible. We also allow the client to request that results of the individual members are processed before they are sent to the client. For example, the client can request to obtain only the maximum value of all individual members. Another important optional extension to CoAP allows clients to continuously observe resources by registering their interest in receiving notifications from CoAP servers once there are changes to the values of the observed resources. By using this publish/subscribe mechanism the client does not need to continuously poll the resource to find out whether it has changed its value. This typically leads to more efficient communication patterns that preserve valuable device and LLN resources. Unfortunately CoAP observe does not work together with the CoAP group communication extension, since the observe extension assumes unicast communication while the group communication extension only support multicast communication. In this PhD we propose to extend our own group communication solution to offer group observation capabilities. By combining group observation with group processing features, it becomes possible to notify the client only about certain changes to the observed group (e.g., the maximum value of all group members has changed). Acknowledging that the use of multicast as well as unicast has strengths and weaknesses we propose to extend our unicast based solution with certain multicast features. By doing so we try to combine the strengths of both approaches to obtain a better overall group communication that is flexible and that can be tailored according to the use case needs. Together, the proposed mechanisms represent a powerful and comprehensive solution to the challenging problem of group communication with constrained devices. We have evaluated the solutions proposed in this PhD extensively and in a variety of forms. Where possible, we have derived theoretical models and have conducted numerous simulations to validate them. We have also experimentally evaluated those solutions and compared them with other proposed solutions using a small demo box and later on two large scale wireless sensor testbeds and under different test conditions. The first testbed is located in a large, shielded room, which allows testing under controlled environments. The second testbed is located inside an operational office building and thus allows testing under normal operation conditions. Those tests revealed performance issues and some other problems. We have provided some solutions and suggestions for tackling those problems. Apart from the main contributions, two other relevant outcomes of this PhD are described in the appendices. In the first appendix we review the most important IETF standardization efforts related to the IoT and show that with the introduction of CoAP a complete set of standard protocols has become available to cover the complete networking stack and thus making the step from the IoT into the Web of Things (WoT). Using only standard protocols makes it possible to integrate devices from various vendors into one bigWoT accessible to humans and machines alike. In the second appendix, we provide an alternative solution for grouping constrained devices by using virtualization techniques. Our approach focuses on the objects, both resource-constrained and non-constrained, that need to cooperate by integrating them into a secured virtual network, named an Internet of Things Virtual Network or IoT-VN. Inside this IoT-VN full end-to-end communication can take place through the use of protocols that take the limitations of the most resource-constrained devices into account. We describe how this concept maps to several generic use cases and, as such, can constitute a valid alternative approach for supporting selected applications

Discovery and Group Communication for Constrained Internet of Things Devices using the Constrained Application Protocol

