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Wireless Sensor Networks

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Title: This Century Challenges: Sensor Networks for Environmental Monitoring Author: Deborah Estrin Last modified by: Sheng-Tzong Cheng Created Date – PowerPoint PPT presentation

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Title: Wireless Sensor Networks


1
Wireless Sensor Networks
Outline
  • Introduction
  • Sensor Node Platforms Energy Issues
  • Time Space Problems in Sensor Networks
  • Sensor Network Protocols

2
Part I Introduction
3
Outline
  • Introduction
  • Motivating applications
  • Enabling technologies
  • Unique constraints
  • Application and architecture taxonomy

4
Embedded Networked Sensing Potential
  • Micro-sensors, on-board processing, and wireless
    interfaces all feasible at very small scale
  • can monitor phenomena up close
  • Will enable spatially and temporally dense
    environmental monitoring
  • Embedded Networked Sensing will reveal previously
    unobservable phenomena

Seismic Structure response
Contaminant Transport
Ecosystems, Biocomplexity
Marine Microorganisms
5
App1 Seismic
  • Interaction between ground motions and
    structure/foundation response not well
    understood.
  • Current seismic networks not spatially dense
    enough to monitor structure deformation in
    response to ground motion, to sample wavefield
    without spatial aliasing.
  • Science
  • Understand response of buildings and underlying
    soil to ground shaking
  • Develop models to predict structure response for
    earthquake scenarios.
  • Technology/Applications
  • Identification of seismic events that cause
    significant structure shaking.
  • Local, at-node processing of waveforms.
  • Dense structure monitoring systems.
  • ENS will provide field data at sufficient
    densities to develop predictive models of
    structure, foundation, soil response.

6
Field Experiment
  • 38 strong-motion seismometers in 17-story
    steel-frame Factor Building.
  • 100 free-field seismometers in UCLA campus
    ground at 100-m spacing

??¾¾¾¾¾¾ 1 km ¾¾¾¾¾¾?
7
Research challenges
  • Real-time analysis for rapid response.
  • Massive amount of data ? Smart, efficient,
    innovative data management and analysis tools.
  • Poor signal-to-noise ratio due to traffic,
    construction, explosions, .
  • Insufficient data for large earthquakes ?
    Structure response must be extrapolated from
    small and moderate-size earthquakes, and
    force-vibration testing.
  • First steps
  • Monitor building motion
  • Develop algorithm for network to recognize
    significant seismic events using real-time
    monitoring.
  • Develop theoretical model of building motion and
    soil structure by numerical simulation and
    inversion.
  • Apply dense sensing of building and
    infrastructure (plumbing, ducts) with
    experimental nodes.

8
App2 Contaminant Transport
  • Science
  • Understand intermedia contaminant transport and
    fate in real systems.
  • Identify risky situations before they become
    exposures. Subterranean deployment.
  • Multiple modalities (e.g., pH, redox conditions,
    etc.)
  • Micro sizes for some applications (e.g.,
    pesticide transport in plant roots).
  • Tracking contaminant fronts.
  • At-node interpretation of potential for risk (in
    field deployment).

Air Emissions
Water Well
Soil Zone
Spill Path
Volatization
Dissolution
Groundwater
9
ENS Research Implications
  • Environmental Micro-Sensors
  • Sensors capable of recognizing phases in
    air/water/soil mixtures.
  • Sensors that withstand physically and chemically
    harsh conditions.
  • Microsensors.
  • Signal Processing
  • Nodes capable of real-time analysis of signals.
  • Collaborative signal processing to expend energy
    only where there is risk.

10
App3 Ecosystem Monitoring
  • Science
  • Understand response of wild populations (plants
    and animals) to habitats over time.
  • Develop in situ observation of species and
    ecosystem dynamics.
  • Techniques
  • Data acquisition of physical and chemical
    properties, at various spatial and temporal
    scales, appropriate to the ecosystem, species and
    habitat.
  • Automatic identification of organisms(current
    techniques involve close-range human
    observation).
  • Measurements over long period of time, taken
    in-situ.
  • Harsh environments with extremes in temperature,
    moisture, obstructions, ...

