Localized Routing and Coordination in Wireless Sensor Networks

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Localized Routing and Coordination in Wireless
Sensor Networks
Tutorial ASI WSN Hong Kong, Dec. 7, 2006 pm
Ivan Stojmenovic Ivan_at_site.uottawa.ca www.site.uot
tawa.ca/ivan
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www.site.uottawa.ca/ivan/adhoc.html

• T0 Introduction (42 slides no time)
• T1 Routing (60 slides, 2pm-3pm)
• T2 Coordination Topology control for sensor area
  and communication coverage (36 slides,
  330pm-430pm)
• T3 Data Gathering (54 slides) Design guidelines
  for reporting, anycasting, multicasting,
  location service(no time)
• T4 Broadcasting (48 slides, no time Dec. 11 at
  HK Polytechnic Univ.)
• T5 Construction and application of sparse
  connected wireless ad hoc and sensor networks
  (57 slides no time Dec. 12, 230pm at HK
  Baptist Univ.)
• T6 Partitioning and connectivity (18 slides, no
  time)
• T7 Challenging issues to the applications of
  large scale sensor networks (16 slides, no
  time)

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Introduction

• Applications
• physical properties
• Research problems in sensor networks
• MAC, TCP, Data centric operations
• Network layer data communication and
  coordination
• Localized algorithms
• Simulations
• How to write research articles

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Sensor may measure

• Distance, Direction, Speed
• Humidity, Soil makeup
• Temperature, Chemicals
• Light, Vibrations, Motion
• Seismic data, Acoustic data
• strain, torque, load, pressure

• Self-configure into wireless multi-hop network

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Sensors Physical layer

• Sensing hardware
• Processor CPU (lt20 Mhz),
• Memory lt 4KB RAM
• (low) Power supply
• Transceiver (lt20 kbps)
• Receivers (0/1/2)
• Low-cost
• Miniature cm
• Multi-functional
• Hundreds/thousands sensors spread

GPS receiver ?? 7mm x 7mm x 2mm accuracy ?
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Physical layer continued

• Wireless communication
• RF noise and multipath fading causes severe
  packet loss
• Easy to eavesdrop and to launch spoofing or
  Denial-of-Service attacks
• Mobility requires rerouting of packets
• Infrared and Optical line of sight alternatives
• Physical risk - nodes are defective, lost,
  damaged, compromised, or expired
• Limited bandwidth and power (battery)
• One-to-all communication by omni-directional
  antennas

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Micro Sensor Hardware Platform

• Berkeley/Crossbow MICA2 Mote
• 250 (MICA2 sensor board)
• www.xbow.com
• ATMEGA microcontroller
• 4 KB RAM, 4 KB EEPROM, 128 KB Flash
• CPU 8 MHZ
• Chipcon CC1000 radio, lt20 kbps
• Multifrequency
• Two AA Batteries
• 1 Duty Cycle can extend lifetime from 5 days to
  3-6 months
• Extension boards for sensors

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More on physical layer

• Routing tables size ? Data replication ?
• Security ? Processing time ?
• Data compression, error control
• Same frequency ? two frequencies ? Frequency
  hopping ?
• Sensors in active state spend considerably more
  energy than sensors in sleep state
• Reliability of individual sensor measurement
  ? Reliability of sensor network measurement?
• There are many types of sensors !

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Journals on sensor networks

• Several journals including mobile computing
• Ad Hoc Networks (Elsevier), Akyildiz, 2003
• ACM Transactions on Sensor Networks 2005
• Int.J.Distributed Sensor Networks, Iyengar,(TF)
  2005
• Int.J. Sensor Networks, Y. Xiao, InderScience,
  2006.
• Ad Hoc Sensor Wireless Networks, An Int. J.
  Stojmenovic, OCP, 2005.
• Handbook of Sensor Networks Algorithms and
  Architectures (Stojmenovic, ed.), Wiley, 2005.
• The number of researchers, publications, journals
  and conferences grows exponentially since 2000

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Research problems

• Physical,MAC,Network,TCP,Application layers, and
  cross-layering
• Energy scavenging (chapter)
• Authentication, key management, security
  (chapter)
• Operating systems (chapter), databases
• Path exposure, target location, classification,
  tracking (chapter)
• Data gathering and fusion (chapter)
• Localization (position determination) (chapter)
• Time synchronization and calibration (chapter)
  is global synchronization needed? Local
  synchronization (like temperature across a
  country)?
• Chapters in Handbook of Sensor Networks
  Algorithms and Architectures (Stojmenovic, ed.),
  Wiley, 2005.

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Physical layer issues

• Distributed signal processing (chapter)
• All models are unrealistic (easy to criticize),
  but some of them are useful
• Unit disk graph? two nodes can communicate if
  and only if the distance between them is at most
  R (transmission range)
• Sensing model ? Event can be sensed if and only
  if it is up to distance S from sensor (sensing
  range)?
• Fixed or variable R/S ranges ?
• (Omni)directional antenna? One or more channels?
• More realistic physical layer ? Indoor-outdoor?
  Air/underwater? Position information?
• Are sensors static or could be mobile?
• One or more sinks? Static or mobile?

