Wireless Sensors and Wireless Sensor Networks (WSN)

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Wireless Sensors and Wireless Sensor Networks
(WSN)

• Darrell Curry

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Overview

• Advantages of Wireless Sensors
• Typical Wireless Sensor Hardware
• Applications
• IEEE 802.15.4
• ZigBee
• Demos

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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.

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Wireless Sensor Node Hardware

• Microcontroller
• Radio Transceiver
• Sensor
• Power Supply

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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

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Radio Transceiver

• Typically operate in the ISM bands
• Use various modulation techniques
• QPSK, BFSK, GFSK
• Low Output Power 0dBm or 1mw
• Low Range around 10-300 feet

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Sensors

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

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Applications

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

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IEEE 802.15.4

• Part of the 802.15 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

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IEEE 802.15.4 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

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IEEE 802.15.4 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

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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)

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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

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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

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Wireless Technology Comparison
Standard Bandwidth Power Consumption Protocol Stack Size Stronghold
Wi-Fi Up to 54Mbps 400mA TX Sleep 20mA 100KB High Data Rate
Bluetooth 1Mbps 40mA TX Sleep .2mA 100KB Interoperability Cable Replacement
Zigbee 250kbps 30mA TX Sleep .003mA 32KB Long Battery Life, Low cost
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Demos
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Questions?