Optimal and nearly optimal binary and multilevel digital transmission systems

A comparison of binary and multilevel digital transmission systems is presented. Intersymbol interference, as well as white or colored noise, is considered. The eye pattern is calculated with the aid of the step response, and related laws are derived. The marginal signal-to-noise ratio for digital transmission systems with code transparency is evaluated. Its maximization leads to optimal systems. A receiver with and without quantized feedback is applied alternatively. For the first case the optimal system is determined using the calculus of variations. Technically more interesting nearly optimal systems are then compared, where the cable attenuation is considered constant or proportional to the square root of frequency. The binary system with quantized feedback proved to be optimal as compared to all other systems.