Proofing and Maintaining Upstream Cable Plant with Digital Signal Analysis Techniques

The deployment of upstream (or reverse) hybrid fiber coax (HFC) cable service is inherently more difficult than downstream cable service for a number of reasons. Traditional tools for maintaining the upstream plant have been similar to the tools used for downstream maintenance: sweep transmitters, sweep receivers, spectrum analyzers, and signal level meters. This equipment is typically unable to accurately capture the high speed impulsive impairments that frequently impair the return transmissions. Additionally, the upstream transmissions are frequently high-speed data packets, which are difficult to capture and analyze with traditional test equipment. This paper discusses the test and maintenance needs of the reverse plant, as well as a set of non-traditional burst-mode tests. In particular, the low frequency range of the return systems (5-40 MHz.) makes it possible to use high-speed digital circuits to generate test and diagnostic signals, and high-speed analog to digital (A-D) converters can capture test and data signals for analysis. A low cost personal computer, located at the headend, can easily perform the numerical processing and format the display of the captured data.