The ubiquitous Internet is rapidly spreading to new domains. This expansion of the Internet is comparable in scale to the spread of the Internet in the ’90s. The resulting Internet is now commonly referred to as the Internet of Things (IoT) and is expected to connect about 50 billion devices by the year 2020. This means that in just five years from the time of writing this PhD the number of interconnected devices will exceed the number of humans by sevenfold. It is further expected that the majority of these IoT devices will be resource constrained embedded devices such as sensors and actuators. Sensors collect information about the physical world and inject this information into the virtual world. Next processing and reasoning can occur and decisions can be taken to enact upon the physical world by injecting feedback to actuators. The integration of embedded devices into the Internet introduces new challenges, since many of the existing Internet technologies and protocols were not designed for this class of constrained devices. These devices are typically optimized for low cost and power consumption and thus have very limited power, memory, and processing resources and have long sleep periods. The networks formed by these embedded devices are also constrained and have different characteristics than those typical in todays Internet. These constrained networks have high packet loss, low throughput, frequent topology changes and small useful payload sizes. They are referred to as LLN. Therefore, it is in most cases unfeasible to run standard Internet protocols on this class of constrained devices and/or LLNs. New or adapted protocols that take into consideration the capabilities of the constrained devices and the characteristics of LLNs, are required. In the past few years, there were many efforts to enable the extension of the Internet technologies to constrained devices. Initially, most of these efforts were focusing on the networking layer. However, the expansion of the Internet in the 90s was not due to introducing new or better networking protocols. It was a result of introducing the World Wide Web (WWW), which made it easy to integrate services and applications. One of the essential technologies underpinning the WWW was the Hypertext Transfer Protocol (HTTP). Today, HTTP has become a key protocol in the realization of scalable web services building around the Representational State Transfer (REST) paradigm. The REST architectural style enables the realization of scalable and well-performing services using uniform and simple interfaces. The availability of an embedded counterpart of HTTP and the REST architecture could boost the uptake of the IoT. Therefore, more recently, work started to allow the integration of constrained devices in the Internet at the service level. The Internet Engineering Task Force (IETF) Constrained RESTful Environments (CoRE) working group has realized the REST architecture in a suitable form for the most constrained nodes and networks. To that end the Constrained Application Protocol (CoAP) was introduced, a specialized RESTful web transfer protocol for use with constrained networks and nodes. CoAP realizes a subset of the REST mechanisms offered by HTTP, but is optimized for Machine-to-Machine (M2M) applications. This PhD research builds upon CoAP to enable a better integration of constrained devices in the IoT and examines proposed CoAP solutions theoretically and experimentally proposing alternatives when appropriate. The first part of this PhD proposes a mechanism that facilitates the deployment of sensor networks and enables the discovery, end-to-end connectivity and service usage of newly deployed sensor nodes. The proposed approach makes use of CoAP and combines it with Domain Name System (DNS) in order to enable the use of userfriendly Fully Qualified Domain Names (FQDNs) for addressing sensor nodes. It includes the automatic discovery of sensors and sensor gateways and the translation of HTTP to CoAP, thus making the sensor resources globally discoverable and accessible from any Internet-connected client using either IPv6 addresses or DNS names both via HTTP or CoAP. As such, the proposed approach provides a feasible and flexible solution to achieve hierarchical self-organization with a minimum of pre-configuration. By doing so we minimize costly human interventions and eliminate the need for introducing new protocols dedicated for the discovery and organization of resources. This reduces both cost and the implementation footprint on the constrained devices. The second, larger, part of this PhD focuses on using CoAP to realize communication with groups of resources. In many IoT application domains, sensors or actuators need to be addressed as groups rather than individually, since individual resources might not be sufficient or useful. A simple example is that all lights in a room should go on or off as a result of the user toggling the light switch. As not all IoT applications may need group communication, the CoRE working group did not include it in the base CoAP specification. This way the base protocol is kept as efficient and as simple as possible so it would run on even the most constrained devices. Group communication and other features that might not be needed by all devices are standardized in a set of optional separate extensions. We first examined the proposed CoAP extension for group communication, which utilizes Internet Protocol version 6 (IPv6) multicasts. We highlight its strengths and weaknesses and propose our own complementary solution that uses unicast to realize group communication. Our solution offers capabilities beyond simple group communication. For example, we provide a validation mechanism that performs several checks on the group members, to make sure that combining them together is possible. We also allow the client to request that results of the individual members are processed before they are sent to the client. For example, the client can request to obtain only the maximum value of all individual members. Another important optional extension to CoAP allows clients to continuously observe resources by registering their interest in receiving notifications from CoAP servers once there are changes to the values of the observed resources. By using this publish/subscribe mechanism the client does not need to continuously poll the resource to find out whether it has changed its value. This typically leads to more efficient communication patterns that preserve valuable device and LLN resources. Unfortunately CoAP observe does not work together with the CoAP group communication extension, since the observe extension assumes unicast communication while the group communication extension only support multicast communication. In this PhD we propose to extend our own group communication solution to offer group observation capabilities. By combining group observation with group processing features, it becomes possible to notify the client only about certain changes to the observed group (e.g., the maximum value of all group members has changed). Acknowledging that the use of multicast as well as unicast has strengths and weaknesses we propose to extend our unicast based solution with certain multicast features. By doing so we try to combine the strengths of both approaches to obtain a better overall group communication that is flexible and that can be tailored according to the use case needs. Together, the proposed mechanisms represent a powerful and comprehensive solution to the challenging problem of group communication with constrained devices. We have evaluated the solutions proposed in this PhD extensively and in a variety of forms. Where possible, we have derived theoretical models and have conducted numerous simulations to validate them. We have also experimentally evaluated those solutions and compared them with other proposed solutions using a small demo box and later on two large scale wireless sensor testbeds and under different test conditions. The first testbed is located in a large, shielded room, which allows testing under controlled environments. The second testbed is located inside an operational office building and thus allows testing under normal operation conditions. Those tests revealed performance issues and some other problems. We have provided some solutions and suggestions for tackling those problems. Apart from the main contributions, two other relevant outcomes of this PhD are described in the appendices. In the first appendix we review the most important IETF standardization efforts related to the IoT and show that with the introduction of CoAP a complete set of standard protocols has become available to cover the complete networking stack and thus making the step from the IoT into the Web of Things (WoT). Using only standard protocols makes it possible to integrate devices from various vendors into one bigWoT accessible to humans and machines alike. In the second appendix, we provide an alternative solution for grouping constrained devices by using virtualization techniques. Our approach focuses on the objects, both resource-constrained and non-constrained, that need to cooperate by integrating them into a secured virtual network, named an Internet of Things Virtual Network or IoT-VN. Inside this IoT-VN full end-to-end communication can take place through the use of protocols that take the limitations of the most resource-constrained devices into account. We describe how this concept maps to several generic use cases and, as such, can constitute a valid alternative approach for supporting selected applications

