Increasing the transmission capacity of digital subscriber lines with phantom circuit and crosstalk cancelation

Abstract

The technique of realizing phantom circuits in multi-pair and multi-quad metallic cables enables creating additional transmission circuits over standard pairs and quads in metallic cables. Theoretically, these phantom circuits can be subsequently used for additional digital subscriber lines and thanks to that the overall transmission capacity of metallic cables can be possibly increased. However, the transmission rates of present digital subscriber lines are limited mainly by physical parameters of used cables, such as attenuation and impedance, and also by the disturbances caused mainly by a crosstalk. One of the most promising solutions for full cancelation of far-end crosstalk is vector discrete multi-tone modulation (VDMT). First, this article contains brief introduction about the current situation in access networks, digital subscriber lines and metallic cables. Next, the practical experiment with metallic cable and necessary equipment was performed, the phantom circuit was created over one star-quad of a cable and its parameters and characteristics were measured and they are presented in the next section of this article. Based on these results, the next part is focused on the simulation of a modern digital subscriber line (VDSL2) using phantom circuit together with and without crosstalk elimination technique using VDMT modulation. The results and calculations of possible transmission capacity of phantom circuit are compared with measured results for two most frequently used VDSL2 profiles.