Estimation of Nonhomogeneous and Multi-Section Twisted-Pair Transmission-Line Parameters

In emerging and future copper access networks, the trend goes towards exploiting higher transmission bandwidths on shorter twisted-pair cables. Methods to accurately determine relevant transmission-line parameters are a prerequisite to exploit the potential of these short-to-medium range access lines. In this paper, we propose a model-based space-frequency optimization approach initially developed for microwave applications. By utilizing the concept of capacitive length, two major advances are achieved. First, we overcome the requirement of a priori information of physical line length. Second, the number of parameters is reduced compared to prior art. We introduce two estimators to illustrate the concept. A low-complexity estimator with only two parameters per spatial unit primarily targets higher frequencies. A wideband estimator with three parameters per spatial unit extends to the lower frequencies used by operational digital subscriber line services. Performance and limitations of the approach are illustrated by both computer simulations and measurements.