CSC344 Wireless and Mobile Computing Department of Computer Science COMSATS Institute of Information Technology
Wireless Sensor Networks
A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations
Battlefield Surveillance Chemical, Biological Weapons Habitat exploration of animals Patient heart rate, blood pressure Seismic Detection Crops and Agriculture Forest Fires and Flood Detection
Large scale Batteries may not be replaceable May not have global identifiers Queries may be data centric rather than address centric: Who's temperature is more than 95 degree vs. What is your temperature? Geographical routing, Data fusion, Data aggregation
Low-Rate Wireless Personal Area Network (LR-WPAN) Physical layer used in ZigBee, WirelessHART, MiWi which add upper layers 10 m reach at 250 kbps (20/40/100 kbps versions) Three Frequency Bands: 868.0-868.6 MHz in Europe 902-928 MHz in North America 2400-2383.5 MHs worldwide Uses Direct Sequence Spread Spectrum (DSSS)
BPSK or QPSK modulation IEEE 802.15.4a-2007 added ultra-wideband, and chirp spread spectrum IEEE 802.15.4c-2009, IEEE 802.15.4d-2009 add more PHYs and modulations
Star, Peer-to-peer (Mesh), Structured star(tree) Full function and reduced function devices Two modes: With Beacon: Coordinator sends start beacon and stop beacon to indicate active time The time is slotted, slotted CSMA/CA, transmissions end at second beacon Without Beacon: Un-slotted CSMA/CA protocol with random exponential back-off
Digital I/O ports A/D Converter Analog I/O Ports Mote: A device with sensors, networking hardware, and power Radio Transceiver Microcontroller Sensor Power External Memory Sensor A very low cost low power computer Monitors one or more sensors A radio link to the outside world Are the building blocks of WSN TinyOS is a public domain operating system designed for sensor nodes
Several standards are currently either ratified or under development by organizations for wireless sensor networks WirelessHART IEEE 1451 ZigBee / 802.15.4 ZigBee IP 6LoWPAN
ZigBee is a simple, low cost, and low power wireless communication technology used in embedded applications Can form mesh networks connecting hundreds to thousands of devices together, uses OQPSK + DSSS Use very little power, can operate on battery for years Three types of ZigBee devices: Zig-Bee coordinator ZigBee router ZigBee end device Standard was publicly available June 2005
Zig-Bee coordinator initiates network formation, stores information, and can bridge networks together ZigBee routers link groups of devices together and provide multi-hop communication across devices ZigBee end device consists of the sensors, actuators, and controllers that collects data and communicates only with the router or the coordinator
Extension of HART (Highway Addressable Remote Transducer Protocol) to Wireless Supports star and mesh topologies Self-organizing and self-healing Uses IEEE 802.15.4-2006 radios in 2.4GHz Frequency hopping with blacklisting to avoid used channels 128-bit AES encryption Uses multi-path routing Messages alternate paths to ensure secondary paths are up
WirelessHART adapter or built-in Gateways: Connect to the backbone network Network Manager: Manages routes, monitors health (can be integrated in to gateways or hosts) Security Manager: Contains list of authorized devices Distributes security keys Repeater: Extends the range Adapter: Attaches to devices without wirelesshart
Location Discovery Quality of a Sensor Network Time Synchronization Transport Layer Issues Real-Time Communication
Location Stamp on data Indoor Localization: Reference nodes in each location Atomic Multi-Lateration: Need 3 references Iterative Multi-Lateration: Nodes with known location become references for others Collaborative Multi-Lateration: Use quadratic equations
US Department of Defense spent $12B 24 satellites and their ground stations Man made stars, triangulation Measures travel time of radio signal (Distance) Satellites broadcast current time and their location using a Direct Sequence Code, 1023 chips per bit 3 satellites give (x, y, z), 4 satellites give (x, y, z, t) Correct for any delays experienced through the atmosphere
Wikipedia Articles http://en.wikipedia.org/wiki/wireless_sensor_network http://en.wikipedia.org/wiki/body_sensor_network http://en.wikipedia.org/wiki/intelligent_sensor http://en.wikipedia.org/wiki/location_estimation_in_sensor_networks http://en.wikipedia.org/wiki/smartdust http://en.wikipedia.org/wiki/tinyos http://en.wikipedia.org/wiki/wirelesshart http://en.wikipedia.org/wiki/zigbee Text Book: Siva Ram Murthy, B.S. Manoj, "Ad Hoc Wireless Networks: Architectures and Protocols", Chapter 12
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