Transfer Function Estimation of Digital Subscriber Lines with Single Ended Line Testing

In order to identify if a subscriber loop is suitable for a certain Digital Subscriber Line (DSL) service, the transfer function of the loop has to be estimated. Several measurement techniques exist, however Single-Ended Line Testing (SELT) is often preferred by the telecom operators because all necessary measurements can be done at the central office. The drawback is that the transfer function cannot be measured directly, but can only be calculated through the estimation of the loop make-up. In contrast to the classical approach where the SELT data is interpreted in the time domain, this paper presents a new approach by doing the identification in the frequency domain. After explaining the drawbacks of the time domain approach, the paper explains how these are avoided by using a frequency domain identification algorithm. Measurement results show the new algorithm leads to a good estimation of the loop make-up and thus of the transfer function.