Forum RF & Wireless – Milano 14/2/2008
Wireless sensors networking:
lo stato dell’arte e i servizi
disponibili
Davide Dardari
WiLab - University of Bologna at Cesena
email: [email protected]
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Wireless Ages…
Past – Group Communications
One wireless communication device per thousands of persons.
Present – Personal Communications
One wireless communication device per person.
Future – Ambient Communications
Every person using thousands wireless communication devices.
The surrounding environment
communicates…
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
The vision: “Internet of Things”
Wireless sensor networks are spatially distributed networks of small devices
with sensing (also actuators) and communication (wireless) capabilities
Key technology to “map” the physical world into the internet space
A potentially huge number of possible applications
Internet
Long-range link
short-range link
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Main application areas
Environment & Habitat
Monitoring
Industrial Sensing
Traffic Control
Seismic Studies
Life Sciences
Infrastructure security
Health
Animal tracking
Planets exploration
Military
Circulatory Net
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Main requirements
Short-range (WSN)
Energy efficiency (lifetime)
Reliability (e.g., interference)
Security
Interoperability (standards?)
………….
Long-range
Data rate
Traffic cost (billing)
………..
Internet
Long-range link
short-range link
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
WSN typical characteristics
random deployment  no a priori topology knowledge - localization
long network lifetime (years)  energy efficiency – distributed proc.
self-organization  no centralized control - no human intervention
large number  scalability - low cost
Information coverage & reliability  connectivity - node density
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Wireless technologies
Short-range
Zigbee (IEEE802.15.4)
RFID
Bluetooth (IEEE802.15.1)
Wibree
UWB (IEEE802.15.4a)
WLAN (IEEE802.11..)
Z-Wave
Ad hoc solutions
short-range link
……………
Long-range
GSM/GPRS/EDGE
UMTS/HSDPA
WiMax (IEEE802.16)
……………
higher speed
Internet
Long-range
link
Main issue: technologies choice and their integration
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Short-range wireless technologies
Wi-Fi
(IEEE 802.11
Bluetooth
ZigBee
(IEEE 802.15.4)
ZigBee
(UWB - IEEE
802.15.4a)
Applications
WLAN (Web,
Email, video)
WPAN (Cable
replacement)
(WPAN/WSN)
Monitoring &
control
(WPAN/WSN)
Monitoring,
control,
localization
Battery life
Hours
Days
Years
Years
Enumeration
latency
Up to 3 sec
Up to 10 sec
30ms
30ms
Network size
10-30
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Up to 65536
Up to 65536
Bit rate
54Mbit/s
1-3Mbit/s
250Kbit/s
850Kbit/s27Mbit/s
Range (meters)
 100
 10
 50-100
 50-100
Network
architecture
Star
Star
Star, Tree, Mesh
Star, Tree, Mesh
Optimized for
Speed
Low cost
Low power,
reliability, low
cost, scalability
Low power,
reliability, low
cost, scalability,
ranging
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Application typical requirements example
Environmental monitoring
Energy efficiency
Low duty cycle (network
synchronization)
Low data rate
One-way communication
Wireless backbone
Industrial
Reliability (e.g., interference)
Security
Interoperability (standards)
High data rate
Two-way communication (actuators)
Wired backbone
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Some advanced topics for WSNs (1/2)
Protocol domain
Secure communication using RF channel reciprocity
Secret key generation and sharing using channel reciprocity
Enhanced security (cryptography)
Network coding
Distributed source coding (reduced network communications)
Distributed error correction to mitigate malicious errors injection
and node failures
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Example: sail surface monitoring
Mainsail
sensor nodes
over the sail
shift pressure over
the sail section
Sensed data are time-spatially correlated
Redundancy can be reduced through distributed source coding
Pressure sensor
Reduced network throughput  longer lifetime
Sortron - Senet s.r.l – Wireless Sensor Network Solutions (www.senet.it)
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Some advanced topics for WSNs (2/2)
Technology domain
Energy scavenging
solar power, thermal energy, wind energy, salinity gradients,
kinetic energy, RF sources
Ultrawide bandwidth (UWB)
Higher data rate
Robustess to interference
High ranging accuracy (centimeters)  localization
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
More on the UWB technology
