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Introduction to Sensor Network
2007. 10
Deokjai Choi
Lecture Outline
• 1st Week: (Introduction: 75 minutes)• Brief History and Overview of Wireless Sensor Network• Technology Trends, Application Classes• Critical Issues and factors (memory constraints, power, uncertainty and loss)• Physical Layer Concepts
• 2nd week: MAC Protocols• MAC in wireless networks• Fairness Issue at the MAC layer• Energy Efficient MAC Protocols• Rate Control and Power Control at MAC layer• Priority Scheduling•
• 3rd week: Routing Protocols• Address assignment for sensor network• Routing in Ad Hoc Networks• Routing in Sensor Networks
7/9/2007 AIIT Summer Course - M1 - Intro 3
This Lecture’s Outline
• Overview of Wireless Sensor Networks
– Technology Enablers
– Application Opportunities
– Systems Challenge
• Introductions
• Ubiquitous Networks => Integration Real World Information
Overview of WSN
• Technology Enabler– Moore’s Law: Microprocessor (18 month)
– Bell’s Law: New System emerges (10yrs)
– Hwang’s Law: Memory (12 month)
– Wireless Communications (WAN, LAN, PAN, BAN)
– Networking: IPv6
• Applications
• Challenges
7/9/2007 AIIT Summer Course - M1 - Intro 5
Broad Technology Trends
Today: 1 million transistors per $
Moore’s Law: # transistors on cost-effective chip doubles every 18 months
Mote!years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
Workstation
PC
Cell
1:1
1:103
Bell’s Law: a new computer class emerges every 10 years
Same fabrication technology provides CMOS radios for communication and micro-sensors
Explosion of New Internet Appliances
IPv6 Coming
Much larger address space
IPv6 Addresses: 3.4X1038
Improved routing Route aggregation reduces the size of routing tablesSimplified header reduces router processing loads
Enhanced security and QoS Mandatory IPsec support all fully IPv6 compliant devices
Improved support for mobile IP and mobile computing devices
IP is everywhere
Data, Voice, Audio and Video integration is a Reality
IPv4 uses 32-bit (4-byte) addresses, which limits the address space to 4,294,967,296 (4.3x109)possible unique addresses.
7/9/2007 AIIT Summer Course - M1 - Intro 8
Enabling Technology
Microcontroller RadioCommunication
FlashStorage
Sensors
IEEE 802.15.4
Network
7/9/2007 AIIT Summer Course - M1 - Intro 9
Enabling Technology
PhysicalWorld
7/9/2007 AIIT Summer Course - M1 - Intro 10
Facts about components
• Microcontrollers: – 1-10 mW active, 1 uW passive => 10-100 uW average
• Micro-sensors (MEMS, Materials, Circuits)– acceleration, vibration, gyroscope, tilt, magnetic, heat, motion,
pressure, temp, light, moisture, humidity, barometric
– chemical (CO, CO2, radon), biological, microradar, ...
