smart dust --- hardware for wireless sensor networks
DESCRIPTION
I gave this talk as part of a seminar on Massively Distributed Systems at the Distributed Systems Group, Chair of Computer Science IV of RWTH Aachen University.TRANSCRIPT
Distributed Systems Group
Chair of Computer Science IV
RWTH Aachen University
http://ds.cs.rwth-aachen.de
1
Martin Jansen
Smart Dust
Hardware forWireless Sensor Networks
2
Agenda
1. Introduction1.1. Use Cases1.2. Requirements1.3. Hierarchies
2. Hardware implementations2.1. Intel Mote2.2. Telos2.3. eXtreme Scale Mote
3. Summary
1. Introduction
• Wireless Sensor Networks are also called „Smart Dust“
• „[N]etworks of interconnected computing devices deeply embedded into the physical environment (...) providing detailed instrumentation of many points over large spaces, both natural and artificial.“
• The nodes of a sensor network are called Motes.
3
1.1 Use Cases: Environmental monitoring
• Outdoor deployments
• Situated in hostile environments and remote areas• Mountain regions• Sea• Primeval forests• Antarctica• Sahara
• Measuring e.g. temperature or humidity
• Monitoring animals
4
1.1 Use Cases: Surveillance
• Important topic these days
• Different targets for surveillance:• Monitoring cars on roads to avoid recurring traffic
jams
• Monitoring people• Airports, train stations
• Stadiums
• Public places
• Battle fields
• Recognising motion
• Taking images
• Recording voice
5
1.1 Use Cases: Industrial Monitoring
• Monitoring complex or expensive equipment• Detect upcoming machine failures• Harvest performance data• Tell engineers when maintenance is necessary
• Deployments spread across huge facilities like refineries or nuclear power plants
• Motes situated indoor and outdoor
• Measuring• Vibration• Temperature• Water level• Pressure• ...
6
1.2 Requirements
Based on these use cases, requirements can be deduced:
7
1.2 Requirements
Based on these use cases, requirements can be deduced:
• Energy Efficiency• Long lifetime is important in all use cases• Replacing batteries usually
• too expensive or time-consuming• not possible at all
• Strategy for saving energy:• Keeping motes in sleep phase for most of their
lifetime• Waking them up regularly in order to collect data
• Not applicable in all cases
7
1.2 Requirements
• Pricing• Deployments can become huge:
• Thousands of motes on a battlefield• Thousands of motes monitoring complex factories• Hundreds of thousands of motes embedded into
a brigde‘s concrete during construction
• Thus motes must be cheap• Price drops when demand rises
8
1.2 Requirements
• Physical Robustness• Especially important in outdoor deployments• Protection against vandalism• Protection against the environment
• Heat• Low temperature
• Precipitation• Humidity
• „Camouflage“• Unobtrusive colours
• Avoid sun reflection
9
1.2 Requirements
• Upgrading-Robustness• Reprogramming manually not desirable
• Motes support being upgraded wirelessly• Faulty upgrades may render motes unusable
• Resetting manually not desirable• Demand for autonomous reset system
• When upgrade failed, reset the mote to a known-good software revision
• This revision is stored in a write-protected storage on the mote
• Saves time in research & experimentation
10
1.2 Requirements
• Size• Motes need to be small and unobtrusive• Battery size needs to be considered• External antennas increase size but also increase networking range
11
1.2 Requirements
• Networking• On the one hand: High transfer rates and good ranges are required• On the other hand: Energy is scarce
• Trade-off between high-traffic and energy-efficiency needed
• Capability of routing around failed nodes
• Possible technologies:• Radio (low bandwidth, little energy)• Bluetooth (higher bandwidth, more energy)
• Wireless LAN (high bandwidth, a lot of energy)
12
1.3 Hierarchies (Type 1)
Depending on its performance data, a mote belongs to one of the following categories:
13
1.3 Hierarchies (Type 1)
Depending on its performance data, a mote belongs to one of the following categories:
• Specialised Sensing Platforms• Single-chip solution• Support only simple sensors• Small network ranges, max. 50 Kb/s• Very little storage < 10 KB
13
1.3 Hierarchies (Type 1)
Depending on its performance data, a mote belongs to one of the following categories:
• Specialised Sensing Platforms• Single-chip solution• Support only simple sensors• Small network ranges, max. 50 Kb/s• Very little storage < 10 KB
• Generic Sensing Platforms• Constructed with off-the-shelf components• Often support sensing and being proxy for specialised sensing motes• Maximum bandwidth of 100 Kb/s• Up to 0.5 MB of storage
13
1.3 Hierarchies (Type 1)
• High-bandwidth Sensing Platforms• High-bandwidth sensor interfaces• Suitable for video or audio sensors• Increased CPU power, more memory (permanent and volatile)• High-bandwidth networking, e.g. using Bluetooth
14
1.3 Hierarchies (Type 1)
• High-bandwidth Sensing Platforms• High-bandwidth sensor interfaces• Suitable for video or audio sensors• Increased CPU power, more memory (permanent and volatile)• High-bandwidth networking, e.g. using Bluetooth
• Gateway Platforms• Collect and store data from other motes• Make the data accessible from the outside
• Database interfaces• Web-based interfaces
• Several MB of RAM• Fast networking, e.g. IEEE 802.11 WLAN
14
