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Wireless sensor networks
Murat Demirbas
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Wireless sensor networks
A sensor node (mote)
8K RAM, 4Mhz processor magnetism, heat, sound, vibration, infrared wireless (radio broadcast) communication up to 100 feet costs ~$10 (right now costs $200)
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New Class of Computing
year
log
(p
eo
ple
pe
r c
om
pu
ter)
streaming informationto/from physical world
Number CrunchingData Storage
productivityinteractive
Mainframe
Minicomputer
Workstation
PC
Laptop
PDA
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Why use a WSN?
• Ease of deployment
Wireless communication means no need for a communication infrastructure setup
Drop and play
• Low-cost of deployment
Nodes are built using off-the-shelf cheap components
• Fine grain monitoring
Feasible to deploy nodes densely for fine grain monitoring
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Challenges in sensor networks
• Energy constraint
• Unreliable communication
• Unreliable sensors
• Ad hoc deployment
• Large scale networks
• Limited computation power
• Distributed execution
: Nodes are battery powered
: Radio broadcast, limited bandwidth, bursty traffic
: False positives
: Pre-configuration inapplicable
: Algorithms should scale well
: Centralized algorithms inapplicable
: Difficult to debug & get it right
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Outline
• Applications
• Platforms (hw&sw)
• WSN services (layers? what layers?)
• Comparison with the Internet architecture
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• Monitoring nesting behavior of birds
Great Ducks experiment
• Detecting forest fires
• Detecting chemical or biological attacks
• Monitoring Redwood trees
Ecology monitoring
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Dense Self-Organized Multihop Network
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8.9
Temperature vs. Time
Date
Tem
pera
ture
(C
)
Humidity vs. Time
35
45
55
65
75
85
95
Rel H
um
idit
y (
%)
101 104 109 110 111
2003, unpublished
Bottom Top
36m
34m
30m
20m
10m
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Precision agriculture
• Wireless sensor networks can be placed on farm lands to monitor temperature, humidity, fertilizer and pesticide levels
• Pesticide and fertilizer can only be applied when and where required
Pesticide and fertilizer per one acre costs $20 Considering 100,000 acres savings of $2 million possible
VineyardsBC
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Equipment Health Monitoring in Semiconductor Fab
Fab Equipment
Mote + Vibration Sensors
Ad Hoc Mote Network
Intranet
802.11 Mesh
Intranet isolation
Root Node
• Equipment failures in production fabs is very costly
Predict and perform preemptive maintenance
• Typical fab has ~5,000 vibration sensors
Pumps, scrubbers, … Electricians collect data by hand few times a year Sample: 10’s kilohertz, high precision, few seconds
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Put tripwires anywhere—in deserts, other areas where physical terrain
does not constrain troop or vehicle movement—to detect, classify &
track intruders
Project ExScal: Concept of operation
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Envisioned ExScal customer application
Gas pipeline
Border control
Canopy precludes aerial techniques
Rain forest – mountains – water
environmental challenges
Convoy protection
IEDHide SiteDetect anomalous activity
along roadside
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ExScal summary
• Application has tight constraints of event detection scenarios: long life but still low latency, high accuracy over large perimeter area
• Demonstrated in December 2004 in Florida
• Deployment area: 1,260m x 288m
• ~1000 XSMs, the largest WSN
• ~200 XSSs, the largest 802.11b ad hoc network
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Line in the sand project
• Thick line allows detection & classification as intruders enter the protected region; also allows fine grain intruder localization
• Grid of thin lines allows bounded uncertainty tracking
Thick Entry Line
A S S E T
1 km
250 m
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ExScal sample scenarios
Intruding person walks through thick line
• (pir) detection, classification, and fine-grain localization
Intruding vehicle enters perimeter and crosses thick line
• (acoustic) detection, classification, and fine-grain localization
Person/ATV traverses through the lines
• coarse-grain tracking
Management operations to control signal chains, change parameters, and programs dynamically; query status and execute commands
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WSN Platforms: Hardware & Software
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Types of sensor platforms
1. RFID equipped sensors
1. Smart-dust tags
typically act as data-collectors or “trip-wires”
limited processing and communications
• Mote/Stargate-scale nodes
• more flexible processing and communications
1. More powerful gateway nodes, potentially using wall power
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Grain-sized nodes
Powered by inductive coupling to a transmission from a reader device to transmit a message back
Available commercially at very low prices
× Computation power is severely limited
× Can only trasmit stored unique id and variable
× Hard to add any interesting sensing capability
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Matchbox-sized nodes
• Mica series, XSM node, Telos
• 8-bit microprocessor, 4MHz CPU
ATMEGA 128, ATMEL 8535, or Motorola HCS08
• ~4Kb RAM
holds run-time state (values of the variables) of the program
• ~128Kb programmable Flash memory
holds the application program Downloaded via a programmer-board or wirelessly
• Additional Flash memory storage space up to 512Kb.
