# Fundamental contributions to Information Theory and computer networks

Contributions to Information Theory and Coding Theory

Professor Gallager has made basic contributions to the foundations of the Information age. As a student of C.E. Shannon he continued information theory in the spirit of its founder. Information theory provides the theoretical foundations to the essentials of the information age: data trans-mission, compression of text, voice, audio, images and video. Gallager’s dissertation already has introduced in 1962 error correcting codes with “Low Density Parity Checks Codes”. He was well ahead of his time, because only 33 years later it was noticed in connection with the so-called turbo codes that Gallager’s codes can achieve the absolute limits of information transmission by a few percent. The practical implication of this work of Gallager is that one can perform radio trans-mission such as in mobile networks with the lowest possible power. This is of utmost importance in the current discussion about electronic radiation. These Gallager codes are further used in deep spce transmission, in satellite communications and for high density magnetic recording.

The second important achievement of Professor Gallager is in the field of computer networks. These networks such as the Internet, satellite networks and optical fiber networks are the backbone nerve system of our society Professor Gallager in a wealth of articles and books has put these methods on the solid basis of mathematical statistics and information theory. His work for instance shows how to perform optimal routing in such networks or how to serve many users on such links.

Last but not least, Professor Gallager is an excellent university teacher who has introduced generations of students, engineers and researchers in the fascinating field of information theory, coding theory and computer networks.

Prof. Dr. Joachim Hagenauer,

Technical University Munich