– actuators too (mirrors, motors, smart surfaces, micro-robots)
• Micro-Radios– CMOS, short range (10 m), low bit-rate (200 kbps), 10 mW
• Micro-Power– Batteries: 1,000 mW*s/mm3, fuel cells
– solar (10 mW/cm2, 0.1 mW indoors), vibration (~uW/gm), flow
• 1 cm3 battery => 1 year at 1 msgs/sec
7/9/2007 AIIT Summer Course - M1 - Intro 11
WSN Applications
• Monitoring Spaces– Env. Monitoring, Conservation biology, ...– Precision agriculture, – built environment comfort & efficiency ... – alarms, security, surveillance, EPA, OSHA, treaty verification …
• Monitoring Things– automated meter reading – condition-based maintenance– disaster management– Civil infrastructure
• Interactions of Space and Things– manufacturing, asset tracking, fleet & franchise– context aware computing, non-verbal communication– Assistance - home/elder care
• Action and control– Optimizing processes– Automation
7/9/2007 AIIT Summer Course - M1 - Intro 12
Early Industrial Examples
Temperature and Energy Monitoring
AMI – NURI Telecom & SK Telecom :
7/9/2007AIIT Summer Course - M1 - Intro 13
Example: A Month in the Life of a Redwood Tree
• Time: 1 month• Period: 5 minutes• Height: 15m to 70m• Angle: west side• Radius: 10-100cm• Count: 33 nodes/tree
– 155 sensors
• Spacing: ~2m
7/9/2007 AIIT Summer Course - M1 - Intro 14
(Mariscal et al. 2004)
The Result: Spatial Gradients over time
Macroscope in the Redwoods, Tolle et all, ACM SENSYS 2005
7/9/2007 AIIT Summer Course - M1 - Intro 15
The Internet today
7/9/2007 AIIT Summer Course - M1 - Intro 16
The Real Internet ahead
0 2 4 6 8 10 12 14 16 18
-1
-0.5
0
0.5
1
Low resolution Sensor, Test4, Increasing frequency
Time (sec)
Accele
ration (
g)
7/9/2007AIIT Summer Course - M1 - Intro 17
Why “Real” Information is so Important?
Improve Productivity
Protect HealthHigh-Confidence Transport
Enhance Safety & Security
Improve Food & H20
Save Resources
Preventing Failures
IncreaseComfort
Enable New Knowledge
7/9/2007 AIIT Summer Course - M1 - Intro 18
The Web Today
Shopping
Weather
Science
Technology
Financial NEWS
Maps
Sports
Integrates the World’s Human Generated Information
7/9/2007 AIIT Summer Course - M1 - Intro 19
Most Real World Information goes “down the drain”
Wate
r Usa
ge, Te
mp.,
Qualit
y
Secu
rity
and A
ccess
Control
Gas
and E
lect
ric
Usa
ge
Heating, AC, and V
entila
tion
Sm
oke
, Fi
re, CO
, Radon
Sm
art
Applia
nce
s
Dig
ital H
ealth D
evi
ces
Baby
Monitor
(Eld
er
care
)
Ente
rtain
ment Sys
tem
Vid
eo G
am
e C
onso
les
Clo
cks
and C
ale
ndars
Exe
rcise U
nits
7/9/2007 AIIT Summer Course - M1 - Intro 20
Physical Information Streams
• Sensors are everywhere– But the data is mostly dropped on the floor
• Physical => Digital => Information
• Each sensor becomes a network citizen
0 2 4 6 8 10 12 14 16 18
-1
-0.5
0
0.5
1
Low resolution Sensor, Test4, Increasing frequency
Time (sec)
Accele
ration (
g)
010010001…
<value>temp=35
<\value>
7/9/2007 AIIT Summer Course - M1 - Intro 22
Our goal: Ubiquitous Real Internet
802.15.4
<value>source=librarytime=12:31temp=25.1
<\value>
0 2 4 6 8 10 12 14 16 18
-1
-0.5
0
0.5
1
Low resolution Sensor, Test4, Increasing frequency
Time (sec)
Accele
ration (
g)
Physical Signal
Wireless Packets
11 010010001Sampled Value010010001int temp;
<request service>
ServiceDescription
< get temp …
set sample_rate
set alarm … >
Web Services www.weather.com
XML information
<value>source=librarytime=12:53temp=26.7
<\value>
11 010110111
7/9/2007 AIIT Summer Course - M1 - Intro 23
Technology Push / Application
PullMonitoring & Managing Spaces and Things
technology
MEMSsensing
Power
Comm. uRobotsactuate
Miniature, low-power connections to the physical world
Proc
Store
7/9/2007 AIIT Summer Course - M1 - Intro 24
Technology Push / Application
Pull
applications
Monitoring & Managing Spaces and Things
technology
MEMSsensing
Power
Comm. uRobotsactuate
Miniature, low-power connections to the physical world
Proc
Store
7/9/2007 AIIT Summer Course - M1 - Intro 25
Battery
Shielding skirt
O-rings
Top endcap
Cylindrical enclosure
Bottom endcap
Top Sensing Surface(incident PAR and TSR)
Bottom Sensing Surface(temperature, humidity,barometric pressurereflected PAR and TSR)
mote
The Node
The Complete Solution
DBMS(PostgreSQL)
TinyDB Sensor Network
TASK Gateway
GPRSModem
The Infrastructure
SELECT
result_time, epoch, nodeid,
parent, voltage, depth,
humidity, humid_temp, hamatop,
hamabot
FROM sensors
SAMPLE PERIOD 5 min
The Program
wake1.3%
sample
log send
forward
sleep98.7%
The Behavior
7/9/2007 AIIT Summer Course - M1 - Intro 26
NIMS RD Merced and San Joaquin River Confluence(Harmon, Kaiser, et al)
confluence
nitrate distribution
San Joaquin R.
