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?