11
Field Experiments
  • Monitoring ecosystem processes
  • Imaging, ecophysiology, and environmental sensors
  • Study vegetation response to climatic trends and
    diseases.
  • Species Monitoring
  • Visual identification, tracking, and population
    measurement of birds and other vertebrates
  • Acoustical sensing for identification, spatial
    position, population estimation.
  • Education outreach
  • Bird studies by High School Science classes (New
    Roads and Buckley Schools).

Vegetation change detection
Avian monitoring
Virtual field observations
12
ENS Requirements for Habitat/Ecophysiology
Applications
  • Diverse sensor sizes (1-10 cm), spatial sampling
    intervals (1 cm - 100 m), and temporal sampling
    intervals (1 ms - days), depending on habitats
    and organisms.
  • Naive approach ? Too many sensors ?Too many data.
  • In-network, distributed signal processing.
  • Wireless communication due to climate, terrain,
    thick vegetation.
  • Adaptive Self-Organization to achieve reliable,
    long-lived, operation in dynamic,
    resource-limited, harsh environment.
  • Mobility for deploying scarce resources (e.g.,
    high resolution sensors).

13
Transportation and Urban Monitoring
14
Intelligent Transportation Project (Muntz et al.)
15
Smart Kindergarten Project Sensor-based
Wireless Networks of Toysfor Smart Developmental
Problem-solving Environments (Srivastava et al)
16
Enabling Technologies
Embed numerous distributed devices to monitor and
interact with physical world
Network devices to coordinate and perform
higher-level tasks
Embedded
Networked
Exploitcollaborative Sensing, action
Control system w/ Small form factor Untethered
nodes
Sensing
Tightly coupled to physical world
Exploit spatially and temporally dense, in situ,
sensing and actuation
17
Sensors
  • Passive elements seismic, acoustic, infrared,
    strain, salinity, humidity, temperature, etc.
  • Passive Arrays imagers (visible, IR),
    biochemical
  • Active sensors radar, sonar
  • High energy, in contrast to passive elements
  • Technology trend use of IC technology for
    increased robustness, lower cost, smaller size
  • COTS adequate in many of these domains work
    remains to be done in biochemical

18
Some Networked Sensor NodeDevelopments
LWIM III UCLA, 1996 Geophone, RFM radio, PIC,
star network
AWAIRS I UCLA/RSC 1998 Geophone, DS/SS Radio,
strongARM, Multi-hop networks
WINS NG 2.0 Sensoria, 2001 Node
development platform multi- sensor, dual
radio, Linux on SH4, Preprocessor, GPS
  • UCB Mote, 2000
  • 4 Mhz, 4K Ram
  • 512K EEProm,
  • 128K code, CSMA
  • half-duplex RFM radio

Processor
19
Sensor Node Energy Roadmap
Source ISI DARPA PAC/C Program
10,000 1,000 100 10 1 .1
Rehosting to Low Power COTS (10x)
  • Deployed (5W)
  • PAC/C Baseline (.5W)

Average Power (mW)
  • (50 mW)

-System-On-Chip -Adv Power Management Algorithms
(50x)
  • (1mW)

2000 2002 2004
20
Comparison of Energy Sources
Source UC Berkeley
With aggressive energy management, ENS might live
off the environment.
21
Communication/Computation Technology Projection
Source ISI DARPA PAC/C Program
Assume 10kbit/sec. Radio, 10 m range. Large cost
of communications relative to computation
continues
22
  • The network is the sensor
  • (Oakridge National Labs)
  • Requires robust distributed systems of thousands
    of physically-embedded, unattended, and often
    untethered, devices.

