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

2. 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…

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 Networks 1

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