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Mica2 and Mica2Dot
• ATmega128 CPU– Self-programming
• Chipcon CC1000– FSK– Manchester encoding– Tunable frequency
• Low power consumption– 2 AA battery = 3V
1 inch
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Basic Sensor Board
• Light (Photo)• Temperature• Prototyping space for
new hardware designs
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Mica Sensor Board
• Light (Photo)• Temperature• Acceleration
– 2 axis– Resolution: ±2mg
• Magnetometer– Resolution: 134G
• Microphone• Tone Detector• Sounder
– 4.5kHz
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Telos Platform
• Low Power
Minimal port leakage
Hardware isolation and buffering
• Robust
Hardware flash write protection
Integrated antenna (50m-125m)
Standard IDC connectors
• Standards Based
USB
IEEE 802.15.4 (CC2420 radio)
• High Performance
10kB RAM, 16-bit core, extensive double buffering
12-bit ADC and DAC (200ksamples/sec)
DMA transfers while CPU off
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Brick-sized node: Stargate
• Mini Linux computers communicating via 802.11 radios
Computationally powerful High bandwidth Requires more energy (AA infeasible)
• Used as a gateway between the Internet and WSN
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Stargate
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Outline
• Hardware
RFID, Spec Mica2, XSM, Telos Stargate
• Software
TinyOS
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TinyOS
• most popular operating system for WSN
developed by UC Berkeley
• features a component-based architecture
software is written in modular pieces called components Each component denotes the interfaces that it provides
An interface declares a set of functions called commands that the interface provider implements and another set of functions called events that the interface user should be ready to handle
• Easy to link components together by “wiring” their interfaces to form larger components
similar to using Lego blocks
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TinyOS
• provides a component library that includes network protocols, services, and sensor drivers
• An application consists of
a component written by the application developer and the library components that are used by the components in (1)
• An application developer writes only the application component that describes the sensors used in the application, the middleware services configured with the appropriate parameters based on the needs of the application
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Benefits of using TinyOS
• Separation of concerns
TinyOS provides a proper networking stack for wireless communicationthat abstracts away the underlying problems and complexity of message transfer from the application developer
E.g., MAC layer
• Concurrency control
TinyOS provides a scheduler that achieves efficient concurrency control An interrupt-driven execution model is needed to achieve a quick
response time for the events and capture the data
For example, a message transmission may take up to 100msec, and without an interrupt-driven approach the node would miss sensing and processing of interesting data in this period
Scheduler takes care of the intricacies of interrupt-driven execution and provides concurrency in a safe manner by scheduling the execution in small threads.
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Benefits of TinyOS
• Modularity
TinyOS’s component model facilitates reuse and reconfigurability since software is written in small functional modules. Several middleware services are available as well-documented components
Over 500 research groups and companies are using TinyOS and numerous groups are actively contributing code to the public domain
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RadioTimingSecDedEncode
The Complete Application
RadioCRCPacket
UART
UARTnoCRCPacket
ADC
phototemp
AMStandard
ClockC
bit
by
tep
ac
ke
t
SenseToRfm
HW
SW
IntToRfm
MicaHighSpeedRadioM
RandomLFSRSPIByteFIFO
SlavePin
noCRCPacket
Timer photo
ChannelMon
generic comm
CRCfilter
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TOS Execution Model
• commands request action
ack/nack at every boundary call command or post task
• events notify occurrence
HW interrupt at lowest level may signal events call commands post tasks
• tasks provide logical concurrency
preempted by events
RFM
Radio byte
Radio Packet
bit
by
tep
ac
ke
t
event-driven bit-pump
event-driven byte-pump
event-driven packet-pump
message-event driven
active message
application comp
encode/decode
crc
data processing
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Event-Driven Sensor Access Pattern
• clock event handler initiates data collection
• sensor signals data ready event
• data event handler calls output command
• device sleeps or handles other activity while waiting
• conservative send/ack at component boundary
command result_t StdControl.start() {
return call Timer.start(TIMER_REPEAT, 200);
}
event result_t Timer.fired() {
return call sensor.getData();
}
event result_t sensor.dataReady(uint16_t data) {
display(data)
return SUCCESS;
}
SENSE
Timer Photo LED
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Programming Syntax
• TinyOS 2.0 is written in an extension of C, called nesC
• Applications are too
just additional components composed with OS components
• Provides syntax for TinyOS concurrency and storage model commands, events, tasks local frame variable
• Compositional support separation of definition and linkage robustness through narrow interfaces and reuse Interpositioning
• Whole system analysis and optimization
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WSN Services:
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WSN services
• MAC protocols (BMAC, SMAC, TMAC, etc.)
• Topology control (GAF, SPAN, CEC, etc.)
• Clustering (Leach, FLOC, etc.)
• Time synchronization (Flooding time sync, reference broadcast)
• Localization (cricket, range-free techniques...)
• Routing (convergecast tree, geographic routing, hierarchical...)
• Querying (DSIB, DQT, directed diffusion, etc.)
• Tracking (Stalk, Trail, etc.)
• Network reprogramming
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Comparison to Internet architecture:
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Compared to Internet
• No clear layering; cross layer design is norm
• No separation between edge vs core of the network
all nodes are both routers and hosts
• End-to-end principle fails
unreliable channels, multihop latency
• Ad hoc deployment
timesync, localization, topology control, clustering etc services needed
• Routing needs are different...