23
New Design Themes
  • Long-lived systems that can be untethered and
    unattended
  • Low-duty cycle operation with bounded latency
  • Exploit redundancy and heterogeneous tiered
    systems
  • Leverage data processing inside the network
  • Thousands or millions of operations per second
    can be done using energy of sending a bit over 10
    or 100 meters (Pottie00)
  • Exploit computation near data to reduce
    communication
  • Self configuring systems that can be deployed ad
    hoc
  • Un-modeled physical world dynamics makes systems
    appear ad hoc
  • Measure and adapt to unpredictable environment
  • Exploit spatial diversity and density of
    sensor/actuator nodes
  • Achieve desired global behavior with adaptive
    localized algorithms
  • Cant afford to extract dynamic state information
    needed for centralized control

24
From Embedded Sensing to Embedded Control
  • Embedded in unattended control systems
  • Different from traditional Internet, PDA,
    Mobility applications
  • More than control of the sensor network itself
  • Critical applications extend beyond sensing to
    control and actuation
  • Transportation, Precision Agriculture, Medical
    monitoring and drug delivery, Battlefied
    applications
  • Concerns extend beyond traditional networked
    systems
  • Usability, Reliability, Safety
  • Need systems architecture to manage interactions
  • Current system development one-off,
    incrementally tuned, stove-piped
  • Serious repercussions for piecemeal uncoordinated
    design insufficient longevity, interoperability,
    safety, robustness, scalability...

25
Sample Layered Architecture
User Queries, External Database
Resource constraints call for more tightly
integrated layers Open Question Can we define
anInternet-like architecture for such
application-specific systems??
In-network Application processing, Data
aggregation, Query processing
Data dissemination, storage, caching
Adaptive topology, Geo-Routing
MAC, Time, Location
Phy comm, sensing, actuation, SP
26
Systems Taxonomy
Metrics
Load/Event Models
  • Spatial and Temporal Scale
  • Extent
  • Spatial Density (of sensors relative to stimulus)
  • Data rate of stimulii
  • Variability
  • Ad hoc vs. engineered system structure
  • System task variability
  • Mobility (variability in space)
  • Autonomy
  • Multiple sensor modalities
  • Computational model complexity
  • Resource constraints
  • Energy, BW
  • Storage, Computation
  • Frequency
  • spatial and temporal density of events
  • Locality
  • spatial, temporal correlation
  • Mobility
  • Rate and pattern
  • Efficiency
  • System lifetime/System resources
  • Resolution/Fidelity
  • Detection, Identification
  • Latency
  • Response time
  • Robustness
  • Vulnerability to node failure and environmental
    dynamics
  • Scalability
  • Over space and time

27
Part II Sensor Node Platforms Energy Issues
28
Sensor Node H/W-S/W Platforms
In-node processing
Wireless communication with neighboring nodes
Event detection
Acoustic, seismic, image, magnetic, etc. interface
Electro-magnetic interface
sensors
radio
CPU
Limited battery supply
battery
Energy efficiency is the crucial h/w and s/w
design criterion
29
Overview of this Section
  • Survey of sensor node platforms
  • Sources of energy consumption
  • Energy management techniques

30
Variety of Real-life Sensor Node Platforms
  • RSC WINS Hidra
  • Sensoria WINS
  • UCLAs iBadge
  • UCLAs Medusa MK-II
  • Berkeleys Motes
  • Berkeley Piconodes
  • MITs ?AMPs
  • And many more
  • Different points in (cost, power, functionality,
    form factor) space

31
Rockwell WINS Hidra Nodes
  • Consists of 2x2 boards in a 3.5x3.5x3
    enclosure
  • StrongARM 1100 processor _at_ 133 MHz
  • 4MB Flash, 1MB SRAM
  • Various sensors
  • Seismic (geophone)
  • Acoustic
  • magnetometer,
  • accelerometer, temperature, pressure
  • RF communications
  • Connexants RDSSS9M Radio _at_ 100 kbps, 1-100 mW,
    40 channels
  • eCos RTOS
  • Commercial version Hidra
  • ?C/OS-II
  • TDMA MACwith multihop routing
  • http//wins.rsc.rockwell.com/

32
Sensoria WINS NG 2.0, sGate, and WINS Tactical
Sensor
  • WINS NG 2.0
  • Development platform used in DARPA SensIT
  • SH-4 processor _at_ 167 MHz
  • DSP with 4-channel 16-bit ADC
  • GPS
  • imaging
  • dual 2.4 GHz FH radios
  • Linux 2.4 Sensoria APIs
  • Commercial version sGate
  • WINS Tactical Sensor Node
  • geo-location by acoustic ranging and angle
  • time synchronization to 5 ?s
  • cooperative distributed event processing

