Abstract: The well-known Shannon capacity expression for the bandlimited additive gaussian-noise
channel is correct from the point-of-view of the mathematics, but incomplete from the point-of-view of
the physics. This is because of the emergent granularity of a lightwave at low signal levels. Quantum
information theory, though formally the proper tool to study this, is a tool too sharp to obtain insightful
answers. We propose an intermediate semiclassical information theory based on the Poisson transform
of Mandel and Wolf. The wave and particle views of a lightwave are seen to be the two sides of
the Poisson transform. The capacity of a photon channel conjectured by Gordon (1962) and Forney
(1963) based on maximum-entropy considerations is proved to be correct, and the Shannon capacity of
the bandlimited gaussian noise channel is shown to be the emergent capacity formula as the number
of photons becomes large.
Biography: Richard E. Blahut was Professor of ECE at the University of Illinois from 1994 to
2014 and Head of that Department from 2001 to 2008. He is now at the University of Pennsylvania
as an Adjunct Professor. Professor Blahut’s own research pertains to coding theory
and algorithms for signal processing and image formation. While at IBM, he pioneered passive
coherent location systems, which are used for U.S. Department of Defense surveillance
systems. He also established error-control codes that have been used in the high-speed
telecommunications systems for military helicopters and long-range cruise missiles.
That research resulted in his first textbook, Theory and Practice of Error Control Codes
(Addison-Wesley), which was published in 1983, while he was simultaneously teaching as a
courtesy professor at nearby Cornell University, his doctoral alma mater. Over the ensuring
decades, he has continued to publish prolifically. His 11th book is entitled Cryptography and
Secure Communication.
