1. Wireless Ad-Hoc Networks
Iyad Kanj
School of CTI, DePaul University

2. The Internet infrastructure
The Internet provides an infrastructure for communication: , WWW, Online games, etc…
The infrastructure consists of fixed, existing cables and hardware routers, etc…

3. 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

4. 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

5. A Solution
A wireless ad hoc network is a decentralized network of mobile devices connected using wireless channels

6. Wireless Ad Hoc Networks1

7. 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

8. How do non-neighbors communicate?
Receiver
Sender

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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