Ref based on material from Sensoria slides
33
Sensoria Node Hardware Architecture
Ref based on material from Sensoria slides
34
Sensoria Node Software Architecture
Ref based on material from Sensoria slides
35
Berkeley Motes
  • Devices that incorporate communications,
    processing, sensors, and batteries into a small
    package
  • Atmel microcontroller with sensors and a
    communication unit
  • RF transceiver, laser module, or a corner cube
    reflector
  • temperature, light, humidity, pressure, 3 axis
    magnetometers, 3 axis accelerometers
  • TinyOS

light, temperature, 10 kbps _at_ 20m
36
The Mote Family
Ref from Levis Culler, ASPLOS 2002
37
TinyOS
  • System composed of concurrent FSM modules
  • Single execution context
  • Component model
  • Frame (storage)
  • Commands event handlers
  • Tasks (computation)
  • Command Event interface
  • Easy migration across h/w -s/w boundary
  • Two level scheduling structure
  • Preemptive scheduling of event handlers
  • Non-preemptive FIFO scheduling of tasks
  • Compile time memory allocation
  • NestC
  • http//webs.cs.berkeley.edu

Bit_Arrival_Event_Handler
State bit_cnt
Start
Yes
Send Byte Eventbit_cnt 0
bit_cnt8
bit_cnt
Done
No
Ref from Hill, Szewczyk et. al., ASPLOS 2000
38
Complete TinyOS Application
Ref from Hill, Szewczyk et. al., ASPLOS 2000
39
UCLA iBadge
  • Wearable Sensor Badge
  • acoustic in/out DSP
  • temperature, pressure, humidity, magnetometer,
    accelerometer
  • ultrasound localization
  • orientation via magnetometer and accelerometer
  • bluetooth radio
  • Sylph Middleware

40
Sylph Middleware
41
UCLA Medusa MK-II Localizer Nodes
  • 40MHz ARM THUMB
  • 1MB FLASH, 136KB RAM
  • 0.9MIPS/MHz 480MIPS/W (ATMega 242MIPS/W)
  • RS-485 bus
  • Out of band data collection, formation of arrays
  • 3 current monitors (Radio, Thumb, rest of the
    system)
  • 540mAh Rechargeable Li-Ion battery

42
BWRCs PicoNode TripWire Sensor Node
Ref from Jan Rabaey, PAC/C Slides
43
BWRC PicoNode (contd.)
Ref from Jan Rabaey, PAC/C Slides
44
Quick-and-dirty iPaq-based Sensor Node!
  • HM2300 Magnetic Sensor
  • - uC Based with RS232
  • Range of /- 2Gausus
  • Adjustable Sampling Rate
  • X, Y, Z output
  • Device ID Management
  • WaveLan Card
  • IEEE 802.11b Compliant
  • 11 Mbit/s Data Rate
  • Familiar v0.5
  • Linux Based OS for iPAQ H3600s
  • JFFS2, read/write iPAQs flush
  • Tcl ported
  • iPAQ 3670
  • Intel StrongARM
  • Power Management (normal, idle sleep mode)
  • Programmable System Clock
  • IR, USB, Serial (RS232) Transmission
  • Acoustic Sensor Actuator
  • Built-in microphone
  • Built-in speaker

45
Sensor Node Energy Roadmap(DARPA PAC/C)
  • Low-power design
  • Energy-aware design

46
Where does the energy go?
  • Processing
  • excluding low-level processing for radio,
    sensors, actuators
  • Radio
  • Sensors
  • Actuators
  • Power supply

