Pavan Kumar: Master's Thesis, May 2006

Cadence Silver Medal - 2006

Best M.Tech. Thesis in the Departments of Computer Science & Engineering and Electrical Engineering for Good Academic Performance, Innovation in Thesis, Development of New Technology and/or Substantial Betterment of Existing Technology

Title: Design, Implementation, and Evaluation of new MAC Protocols for Long Distance 802.11 Networks

Abstract: 802.11 MAC is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and was designed to be used in an indoor environment where a small number of wireless nodes share a common channel. It has been shown in Digital Gangetic Plains project that 802.11 hardware can be used beyond its intended use of WLANs by connecting long distance wireless links spread over tens of kilometers. These links have been used to operate voice (telephone through Voice over IP) and video (telemedicine through Video over IP) applications. But the existing MAC protocols like CSMA/CA that operate on 802.11 hardware do not work well in these outdoor wireless networks because of hidden node problem, huge Round Trip Time (RTT) and unnecessary contention.

In this thesis, we therefore motivate the need for design and development of new MAC protocols to operate on point-to-point and point-to-multipoint long distance links to obtain better performance and flexibility compared to CSMA/CA. This report describes the implementation of two new MAC protocols 2P and SRAWAN that are suited for these long distance 802.11 networks. SRAWAN is designed from scratch. Even though the design of 2P exists, a significant challenge here is the implementation of these protocols on the off-the-shelf 802.11 Atheros hardware to preserve cost benefits. We have implemented 2P and SRAWAN by exploiting the flexibilities in the HAL code and Madwifi driver of Atheros AR5212 chipsets. The report then presents experimental evaluation of 2P and SRAWAN. The outdoor experimental results on a network of two links show that 2P achieves significant performance (throughput) improvement over CSMA/CA (by more than 45%) for point-to-point links and SRAWAN outperforms CSMA/CA by more than 40% for point-to-multipoint long distance links. On larger networks, we expect an even higher throughput improvement. We expect the protocols and the implementation to be deployed on Ashwini network in Bhimavaram, Andhra Pradesh for providing Internet connectivity to remote rural villages.

Bhaskaran Raman
Last modified: Mon Aug 7 23:17:57 IST 2006