Sensor Networks for Environmental Monitoring: Lessons for DERNs?

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Sensor Networks for Environmental
MonitoringLessons for DERNs?

• Deborah Estrin
• Director, NSF Science and Technology Center for
  Embedded Networked Sensing (CENS)
• Professor, UCLA Computer Science Department
• destrin_at_cs.ucla.edu
• http//lecs.cs.ucla.edu/estrin

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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
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• The network is the sensor
• (Oakridge National Labs)
• Requires robust distributed systems of thousands
  of physically-embedded, unattended, and often
  untethered, devices.

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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

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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...

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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
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ENS Research

• Some building blocks for experimental systems
• Fine grained time and location
• Adaptive MAC
• Adaptive topology
• Data centric routing

New designs motivated bynew combination
ofconstraints and requirements
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Fine Grained Time and Location(Elson, Girod, et
al.)

• Unlike Internet, the location of nodes in time
  and space is essential for local and
  collaborative detection
• Fine-grained localization and time
  synchronization needed to detect events in three
  space and compare detections across nodes
• GPS provides solution where available (with
  differential GPS providing finer granularity)
• Acoustic or Ultrasound ranging and
  multi-lateration algorithms promising for non-GPS
  contexts (indoors, under foliage)
• Fine grained time synchronization needed to
  support ranging

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Tiered System Design IPAQs and UCB Motes

• Localization
• Mote periodically emits coded acoustic chirps
  (511 bits)
• IPAQs listen for chirps (buffer time series -
  mote cant do this)
• run matched filter and record time diff btwn
  emit- and receive-time of coded sequence
• Share ranges with each other via 802.11
  trilaterate
• IPAQs currently configured with their position
  future range to each other self-configure
• Time sync
• Allows computation of acoustic time-of-flight
• One IPAQ has a MoteNIC to sync mote and IPAQ
  domains

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Energy Efficient MAC design(Wei et al.)

• Major sources of energy waste
• Idle listening when no sensing events,
  Collisions, Control overhead, Overhearing
  
• Major components in S-MAC
• Massage passing
• Periodic listen and sleep
• Combine benefits of TDMA contention protocols
• Tradeoff latency and fairness for efficiency

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Adaptive Topology An example of
Self-Organization with Localized Algorithms

• Self-configuration and reconfiguration essential
  to lifetime of unattended systems in dynamic,
  constrained energy, environment
• Too many devices for manual configuration
• Environmental conditions are unpredictable
• Example applications
• Efficient, multi-hop topology formation node
  measures neighborhood to determine participation,
  duty cycle, and/or power level
• Beacon placement candidate beacon measures
  potential reduction in localization error
• Requires large solution space not seeking unique
  optimal
• Investigating applicability, convergence, role of
  selective global information

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Context for creating a topology connectivity
measurement study (Ganesan et al)
Packet reception over distance has a heavy tail.
There is a non-zero probability of receiving
packets at distances much greater than the
average cell range
Cant justdetermine Connectivity clusters
thrugeographic CoordinatesFor the same
reason you cant determine coordinates
w/connectivity
169 motes, 13x13 grid, 2 ft spacing, open area,
RFM radio, simple CSMA
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Example Performance Results (ASENT)(Cerpa et
al., Simulations and Implementation)
Energy Savings (normalized to the Active case,
all nodes turn on) as a function of density.
ASCENT provides significant amount of energy
savings, up to a factor of 5.5 for high density
scenarios.
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Data Centric vs. Address Centric approach

• Address Centric
• Distinct paths from each source to sink.
• Traditional IP model
• Works well when energy (and thus communication)
  is not at a premium
• Data Centric
• Name data (not nodes) with externally relevant
  attributes
• Data type, time, location of node, SNR, etc
• Publish/Subscribe
• Support in-network aggregation and processing
  where paths/trees overlap
• Essential difference from traditional IP
  networking

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Comparison of energy costs(Krishnamachari et.al.)
Data centric has many fewer transmissions than
does Address Centric independent of the tree
building algorithm.
Address Centric Shortest path data centric Greedy
tree data centric Nearest source data
centric Lower Bound
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ENS Research in progress

• Work in progress--in network processing
  mechanisms and models
• Fine grained data collection, methods, tools,
  analysis, models (D. Muntz (UCLA), G. Pottie
  (UCLA), J. Reich (PARC))
• Collaborative, multi-modal, processing among
  clusters of nodes (e.g., F. Zhao (PARC), K. Yao
  (UCLA)
• Enable lossy to lossless multi-resolution data
  extraction (Ganesan (UCLA), (Ratnasamy (ICSI))
• Primitives for programming the sensor network
  (Estrin (UCLA), Database perspective S. Madden
  (UCB))
• Modeling capacity and capability (M.
  Francischetti (Caltech), PR Kumar (Ill), M.
  Potkonjak (UCLA), S. Servetto (Cornell))
• Future areas--constructing models
• Architecture design principles
• Global properties responsiveness,
  predictability, safety

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Follow up

• Embedded Everywhere A Research Agenda for
  Networked Systems of Embedded Computers, Computer
  Science and Telecommunications Board, National
  Research Council - Washington, D.C.,
  http//www.cstb.org/
• Related projects at UCLA and USC-ISI
• http//cens.ucla.edu
• http//lecs.cs.ucla.edu
• http//rfab.cs.ucla.edu
• http//www.isi.edu/scadds
• Many other emerging, active research programs,
  e.g.,
• UCB Culler, Hellerstein, BWRC, Sensorwebs,
  CITRIS
• MIT Balakrishnan, Chandrakasan, Morris
• Cornell Gehrke, Wicker
• Univ Washington Boriello
• Wisconsin Ramanathan, Sayeed
• UCSD Cal-IT2
• DARPA Programs
• http//dtsn.darpa.mil/ixo/sensit.asp
• http//www.darpa.mil/ito/research/nest/