The goal of this research is to investigate transmission scheduling, routing, and multiple access in the context of a mobile radio network, using spread spectrum signal modulation. Particular emphasis is currently being paid to strategies that thwart traffic analysis by unauthorized stations and data compression schemes for packet networks, with particular attention to priority assignments.

Performance evaluation and design for communication networks of the future is conducted. Emphasis is placed on large, high-speed networks. Both optical and electronic networks are considered. Topics include (1) spectral response of queues and diffusion approximation, (2) continuous traffic in packet switches, (3) multirate circuit switches, (4) optical interconnection, and (5) dynamic load balancing. Analysis consists of a mixture of exact probabilistic and combinatorial methods and simulation. Design is motivated by modeling and analysis and aided by optimization tools of both combinatorial and nonlinear iterative types.

The goal of this study is to develop new methods for the analysis of acquisition schemes for spread-spectrum communication. Much of the recent research is concerned with new techniques for serial and parallel acquisition with emphasis on suboptimal schemes that are easy to implement and yet have performance that is only slightly worse than that of optimal schemes.

Our objective is to investigate block and lattice charged codes with a new approach and to exploit the advantages of this approach to provide bounds on decoding complexity and to develop efficient maximum-likelihood decoders. The precise trade-off between complexity and performance is studied. We also investigate modulation codes for input-constrained channels. Viewing block codes as dynamical systems makes it natural to consider applying results from algebraic coding theory for the design of modulation encoders. Ways of integrating a prescribed error-correction capability within such encoders are also studied.

We will investigate creative new techniques for reliable transmission of digital information. The main objectives are to achieve a deep theoretical understanding of the underlying problems and to develop practical coding schemes that can be implemented in real applications. Intersymbol interference channels are emphasized, as are the digital speech and image transmission channels characterized by unequal input probabilities and subjective distortion criteria. Our research comprises two major activities: to extend prior work in trellis structure and trellis decoding of block and lattice error-correcting codes and to develop novel data transmission techniques particularly suited to specific channels of practical importance and extending beyond the classical error-control approach.

The goal is to study lossy source coding techniques with applications to image and speech coding. Low-complexity data compression techniques are investigated both theoretically and algorithmically. One important tool used in this research is vector quantization. Robust or universal source coding is studied, where the source is assumed unknown in advance. Also, joint source/channel coding is studied with an emphasis on discovering good codes and obtaining some theoretical understanding of the performance of source coders in the presence of channel noise under a complexity constraint.

The purpose of this grant is to conduct joint research with scientists at the Technical University of Budapest in Hungary. The research areas have so far focused on such problems as: universal lossy source coding theory, convergence rates for source coding problems, nonparametric estimation theory, noisy channel vector quantization, pattern matching, and concept learning.

This research project has been studying two different problems. The first is source coding techniques and theory for packet networks, which includes priority control strategies for buffers accepting speech and image data. The second area of research is the design of spherical codes for channel coding, which involves theoretical analysis and practical implementation.