Zipper - a Duplex Method for VDSL based on DMT

We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise source

Protecting The Robustness Of ADSL And VDSL DMT Modems When Applying DSM

When transmitting data over an ADSL or VDSL link, performance is very important. In order to improve the bit rate that can be achieved over the copper link, a lot of techniques like power backoff (PBO) and dynamic spectrum management (DSM) focus on the crosstalk and try to operate with lower noise margin. Today's ADSL and VDSL modems are very robust. Both in ADSL and VDSL there exist reconfiguration protocols that take care of changing noise environments. The intent of the paper is to know what the impact is of DSM on the robustness of these systems. If the noise increases, the modem may lose showtime, unless the modem can adapt its PSD to compensate for the increase of noise. In this paper, we investigate for DSM the speed and robustness of various online reconfiguration protocols that exist today. We will consider a worst case noise : a noise that also impacts the communication channel that is needed to reconfigure the modem. Since reconfiguration is essential to recover from a degraded environment, the speed and the robustness of this reconfiguration protocol is very important

An improved channel model for ADSL and VDSL systems

This paper examines existing channel models used with xDSL systems and identifies a key shortcoming - namely, the implicit assumption that all impulse noise originates at the transmitter. Based on extensive data collected from the local loop, a new model is proposed which addresses this problem by combining a digital filter model of the transmission line with a distributed noise source. This better reflects the nature of a real telephone line, and thus provides a more solid basis for simulation and optimisation of xDSL systems

Simulation of DSL systems

-This report contains simulations of performance for different versions of ADSL, VDSL and SHDSL in 0.4 mm twisted pair cables. An important part of the work has been to investigate the compatibility between different DSL systems. The range of SHDSL system compliant with ITU G.991.2 Annex G has been analysed. These systems allow for bitrates up to 3.848 Mbit/s and 5.696 Mbit/ for 16-PAM and 32-PAM systems respectively. The overall conclusion is that downstream ADSL and ADSL2+ is compatible with both SHDSL Annex G and HDSL systems. The degradation in bitrate of downstream ADSL due to these systems is moderate, less than 13% compared to a cable containing only ADSL systems. ADSL subloop means that an ADSL DSLAM is installed between the local exchange and the subscriber. The purpose is to reduce the loop length between the DSLAM and the subscriber in order to increase the bitrate. This subloop signal will represent a strong interference in the downstream direction of the ADSL systems from the local exchange. As is shown in Section 7 in this report there is a severe degradation in the downstream direction of the ADSL system from the local exchange. The remedy to reduce this degradation is to use power backoff in the subloop systems. Use of power backoff regimes is not analysed in this report. The potential bitrates for VDSL2 systems have been analysed for bandplans 997 and 998. The simulations show that bandplan 997 will give almost symmetrical up- and downstream bitrates for the cables less than 800 meters, whereas for bandplan 998 the downstream/upstream ratio is close to 2:1. Three different bandwidths have been analysed, 12 MHz, 17 MHz and 30 MHz. The frequency bands above 12 MHz are used only for loop lengths less than 800 meters. The frequency bands above 17 MHz are used only for loop lengths less than 650 meters. Bandplans that makes use of the lowest upstream band U0 can still provide adequate upstream capacity (1 Mbit/s) even for loop lengths in excess of 2 km. The downstream bitrate is significant (17-18 Mbit/s) for both 997 and 998 at these lengths. A discussion of the use of ADSL in equalisation cables is given in Section 9. Alternative ways to install ADSL in pairs that contain 1+1 systems are presented in Section 10. Oppdragsgiver: Post- og teletilsyne

Optimal multi-user spectrum balancing for digital subscriber lines

Crosstalk is a major issue in modern digital subscriber line (DSL) systems such as ADSL and VDSL. Static spectrum management, which is the traditional way of ensuring spectral compatibility, employs spectral masks that can be overly conservative and lead to poor performance. This paper presents a centralized algorithm for optimal spectrum balancing in DSL. The algorithm uses the dual decomposition method to optimize spectra in an efficient and computationally tractable way. The algorithm shows significant performance gains over existing dynamic spectrum management (DSM) techniques, e.g., in one of the cases studied, the proposed centralized algorithm leads to a factor-of-four increase in data rate over the distributed DSM algorithm iterative waterfilling

Asymmetric digital subscriber line technology and the future of remote access networking

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