By Dr. Robert L. Howald, Erik Metz, Rob Thompson , Motorola Broadband Communications Sector
With HFC reaching saturation levels in North America, much of the focus of the vendor community for infrastructure development is in the international arena. As a result, there is a wide variation in frequency plans, bandwidths implemented, transport methods, and cascade requirements. This variation occurs simply because of global differences in demographics, topology, and standards used. As a basic example, it is now quite common to require system analysis and design for deployments featuring a mixed set of analog and digital signals, where digital channels of multiple bandwidth and modulation formats exist between groupings of analog channels, within different segments of the forward band. This situation means that a mechanism for analyzing, characterizing, and understanding the effects on performance of these systems is necessary to optimally develop system solutions in these cases. Because of these needs, a user–friendly tool has been developed that predicts performance based on manual inputs on all of the key system variables – analog and digital frequency multiplexes, relative levels, slopes, output levels, and distortion variables. Perhaps the simulator’s most important task is its ability to calculate the distortion performance of any set of channels – from all analog to all digital – at any relative level of each, for any slope and output level, and for any particular distortion baseline. The simulator output can be delivered in numerical tables of every analog and digital distortion component, or plotted. Output plots can be broken down into each individual contributing analog and digital distortion component, by the order of distortion component. They can be combined into a single composite plot that includes both the analog and digital components individually by order. Or, the output can be combined into one composite map. These outputs are critically important to understanding performance characteristics, and ultimately in designing and recommending hardware for such systems.