The Design Space of Wireless Sensor Networks Xin-Xian Liu

Outline Background Performance Metrics Sensor Network Architecture Design Space Conclusion

Background Initial research into WSN was mainly motivated by military application A de facto definition of WSN as a large-scale, ad hoc, multihop, tiny, resource-constrained

Sensor network

The components of a sensor node

Performance Metrics Energy efficiency / system lifetime Latency Accuracy Fault-tolerance Scalability

Sensor Network Architecture The network protocol is responsible for supporting all communication between the sensors and the observer The performance of the protocol will be highly influenced by the network dynamics and by the specific data delivery model employed

Communication Models Communication within a sensor network can be classified into two categories – Application communication – Infrastructure communication Application communication is related to the transfer of sensed data with the goal of informing the observer about the phenomena

Communication Models Within application communication, there are two models: – Cooperative – Non-cooperative

Communication Models Infrastructure communication refers to the communication needed to configure, maintain and optimize operation In sensor networks, an initial phase of infrastructure communication is needed to set up the network

Data Delivery Models Sensor networks can be classified in terms of the data delivery required by the application interest as: – Continuous – Event-driven – Observer-initiated – hybrid

Data Delivery Models Continuous – The sensors communicate their data continuously at a prespecified rate Event-driven – The sensors report information only if an event of interest occurs Observer-initiated – The sensors only report their results in response to an explicit request from the observer

Data Delivery Models The actual flow of data packets between the sensors and the observer – Flooding – Unicast – Multicast

Network Dynamics Models The approach to construct and maintain a path between observer and phenomenon will differ depending on the network dynamics, which we classify as – Static sensor networks – Dynamic sensors networks

Static Sensor Networks In static sensor networks, there is no motion among communication sensor, the observer and the phenomenon

Dynamic Sensor Networks In dynamic sensor networks, either the sensors themselves, the observer, or the phenomenon are mobile Dynamic sensor networks can be further classified by considering the motion of the components – Mobile observer – Mobile sensors – Mobile phenomena

Design Space We informally characterize each of the dimension and, where appropriate, identify property classes in order to support a coarse-grained classification of sensor network application

Design Space Deployment – Random vs. Manual – One-time vs. Iterative Mobility – Immobile vs. Partly vs. All – Occasional vs. Continuous – Active vs. Passive

Design Space Cost – The cost of a single device may vary from hundreds of Euros to a few cents Size – The form factor of a single sensor node may vary from the size of a shoebox to a microscopically small particle

Design Space Resources and Energy – Varying size and cost constrains directly result in corresponding varying limits on the energy available, as well as on computing, storage and communication resources – We partition sensor nodes roughly into four classes based on their physical size brick, matchbox, grain, and dust

Design Space Heterogeneity – Homogeneous vs. Heterogeneous Communication Modality – Radio vs. Light vs. Inductive vs. Capacitive vs. Sound Infrastructure – Infrastructure vs. Ad Hoc

Design Space Network Topology – Single-hop vs. Star vs. Networked Start vs. Tree Coverage – Sparse vs. Dense vs. Redundant Connectivity – Connected vs. Intermittent vs. sporadic

Design Space Network Size – The network size may vary from a few nodes to thousands of sensor nodes or even more Lifetime – Depending on the application, the required lifetime of a sensor network may range from some hours to several years

Design Space Other QoS Requirement – Depending on the application, a sensor network must support certain QoS aspects such as Real-time Robustness Tamper-resistance Eavesdropping resistance

Conclusion Clearly, a single hardware platform will most likely not be sufficient to support the wide range of possible applications A modular approach, where the individual components of a sensor node can easily exchanged

References [1] S. Tilak, N. B. Abu-Ghazaleh, and W. Heinzelman, “A Taxonomy of Wireless Micro- Sensor Network Models,”MR2C, vol. 6, no. 2, Arp.2002, pp [2] Kay Romer and Friedemann Mattern, ETH Zurich, “The Design Space of Wireless Sensor Networks,” IEEE Communications Magazine, pp.54-61,December 2004