Wireless Sensors and Wireless Sensor Networks (WSN) Darrell Curry

Overview Advantages of Wireless Sensors Typical Wireless Sensor Hardware Applications IEEE ZigBee Demos

Advantages of Wireless Sensors Much cheaper to deploy than wired sensors Sensor nodes can be added or removed easily Node location can be changed without rewiring Can be configured into different network topologies  Star, Mesh, etc.

Wireless Sensor Node Hardware Microcontroller Radio Transceiver Sensor Power Supply

Microcontroller Contains CPU, Memory and Peripherals on same chip Typically 8-bit or 16-bit Operate at less than 20MHz Memory less than 128kB Low power consumption to ensure long run times

Radio Transceiver Typically operate in the ISM bands Use various modulation techniques  QPSK, BFSK, GFSK Low Output Power 0dBm or 1mw Low Range around feet

Sensors Temperature Humidity Atmospheric Pressure Light Acceleration ( Accelerometer ) Angular Rate ( Gyroscope) Strain

Applications HVAC Systems Home Automation Structural Monitoring ( Bridges, Buildings) Area Monitoring Monitoring condition of Machinery Agricultural

IEEE Part of the wireless PAN standard Specifies the PHY and MAC layers Created for low data rate and multi-month or multi-year battery life Targeted Applications  Sensors  Interactive Toys  Smart Badges  Remote Controls  Home Automation

IEEE Specifications 16 Channels in 2.4GHz band – 250kbps 10 Channels in 915MHz band – 40kbps 1 Channel in 868MHz band – 20kbps DSSS used in all bands 2.4GHz band uses O-QPSK modulation 915MHz and 868MHz bands use BPSK

IEEE Specifications CSMA-CA channel access AES 128 bit encryption Maximum Packet size of 128 Bytes Two addressing modes supported 16-bit short addresses and 64-bit IEEE addresses

Zigbee Regulated by the Zigbee Alliance Intended to be simpler and less expensive than Bluetooth Handles aspects such as messaging, configuration, security and application profile layers Topologies supported are Star, Mesh and Cluster Tree (Hybrid)

Zigbee Device Classes Zigbee Coordinator (ZC)  Most capable deviece  Forms the root of the network tree and bridge to other networks  Acts as repository for security keys Zigbee Router (ZR)  Can pass data from one device to another Zigbee End Device (ZED)  Contains just enough functionality to talk to its parent node either ZC or ZR

Zigbee Supports beacon and non-beacon modes In non-Beacon mode CSMA/CA channel access is used  Requires routers to always be in receive mode thus increasing power consumption Beacon mode allows devices to sleep between beacons

Wireless Technology Comparison StandardBandwidthPower Consumption Protocol Stack Size Stronghold Wi-FiUp to 54Mbps 400+mA TX Sleep 20mA 100+KBHigh Data Rate Bluetooth1Mbps40mA TX Sleep.2mA 100+KBInteroperability Cable Replacement Zigbee250kbps30mA TX Sleep.003mA 32KBLong Battery Life, Low cost

Demos

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