47
Processing
  • Common sensor node processors
  • Atmel AVR, Intel 8051, StrongARM, XScale, ARM
    Thumb, SH Risc
  • Power consumption all over the map, e.g.
  • 16.5 mW for ATMega128L _at_ 4MHz
  • 75 mW for ARM Thumb _at_ 40 MHz
  • But, dont confuse low-power and
    energy-efficiency!
  • Example
  • 242 MIPS/W for ATMega128L _at_ 4MHz
    (4nJ/Instruction)
  • 480 MIPS/W for ARM Thumb _at_ 40 MHz (2.1
    nJ/Instruction)
  • Other examples
  • 0.2 nJ/Instruction for Cygnal C8051F300 _at_ 32KHz,
    3.3V
  • 0.35 nJ/Instruction for IBM 405LP _at_ 152 MHz, 1.0V
  • 0.5 nJ/Instruction for Cygnal C8051F300 _at_ 25MHz,
    3.3V
  • 0.8 nJ/Instruction for TMS320VC5510 _at_ 200 MHz,
    1.5V
  • 1.1 nJ/Instruction for Xscale PXA250 _at_ 400 MHz,
    1.3V
  • 1.3 nJ/Instruction for IBM 405LP _at_ 380 MHz, 1.8V
  • 1.9 nJ/Instruction for Xscale PXA250 _at_ 130 MHz,
    .85V (leakage!)
  • And, the above dont even factor in operand size
    differences!
  • However, need power management to actually
    exploit energy efficiency

48
Radio
  • Energy per bit in radios is a strong function of
    desired communication performance and choice of
    modulation
  • Range and BER for given channel condition (noise,
    multipath and Doppler fading)
  • Watch out different people count energy
    differently
  • E.g.
  • Motes RFM radio is only a transceiver, and a lot
    of low-level processing takes place in the main
    CPU
  • While, typical 802.11b radios do everything up to
    MAC and link level encryption in the radio
  • Transmit, receive, idle, and sleep modes
  • Variable modulation, coding
  • Currently around 150 nJ/bit for short ranges
  • More later

49
Computation Communication
Energy breakdown for MPEG
Energy breakdown for voice
Decode
Decode
Transmit
Encode
Encode
Receive
Receive
Transmit
Radio Lucent WaveLAN at 2 Mbps
Processor StrongARM SA-1100 at 150 MIPS
  • Radios benefit less from technology improvements
    than processors
  • The relative impact of the communication
    subsystem on the system energy consumption will
    grow

50
Sensing
  • Several energy consumption sources
  • transducer
  • front-end processing and signal conditioning
  • analog, digital
  • ADC conversion
  • Diversity of sensors no general conclusions can
    be drawn
  • Low-power modalities
  • Temperature, light, accelerometer
  • Medium-power modalities
  • Acoustic, magnetic
  • High-power modalities
  • Image, video, beamforming

51
Actuation
  • Emerging sensor platforms
  • Mounted on mobile robots
  • Antennas or sensors that can be actuated
  • Energy trade-offs not yet studied
  • Some thoughts
  • Actuation often done with fuel, which has much
    higher energy density than batteries
  • E.g. anecdotal evidence that in some UAVs the
    flight time is longer than the up time of the
    wireless camera mounted on it
  • Actuation done during boot-up or once in a while
    may have significant payoffs
  • E.g. mechanically repositioning the antenna once
    may be better than paying higher communication
    energy cost for all subsequent packets
  • E.g. moving a few nodes may result in a more
    uniform distribution of node, and thus longer
    system lifetime

52
Power Analysis of RSCs WINS Nodes
  • Summary
  • Processor
  • Active 360 mW
  • doing repeated transmit/receive
  • Sleep 41 mW
  • Off 0.9 mW
  • Sensor 23 mW
  • Processor Tx 1 2
  • Processor Rx 1 1
  • Total Tx Rx 4 3 at maximum range
  • comparable at lower Tx

53
Power Analysis of Mote-Like Node
54
Some Observations
  • Using low-power components and trading-off
    unnecessary performance for power savings can
    have orders of magnitude impact
  • Node power consumption is strongly dependent on
    the operating mode
  • E.g. WINS consumes only 1/6-th the power when MCU
    is asleep as opposed to active
  • At short ranges, the Rx power consumption gt T
    power consumption
  • multihop relaying not necessarily desirable
  • Idle radio consumes almost as much power as radio
    in Rx mode
  • Radio needs to be completely shut off to save
    power as in sensor networks idle time dominates
  • MAC protocols that do not listen a lot
  • Processor power fairly significant (30-50) share
    of overall power
  • In WINS node, radio consumes 33 mW in sleep vs.
    removed
  • Argues for module level power shutdown
  • Sensor transducer power negligible
  • Use sensors to provide wakeup signal for
    processor and radio
  • Not true for active sensors though

