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"Utilizing Beamforming Antennas in Wireless Networks", by Romit Roy Choudhury, University of Illinois at Urbana Champagne

I read this thesis mainly due to two reasons:
a) It is recent (2006) and
b) It is close to my field of interest.

Romit Roy Choudhury, in his thesis, proposes the use of directional/beamforming antenna in wireless multihop networks. With beamforming antennas, the ability to guide RF energy in desired directions can lead to higher spatial reuse of the channel. Also, the higher communication range of beamforming antennas can be exploited to achieve stronger network connectivity, and to obtain fewer hop routes. However, existing protocols considered suitable for omnidirectional antennas are incapable of achieving these benefits. Hence, his thesis studies the impact of beamforming and proposes efficient utilization of directional antennas in developing new Medium Access Control (MAC) and Routing protocols. He identified the problems with basic directional MAC protocol, like the new hidden terminal problem and deafness.

To handle deafness, he proposed ToneDMAC, where an out-of-band tone is used to inform neighbors about ongoing communication. He also proposed Capture-Aware Directional MAC protocol, where each beam pattern of antenna is monitored and checked whether it captures only overheard packets, and if so, it is black-listed for some time and monitored again.

In Routing layer protocol, he optimizes Dynamic Source Routing (DSR) protocol for utilizing directional antenna's efficiency. He proposes to transmit the route request packets in each of the antenna patterns, and then improved the idea by partially sweeping over fewer antenna patterns in coarser grain. Also, the route request is not transmitted to the direction from which it is arriving. He introduces the capture effect as well in his next routing protocol, which he terms as "Capture-Aware Routing Protocol". Each route is associated with a cost of capture-effect that it experiences, and based on this cost, the route is chosen.

The last chapter of his thesis summarizes the proof of concept of some fundamental knowledge in wireless domain, using electronically steerable passive array radiator (ESPAR) antenna. He also demonstrates the improvement in throughput and latency of using directional antennas over omni-directional antennas in wireless network. However, we do not see any implementation of the proposed protocols in real-life. All the results shown in his thesis are from simulation.

The most interesting part of his thesis is his approach towards the problem and the resultant solution. I liked the way he defines and points out the problems in wireless domains. His work is not restricted in a single-layer approach to utilize beamforming antennas efficiently, rather he shows how cross-layer design can improve and motivates the use of directional antennas in multi-hop wireless network. I often come across papers which deal with implementation approaches and lessons learnt in doing the experiments. Some people would criticise this thesis due to lack of implementation, but I find this thesis much appealing than those which cannot show any solution, rather just hand waves about the implementation issues and lessons learnt during deployment. This thesis definitely contributes in wireless domain scenario and is a genuine motivation for using beam steering antennas in radio layer of wireless networks.

Last modified 4 December 2007 at 7:25 pm by sahad