Characteristics of upstream channel noise in CATV-networks

Currently there is a growing demand towards interactive multimedia services using high capacity hybrid fibre-coax (HFC) CATV-networks. With regards to the realisation of upstream traffic, many problems occur with the accumulation of noise due to the tree and branch architecture of the coaxial access network. The properties of the spectral noise signature resulting from the accumulation of noise have been studied by performing measurements in two major CATV-networks in Europe. Serious noise accumulation was found with levels up to resp. -70 dBm and -50 dBm in the two networks. Interference from short-wave broadcasting caused interference levels up to resp. -60 dBm and -40 dBm. We show that upstream noise is time dependent, and is not only caused by CATV-network subscribers.