Study on a noise reduction system of CATV network upstream for data communication

Abstract

All cable modems used in the CATV network use the same upstream and downstream frequencies to establish bidirectional communication with their central system. The upstream frequency band usually suffers from ingress impulse noises that cause severe interference to upstream communication. We have developed a method to detect, at the central system, the places where these noises get into the coaxial cable, using signals/radio waves in the atmosphere in the downstream frequency range such as mobile phones, which are not used in the CATV infrastructure. We also developed a new tap-off system, in which the central system can turn on and off high pass filters connected to output connections in a tap to disable the upstream frequency band on each coaxial subscriber's line, when the line carries excess noises. With this detection system of ingress noise and the new tap-off system, the vulnerability of the security and the stability of the upstream channels in CATV can be improved.