| 1. |
- Acatauassu, Diogo, et al.
(author)
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Simple and Causal Copper Cable Model Suitable for G.fast Frequencies
- 2014
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In: IEEE Transactions on Communications. - 0090-6778. ; 62:11, s. 4040-4051
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Journal article (peer-reviewed)abstract
- G.fast is a new standard from the International Telecommunication Union, which targets 1 Gb/s over short copper loops using frequencies up to 212 MHz. This new technology requires accurate parametric cable models for simulation, design, and performance evaluation tests. Some existing copper cable models were designed for the very high speed digital subscriber line spectra, i.e., frequencies up to 30 MHz, and adopt assumptions that are violated when the frequency range is extended to G.fast frequencies. This paper introduces a simple and causal cable model that is able to accurately characterize copper loops composed by single or multiple segments, in both frequency and time domains. Results using G.fast topologies show that, apart from being accurate, the new model is attractive due to its low computational cost and closed-form expressions for fitting its parameters to measurement data.
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| 2. |
- Medeiros, Eduardo, et al.
(author)
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How Vectoring in G.fast May Cause Neighborhood Wars
- 2014
-
In: [Host publication title missing]. - 9781479920037 ; , s. 3865-3870
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Conference paper (peer-reviewed)abstract
- Emerging wireline transmission systems such as G.fast use bands up to around 200 MHz on short cables. A key enabler for achieving the aspired throughput of several hundred Mbit/s is joint processing of transmit signals in downstream direction as well as joint processing of receive signals in upstream direction through techniques referred to as vectoring. A new challenge in such systems are sudden and severe changes in the channel matrix caused by changing terminations on lines outside the vectoring group. Such events can be caused by users disconnecting their modems, turning them on or off, or on-/off- hook events on lines that still support the plain old telephony service. This work presents channel measurements capturing the impact of termination changes caused by modems or handsets. An analysis of the impact of these sudden changes on the signal- to-noise-power-ratio in vectoring systems reveals that throughput and stability can be seriously degraded. The potential of decision- directed channel tracking based on least squares estimation is investigated.
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| 3. |
- Medeiros, Eduardo, et al.
(author)
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Modeling Alien-Line Impedance Mismatch in Wideband Vectored Wireline Systems
- 2014
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In: IEEE Communications Letters. - 1089-7798. ; 18:9, s. 1527-1530
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Journal article (peer-reviewed)abstract
- Sudden changes of channel coefficients in a wideband vectored wireline system (such as G.fast) due to changes in the terminating impedance of lines outside the vectored group can seriously degrade stability and throughput. This letter presents a model that predicts the impact of termination mismatch based exclusively on crosstalk data for the properly-terminated state. Experimental results confirm a tight fit between model and mea- surements. The model allows analysis of system performance and stability without dedicated crosstalk measurements for mismatch cases.
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| 4. |
- Müller, Francisco, et al.
(author)
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Optimizing Power Normalization for G.fast Linear Precoder by Linear Programming
- 2014
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In: 2014 IEEE International Conference on Communications, ICC 2014. - 9781479920037 ; , s. 4060-4065
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Conference paper (peer-reviewed)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.
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