Baseband Pulse Transmission in a Chain of Analog Repeaters

Simple methods that compensate for low- and highfrequency delay distortions, which are the predominant distortions in a baseband hybrid digital transmision line, have been developed. Compensation for low frequency distortion is optimized by a rational minimum-phase function. Compensation for high-frequency distortion is attained by a combination of an optimum cutoff shape and an all-pass network. A local minimum problem in the optimization of the all-pass network is eliminated by a procedure that provides appropriate initial conditions. Combined realization of both low- and high-frequency delay compensation by a slightly active network results in very simple circuitry. The efficiency of this simple compensator is confirmed experimentally in a subline with 15 analog repeaters. In this experimental system, two subpredominant distortions, nonlinear distortion and equalization error, were experienced. Compensation for these distortions is also studied by the method reported in the literature and by a simple adaptive equalizer, respectively. Based on the results obtained above, the feasibility of a baseband hybrid digital transmission system is discussed. The simple compensator mentioned above will be very useful in realizing an economical hybrid digital transmission system with the help of the simple adaptive equalizer. A system that utilizes alternate mark inversion (AMI) pulse train seems to be feasible without the help of the adaptive equalizer.