This paper presents the development of repeaters and line equipment for an experimental digital long-haul transmission system using coaxial cable. A comparison, of different types of digital transmission systems indicates that the digital repeater hybrid system with binary transmission code is the most desirable. This development has resulted in digital pulse reshaping repeaters with very small dimensions, low cost, and good reliability. Both digital repeaters that are without timing and regenerators that include timing have been developed. Their circuitry and the corresponding signal shapes are described. The dc power-feeding system and the fault-location system are also discussed. An experimental field trial with the Deutsche Bundespost was performed over 10-repeater sections of the International Telephone and Telegraph Consultative Committee (CCITT) normal coaxial tube with a section length of 1/2 mi, The experiments confirmed that a long-haul digital transmission system of 560 Mbits/s, and later of 1100 Mbits/s using the described system concept and technology, can be established with relatively low cost and good reliability.

This paper describes a layer structured system suitable for pattern recognition which operates similar to the afferent nervous system of vertebrates. The ``system theory of homogeneous layers'' has been developed to describe signal transmission and signal processing between neuronal layers. Feature extraction in the sense of spatial filtering is performed by such a layered system with a few hierarchical stages. The last stage contains adaptive coupling which is adjusted by a learning process. The system has been simulated with a computer and parts of it with a coherent light arrangement. Its performance im recognizing handprinted characters (alphanumerics) is highly satisfactory and corresponds approximately to the human capability for this task.

A generalization of information theory is presented with the aim of distinguishing the direction of information flow for mutually coupled statistical systems. The bidirectional communication theory refers to two systems. Two directed transinformations are defined which are a measure of the statistical coupling between the systems. Their sum equals Shannon's transinformation. An information flow diagram explains the relation between the directed transinformations and the entropies of the sources. An extension to a group of such systems has also been proposed. The theory is able to describe the informational relationships between living beings and other multivariate complex systems as encountered in economy. An application example referring to group behavior with monkeys is given.