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Transcript Embedded System Design
Wireless Sensors and
Wireless Sensor
Networks (WSN)
Darrell Curry
Overview
Advantages of Wireless Sensors
Typical Wireless Sensor Hardware
Applications
IEEE 802.15.4
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 10-300 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 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
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
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
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
Standard
Bandwidth
Power
Consumption
Protocol
Stronghold
Stack Size
Wi-Fi
Up to
54Mbps
400+mA TX
Sleep 20mA
100+KB
High Data Rate
Bluetooth
1Mbps
40mA TX
Sleep .2mA
100+KB
Interoperability
Cable
Replacement
Zigbee
250kbps
30mA TX
32KB
Sleep .003mA
Long Battery
Life, Low cost
Demos
Questions?