In mobile multiple-access communications, not only the location of active users, but also their number varies with time. In typical analyses, multiuser detection theory assumes that the number of active users is constant and known at the receiver, and coincides with the maximum number of users entitled to access the system. This assumption is often overly pessimistic, since many users might be inactive at any given time, and detection under the assumption of a number of users larger than the real one may impair performance.

This talk describes a different, more general approach to the problem of identifying active users and estimating their parameters and data in a dynamic environment where users are continuously entering and leaving the system. The goal is to lay the foundation of multiuser detection theory in an environment where the number and the parameters of active users are unknown at the receiver, and in addition may change from one observation time to the next following a known dynamic model.

Using a mathematical tool known as Random Set Theory (which will be described, along with its applications), I shall show Bayesian-filter equations which describe the evolution with time of the a posteriori probability density of the unknown user parameters, and use this density to derive optimum detectors.

Dr. Ezio Biglieri received his training in Electrical Engineering from Politecnico di Torino (Italy), where he received his Dr. Engr. degree in 1967. In 1996--1997 he served as chairman of the IEEE Communications Society Awards Committee. In 1988, 1992, and 1996 he was elected to the Board of Governors of the IEEE Information Theory Society. In 1999 he was the President of the Society. He was the co-chairman of the IEEE 2000 International Symposium on Information Theory, Sorrento, Italy, and of ISITA 2004, Parma, Italy. He is a Distinguished Lecturer for the IEEE Information Theory Society and the IEEE Communications Society. From 1988 to 1991 he was an Editor of the IEEE Transactions on Communications, and from 1991 to 1994 an Associate Editor of the IEEE Transactions on Information Theory. From 1997 to 1999 he was an Editor of the IEEE Communications Letters, and its Editor-in-Chief from 2003 to 2005. From 1991 to 1997 he was an Editor of the European Transactions on Telecommunications, and its Editor in Chief from 1997 to 2001. Presently he is a member of the Advisory Board of the journals "Wireless Communications and Mobile Computing" and "European Transactions on Communications", a Division Editor of the "Journal of Communications and Networks," a member of the Editorial Board of the book series "Signal Processing and Communications," Marcel Dekker, Inc., and of the journal "Foundation and Trends in Communications and Information Theory." Among other honors, in 2000 he received the IEEE Third-Millennium Medal, and, jointly with John Proakis and Shlomo Shamai, the "IEEE Donald G. Fink Prize Paper Award." In 2001 he received the "IEEE Communications Society E. H. Armstrong Achievement Award." In 2004 he was presented the "Journal of Communications and Networks Best Paper Award."