UWB signal is formally
defined as any signal that:
• occupies more than 500 MHz
of spectrum
• or has a fractional bandwidth
in excess of 20%
fH fL
BF
0.2
(f H f L ) / 2
• Feb 14, 2002 FCC adopted the First Report and Order (RO) that
permits the marketing and operation of certain types of UWB products
Full report released Apr 22, 2002
• Feb 21, 2007 EU commission released the “commission decision” on
the implementation of an UWB radio regulatory framework for the EU
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Comparison between FCC and EU masks
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Main advantages of the UWB technology
•High temporal resolution (localization, multipath)
•High material penetration (according to the band used)
•Underlay technology (efficient spectrum usage)
•Multiple access
•Low probability of detection (LPD)
Narrowband (30kHz)
Wideband CDMA (5 MHz)
Part 15 Limit
UWB (several GHz)
Frequency
Adopted in the IEEE 802.15.4a standard (2007) for WPANs and WSNs
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
UWB-based standards
WiMedia (ex IEEE 802.15.3a)
• d ≤10 m, data-rate larger than 100Mbit/s
• Applications: Wireless Video Projection, Image
Transfer, High-speed Cable Replacement
(Wireless USB)
IEEE802.15.4a (2007)
• d=10-50m, data-rate 850-27Mbit/s, low energy
consumption
• Applications: WPANs and WSNs
• Ranging capability (precision<1m)
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
New services
context aware applications
(e.g., real-time location systems, RTLS)
new market opportunities ($6 Billion in 2017*)
* R. Das and P. Harrop "RFID Forecast, Players and Opportunities 2007-2017", 2007, http://www.idtechex.com.
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Some examples of new localization-enabled services
• inventory/people tracking (RFID)
• surveillance/security
• virtual immersive and augmented reality applications
Virtual Guide
Service Avatar
Travel Info
Distance
Speed
Time to go
MAP
R3
R4
R2
R1
[VICOM Project
www.vicom-project.com]
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
In Wireless Sensor Networks ……
Sensed data without position and time information is often meaningless
For example, in habitat environments monitored sensed events must
be ordered both in time and space to permit a correct interpretation.
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
In addition…
In many schemes proper time synchronization is required to
achieve high ranging accuracies in positioning techniques
Positioning and time synchronization are also essential for basic
mechanisms composing the network to work efficiently:
•MAC scheduling algorithms can reduce packet collisions
•power-saving strategies (wake-up sleeping times)
•networking protocols to improve performance of routing algorithms
(geo-routing)
•enabling interference avoidance techniques in future cognitive
radios
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Example of UWB-based localization platform
N = 5 fixed UWB beacons (tx1-5) was
deployed to localize one or more UWB
targets.
Each ranging device, placed 88 cm
above the ground, consisted of one UWB
radio operating in the 3.2-7.4 GHz 10dB
RF bandwidth.
These commercial radios are equipped
to perform ranging by estimating the ToA
of the first path
A grid of 20 possible target positions
(numbered 1-20) defined the points from
which range (distance) measurements
were taken at 76 cm height. For each
target position, 1, 500 range
measurements were collected from each
beacon.
The measurement environment at the WiLAB, University of Bologna.
Work done in cooperation with the W-Group of the Massachusetts
Institute of Technology (MIT), USA
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
Position estimation root mean square error
RMSE as a function of target position in the absence and presence of priori
information (i.e. with bias and after removing bias, respectively). N = 5
beacons are considered.
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Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
In conclusion…
No ‘one size fits all’, it depends on the application
Integration of heterogeneous wireless technologies
New applications  new markets
Heterogeneous expertise required
TLC
Electronic
-Sensors
-Embedded sys.
-Low-power devices
ICT
-Signal processing
-Transmission techniques
- ad-hoc networks
-…………..
Computer Science
- agents
- distributed systems
-…………
….but also in
Biology
Geology
Biochemistry
Structural Engineering
Environmental Engineering
…………
Forum RF & Wireless – Milano 14/2/2008
Davide Dardari
For further information…………
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