Manikantah Kodali: Master's Thesis, June 2006

Title: Improving Fault Tolerance in 802.11 Wireless Long Distance Rural Networks

Abstract: Wireless technology is a promising solution for providing communication facilities to rural areas. We consider a network deployment with long-distance wireless links between rural locations. One of the network locations consists of a wired connection/communication, to connect the other locations to the Internet. We call this location the central node. Towers and antennae are used for setting up long-distance wireless links in the network. Directional or sector antennae with high directional gain are used which are fixed and static. The network may be multi-hop. Individual village locations can be a few hops (say 2 or 3 hops) from the central node. One of the major issues with these types of networks is fault tolerance. When an intermediate node fails, a part of the network could get disconnected from the central node.

This thesis work focuses on improving the fault tolerance of the above type of networks. For improving the fault tolerance we propose and explore three solutions. The basic idea in these solutions is to use another node as a backup node when the intermediate node fails.

The first solution termed replication uses multiple directional antennae at the far-away nodes. A programmable RF-Switch is connected between the multiple antennae and the radio, the switch is programmed to select one of the directional antennae for transmission/reception as required. The second solution termed rotation uses a Stepper Motor to rotate the directional antenna for changing the link of the node from the intermediate node to the backup node. The third solution Cantenna uses a home made sector antenna called Cantenna at nodes where the beam width reaches both the intermediate node and the backup node. The link is changed simply by selecting an alternate route at layer-3 of the network stack. We document the cost and performance trade offs of these three solutions.

Bhaskaran Raman
Last modified: Mon Aug 7 23:58:52 IST 2006