Wireless Ad-Hoc Networks

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Wireless Ad-Hoc Networks
Iyad Kanj School of CTI, DePaul University
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The Internet infrastructure

• The Internet provides an infrastructure for
  communication Email, WWW, Online games, etc
• The infrastructure consists of fixed, existing
  cables and hardware routers, etc

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Wireless devices and the Internet

• Wireless devices such as
• your cell phone or PDA
• make use of the Internet
• by connecting to its fixed
• and wired infrastructure
• through fixed antennas
• Wireless devices can then
• take full advantage of the
• Internet infrastructure for
• communication and other applications

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No infrastructure?

• What if no infrastructure is available?
• Emergency/rescue operations in deserts,
  mountains, seas,
• Battlefields
• In all of these cases, a fixed, wired
  infrastructure does not exist

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A Solution
A wireless ad hoc network is a decentralized
network of mobile devices connected using
wireless channels
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Wireless Ad Hoc Networks
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How do devices communicate?

• Devices in each others transmission range, i.e.
  neighbors in the network, communicate directly
• What if two distant devices (non-neighbors in the
  network) need to communicate with each other?
• Non-neighbors communicate through messages
  relayed by intermediate neighbors

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How do non-neighbors communicate?
Receiver
Sender
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How is a message routed?

• It is not obvious how a message should be routed
  in a wireless ad-hoc network
• For each message the sending device will consume
  power proportional to its distance to the
  receiver device
• Each wireless device is typically battery powered
  and has limited power capacity
• Messages between non-neighbors should travel
  along shortest paths in the wireless ad hoc
  network

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Goal

• Devise a way to route messages in the network so
  minimal power is used
• In other words, we would like to route messages
  between sending and receiving devices along
  short paths in the network
• Easily done on a fixed, wired Internet
• Not so easy on wireless ad-hoc networks because
  no fixed infrastructure and centralized server
  exists

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Problems

• It is unclear how messages should be routed in
  the wireless ad-hoc network
• the network topology should be planar because it
  is then amenable to guaranteed and efficient
  routing.
• Radio interference issues devices have limited
  communication capacities
• each device should maintain links to only a few
  devices in its transmission range

planar
Not planar
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The need for a sub-network

• Need to construct a bounded-degree planar
  sub-network of the original network
• The sub-network topology should be energy
  efficient
• The construction of the sub-network should be
  distributed and localized
• The sub-network topology should be robust

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Other sub-network requirements

• In a military environment, preservation of
  security, reliability, and recovery from failure
  are significant concerns
• Military networks are designed to maintain a low
  probability of intercept and/or a low probability
  of detection
• Hence, nodes prefer to radiate as little power as
  necessary and transmit as infrequently as
  possible, thus decreasing the probability of
  detection or interception

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Current work at CTI

• At CTI, Prof. Kanj and Prof. Perkovic are
  investigating the problem of topology control of
  wireless ad-hoc networks
• We have obtained highly efficient algorithms for
  constructing (near-optimal, in some cases)
  robust, planar, bounded-degree sub-networks of
  wireless ad-hoc networks