RESEARCH INTERESTS Multiuser information theory Communication theory Communication networks Cryptography Information theory and statistics.

My current research is in the field of multiuser information theory and coding. It deals with the study of models for reliable digital communication between multiple users, characterization of the fundamental limits of performance, and analysis of coding and modulation schemes for attaining this performance. Applications include satellite communication, mobile cellular and adhoc networks, and wideband data communication in radio frequency (RF) and optical modes. One aspect involves studying communication systems in which the transmitters and receivers lack a full knowledge of signal degradation in the transmission channel. This occurs, for instance, in mobile wireless RF communication owing to unpredictable time-varying channel "fading," and in free-space optical communication when the intensity of a propagating optical signal fluctuates according to random changes in refractive index caused by atmospheric turbulence. Such variations in the characteristics of the transmission channel can sometimes be measured or estimated as in the examples above, or can be completely arbitrary (as when an RF link is jammed). Considering such models for wireline as well as wireless RF and optical applications, I am investigating fundamental performance limits of coded communication, including how any knowledge of channel conditions can be used optimally in devising suitable transmitter and receiver schemes. Multiuser communication systems have the distinctive feature that data to be compressed and transmitted by various users are often correlated across the users, e.g., measurements by the nodes in a sensor network. I am investigating connections between distributed source coding and channel coding for such correlated data by multiple users on the one hand, and secret key generation for encrypted connection among these users on the other hand. In particular, I am exploring the use of algorithms for multiterminal source coding and channel coding in developing schemes for network security using information theoretic principles.

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