Wireless Sensor Networks (WSNs) have introduced an innovative way of monitoring and interacting with the environment. WSNs are networks composed of small embedded devices, called motes. Motes are self-powered devices that can sense the environment using onboard sensors and are able to communicate with each other by means of wireless transceivers and when deployed in large scenarios they form self-organizing networks that can effectively monitor large areas. The lack of wiring and their self-powered nature makes them really flexible. Moreover, the use of a large number of these devices introduces node redundancy which can be used to provide a high fault tolerance. This technology allows information to be sensed from the environment and transformed into digital data that can be stored and analyzed. Normal sensor devices are passive elements in the sense that they can only perceive the environment. However, applications can make use of actors, namely, resource rich devices that are capable not only of perceiving the environment but also of acting on it. These types of networks which include actors and sensors are called Wireless Sensor and Actors Networks (WSANs).
There are a great number of applications where WSANs can be applied and their advantages have long been acknowledged in the research community. In spite of all the advatanges they provide and despite being heralded as one of the most important technologies for the 21st century, WSANs have not yet become ubiquitous. It has been more than 30 years since the first research took place but, until now, the number of real applications (long-term deployments) where this technology has been applied is relatively low. What has hampered the transition of WSANs from being a promising technology to being a fully-integrated technology in our daily lives? Some of the factors that may have hindered their development are the unreliable nature of wireless communications and the limited resources of the devices. Moreover, WSANs constitute a distributed system and as such all the difficulties of these kinds of systems equally apply to them. Furthermore, developing WSAN applications is not an easy task and intense research has been carried out to find new frameworks, tools, and middleware that provide higher levels of abstraction in order to simplify the developers’ task. In addition, new applications forWSANs demand new requirements and features from the sensor devices. For example, in recent years the possibilities ofWSANs have been acknowledged as promising for the Critical Infrastructure Protection (CIP) field.
In this regard,WSANs have the potential to become an integral part of the protection of CIs such as electricity generation and transmission facilities, telecommunication systems, water supply, etc. Their distributed nature makes them particularly suitable against failures and attacks as they are much more rarely affected in their entirety, unlike wired systems. One of the main barriers, researchers and industry need to tackle in order for WSAN to become pervasive in this application domain is the lack of Quality of Service (QoS) support (reliability, dependability, security, etc), mainly due to their wireless nature. Finally, WSANs need to address the integration and representation problem that deals with how to make the information sensed by the network easily accessible and to provide users with a way of representing and querying the information collected by the WSAN.
The work presented in this website aims to investigate each of the aforementioned challenges that hinder WSANS from becoming widely used. The final goal is to provide WSAN developers and users with a middleware, called PS-QUASAR (Publish/Subscribe QUAlity of Service Aware middlewaRe), that they can use to program these devices in an easy and non errorprone manner and allow QoS requirements to be handled automatically. In addition, a way of achieving communication between different devices, WSANs and a Supervisory Control and Data Acquisition (SCADA) is presented.
In general terms, this work contributes to mitigating the problems of actual WSAN
technology by providing solutions at different levels. In particular these are:
1) An extensive study of current MAC protocols, routing protocols and middlewares focusing on their application to the CIP problem. Desirable features are identified and the challenges are described and analyzed. Link
2) A routing protocol for WSANs that support a many to many communication pattern, and that can handle QoS requirements. This protocol lays the foundation over which a publish/subscribe programming model is used. QoS requirements supported by the PS-QUASAR routing protocol are reliability, deadline and priority. Developers specify their QoS needs and the middleware automatically handles the requirements. Link
3) An analysis of the performance of common queue-based priority mechanisms by means of the PS-QUASAR middleware, as well as a study of the performance of the network under different workloads, in terms of reliability, delay and queue occupation using different network topologies and network sizes. This study aims to identify the importance of matching network level capabilities to data link layer capabilities and comments on the existence of a noticeable tradeoff between reliability and priority. Link
4) A case study is presented to validate the PS-QUASAR middleware. The case study consists of a WSAN for monitoring a railway bridge. The application shows ways of coping with large amounts of data and deals with mobility issues. Specifically, passing trains are used as data-mules to collect the information sensed by theWSAN. Link
5) A general architecture consisting of a SCADA that connects and collects information from multiple WSANs. Information is stored in a database and can be queried over the internet using a common browser. This architecture makes use of open source software and widely used technologies such as web services over HTTP. Link
This work was supported by the the Spanish grant FPU-2010 (Formación de Personal Universitario) and the following projects:
MIsTIca: Monitorización de Infraestructuras Críticas basada en Tecnologías Inalámbricas (TIC-1572)
WSAN4CIP: Wireless Sensor and Actuator Networks for the Protection of Critical Infrastructures (ITC-2007-225186).
WiCMaS:Wireless based Critical InformationManagement Systems (TIN2011-23795).
Desarrollo de Software para Redes Inalámbricas de Sensores y Actores (TIC-03085).
MDD-MERTS: Dise˜no y Monitorización Dirigido por Modelos de Sistemas Empotrados y Tiempo Real (TIN2008-03107).