Merced R.
mixing zone
gaging station
river bedmap
Sonar-based bathymetry (depth)
7/9/2007 AIIT Summer Course - M1 - Intro 27
Environmental Monitoring Characteristics
• Large number of nodes spread over physical space of interest
• Low sample rate (of multiple sensor modes)– Further reduced by node signal processing and compression
• Reliable dissemination of configuration, command, or query
• Low-rate scalar data collection– Many options for reliability, Predictable reporting delays
• Low duty cycle for long lifetime
• Energy availability is application specific
• Extension to event detection and triggering demands more responsive protocols
• Extension to control requires predictable outward routing
7/9/2007AIIT Summer Course - M1 - Intro 28
Intel Fab & BP Machine Monitoring
• Goal: Pre-empt equipment failures through non-destructive analysis
• Media Gap: Majority of data is collected by hand– Thousands of sense points
• Intel Fab and an Oil Tanker engine room• Wireless vibration data collection
– High-speed sampling, reliable bulk transfer– Sensor-to-Analysis App flow– Overcome interference– Support disconnected operation
• Loch Rannoch Network– 150 accelerometers– 26 motes– 4 stargates– 1 PC
• Efficient installation and management– 36hr install period on tanker– No crew intervention
Intranet
802.11
Backbone
Cluster Head
Root
Stargate
Enterprise
Server
Sensor
Clusters
Stargate Gateway
Bridge
Stargate
Intranet
802.11
Backbone
Cluster Head
Root
Stargate
Enterprise
Server
Sensor
Clusters
Stargate Gateway
Bridge
Stargate
7/9/2007 AIIT Summer Course - M1 - Intro 29
GGB Structural Monitoring
Base Station
Berkeley SF Bay
mid-spanquarter-span
59260ft
16ft27 1
1310 38 41211
14
L3L5 L1L4 L2
50 51 52 53 54 55 56 57 58 59 60-15
-10
-5
0
5
10
15
Time (sec)
Acc
ele
ration (m
g)
V2V4V13V7V9
-0.99
0.19-0.73
1.000.74
Frequency: 1.41 Hz
Damping Ratio: 2%
7/9/2007 AIIT Summer Course - M1 - Intro 30
Machine Monitoring Characteristics
• Nodes clustered on specific equipment• High sample rate (over short bursts)
– Substantial local signal processing• Control and management is like Env.
