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