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Medium access for sensors

• Ideal MAC (for initial simulations), or
• IEEE 802.15.4 Zigbee standard for low rate
  wireless networks (chapter)
• Two network topologies are allowed by the
  standard, both relying on the presence of central
  coordinator.
• peer-to-peer topology sensors may
  communicate directly,
• star-shaped topology they must communicate
  through coordinator.
• Sensors are time synchronized,
• and follow a joint sleep-active schedule.
• they are active at the same time, followed by
  longer sleep periods. At the beginning of active
  periods, they compete for upcoming slots to send
  messages

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Embedded Sensor Lightweight Operating Systems

• Embedded OS memory footprint too large, not
  truly open source, too limited
• Berkeleys TinyOS
• Program in NesC
• Event-driven OS run-to-completion
• Run-to-completion operating systems are very
  small, simple, and efficient, but because most of
  the scheduling and synchronization burden is
  pushed to the individual tasks, they are only
  applicable to very simple uses. NRC Report
• Mote sensor board programming board

Simple multithreading (MANTIS OS, open source)
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Transport layer in sensornets

• Reduced traffic ? reduced congestion
• error rate is increased due to MAC problems,
  disconnection is possible due to mobility or
  power failure ? Wireless TCP ? TCP
• Traditional end-to-end reliability does not apply
• Acknowledgements are power consuming
• Buffering abilities limited
• QoS issues are of different type reliability of
  little information rather than quantity/delay

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Reliability

• Multiple correlated data flow from event to sink
• Spatial correlation among data
• Several reports arrive at sink, or
• Several reports are combined at intermediate
  nodes to reduce communication (data fusion)
• Collective reliability
• Transport problem configure the reporting rate
  to achieve the required event detection
  reliability at the sink with minimum resource
  utilization.

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Basic scenario for area monitoringone sink,
thousands sensors
event
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Deployment strategies

• Embedded sensors to objects in factories
• Deterministic placement by humans, robots
• Randomized placement by plane, artillery, by
  humans or robots
• Initial deployment and redeployments

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Query types

• Event-driven when sensor decides that it has
  something to report (e.g. high temperature)
• On-demand by request from monitoring station
• On-demand whole sensing region, or
• On-demand geocasting region (only sensors inside
  a geographic region to report)
• On-demand multicasting regions (sensors inside
  few regions)

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Addressing queries

• Address centric query to an individual node
  (e.g. IP routing)
• Data-centric addressing query to a geographic
  region (position information essential)
• Sensors may not have IDs to reduce overhead
• Route based on contents of data
• Send me all sensor readings with Temp gt 40 C
  (data-driven routing)

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Data fusion in sensor networks

• New datum important to forward?
• Combine it with other received data
• Minimize of bits to forward
• Coding
• Reliability of new datum sensing distance and
  malfunctioning ?

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Data aggregation

• Some sensors may aggregate data by doing some
  computation average, summation, highest etc
• Collaborative signal processing fuse data
  from multiple sensors
• Sensors may divide jobs some are sensing and
  forwarding, some are receiving and
  forwarding some are aggregating data and
  forwarding

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Network layer Data communication

• Routing find a path from a source to
  destination
• Broadcasting send from source to all nodes
  data dissemination
• Multicasting send from source to several nodes
• Geocasting send a packet from source to all
  nodes inside a region
• Design guidelines for efficient data
  communication

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Network layer coordination

• Sensor area coverage decide which sensors should
  sleep and which ones should be active
• Backbone creation which active sensors should be
  in backbone for more efficient routing,
  broadcasting etc.
• backbones clusters, connected dominating sets
• Choose links, transmission radii, for desired
  protocol operation

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Localized algorithms

• Scalability algorithms work well (or still work)
  on ad hoc networks with large number of nodes
• Globalized algorithms global network information
  or global structure required (e.g. for shortest
  path)
• Localized algorithms Decisions made based only
  on information from neighbors and natural
  additional information (e.g. destination for
  routing)
• Local localized Maintenance remains local
• Quazi-local localized Local changes may trigger
  global updates
• Mobility or changes between active and sleep
  periods in ad hoc and sensor networks require
  localized algorithms, preferably local localized

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Memorization and message count ?