Monitoring• Data collection in single-point streams
– Reliable end-to-end transport• Shallow networks in practice
• Well understood– but not yet well supported
• Energy availability is site specific• Natural extensions for local access (inspector)• Structural monitoring is much harder than CBM
– Time coordinated samples, cross-node data analysis
• Environmental factors critical to sensing accuracy
7/9/2007AIIT Summer Course - M1 - Intro 31
Medical Monitoring
Wireless module
7/9/2007 AIIT Summer Course - M1 - Intro 32
Large-Scale Security and Tracking
• 557 nodes over several km
• Self-powered, self-maintaining
• 2 person-day deployment
• OTA programming and management infrastructure
Solar Cell
Buzzer
Passive IR x4
User / Reset
USB Port
Microphone
Magnetometer
7/9/2007AIIT Summer Course - M1 - Intro 33
Example Tiers
telos-USB
telos
USB-WiFi
WiFi repeater
WiFi AP
Root Server
trio
557 node DARPA NEST Aug 05
UCB Trio node
802.15.4 – 802.11 gateway
Transit Network(IP or not)
Access point- Base station- Proxy
Sensor PatchPatch Network
Data Service
Intranet/Internet (IP)
Client Data Browsingand Processing
Sensor Node
Gateway
Other information sources
Sensor Node
7/9/2007 AIIT Summer Course - M1 - Intro 34
Sensing => Understanding
Plus UAV exfiltration, distributed tracking
Wireless PIR readings
7/9/2007 AIIT Summer Course - M1 - Intro 35
Transit Network(IP or not)
Access point- Base station- Proxy
Sensor Patch
Patch Network
Data Service
Intranet/Internet (IP)
Client Data Browsingand Processing
Sensor Node
GatewayGateway
Verification links
Other information sources
Sensor Node
Canonical SensorNet Network Architecture
7/9/2007 AIIT Summer Course - M1 - Intro 36
Proximity, Tracking, Compliance
Industrial:Asset mgmt
CBMProcess controlEnergy mgmtenvironmental
MedicalAgriculture
HLS…
Home:LightingHVACaccess
Prox. Tracking Shipping QoS:Vibration threshold
Temperature/humidity threshold
Safety:Chemical-to-chemical
safety alertsHuman-to-chemical
safety alerts
Building:SecurityHVACAMR
LightingAccess control
“The information about the package is as valuable as the delivery of the package itself.”
-Fred SmithCEO, FedEx
Current Conditions:
In Motion, No Magnetic Fields, 67°
• Humidity Range: 30-35%
• Temp. Range: 55 ° - 78 °
7/9/2007 AIIT Summer Course - M1 - Intro 37
Interaction Monitoring Characteristics
• Many different forms of monitoring– Untagged vs tagged items
• Mobility is central– Mobile nodes moving through stationary
networks– Networks moving through networks– Proximity detection and action
• Wide range of communication patterns– Mobile-mobile routing
• Adaptive protocols• Sophisticated routing• Reliability through custody transfer• Deep interactions with IT infrastructure
7/9/2007 AIIT Summer Course - M1 - Intro 38
Example: Petroleum Industry
Condition-based Maintenance
Safety
workers
storage
process
Pipelines
integrity
security
Tracking
tank
cars
construction
assets
“This technology will transform everything we touch, not just in
business but in our personal lives as well.”
--P.P. Darukhanavala, CTO, British Petroleum
7/9/2007 AIIT Summer Course - M1 - Intro 40
Core challenges• Long-lived, unattended, reliable operation
– Power• Wireless often means self-powered
– Batteries
– Ambient sources (light, current, vibration, heat, …)
– Limited Memory
– Self-organization and Management
– Error, fault, noise mitigation
• Ease of broad application development– New forms of information
– Integration into enterprise processes and actions
– Extracting value from vast, novel sources of information
7/9/2007 AIIT Summer Course - M1 - Intro 41
A Systems Challenge
applications
service
network
system
architecture
data mgmt
Monitoring & Managing Spaces and Things
technology
MEMSsensing
Power
Comm. uRobotsactuate
Miniature, low-power connections to the physical world
Proc
Store
