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

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…

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

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

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

Wireless Ad Hoc Networks 1

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

How do non-neighbors communicate? Receiver Sender

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

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

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

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

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

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