Single-ended Line Testing - a White Box Approach

A measurement, modelling and identification system is proposed to qualify a subscriber line with the constraint that only measurements can be conducted at the Central Office. The system uses the one-port scattering parameter as a base measurement of the loop. The time domain version of this scattering parameter will be pre-processed so that the features, which are the start, maximum and end positions of a reflection, are clearly visible and hence detectable. These features are used by the interpreting expert system which performs a topology estimation of that loop. Once the topology is known, a loop model, based on the physical properties of a twisted pair line, is build and the loop can be identified using a Maximum Likelihood Estimator. Next, the end-to-end transfer function will be calculated. The results and observations of a measurement campaign using a France Telecom cable plant will illustrate the proposed Single-Ended Line Testing approach.