7/9/2007 AIIT Summer Course - M1 - Intro 42
Mote Architecture Evolution
SmartDustWeC
Rene Mica
Intel/UCBdot
InteliMOTE
XBOWcc-dot
XBOWmica2
Intel
rene’
XBOWrene2
Intelcf-mica
Boschcc-mica
Dust Incblue cc-TI
digital sunrain-mica
XBOWmica
zeevo BT
Telos
XBOWmicaZ
IntelMOTE2
EyesBTNode
trio
97
LWIM-III(UCLA)
9998 00 01 0302 04 0605 07
DARPA
SEN
SIT
LWIM
Expeditio
n
NEST
NETS/
NO
SS
CEN
S
STC
NSF
Cyb
er-
Phys
ical
WINS(UCLA/ROckwell)
7/9/2007 AIIT Summer Course - M1 - Intro 43
Storage ProcessingWireless SensorsWSN mote platform
Operating Systems and Networking
Radio Serial
Flash ADC, Sensor I/F
MCU, Timers, Bus,…
Link
NetworkProtocols Blocks,
Logs, FilesScheduling, Managemen
t
Streaming drivers
Over-the-air Programming
Applications and Services
Communication CentricResource-ConstrainedEvent-driven Execution
Tin
yOS 2
.0
7/11/2007 AIIT Summer Course - W2 Low Power 44
What we mean by “Low Power”• 2 AA => 1.5 amp hours (~4 watt hours)
• Cell => 1 amp hour (3.5 watt hours)
Cell: 500 -1000 mW => few hours active
WiFi: 300 - 500 mW => several hours
GPS: 50 – 100 mW => couple days
WSN: 50 mW active, 20 uW passive
450 uW => one year
45 uW => ~10 years
Ave Power = fact * Pact + fsleep * Psleep + fwaking * Pwaking
* System design
* Leakage (~RAM)
* Nobody fools mother nature
7/11/2007 AIIT Summer Course - W2 Low Power 45
Where the energy goes• Sleep
– 7 uA for TI MSP
• Sensing• Transmitting results• Management Traffic• Routing Structure Maintenance
– only parent tracking for leaf
• Listening• Forwarding
– non-leaf
• Overhearing packets destined for others
7/11/2007 AIIT Summer Course - W2 Low Power 46
The “Idle Listening” Problem
• The power consumption of “short range” (i.e., low-power) wireless communications devices is roughly the same whether the radio is transmitting, receiving, or simply ON, “listening” for potential reception– includes IEEE 802.15.4, Zwave, Bluetooth, and the many
variants– WiFi too!– Circuit power dominated by core, rather than large
amplifiers
• Radio must be ON (listening) in order receive anything.– Transmission is infrequent. Reception α Transmit x Density– Listening (potentially) happens all the time
Total energy consumption dominated by idle listening
7/11/2007 AIIT Summer Course - W2 Low Power 47
Communication Power Consumption
Sleep~10 uA
Transmit~20 mA x 1-5 ms[20 - 100 uAs]
I
I
Time
Time
Listen~20 mA
Receive~20 mA x 2-6 ms
7/11/2007AIIT Summer Course - W2 Low Power 48
Radio
• Trade-offs: – resilience | performance => slow wake up
– Wakeup vs interface level
– Ability to optimize vs dedicated support
* Polastre, Culler, BMAC, Sensys 2005
7/11/2007 AIIT Summer Course - W2 Low Power 49
Power States at Node Level
Sleep WakeUP Work Sleep WakeUP Work
Active Active
Telos: Enabling Ultra-Low Power Wireless Research, Polastre, Szewczyk, Culler, IPSN/SPOTS 2005
7/11/2007 AIIT Summer Course - W2 Low Power 50
3 Basic Solution Techniques
Goal: listen only when there is likely to be something useful to hear.
• Listen during scheduled time slots– Arrange a schedule of possible communication opportunities– Maintain appropriately coordinated clocks and schedule– Only listen during specific “slots”– Many variants: Aloha, Token-Ring, TDMA, Beacons, Bluetooth piconets, …
TSMP, …
• Sampled Listening– Listen for very short intervals to detect eminent transmissions– On detection, listen actively to receive
• Listen after send (with powered infrastructure)– Generally, device is not listening and will not receive.– After it transmits to a receptive device, it listens for a time window– Many variants: 802.11 AMAT, Key fobs, remote modems, …
7/11/2007 AIIT Summer Course - W2 Low Power 51
Approaches
• Powered Router / Duty cycle Leaf
• Coordinator / Beacon
• Network schedule
• Preamble Sampling
• Slotted Preamble Sampling
• Quasi-scheduled
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