Hybrid Digital Transmission Systems Part II: Information Rate of Hybrid Coaxial Cable Systems

Abstract

The information rate of a hybrid coaxial cable transmission system using multilevel pulse amplitude modulation is studied, assuming that the additive repeater noise has a flat spectral density and that statistically independent message symbols are transmitted. Questions considered theoretically are: (i) Reduction in information rate when some repeaters in an “all digital repeater” system are replaced by analog repeaters, (ii) Number of digital repeaters required for converting an analog system to digital service, (iii) Information rate versus number of added analog repeaters in a fixed digital repeater section, (iv) System sensitivity to repeater output power and noise spectral density variations, and (v) Bit rate versus baud rate and achieving the greatest bit rate. Curves and tables answer these questions. It is economical and theoretically optimum to use identical analog repeaters and uniform repeater spacing for the coaxial cable systems considered. The optimum gain-frequency characteristic for the analog repeaters is the same for both analog and digital transmission. Analog cable systems can be adapted directly to hybrid digital service with no compromise in theoretical performance.