Optimizing power normalization for G.fast linear precoder by linear programming

Abstract

The use of vectoring for crosstalk cancellation in the new ITU-T G.fast standard for next generation DSL systems becomes essential for efficient utilization of the extended bandwidth (up to 200 MHz). In VDSL2 (up to 30 MHz), a zero-forcing-based linear precoder is used in downstream which approaches single-line performance. However, at high frequencies, the linear precoder may amplify the signal power substantially since the crosstalk channel is much stronger than at lower frequencies. Performance could be significantly degraded by power normalization to keep the PSD below the mask. In this work, we extended a per-line power normalization scheme by linear programming (LP) optimization. By simulations using measured cable data it is shown how the LPbased scheme further improves the linear precoder and it is also capable of balancing the data rate between lines. Further, the simulations also show the non-linear Tomlinson-Harashima precoder performs better than the linear precoders.

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.…”

“…represents the channel gain from the mth transmitter to the nth receiver on frequency tone k. The extent of RWDD of a copper access cable can be assessed quantitatively by the following indicator 11 :…”

Zero-Forcing and MMSE Precoding for G.fast

“…Linear MMSE precoding performs the signal processing steps of Eq. (1) and (2). Therefore, the precoding complexity is equal to linear zero-forcing precoding which gives an advantage to nonlinear precoding.…”

“…For G.fast, mostly linear and nonlinear zero-forcing (ZF) precoding methods are discussed [2], [3]. Spectrum optimization for linear zeroforcing precoding is investigated in [4], This paper extends the approach of [4] to nonlinear precoding and demonstrates a different optimization algorithm based on quadratic programming.…”

Rate-Boosting Using Strong Crosstalk in Next Generation Wireline Systems

“…In order to transmit below the regulated power spectrum density (PSD) mask on each line and each subcarrier, power normalization is included in the linear precoder which, however, degrades the system performance at very high frequencies [9], [10]. In [11], the choice of the power normalization factor for linear precoding is posed as a linear programming problem, resulting in a moderate increase in delivered data-rate.…”