55
Energy Management Problem
  • Actuation energy is the highest
  • Strategy ultra-low-power sentinel nodes
  • Wake-up or command movement of mobile nodes
  • Communication energy is the next important issue
  • Strategy energy-aware data communication
  • Adapt the instantaneous performance to meet the
    timing and error rate constraints, while
    minimizing energy/bit
  • Processor and sensor energy usually less important

MICA mote Berkeley
Transmit 720 nJ/bit Processor 4 nJ/op
Receive 110 nJ/bit 200 ops/bit 200 ops/bit
Transmit 6600 nJ/bit Processor 1.6 nJ/op
Receive 3300 nJ/bit 6000 ops/bit 6000 ops/bit
WINS node RSC
56
Processor Energy Management
  • Knobs
  • Shutdown
  • Dynamic scaling of frequency and supply voltage
  • More recent dynamic scaling of frequency, supply
    voltage, and threshold voltage
  • All of the above knobs incorporated into sensor
    node OS schedulers
  • e.g. PA-eCos by UCLA UCI has Rate-monotonic
    Scheduler with shutdown and DVS
  • Gains of 2x-4x typically, in CPU power with
    typical workloads
  • Predictive approaches
  • Predict computtion load and set voltage/frequency
    accordingly
  • Exploit the resiliency of sensor nets to packet
    and event losses
  • Now, losses due to computation noise

57
Radio Energy Management
Tx
Rx
?
?
time
  • During operation, the required performance is
    often less than the peak performance the radio is
    designed for
  • How do we take advantage of this observation, in
    both the sender and the receiver?

58
Energy in Radio the Deeper Story.
Tx Sender
Rx Receiver
Incoming information
Outgoing information
Channel
Power amplifier
Transmit electronics
Receive electronics
  • Wireless communication subsystem consists of
    three components with substantially different
    characteristics
  • Their relative importance depends on the
    transmission range of the radio

59
Examples
Medusa Sensor Node (UCLA)
Nokia C021 Wireless LAN
GSM
nJ/bit
nJ/bit
nJ/bit
50 m
10 m
1 km
  • The RF energy increases with transmission range
  • The electronics energy for transmit and receive
    are typically comparable

60
Energy Consumption of the Sender
  • Parameter of interest
  • energy consumption per bit

Tx Sender
Incoming information
RFDominates
Electronics Dominates
Energy
Energy
Energy
Transmission time
Transmission time
Transmission time
61
Effect of Transmission Range
62
Power Breakdowns and Trends
Radiated power 63 mW (18 dBm)
Intersil PRISM II (Nokia C021 wireless LAN)
Power amplifier 600 mW (11 efficiency)
Analog electronics 240 mW
Digital electronics 170 mW
  • Trends
  • Move functionality from the analog to the digital
    electronics
  • Digital electronics benefit most from technology
    improvements
  • Borderline between long and short-range moves
    towards shorter transmit distances

63
Radio Energy Management 1 Shutdown
  • Principle
  • Operate at a fixed speed and power level
  • Shut down the radio after the transmission
  • No superfluous energy consumption
  • Gotcha
  • When and how to wake up?
  • More later

64
Radio Energy Management 2 Scaling along the
Performance-Energy Curve
  • Principle
  • Vary radio control knobs such as modulation and
    error coding
  • Trade off energy versus transmission time

Modulation scaling fewer bits per symbol Code
scaling more heavily coded
Energy
Energy
transmission time
transmission time
65
When to Scale?
RF dominates
Electronics dominates
Energy
Scaling beneficial
Scaling not beneficial
Emin
transmission time
t
  • Scaling results in a convex curve with an energy
    minimum Emin
  • It only makes sense to slow down to transmission
    time t corresponding to this energy minimum

66
Scaling vs. Shutdown
  • Use scaling while it reduces the energy
  • If more time is allowed, scale down to the
    minimum energy point and subsequently use
    shutdown

