Towards proliferation of ad hoc wireless networks

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Towards proliferation of ad hoc wireless networks

• P. R. Kumar
• (with V. Borkar, G. Baliga, S. Graham, P. Gupta,
  K. Huang, V. Kawadia, S. Narayanaswamy, V.
  Raghunathan, R. Rozovsky, L-L. Xie)
• Dept. of Electrical and Computer Engineering, and
• Coordinated Science Lab
• University of Illinois, Urbana-Champaign

Email prkumar_at_uiuc.eduWeb
http//black.csl.uiuc.edu/prkumar
Microsoft Mesh Networking Summit, Snoqualmie,
June 23, 2004
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One modest effort-in-the-making towards
proliferation

• How to proliferate ad hoc networks?
• We dont know what the killer applications are
• Much genius in society
• Applications will emerge
• Great hunger for communication
• Instant Messenger
• Our attempt in the making Idea
• Develop a product
• Give it away free
• See what happens
• Have developed software which will self-install
• Addresses, routing, anonymity
• Linux and Windows
• Have not yet developed a distributed chat
  application
• How to spark adoption?
• A business model for giving it away free

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Another vision Interaction with world

• The next phase of IT revolution may involve the
  active interaction and alteration with the
  environment
• Achieved through the convergence of control
  (sensing and actuation) with communication and
  computation
• Question How do we organize them?
• Distributed Real-time Physics-based systems

What are the right abstractions?What is the
architecture?

• What are the right abstractions?
• What should be the architecture of the system?
• Application independent, Context independent
  architecture
• Same architecture for
• Building-wide temperaturecontrol system?

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The importance of architecture

• Success of Internet is due to its architecture
• Notion of peer-to-peer protocols
• Hierarchy of layers
• Allows plug-and-play
• Proliferation of technology

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Middleware EtherArch Software

• Time translation
• Knowledge of per-packet delay important for
  control
• Location independence
• Car can request for a camera covering
  coordinates(50,50) - Infrastructure finds the
  corresponding camera
• Car need not know the IP address or port
• System startup and evolution during execution
• Installing application code components at
  start-up/run-time
• Automatic migration of components to reduce
  communication or computation burden

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Information TechnologyConvergence LabThe
Systems
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IT Convergence Lab

• Movie

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Ad Hoc Wireless Networks

• Ad Hoc Networks
• Current proposal for operation Multi-hop
  transport
• Nodes relay packets until they reach their
  destinations
• Fully decode packets at each stage treating
  allinterference as noise

• Interfering packets destructively collide
  witheach other

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However wireless networks are not wired networks

• Wireless networks are formed by nodes with radios
• There is no a priori notion of links
• Nodes simply radiate energy

• Nodes can cooperate in many complex ways

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Nevertheless the good news is

• Multi-hop is nearly optimal
• Transport packets over manyhops of distance
• Nearly optimal multi-hop architecture

• To execute this we need
• Power control
• MAC
• Routing
• Transport
• What are some second generation protocols for
  these?

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The Power Control problem

• How do we choose power levels of transmissions in
  wireless networks?
• Power level influences range
• Power levels determine interference
• Power levels affect routes
• Conceptualization problem for Power Control
• Which Layer?
• Physical layer
• Quality of reception
• Network layer
• Impact on routing
• Transport layer
• Higher power impacts congestion
• How to fit Power Control in the hierarchical OSI
  framework?

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Our own suggestion Network Layer solution for
Power Control

• Power Control has global impact
• Connectivity is a global property
• Clustering is regional
• Routing is over network
• Interdependence of Power Control and Routing
• So joint solution for Power Control and Routing
  situated at the Network Layer

• Our own attempts
• COMPOW, CLUSTERPOW, etc

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Can we develop a better second generation higher
performance MAC?

• IEEE 802.11 MAC
• Silences two neighborhoods
• Real as well as virtual carrier sensing
• Backoff counters
• PLCP header at low rate
• Our own attempt SEEDEX
• Based on exchanging pseudo-randomnumber seeds to
  coordinate schedules
• Reservations without making reservations
• Silences only one neighborhood
• No backoff counters
• But is a slotted protocol
• Slot synchronization needed

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Additional functionalities of routing

• Forwarding
• Delivering packets to the right destination
• Load adaptation
• Can we design an adaptive distributed
  asynchronousrouting algorithm that adapts routes
• To the topology of the network
• To the prevailing traffic conditions, e.g., is
  delay adaptive?
• Load balancing
• How to distribute the loading on different areas
  of the network
• Our own attempt Wardrop algorithm
• All used paths have same delay
• All unused paths have larger delay

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Last but not least

• Hardware
• That we can develop on
• That gives enough interfaces that we can write
  software
• That we can experiment with
• That will spark proliferation
• A la IEEE 802.11

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To obtain papers

• Papers can be downloaded from
  http//black.csl.uiuc.edu/prkumar
• For hard copies send email to
  prkumar_at_uiuc.edu

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Some thoughts on Mesh Networks
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Some preliminaries on accessing a base-station

• Multiple-access channel
• Capacity region is completely characterized
• All rate vectors satisfying
• for some distribution are
  feasible

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Optimal strategy vs. TDMA

• Optimal strategy
• Successive subtraction and decoding strategy
• Decode one user
• Subtract that users signal if channel known
• Decode next user
• Requires multi-user decoding
• Optimal capacity per user is
• On the other hand simple TDMA can yield
• Every user simply transmits directly to
  base-station

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So what are the issues in multi-hopping to a
base-station?

• Protocol issues
• Power control can be used to
• Save energy at mobile nodes
• Trade-off between energy and delay
• Medium access issues may get complicates
• If power control gets sophisticated
• Routing may be simplified if there is only one
  sink
• Transport level may need design due to need for
  interfacing multi-hop wireless with wired
  Internet
• Interesting cross-layer design issues
• Power control, medium access, routing, transport
• Further interesting issues when allowing
  operation in ad hoc as well as just reaching
  base-station