By Jerry Monroe, Philips Broadband Networks and Ray Thomas, Time Warner Cable
Standardization of digital capabilities of existing and to-be deployed HFC networks calls for advanced techniques of measuring digital performance.
The authors quantify high-speed forward (downstream) data capabilities through the use of the Bit Error Rate in the Noise Notch (BNN) technique. Additive White Gaussian Noise (AWGN) is used to simulate full forward path digital loading on a selected portion of a network under test. Inserted into this fully loaded bandwidth is a non-forward-errorcorrected 6 MHz, 256 QAM evaluation signal.
Signal levels are varied, and as a result, the true bit-by-bit dynamic range of operation is fully understood. Additionally, the effects of the digital tier on analog channels can also be measured by this technique.
Benefits for the manufacturer are a repeatable test, which quantifies predicted performance and can easily be demonstrated for network operators. Benefits for the operator include the ability to certify and to re verify performance of recently deployed networks.
This technique can also be used successfully in predicting performance of legacy networks when a fully loaded digital tier is to be added.
The authors present lab tests using this technique with analog loading provided by CW carriers or analog headend signals.
By using this technique, bandwidth management of the forward path can be easily achieved, since the dynamics of the path will be understood. This tool will be very important to deployed networks and their need to know how much headroom is available for future digital services.