Region of scaling
Region of shutdown
Energy
Emin
time
t
67
Long-range System
  • The shape of the curve depends on the relative
    importance of RF and electronics
  • This is a function of the transmission range
  • Long-range systems have an operational region
    where they benefit from scaling

Region of scaling
t
68
Short-range Systems
  • Short-range systems have an operational region
    where scaling in not beneficial
  • Best strategy is to transmit as fast as possible
    and shut down

realizable region
Energy
Region of shutdown
t
transmission time
69
Sensor Node Radio Power Management Summary
  • Short-range links
  • Shutdown based
  • Turn off sender and receiver
  • Topology management schemes exploit thise.g.
    Schurgers et. al. _at_ ACM MobiHoc 02
  • Long-range links
  • Scaling based
  • Slow down transmissions
  • Energy-aware packet schedulers exploit thise.g.
    Raghunathan et. al. _at_ ACM ISLPED 02

70
Another Issue Start-up Time
Ref Shih et. al., Mobicom 2001
71
Wasted Energy
  • Fixed cost of communication startup time
  • High energy per bit for small packets

Ref Shih et. al., Mobicom 2001
72
Sensor Node with Energy-efficient Packet Relaying
Tsiatsis01
  • Problem sensor noes often simply relays packets
  • e.g. gt 2/3-rd pkts. in some sample tracking
    simulations
  • Traditional main CPU woken up, packets sent
    across bus
  • power and latency penalty
  • One fix radio with a packet processor handles
    the common case of relaying
  • packets redirected as low in the protocol stack
    as possible
  • Challenge how to do it so that every new routing
    protocol will not require a new radio firmware or
    chip redesign?
  • packet processor classifies and modifies packets
    according to application-defined rules
  • can also do ops such as combining of packets with
    redundant information

zZZ
MultihopPacket
MultihopPacket
CommunicationSubsystem
Rest of the Node
GPS
RadioModem
MicroController
CPU
Sensor
Energy-efficient Approach
Traditional Approach
73
Putting it All Together Power-aware Sensor Node
Sensors
Radio
CPU
Dynamic Voltage Freq. Scaling
Scalable Sensor Processing
Freq., Power, Modulation, Code Scaling
Coordinated Power Management
PA-APIs for Communication, Computation, Sensing
Energy-aware RTOS, Protocols, Middleware
PASTA Sensor Node Hardware Stack
74
Future Directions Sensor-field Level Power
Management
  • Two types of nodes
  • Tripwire nodes that are always sense
  • Low-power presence sensing modalities such as
    seismic or magnetic
  • Tracker nodes that sense on-demand
  • Higher power modalities such as LOB
  • Approach
  • Network self-configures so that gradients are
    established from Tripwire nodes to nearby Tracker
    nodes
  • Radios are all managed via STEM
  • Event causes nearby Tripwire nodes to trip
  • Tripped Tripwire nodes collaboratively contact
    suitable Tracker nodes
  • Path established via STEM
  • Tracker nodes activate their sensors
  • Range or AoA information from Tracker Nodes is
    fused (e.g. Kalman Filter) to get location
  • In-network processing
  • Centralized where should the fusion center be?
  • Distributed fusion tree
  • Result of fusion sent to interested user nodes
  • Set of active Tracker Nodes changes as target
    moves
  • Process similar to hand-off

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Tools
  • Sensor Network-level Simulation Tools
  • Ns-2 enhancements by ISI
  • Ns-2 based SensorSim/SensorViz by UCLA
  • C-based LECSim by UCLA
  • PARSEC-based NESLsim by UCLA
  • Node-level Simulation Tools
  • MILAN by USC for WINS and ?AMPS
  • ToS-Sim for Motes
  • Processor-level Simulation Tools
  • JoulesTrack by MIT

76
SensorSim
  • SesnorSim based on ns-2

77
SensorViz
SensorViz
Power Measurements
Trace Data fromExperiments
Power Models
Node LocationsTarget TrajectoriesSensor
ReadingsUser TrajectoriesQuery Traffic
SensorSim Simulator
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