References Introduction 1 K. Sohraby, D. Minoli, and T. Znadi. Wireless Sensor Networks: Technology, Protocols, and Applications. John Wiley & Sons, 2007. H. Karl and A. Willig. Protocols and Architectures for Wireless Sensor Networks. John Wiley & Sons, 2005. 2 The vision of ambient intelligence The major form of information processing has been in two classes of applications: Human-centric such as office applications Embedded where the computation is integrated with the control According to a recent study, up to 98% of all computing devices are used in an embedded context. t Technological advances are taking this spreading of embedded control in our lives one step further. Eventually, Mark Weiser's s vision of Ambient Intelligence, where many different devices will gather and process information from many different sources to both control physical processes and to interact with human users, will be realized. 3 The missing component... 4 The embedded d systems does the computation ti and control, however, with those alone, the vision cannot become a reality. All the sources of information have to communicate this information to a place where it is needed an actuator or a user, where a precise view of the surrounding real world is provided. For many application scenarios the networking of the sensors and actuators can be achieved by using the existing (wired) technologies. For some others, however, the wiring could be very costly (up to $200 per sensor). Hence, wireless communication between such devices is an inevitable requirement....and a new class of networks is born.
Wireless sensor networks... A wireless sensor network (WSN)i is an infrastructure t comprised of sensing (measuring), computing, and communication elements that gives a user the ability to instrument, observe, and react to events and phenomena in a specified environment. There are four basic components in a WSN: An assembly of distributed or localized sensors (sensing and computation nodes An interconnection network, A central point of information gathering, and A set of computing resources at the central point (or beyond) to handle data correlation, event trending, status querying, and data mining. 5 Applications of WSN Traditionally, the sensors have been used in high-end h applications, such as radiation detection systems Later, they were used to in factory automation Most recently, they have a focus of much simpler applications, such as habitat and seismic monitoring, and others directed to consumer applications 6 Application examples Broadly, WSN applications can be categorized into the following groups: 7 Military applications Monitoring friendly and enemy forces and equipment; military theater or battlefield surveillance; targeting; battle damage assessment; and more Industrial and business applications Machine surveillance; preventive maintenance; logistics; facility management; inventory control; and more Environmental applications Climate changes; forest fire detection; flood detection; precision agriculture; and more Health applications Monitoring of vital signs; tracking and monitoring doctors and patients; drug administration; and more Home applications Home automation; instrumented environment; and more Types of applications another look Most of the applications mentioned share a common characteristic: a clear difference between source(s) of data and the destination (called sinks). They usually have an actuator that is usually controlled by the source(s). 8
Players of a WSN Sources of data: Measure data, report them to somewhere Typically y equipped with different kinds of actual sensors 9 Players of a WSN 2 Actuators: t Control some device based on data; usually also a sink 10 Sinks of data: Interested in receiving data from WSN May be part of the WSN or an external entity, such as a PDA, or a gateway Before After Other characteristics of WSNs Others have interaction ti patterns between sources and sink(s): Event detection Sensors report to the sink(s) once they have detected the occurrence of a specified event Periodic measurements Sensors periodically report measured values 11 Function approximation and edge detection Sensors could be used to approximate the measured phenomena (e.g., temperature changes) as a function of location; or they could be asked to find the areas or points of the same value Tracking Sensors could be used to report updates on the event source s position Deployment options of WSNs Random deployment Usually uniform random distribution for nodes over finite area is assumed Is that a likely proposition? Fixed deployment 12 E.g., in preventive maintenance or similar Not necessarily geometric structure, but that is often a convenient assumption Mobile sensor nodes Can move to compensate for deployment shortcomings Can be passively moved around by some external force (wind, water) Can actively seek out interesting areas
Maintenance options Feasible and/or practical to maintain i sensor nodes? E.g., to replace batteries? Unattended d operation? 13 Impossible but not relevant? Mission s lifetime might be very small Energy supply? Limited from point of deployment? Some form of recharging, energy scavenging from environment? E.g., solar cells Challenges for WSNs Characteristics Type of service Not simply moving bits like another network Rather: provide answers (not just numbers) Issues like geographic scoping are natural requirements, absent from other networks Quality of service Traditional QoS metrics do not apply Sill Still, service of WSN must be good : Right answers at the right time Fault tolerance 14 Be robust against node failure (running out of energy, physical destruction, ) Challenges of WSNs Characteristics 2 Lifetime The network should fulfill its task as long as possible definition depends on application Lifetime of individual nodes relatively unimportant But often treated equivalently Scalability Support large number of nodes Wide range of densities 15 Vast or small number of nodes per unit area, very applicationdependent Challenges of WSNs Characteristics 3 Programmability Re-programming of nodes in the field might be necessary, improve flexibility Maintainability 16 WSN has to adapt to changes, self-monitoring, adapt operation Incorporate possible additional resources; e.g., newly deployed nodes
Challenges for WSNs Mechanisms Multi-hop wireless communication Use of intermediate nodes as relays Energy-efficient i operation 17 Both for communication and computation, sensing, actuating Auto-configuration Manual configuration just not an option Collaboration and in-network processing Nodes in the network collaborate towards a joint goal Pre-processing data in network (as opposed to at the edge) can greatly improve efficiency Challenges for WSNs Mechanisms 2 Data centric networking Focusing network design on data, not on node identities (id-centric networking) To improve efficiency Locality Do things locally (on node or among nearby neighbors) as far as possible Exploit tradeoffs E.g., between invested energy and accuracy 18 MANETs 19 A mobile ad hoc network (MANET) is a type of ad hoc (developed on-the-fly for a specific purpose) network that can change locations and configure itself on the fly. In terms of computer networking, an ad hoc network refers to a network connection established for a single session and does not require a router or a wireless base station) that can change locations and configure itself on the fly. Because MANETS are mobile, they use wireless connections to connect to various networks (connections can be a standard Wi-Fi connection, or another medium, such as a cellular or satellite transmission). MANETs visually 20
MANET versus WNS MANETs and WSN have many commonalities, including self-organization, energy efficiency, and often wireless multi-hop However, there are some principle differences between them: 21 Applications, equipment: MANETs assume more powerful (and expensive!) equipment, often human in the loop -type applications, higher data rates, more resources Application-specific: p WSNs application dependence is much greater; i.e., one-size-does-not-fit-all; MANETs are comparably uniform MANET versus WNS 2 22 Environment interaction: is in the core of WSN; irrelevant in MANET Scale: WSN might have much larger number of nodes; MANETs scale to a smaller number Energy: both are short in energy resources, but WSNs have tighter requirements, maintenance issues Dependability and QoS: in WSNs, an individual node may be dispensable (network matters), QoS is different because of different applications Data centric: WNSs are; MANETs are id-centric Mobility: different mobility patterns (e.g., in WSN, sinks might be mobile, but source nodes are generally static) Enabling technologies for WSNs Cost reduction 23 For wireless communication, simple microcontroller, sensing, batteries Miniaturization Some applications demand small size Smart dust as the most extreme vision Energy scavenging Recharge batteries from ambient energy (light, vibration, ) Summary MANETs and WSNs are challenging and promising i system concepts Many similarities, il i i many differences Both require new types of architectures & protocols compared to traditional wired and wireless networks In particular, application-specific nature is a new concept 24