1.3 Hierarchies (Type 2)
Motes can also be categorised based on how they work:
15
1.3 Hierarchies (Type 2)
Motes can also be categorised based on how they work:
(A) Data collection• Wake up shortly to collect and transmit sensor data
• Remain in sleep phase the rest of the time
15
1.3 Hierarchies (Type 2)
Motes can also be categorised based on how they work:
(A) Data collection• Wake up shortly to collect and transmit sensor data
• Remain in sleep phase the rest of the time
(B) Event detection• Monitoring their surroundings for random and ephemeral events all the
time
• Wake up/Sleep procedure not applicable
• Motes can be shut down only partially while monitoring for events
15
2.1: Intel Mote
• Developed by Intel Research
• High-bandwidth sensing mote
• Size: 3x3 cm
• Four D-cell batteries
• Bluetooth networking, max. 2.1 Mbit/s
• Scatternet functionality coming with Bluetooth
• Lifetime:
16
Sleep duration Network connected Network disconnected
1 hour 2 months 2-3 months
12 hours 3 months 10-12 months
24 hours 3-4 months 12-14 months
1 week 4 months 15 months
1 month 4 months 15-16 months
2.2 Telos
• Developed by UC Berkeley
• Dimensions: 8x3.2 cm (plus batteries)
• Power supply• via two AA batteries• via USB
• Lifetime: 3 years with 1% activity time
• Wideband radio, max. 250 Kb/s
17
2.2 Telos
• Sophisticated radio interface:• Encryption of data before sending
• Authentication
• Auto-acknowledgement• Packets not addressed to the mote are not passed to the OS
• Wideband was chosen because it is more stable
• Narrowband radio consumes less energy
18
2.2 Telos
• Upgrading-Robustness through watchdog timer• Part of the microcontroller• Independent of the operating system• Resets mote if pulse signals stay away• Golden image stored in write-protected flash storage
19
2.2 Telos
• Upgrading-Robustness through watchdog timer• Part of the microcontroller• Independent of the operating system• Resets mote if pulse signals stay away• Golden image stored in write-protected flash storage
• Available for $130
19
2.3 eXtreme Scale Mote
• Developed as part of the ExScal project• 10,000 nodes spread over 10 km2
• Lifetime of 1,000 hours• Detect objects and classify them as civilians,
soldiers, and vehicles
• Event detection mote, generic sensing platform
• Dimensions: 8.89 x 8.89 x 6.35 cm
• Two AA batteries
• Narrowband radio, max. 76.8 Kb/s
20
2.3 eXtreme Scale Mote
• Event detection with three sensors:• Infrared sensor → warmth• Acoustic sensor → noise• Magnetic sensor → metal
21
2.3 eXtreme Scale Mote
• Event detection with three sensors:• Infrared sensor → warmth• Acoustic sensor → noise• Magnetic sensor → metal
• Classification:• vehicle = infrared ∧ acoustic ∧ magnetic
• soldier = infrared ∧ ¬acoustic ∧ magnetic
• civilians = infrared ∧ ¬acoustic ∧ ¬magnetic
21
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network• Comparable to people‘s behaviour when sleeping
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network• Comparable to people‘s behaviour when sleeping
• Infrared sensor is necessary for all three targetclasses. Keep it active all the time.
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network• Comparable to people‘s behaviour when sleeping
• Infrared sensor is necessary for all three targetclasses. Keep it active all the time.
• Launch other sensors if the infrared sensortriggers.
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network• Comparable to people‘s behaviour when sleeping
• Infrared sensor is necessary for all three targetclasses. Keep it active all the time.
• Launch other sensors if the infrared sensortriggers.
• Collect data, process it and activate radio.Transmit data and „doze“.
22
2.3 eXtreme Scale Mote
• Energy saving is a problem because the mote cannot be powered down completely.
• Solution: Chained trigger network• Comparable to people‘s behaviour when sleeping
• Infrared sensor is necessary for all three targetclasses. Keep it active all the time.
• Launch other sensors if the infrared sensortriggers.
• Collect data, process it and activate radio.Transmit data and „doze“.
• Lifetime: 1,000 hours at 6 events/hour
22
2.3 eXtreme Scale Mote
• Physical robustness through solid enclosure• Primary field of application: battle field
23
2.3 eXtreme Scale Mote
• Physical robustness through solid enclosure• Primary field of application: battle field
• Upgrading-Robustness through grenade timer• Resets the mote regularly
• Even if functioning properly
• Mote are never defunct longer than the timer interval
• More solid than a watchdog timer
• However: Unnecessary resets
23
3. Summary
• Requirements: energy-economical, cheap, robust, small
• 4 classes
• 2 modus operandi• Data collection• Event detection
• 3 motes• Intel Mote• Telos• eXtreme Scale Mote
24
The End.
• Questions?
25
The End.
• Questions?
• Thank you!
25
The End.
• Questions?
• Thank you!
• Some images were taken from Flickr.com and require attribution:
• http://flickr.com/photos/halloweenjack/47269493/• http://flickr.com/photos/vanityfailed/325592829/ • http://flickr.com/photos/78169939@N00/229466536/, • http://flickr.com/photos/chrischris/119272930/• http://www.flickr.com/photos/a_mason/27659607/• http://www.flickr.com/photos/ftf/43813301/• http://www.flickr.com/photos/mrflip/36854420/• http://www.flickr.com/photos/illogicnet/111537408/
25