Hfc Network Transmission Of Digital Television Signals

Nowadays, the digital TV broadcasting service is developing quickly in many cities in China. The changing of TV broadcasting from analog to digital will be a challenge to most of our television technicians. The main structure of China's present Community Antenna Television Network is HFC (Hybrid Fiber Coax). What we need to do to complete the change is adding coders and modulators in Head-end and decoders and demodulators in Set-Top-Box, the consumer's digital television receiver, then change the signals transmitting in HFC network from analog to digital. However, as an analog signal and a digital signal are coded and modulated in different ways, it's difficult to predict if there will be new problems when digital signal travels in the HFC network which is used for transmitting analog one only in theory. As the result, synthesizing the servicing work of digital television in four months since digital television generalization project began in Nanjing, here are some analyses in theory and experimentations in real situation to study whether the status of HFC network will influence the QAM signal traveling in it. In this thesis, some common defects in HFC network system likely to influence the digital television signal were simulated, and some typical external interference which will influence the digital signals was discussed. At the end of this thesis, considering the characteristics of the two kind malfunctions which will influence the digital signals'transmission, how to eliminate them was discussed.