Environmental Monitoring Using Sensor Networks... 2. Dezember 2010 Communication Systems Seminar HS10 Prof. Dr. Burkhard Stiller Institut für Informatik Universität Zürich
Overview From Environmental Monitoring to the Use of Sensor Networks Main Challenges Generic Approaches Specific Approaches exemplified through Use Cases Summary Questions and Discussion 2
What is Environmental Monitoring? The aim is to collect data about a specific field of interest in the natural environment in order to understand its functionality and to make predictions about the future. Examples: Glaciers Habitats (e.g. of a bird population) Hazard warnings (e.g. floods) Post-closure monitoring (e.g. for nuclear sites, waste burial grounds) Military purposes (e.g. target detection) 3
The Concept of Sensor Networks A spatially distributed network consisting of autonomous sensors Cooperative monitoring of physical or environmental conditions such as temperature, pressure, motion or pollutants Communication between sensors is usually wireless, therefore every sensor node is equipped with a communication device such as a radio transceiver, a small microcomputer and an energy source 4
Environmental Sensor Network (ESN) A Wireless Sensor Network used for Environmental Monitoring Sensors sample data about immediate environment Collected data are made available to Users Communication between: Autonomous sensors in remote locations Base Station (BS) Sensor Network Server (SNS) 5
Generic Architecture of an ESN (Source: K. Martinez, J.K. Hart, R. Ong: Environmental Sensor Networks; Computer - IEEE Computer Society, 2004) 6
The Use of Sensor Networks No manual data collection necessary Reduced interference with natural environment Previously inaccessible fields are now possible to monitor Remote Maintenance and Retasking Inter-network communication: Aggregation possible Future prospect: Connecting different ESNs and aggregation of data in order to obtain a better picture of the environment as a whole 7
Challenges (1/3): Reliability Deployment in natural environment means harder conditions: Weather (rain, wind...) Transmission through water or ice Occlusion of sensor nodes Obstacles in direct communication path 8
Challenges (2/3): Network Retasking &Health Monitoring Network Retasking: From Readjustment of sensor parameters...... to a replacement of the entire code Doing it remotely prevents high costs and interference of the environment Health Monitoring: Helps to analyze sensor readings Useful to plan Network Retasking 9
Challenges (3/3): Power-Efficiency Power from the grid not feasible: Remote deployment Wiring could interfere with the environment Nodes can be moving (e.g. on a glacier) Nodes need to be small Capacity of battery or power generator very limited Long deployment (e.g. one whole breeding season in habitat monitoring) 10
Generic Approaches 3-tier architecture Single-hop... Simple: No dependencies on other nodes, no overhead, no collisions Feasible only for a small number of nodes within the range of a single connection to the BS... vs. Multi-hop: Routing necessary Improves reliability and power-efficiency 11
Use Case 1: GlacsWeb ESN on a glacier in order to understand its contribution to the rising sea-level 8 sensor nodes, 1 BS on glacier surface, 1 reference station, 1 SNS Schedule: Every 4 hours measurement of state and movement, weather conditions once a day (Source: K. Martinez et. al.: Glacial Environment using Sensor Networks; Real-World Wireless Sensor Networks, 2005) 12
GlacsWeb: Reliability Reduce frequency to enlarge wavelength in order to bypass water obstacles Increase transmission power to penetrate ice Fixed schedule to avoid collision and overhead Store-and-forward communication and alternative communication channels Specifically designed communication packet: checksum & retries 13
GlacsWeb: Retasking & health Monit. Network Retasking: BS: Replacement of Shell-Scripts Nodes: Alterable segment in firmware, watchdog timer Health Monitoring: Battery status recorded with every measurement 14
GlacsWeb: Power-Efficiency Limiting wake-up state Infrastructure-based network & Fixed schedule: some energy waste unavoidable (Source: K. Martinez et. al.: Glacial Environment using Sensor Networks; Real-World Wireless Sensor Networks, 2005) 15
Use Case 2: Habitat Monitoring on GDI Seabird breeding site at Great Duck Island (GDI), USA Record usage pattern of nests & environment cond. Measurement schedule according to time of day Several patches of around 100 static nodes Multi-hop network (Source: A. Mainwaring et. al.: Wireless Sensor Networks for Habitat Monitoring; Workshop on Wireless Sensor Networks and Applications, 2002) 16
Habitat Monitoring on GDI Reliability: Multi-hop architecture: Bypassing obstacles, robust against occlusion and component failure Data back-ups at each layer Network Retasking & Health Monitoring: Network maintenance packets Gizmo to interactively adjust parameters Health status recorded including battery voltage 17
GDI: Power-Efficiency Energy bottlenecks near gateway 2 scheduling approaches: Horizontal approach Vertical approach Location-based routing algorithms (like GAF / SPAN) Data compression (standard Unix utilities): (Source: A. Mainwaring et. al.: Wireless Sensor Networks for Habitat Monitoring; Workshop on Wireless Sensor Networks and Applications, 2002) 18
Use Case 3: ZebraNet Monitor migration patterns of zebras in Mpala, Kenya Represantative zebras wearing a GPS-collar 1 sample / 2 mins Very remote, wide area, mobile BS: peer-to peercommunication between zebras (Source: H.-J. Hof: Applications of sensor networks; In Algorithms for Sensor and Ad Hoc Networks, 2007, 1-20) 19
ZebraNet Reliability: High latency possible: large data log storage Peer-to-peer: Dedicated MAC-Protocol avoids collisions using GPS clock and accurate schedule Peer-to-base: FDMA avoids collisions Network Retasking & Health Monitoring: Uses a middleware named Impala Application Adapter: Health monitoring Application Updater: Manages SW-updates 20
ZebraNet: Power-Efficiency History-based protocol: notes rated on past success in data delivery Compression 2 different radios used: One for peer-to-peer: short range, low powerconsumption One for peer-to-base: long range, power-hungry but necessary to assure connectivity 21
Summary Higher challenges to ESNs Power-efficiency as an all-dominant factor Varying challenges need project specific solutions Standard technologies often not used Standardization difficult First steps: Impala middleware 22
Questions? 23
Discussion We've seen how sensor networks can be useful in several fields of environmental monitoring. What other fields could be imagined where sensor networks can be useful and how can they help? 24
Discussion One future prospect is the connection of networks and aggregation of data. Which networks would you connect and what could be interpreted from this aggregated data? 25
Discussion Is there a danger that this kind of technology will be used for a complete surveillance of all citizens with the result of a loss of privacy? 26
Discussion What is the environmental impact of monitoring the natural environment using ESNs? 27