• Avoid/reduce memorization at nodes, because that
  node may not be active or at expected place when
  the stored information is needed
• Number of messages between neighbors few ?
  O(degree) ? More ?
• Number of messages between neighbors to run a
  protocol should be very limited (e.g. under
  five), possibly even zero after hello messages
  for backbone construction, since
• Bandwidth and power are limited, and
• Impact of realistic physical layer unreliable
  receptions

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Community differences

• Engineers dominated by 2000 with almost full
  control
• Computer scientists algorithms are more
  important than simulations simplified
  simulations to extract major properties if
  routing A is better than routing B on a single
  routing task with ideal MAC layer and home-made
  simulator, it is highly likely that 1000 routing
  tasks A will be better than 1000 routing tasks B
  with 802.11 and NS-2, Glomosym..
• Mathematicians very good theoretical results,
  with lot of theorems/proofs, not much practical
  relevance, not much support to computer
  scientists either (your algorithm is too
  simple, there are no theorems..) worst case
  performance more important than average case

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Simulations and writing traps to avoid

• I am best approach compare with something
  expected to be worse, ignore existing better
  solutions
• Use simulator that was used by others hide many
  detail, but add transport and medium access layer
  immediately to network layer
• Literature review incomplete
• Simulation diagrams to be impressive, choose
  parameter values showing good performance
• Algorithmic description incomplete, vague, or
  given by pseudo-code
• Discuss the impact of ten parameters at once, not
  isolating one and making conclusions on it before
  introducing the next one.
• Assumptions are mostly realistic, but often
  forgetting to measure something, e.g.
  communication overhead for mobile ad hoc networks
  when applying centralized solution

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How to write research articles

• See manuscript at www.site.uottawa.ca/ivan
• Repeat contribution in four sizes title,
  abstract, introduction, full text, as if each was
  stand-alone
• Problem statement, including assumptions and
  limitations
• Existing solutions why they are (not) competing
• New solution(s)
• Comparison with competing solutions analytical,
  simulation
• Advantages and drawbacks
• References and Conclusions

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Broadcasting Data dissemination

• Blind flooding each node retransmits when first
  copy received, ignores other copies
• For dense networks, blind flooding is unreliable
  at MAC layer contentions, collisions,
  redundancy, increased latency
• Blind flooding works well on area dominating set,
  when sensing range communication range, since
  it is not dense ?20 packets sent without need
• Sensing range lt comm. range ? blind flooding
  becomes less efficient
• Improved solution connected dominating sets
  (CDS)
• DSeach node is either in DS or has a neighbor in
  DS
• Dozens solutions recently proposed

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Wireless sensor and actor networks
Actors active nodes, higher energy and
computation, action possible, may be mobile
Task Manager Node
Sink
Sensor
Actor
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Coordinated actuator movement- move/place
sensors to improve area coverage- move to help
sensors determine positions- move to create
fault tolerant network
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Data communication in sensor actuator networks

• Sensor-sensor, sensor-actuator,
  actuator-actuator data communication
• Anycasting sensor to report to any actuator
• Anycasting with guaranteed delivery
• Multicasting sending report to certain actuators
• Routing, broadcasting minimal hop count, minimal
  power consumption, bounded delay
• Controlled mobility to improve data communication
• Currently hot subject with small number of
  seed articles

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Info at www.site.uottawa.ca/ivan

• articles book chapters, papers
• WWASN June 2007 (General co-chair) Dec. 15
  (deadline)
• IEEE MASS Oct. 2007 (Program co-chair) March 31
  (deadline)
• Four books edited
• EIC for journals AHSWN, IJPEDS
• Advice for writing theses and papers

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(No Transcript)
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Who is the father of radio broadcasting and
wireless communications ?
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Nikola Tesla 1856-1943
The Father of wireless communication

• The Serbian-American
• inventor,
• electrical engineer,
• and scientist
• www.teslasociety.com

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Radio/wireless transmission
- was invented by Nikola Tesla in 1893 - Tesla
demonstrated it to the public in 1898 in New
York - Radio remote controlled submarine by
logic gate and three separate radio frequencies
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The US Supreme Court awarded the patent for
radio communications to Tesla in 1945, taking it
away from Marconi
The "World's radio station, Long Island, build
in 1900 for remote wireless control transmission
throughout the world news, music, photographs
and even electricity! However, that great plan
could not be carried out because Tesla did not
have sufficient resources finish it.
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Tesla the genius who lit the world

• Transformers for long distance transfers of
  alternate current electricity
• Polyphase motors to use the current
• Built the worlds first hydroelectric plant at
  Niagara Falls, 1895

Winning over Edisons direct current proposal
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Teslas other inventions

• Tesla experimented and published on x rays in
  1895-6, independently in parallel with Roentgen
• Neon and fluorescent lighting
• Wireless lighting
• NASAs robot on Mars, Shanghais fast train etc.
  based on Teslas inventions

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Lost inventions

• When Nikola Tesla announced he was working on the
  transmission of free wireless electric energy,
• His laboratory was destroyed.
• And he lived in poverty
• Among other achievements
• Made a ship invisible to a live audience!
• Worked on time/space object transfer (USA army
  project including Einstein)
• His documentation is still classified by the US
  government

After his withdrawal from the army project, there
is evidence that he was assassinated
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Celebrating the 150th anniversary of Nikola
Tesla's birth in 2006