Analysis of VOD Technology and the Noise in Transmission Channel of HFC

By analyzing the system structure of video on demand (VOD) and spectrum characteristics based on hybrid fiber coaxial (HFC) transmission system, the conclusion that there are several different kinds of signals in HFC is drawn. And the reasons that cause the uplink transmission noise and downlink transmission noise have been analyzed deeply. Finally, some points for attention are presented for design and installation: (1) limit the concatenated level of CATV cable amplifier and reduce the structural noise produced by circuit; (2) increase optical access point and limit the user number in every access point: (3) adopt the way of simple cable coiling and to bring down the interference of impulse noise that users´ produce to system; (4) adopt high-pass filter with high performance and coaxial cable with good shielding performance; (5) When transmission line is set, it should be set far from the circumstances as possible where there are much heavy electromagnetic interference such as high voltage wire, distribution station, etc, to raise the function of the whole system.