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Communications
^ Fair Scheduling and Admission Control for Shared-Channel Wireless Packet Networks
V. Bharghavan,* R. Srikant,* S. Shakkottai, A. Eryilmaz
National Science Foundation

Fair scheduling of traffic sources in wireless networks is difficult due to bursty channel errors and location-dependent channel capacity. In this project, researchers study MAC, scheduling and admission control algorithms for indoor and outdoor wireless networks that allocate the available bandwidth in a fair manner to competing sources.

^ High-Performance Decoding of Algebraic Codes Beyond their Packing Radii
R. Blahut,* N. Shanbhag, R. Koetter
National Science Foundation, CCR-0073490

The objective of this research is to investigate practical and theoretical aspects of interpolation/factorization algorithms that were pioneered by M. Sudan for decoding beyond half the minimum distance of Reed-Solomon, Bose-Chaudhuri-Hocquenghem (BCH), and algebraic geometry codes. The research has two main thrusts. The first is the characterization of the decoding algorithm and its complexity or performance trade-off, together with subsequent improvements in the decoding of BCH and algebraic geometry codes; these are at the theoretical core of this proposal. The second main thrust is the development of efficient computational architectures for implementing the algorithms and the demonstration of the feasibility and practicality of very large scale integrated circuit (VLSI) implementation of decoders that will dramatically outperform the decoding algorithms that are in use in current commercial communications and storage systems.

^ Codes on Graphs, Factor Graphs, and Iterative Algorithms
R. Koetter*
National Science Foundation Career Award, CCR 99-84515

The primary focus of this research is the investigation of creative new methods for reliable transmission of information in the context of modern error-control techniques. Error-correcting codes are an essential part of modern communication and storage systems and much of today's technology would not be possible without them. This study is focused on graph-based, iterative decoding algorithms, which, without doubt, are one of the most significant coding-theoretic developments of the last decade. The goal of the investigator's research is to develop a broad, analytical, and constructive approach to research and education, unifying graphical models, coding theory, and iterative algorithms. The interplay between codes on graphs and other areas, like iterative graph-based algorithms, system theory, and network information theory, is in the focus of this investigation with the goal of discovering and utilizing fundamental connections between these fields.

^ High-Performance Short Iterative Codes
R. Koetter*
Motorola, Inc.

This project aims at developing excellent codes for application requiring short- to moderate-length (64 bits to <1,000 bits) codes. Traditional coding schemes for these lengths rely typically on algebraic constructions or convolutional codes. Researchers strive to make the tremendous gains achievable for long blocklengths (> 10,000 bits) by turbo and other iteratively decodable codes available for much shorter code length.

^ Unwrapping Phase Images: Theory and Applications Using Probabilistic Inference Techniques
R. Koetter,* B. Frey, D. Munson
National Science Foundation, CCR 01-05719

Phase unwrapping in two-dimensional topologies is a signal processing problem that has been studied extensively over the past 20 years and has important applications, such as medical imaging and synthetic aperture radar. However, despite its importance in science and engineering, to date, phase unwrapping in two-dimensional grids has remained an essentially unsolved problem. This research takes a fresh approach to the problem using methods from probabilistic inference. The work not only holds the promise of resulting in powerful phase unwrapping schemes based on the sum-product algorithm and structured variational methods, but also has the potential to provide deep theoretical insight into the ill-posed nature and solvability of the phase unwrapping problem. Such an insight is extremely important for guiding the development of practical algorithms.

^ Design Principles for Wideband Wireless Communications
V. V. Veeravalli,* Ashok Mantravadi
Cornell University (NSF CCR-9980616)

This research is aimed at enhancing the performance of wideband wireless multi-access systems by optimizing tradeoffs between coding and spreading, capitalizing on advantages afforded by spatial diversity, and developing techniques for accommodating multirate users.

^ New Techniques for Optimizing the Quality and Capacity of Wireless Communication Systems
V. V. Veeravalli,* J. F. Chamberland, Y. Liang, N. Wang
National Science Foundation, Faculty Early Career Development, Presidential Early Career Award for Scientists and Engineers, CCR-0049089

The research in this project is directed toward the development of future generation multimedia wireless communication systems. Specifically, the research spans the following four areas: wireless channel modeling and analysis; information theory for wireless systems; wireless CDMA systems; and dynamic radio resource management.

^ Research at the Frontier of the Physical Layer
V. V. Veeravalli,* R. Prakash, K. C. Reddy
National Science Foundation, CCR-0049085

The research conducted under this grant has a broad perspective from the viewpoint of the physical medium in that it covers wireline (twisted pair or a coaxial cable); wireless (satellite, cellular/PCS, or wireless local area network, WLAN); and recording, (magnetic or optical disc) media. The research has a narrow focus in that the problems addressed all involve some form of forward error control (FEC). A major component of the project is on coding and information theory for wireless CDMA systems.


Summary of Engineering Research