Performance of linear and non‐linear precoders in G.fast ultra‐broadband DSL networks

Abstract

Summary The new International Telecommunication Union Telecommunication G.fast standard for next‐generation ultra‐broadband digital subscriber line systems has stipulated mandatory use of vectoring for crosstalk mitigation. In this paper, we study the performance of downstream precoders in G.fast networks utilising the extended bandwidth up to 212 MHz. In particular, the issue of strong crosstalk encountered in practical copper cable bundles at high frequencies giving rise to channel matrices which are not row‐wise diagonally dominant (RWDD) as predicted theoretically, as well as the ramification of deploying precoders designed based on the RWDD assumption in practical G.fast channels are studied. To serve these purposes, an enhanced stochastic far‐end crosstalk (FEXT) model which provides distinct FEXT transfer functions with the dispersion range characterised experimentally whilst encompassing the dual‐slope FEXT encountered in non‐RWDD cables is used for evaluating the performance of precoders in diverse G.fast deployment scenarios. Furthermore, the performance sensitivity of precoders under realistic amount of channel estimation errors is investigated on a common framework, allowing a direct and fair comparison between linear and non‐linear precoders. Results show that the nonlinear optimal precoder outperforms linear precoders in all channel conditions; however, the former is found to be slightly more sensitive to channel estimation errors on shorter loops. Copyright © 2016 John Wiley & Sons, Ltd.

Multimode precoding for crosstalk mitigation in ultra‐broadband DSL systems

“…More explicitly, the modelled FEXT is assumed to exhibit a first-order slope of 20 dB/decade in the equal-length FEXT up to 75 MHz and a second-order slope of 40 dB/decade above 75 MHz. 11,14 Although the performance of PTCM-QMP and PTCA-QMP is very close, the PTCA-QMP is found to exhibit slight performance gain over the PTCM-QMP counterpart for all the users with maximum data rate gain of 0.57%. For the sake of fair comparison, both the PTCM-QMP and the PTCA-QMP adopt identical switching thresholds as follows: ε = 10 −4 , δ = 1.3 × 10 −4 , α = 1.1 × 10 −2 , and β = 0.1.…”

“…Because of QR decomposition, the THP can even outperform the FEXT-free scenario. 11,14 Although the performance of PTCM-QMP and PTCA-QMP is very close, the PTCA-QMP is found to exhibit slight performance gain over the PTCM-QMP counterpart for all the users with maximum data rate gain of 0.57%.…”

“…From (14), the achievable bits per symbol of user n on frequency tone k using the THP can be expressed as …”

“…Throughout the simulations, it is assumed that perfect channel state information is available at the DSLAM and the simulation setup for the G.fast 212 MHz system, direct channel, and FEXT model follows that adopted in Chuah et al 14 In particular, the nine-parameter the Netherlands Organisation for applied scientific research (TNO) model proposed in van den Brink and van den Heuvel 15 is used to characterize the direct channel, whose parameters are set according to Chuah et al, 14 which have been experimentally obtained from an in-house measurement campaign, followed by parameters extraction using the two-port iterative cable modeler (TICAM) software module 16 to replace measured data by a parametric model. To accurately model the FEXT inflicted over the 212 MHz spectra, the enhanced European Telecommunications Standards Institute (ETSI) stochastic dual-slope FEXT model 14 is adopted.…”

“…The performance of precoders will be evaluated under two deployment scenarios. Firstly, we consider a four-user mixed-length scenario with loop lengths of 40, 110, 180, and 250 m. Secondly, to investigate the performance of precoders under more diverse loop lengths, the 16-user mixed-length scenario adopted in Chuah et al 14 is considered. The shortest and longest loop lengths of this loop configuration are 25 and 250 m, respectively, with a 15 m increment from CPE#1 until CPE#16.…”