Wireless Sensor Networks for Use in Aircraft Systems ... · Wireless Sensor Networks for Use in...
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Wireless Sensor Networks for Use in Aircraft Systems Monitoring Michael Sessinghaus [email protected]
Transcript of Wireless Sensor Networks for Use in Aircraft Systems ... · Wireless Sensor Networks for Use in...
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Motivation – 6000 Measurement Points
VibrationVibration StrainStrainStructureStructure
AcousticWaves
AcousticWaves
Temp
WingWing
Humidity
Vibration
TempTempVibrationVibration
EngineEngine
PressurePressure
TempTemp
LandingGear
HumidityHumidityTempTemp Control
System
On-groundTemporary Inspections
No Safety-critical
WirelessData Acquisition
Battery-operateddevices
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Content
Data Acquisition Technology
Wireless Sensor Networks
Wireless Standards – Low Power Communication
Case Study: Wireless Temperature Data Acquisition
Application Performance
Real-time Data Visualization
Summary
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Data Acquisition Technology
Wired based Data AcquisitionComplex & time-consuming installationsStatic configuration (no reusability)Very large data sets & measurement pointsLong time measurement campaigns
-> Trend: Ethernet standard
Wireless based Data AcquisitionNo device wiring (only data sink)Faster installations & flexible configurationsSmall data sets & measurement points
Short time measurement campaigns
-> Wireless Sensor Networks
Wiring Harness & Routing
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Wireless Sensor Networks
Smart sensor/actuator with wireless communication capability
Trend goes to System-in-Package (SiP) or System-on-Chip (SoC) on a silicon
Very small size & low weight
Limited operation due to battery supply
Ability to operate under harsh environmentsReliable & robust communication profileUse for low-power and low-data rate applications
Memory
Controller Sensor(s)/actuator(s)
Transceiverdevice
Power supply
Silicon
Main Sensor Node Components
Sensor Node in SiP Layout
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Wireless Communication Standards
Range ~ transmission power ∧ path loss ∧ receiver sensitivity
Data Rate ~ bandwidth ∧ modulation ∧coding ∧ noisy channel
Battery Lifetime ~ transmission power ∧ duty cycle
Wireless standard available worldwide -> Low-power ZigBee (IEEE 802.15.4)
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ZigBee (IEEE 802.15.4)
Designed for energy-efficient wireless control and sensor monitoring applications
Data rate of up to 250kbps@2MHz bandwidth/channel
Network topology & routingReliable data transfer (by acknowledgments) Medium Access Control (MAC): CSMA-CA and GTSPhysical (PHY): Modulation (e.g. OQPSK), Direct
Sequenced Spread Spectrum (DSSS)
16 channels in the license-free 2.4GHz (worldwide), 10 channels in the 915MHz and one channel in the European 868MHz band
Customer
IEEE 802.15.4
ZigBeeAlliance
Application
NetworkStar / Mesh / Cluster-Tree
MACCSMA-CA / GTS
PHY868 / 915 MHz / 2.4GHz
Security32 / 64 / 128bit encryption
APIConnection Manager
StackSilicon App
Communication Layers
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Low-power Wireless Transceiver
Transceiver is primary source of energy consumption compared to microcontroller tasks -> Low duty cycle
Energy efficient operation: Send fast (high data rate) and go immediately to sleep (inactive mode)
Low-power transceivers based on IEEE 802.15.4 specification in 2.4GHz band
Texas Instruments CC2520 (active 30mA@(3dBm, 250kbps), inactive: 1µA)Atmel AT86RF231 (active 14mA@(3dBm, 250kbps), inactive: 0.02µA)
high
very low
active
PowerConsumption
inactive Time
Transceiver’s duty cycle
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Case Study
Point-to-point connectionsDistributed access via CSMA-CA, non-beacon modeTemperature data: sample 16bit@TX interval 0.5-2sSystem parameters
Transceiver: +3dBm@14mA , -101 dBm RX sensitivityData rate of [email protected] and 1% packet error rate (channel quality)Battery capacity of 1200mAh
Star Network Setup for Case Study – Wireless Temperature Data Acquisition
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Communication Performance
IEEE802.15.4 CSMA-CAChannel idle -> transmitChannel busy -> wait for a random
period (backoff)
Max. data payload can be 114bytes (MAC) + 6bytes (PHY) overhead
Data rate (bandwidth) is 250kbps
Error-control via acknowledgement 11bytes
TX/RX transceiver switching
Channel access time = 2.368ms
Data frame transfer time = 4.256ms
ACK transfer time = 0.352ms
Turnaround time = 192µs
With a max. data payload of 114*8bits / 7.168ms = 127kbps
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Application Performance
Max. 127kbps achievable data rate per channel
~30 nodes can be supported with max. achievable data rate by
one network /channel
Maintenance-free battery interval varies btw 6.6 and
0.8months
Medium AccessControl ?
+3dBm (2mW) transmit power with 14mA TX, data rate 250kbps, data packet size of 36bytes (4bytes sensor data + 32 protocol overhead), fully-charged battery of 1200mAh
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Technical Challenge – Node Scalability?
IEEE 802.15.4 defines a hybrid schemeCarrier Sense Multiple Access – Collision Avoidance (CSMA-CA):
Distributed access without coordination and synchronization (non-beacon) -> data collisions and no latency-bounded -> node scalability (~30 nodes per network/channel)
Guaranteed Time Slots (GTS): Coordinated time slotting with a superframe and synchronization (beacons) -> no data collisions, latency-bounded but large protocol overhead -> node scalability
Support more nodes requires MAC adaptation-> Pure GTS scheme with larger superframe structure / #slots shall be provided with a minimum of protocol overhead
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Real-time Sensor Data Visualization
Tree view shows deployed nodes
Graphical view
sensor data time series
Auto-configuration (temp. limits, sensor rate)
logs of events (time, warning
messages)Network status
(connected nodes)
numeric view of sensor data,
battery status, signal quality
temperature data (node, time stamp)
Measurement campaign
report
Measurement data report / export files
Graphical sensor data
output View
selection
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Summary
Data acquisition via Wireless Sensor Networks promises No wiring anymore thanks to the use of battery-operated devices with
large maintenance-free intervalsEasier installations & flexible reconfiguration for temporary
measurement campaigns
Application PerformanceAppropriate for low data rate applications and moderate network
dimensionsSupport larger number of nodes requires GTS adaptation
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