From Radio Channel Modeling to a System Level Perspective in Body-Centric Communications

Body-centric communications are emerging as a new paradigm in the panorama of personal communications. Being concerned with human behaviour, they are suitable for a wide variety of applications. The advances in the miniaturization of portable devices to be placed on or around the body, foster the diffusion of these systems, where the human body is the key element defining communication characteristics. This thesis investigates the human impact on body-centric communications under its distinctive aspects. First of all, the unique propagation environment defined by the body is described through a scenario-based channel modeling approach, according to the communication scenario considered, i.e., on- or on- to off-body. The novelty introduced pertains to the description of radio channel features accounting for multiple sources of variability at the same time. Secondly, the importance of a proper channel characterisation is shown integrating the on-body channel model in a system level simulator, allowing a more realistic comparison of different Physical and Medium Access Control layer solutions. Finally, the structure of a comprehensive simulation framework for system performance evaluation is proposed. It aims at merging in one tool, mobility and social features typical of the human being, together with the propagation aspects, in a scenario where multiple users interact sharing space and resources

Caracterització de l'impacte dels esdeveniments acústics en els nivells equivalents sonors i en la percepció dels ciutadans per a la confecció de mapes dinàmics de soroll

La contaminació acústica ha esdevingut un greu problema de salut pública, provocant diversos tipus de malalties i trastorns en les persones. Segons l'Organització Mundial de la Salut, cada any es perden a l'Europa occidental, un milió d'anys de vida saludables per culpa de l'exposició al soroll ambiental. Per tal d'avaluar i gestionar el soroll ambiental a la Unió Europea, la directiva END 2002/49/CE requereix als estats membres la preparació i publicació de mapes de soroll actualitzats i els plans d'acció relatius, cada cinc anys. Això inclou aglomeracions de més de 100.000 habitants i les principals carreteres, vies de tren i aeroports. Gràcies als avanços tecnològics recents, el paradigma de creació de mapes de soroll ha canviat substancialment, permetent l'automatització de les mesures dels nivells sonors utilitzant xarxes de sensors acústics sense fils per a la generació de mapes de soroll en temps real. Així i tot, aquestes xarxes no poden prevenir una sèrie de situacions que esbiaixarien la mesura real dels nivells equivalents sonors, ocasionant que el mapa no sigui fidel a la realitat que percep el ciutadà, p. ex., el so de les aus, de la indústria, els clàxons, les sirenes, les converses que ocorren prop dels sensors o fenòmens meteorològics com la pluja i el vent. Aquesta tesi estudia la caracterització dels esdeveniments acústics per a la confecció de mapes dinàmics de soroll de trànsit. L'estudi comença presentant el context de la tesi, el projecte LIFE DYNAMAP, que pretén mesurar els nivells de soroll de trànsit en dues àrees pilot i integrar-los dinàmicament en un mapa de soroll que s'actualitza a temps real. A continuació, es presenta una anàlisi exhaustiva dels esdeveniments que es troben en les dues àrees, la urbana i la suburbana, i s'hi apliquen diverses caracteritzacions. Una de les mesures que es presenta és la de l'impacte en el nivell equivalent sonor (Leq), que permet mesurar el biaix que provoca la presència de certs esdeveniments acústics en la confecció dels mapes de soroll de trànsit. També es planteja l'ús de tests perceptius mitjançant mètriques psicoacústiques per tal d'adaptar la caracterització d'aquests esdeveniments a la percepció ciutadana. L'objectiu principal de la tesi és caracteritzar els esdeveniments d'entorns urbans i suburbans per oferir mapes de soroll més fidels a la realitat percebuda pel ciutadà en relació amb el paisatge sonor on es troba. I durant la tesi es mostra la importància de la detecció de sons en una xarxa de sensors acústics per tal de prevenir errors de mesura en els nivells equivalents i la necessitat d'entrenar el sistema de detecció amb dades obtingudes en els mateixos sensors de la xarxa.La contaminación acústica se ha convertido en un grave problema de salud pública, provocando varios tipos de enfermedades y trastornos en las personas. Según la Organización Mundial de la Salud, cada año se pierden en la Europa occidental, un millón de años de vida saludables por culpa de la exposición al ruido ambiental. Para evaluar y gestionar el ruido ambiental en la Unión Europea, la directiva END 2002/49/CE requiere a los estados miembros la preparación y publicación de mapas de ruido actualizados y los planes de acción relativos, cada cinco años. Esto incluye aglomeraciones de más de 100.000 habitantes y las principales carreteras, vías de tren y aeropuertos. Gracias a los avances tecnológicos recientes, el paradigma de creación de mapas de ruido ha cambiado sustancialmente, permitiendo la automatización de las medidas de los niveles sonoros utilizando redes de sensores acústicos inalámbricos para la generación de mapas de ruido en tiempo real. Aun así, estas redes no pueden