Ad Hoc Wireless
Channel-Adaptive Protocols for Exploiting Spatial Diversity
Michael Souryal and Nader Moayeri (Advisor)
This work is developing new communication techniques for multihop, ad hoc wireless networks enabling them to adapt to the time-varying nature of the wireless channel and to exploit the inherent spatial diversity of these networks. Ad hoc networks are decentralized versions of today's cellular networks and wireless LANs that, due to their flexibility and robustness, are envisioned for use in a variety of civilian and military applications, including public safety, disaster recovery and homeland security. Incorporating channel-adaptive techniques, such as adaptive routing and modulation, can increase the capacity and quality of service of these networks.
Ad hoc networks achieve greater geographic coverage and improved energy and spectral efficiency through multihop relaying¾that is, relaying data through multiple nodes to reach the final destination. However, each link in the path is subject to unpredictable, time-varying signal fluctuation due to multipath fading and interference from other transmissions in the network. Most previous work in ad hoc networking has assumed very simple channel models, at times ignoring the fading and interference effects. As a result, existing communication protocols for multihop routing suffer adverse effects when operating in realistic environments.
Taking advantage of the spatial diversity available in multihop networks through alternate routes, we are developing new cross-layer protocols that permit selection of and rapid adaptivity to high capacity routes. The medium access control (MAC) and routing layers are given access to information at the physical layer in the form of signal strength and interference measurements. Based on this information, these layers opportunistically select favorable links on each hop of the multihop path. The routing and MAC layers coordinate to perform this link selection in a timely manner to adapt to short-term fading processes. Preliminary results indicate a decrease in end-to-end delay and jitter, important quality-of-service parameters for real-time applications.
Michael R. Souryal
(Advisor: Nader Moayeri)
Advanced Network Technologies Division
Information Technology Laboratory
National Institute of Standards and Technology
100 Bureau Drive, Mail Stop 8920
Building 820, Room 442
Gaithersburg, MD 20899-8920
Tel: (301) 975-4342
Fax: (301) 590-0932
Sigma Xi membership: No