Transfer Function Estimation of Telephone Lines from Input Impedance Measurements

The ability of a specific telephone line to support a certain digital subscriber line (DSL) service is determined by its downstream and upstream data rates, which are mainly dependent on the line´s transfer function. In this way, methods for transfer function estimation play an important role on proper DSL deployment. Most of the existing methods derive the transfer function via line topology identification (LTI) processes. This paper proposes a method which directly estimates the transfer function of telephone lines without any previous LTI process. The results obtained from both simulations and experimental procedure using twisted-pair cables indicate that the proposed method achieves accurate estimations even for lines with bridged-taps.