Simulations of Far-end Crosstalk based on Modified Matrices of Transmission Line

P Lafata,J Vodrazka

doi:10.5755/j01.eee.116.10.876

P Lafata, J Vodrazka

Open Access

https://doi.org/10.5755/j01.eee.116.10.876

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Abstract

Far-end crosstalk (FEXT) is the dominant source of disturbance in digital subscriber lines. One of the most promising solutions for FEXT cancellation is Vectored Discrete Multi-tone modulation (VDMT). However, this process of elimination by VDMT is mathematically very complex and it causes high computational demands in multiplexors and terminals. The promising solution would be performing VDMT only for a limited number of the most disturbing pairs in a cable. However, this method would require very accurate and realistic simulations of FEXT and its individual prediction for each pair in a metallic cable. The standard simple FEXT model is not very accurate and does not provide realistic results. That’s why a new advanced method for modeling of FEXT was developed and is presented here. This advanced FEXT model is based on the modified transmission matrices together with calculation of capacitive and inductive unbalances between pairs in a cable and it also respects cable’s internal structure. This paper includes mathematical derivation of the advanced FEXT model as well as examples of obtained results, which are also compared with standard FEXT model and with measured characteristics. Ill. 4, bibl. 8, tabl. 1 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.116.10.876

Highlights

The current access telecommunication networks still consist mostly of metallic pairs
It would be possible to perform the Vectored Discrete Multi-tone modulation (DMT) modulation (VDMT) modulation only for a limited number of the most disturbing pairs in a cable, which would simplify the whole process of coordination [6]
It is obvious that such model cannot be very accurate and provides only approximate and not very realistic results, as presented in [8]. The accuracy of this model can be sufficient for some specific applications, but the simple standard FEXT model is not very useful for the precise modeling of perspective VDSL2 lines using VDMT concept

Summary

Introduction

The current access telecommunication networks still consist mostly of metallic pairs. This paper presents a new innovative method of FEXT modeling, which is based on simulations and calculations of capacitive and inductive unbalances between pairs in a cable and using cascade matrices of a transmission line. The first part brings a description and calculations of capacitive and inductive unbalances and their influence on resulting crosstalk currents for the case of two parallel pairs in a cable This derivation will be compared with a formula for standard simple FEXT model to verify its mathematical correctness. It is possible to assume both unbalances constant and equal to their mean values for the whole length of a cable l in case of the simplified standard FEXT model, so they are constant and independent on their positions x Thanks to this assumption, it is possible to consider the element x as infinitely short and to express it by using differential term dx.

The FEXT power transfer function is defined by

Conclusions