prevenir una serie de situaciones que sesgarían la medida real de los niveles equivalentes sonoros, ocasionando que el mapa no sea fiel a la realidad que percibe el ciudadano, p. ej., el sonido de las aves, de la industria, los cláxones, las sirenas, las conversaciones que ocurren cerca de los sensores o fenómenos meteorológicos como la lluvia y el viento. Esta tesis estudia la caracterización de los eventos acústicos para la confección de mapas dinámicos de ruido de tráfico. El estudio empieza presentando el contexto de la tesis, el proyecto LIFE DYNAMAP, que pretende mesurar los niveles de ruido de tráfico en dos áreas piloto e integrarlos dinámicamente en un mapa de ruido que se actualiza a tiempo real. A continuación, se presenta un análisis exhaustivo de los acontecimientos que se encuentran en las dos áreas, la urbana y la suburbana, y se aplican varias caracterizaciones. Una de las medidas que se presenta es la del impacto en el nivel equivalente sonoro (Leq), que permite mesurar el sesgo que provoca la presencia de ciertos acontecimientos acústicos en la confección de los mapas de ruido de tráfico. También se plantea el uso de macetas perceptivas mediante métricas psicoacústicas para adaptar la caracterización de estos eventos a la percepción ciudadana. El objetivo principal de la tesis es caracterizar los acontecimientos de entornos urbanos y suburbanos para ofrecer mapas de ruido más fieles a la realidad percibida por el ciudadano en relación con el paisaje sonoro donde se encuentra. Y durante la tesis se muestra la importancia de la detección de sonidos en una red de sensores acústicos para prevenir errores de medida en los niveles equivalentes y la necesidad de entrenar el sistema de detección con datos obtenidos en los mismos sensores de la red.Acoustic pollution has become a serious public health problem, causing various types of disease and disorders in people. According to the World Health Organisation, one million years of healthy life are lost in Western Europe every year due to exposure to environmental noise. In order to evaluate and manage environmental noise in the European Union, Directive END 2002/49/EC requires Member States to prepare and publish updated noise maps and relative action plans every five years. This includes agglomerations of more than 100,000 inhabitants and major roads, train tracks and airports. Thanks to recent technological advances, the noise map creation paradigm has changed substantially, allowing noise level measurements to be automated using wireless acoustic sensor networks for real-time noise map generation. However, these networks cannot prevent a series of situations that would bias the actual measurement of sound equivalent levels, causing the map not to be true to the reality perceived by the citizen, e.g., the sound of birds, the industry, the claxons, the mermaids, conversations that occur near sensors or weather phenomena such as rain and wind. This thesis studies the characterization of acoustic events for the tailoring of dynamic traffic noise maps. The study begins by presenting the context of the thesis, the LIFE DYNAMAP project, which aims to measure traffic noise levels in two pilot areas and dynamically integrate them into a noise map that is updated in real time. After that, a detailed analysis is presented for the events in the two areas, urban and suburban, and various characterizations are applied. One of the presented measures is the impact on the equivalent sound level (Leq), which allows the measurement of bias resulting from the presence of certain acoustic events in the making of traffic noise maps. The use of perceptual tests using psychoacoustic metrics is also considered in order to adapt the characterization of these events to citizen perception. The main purpose of the thesis is to characterize the events of urban and suburban environments to offer noise maps more faithful to the reality perceived by the citizen in relation to the sound environment where it is found. And during the thesis, the importance of sound detection on a network of acoustic sensors is shown in order to prevent measurement errors at equivalent levels and the need to train the detection system with data obtained from the same sensors on the network

Selected Papers from the 5th International Electronic Conference on Sensors and Applications

This Special Issue comprises selected papers from the proceedings of the 5th International Electronic Conference on Sensors and Applications, held on 15–30 November 2018, on sciforum.net, an online platform for hosting scholarly e-conferences and discussion groups. In this 5th edition of the electronic conference, contributors were invited to provide papers and presentations from the field of sensors and applications at large, resulting in a wide variety of excellent submissions and topic areas. Papers which attracted the most interest on the web or that provided a particularly innovative contribution were selected for publication in this collection. These peer-reviewed papers are published with the aim of rapid and wide dissemination of research results, developments, and applications. We hope this conference series will grow rapidly in the future and become recognized as a new way and venue by which to (electronically) present new developments related to the field of sensors and their applications