By Donald Kirk and Michael J. Paolini, St. Petersburg Communications Corporation
A digital PCM system is proposed to implement long- haul video systems for the CATV industry. A comparison is made between PCM systems and wideband FM systems in terms of repeaterability versus additional occupied signal bandwidth. This is followed by a noise analysis of coaxial cable to determine the correct PCM format and bit information rate. An eighty megabit system is selected, which uses an eight bit code in a four level-eight level-eight level pulse sequence per video sample. The selected PCM system is then evaluated for its performance on both a long-haul cable system and a long-haul microwave system. Performance calculations are made on a 500 mile cable system in terms of error rate and its related video signal to noise ratio. Repeater spacings are computed for various configurations, including the replacement of the digital regenerators with analog amplifiers. Additional performance calculations are then made on a 3000 mile microwave system, including the effect of simultaneous Rayleigh fading.