Joint Spectrum Management and Constrained Partial Crosstalk Cancellation in a Multi-User xDSL Environment

Publication in the conference proceedings of EUSIPCO, Florence, Italy, 200

Improved Linear Crosstalk Precompensation for DSL

Crosstalk is the major source of performance degradation in next generation DSL systems such as VDSL. In downstream communications transmitting modems are co- located at the central office. This allows crosstalk precompensation to be employed. In crosstalk precompensation the transmitted signal is pre-distorted such that the pre-distortion destructively interferes with the crosstalk introduced by the channel. Existing crosstalk precompensation techniques either give poor performance or require modification of customer premises equipment (CPE). This is impractical since there are millions of legacy CPE modems already in use. We present a novel crosstalk precompensation technique based on a diagonalization of the crosstalk channel matrix. This technique does not require modification of CPE. Furthermore, certain properties of the DSL channel ensure that this diagonalizing precompensator achieves near-optimal performance

Optimal Multi-user Spectrum Management for Digital Subscriber Lines

Crosstalk is a major issue in modern DSL systems such as ADSL and VDSL. Static spectrum management, the traditional way of ensuring spectral compatibility, employs spectral masks which can be overly conservative and lead to poor performance. In this paper we present a centralized algorithm for optimal spectrum management (OSM) in DSL. The algorithm uses a dual decomposition to solve the spectrum management problem in an efficient and computationally tractable way. The algorithm shows significant performance gains over existing DSM techniques, e.g. in an upstream VDSL scenario the centralized OSM algorithm can outperform a distributed DSM algorithm such as iterative waterfilling by up to 380%

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

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

Spectrally Compatible Iterative Water Filling

Until now static spectrum management has ensured that DSL lines in the same cable are spectrally compatible under worst-case crosstalk conditions. Recently dynamic spectrum management (DSM) has been proposed aiming at an increased capacity utilization by adaptation of the transmit spectra of DSL lines to the actual crosstalk interference. In this paper, a new DSM method for downstream ADSL is derived from the well-known iterative water-filling (IWF) algorithm. The amount of boosting of this new DSM method is limited, such that it is spectrally compatible with ADSL. Hence it is referred to as spectrally compatible iterative water filling (SC-IWF). This paper focuses on the performance gains of SC-IWF. This method is an autonomous DSM method (DSM level 1) and it will be investigated together with two other DSM level-1 algorithms, under various noise conditions, namely, iterative water-filling algorithm, and flat power back-off (flat PBO)

A Single-Trim frequency reference system with 0.7 ppm/°C from −63 °C to 165 °C Consuming 210 μW at 70 MHz

This article presents a frequency reference system that combines high frequency accuracy and low power consumption using a single-point temperature trim and batch calibration. The system is intended as a low-cost fully integrated crystal oscillator replacement. In this system, the oscillation frequency of a power-efficient, but process, voltage, temperature (PVT) and lifetime (L)-sensitive current-controlled ring oscillator (CCO) is periodically (re)calibrated by the well-behaved frequency stability of an untuned LC -based Colpitts oscillator (LCO), which is optimized for stability over PVT variations and lifetime (PVTL). During the single-point room temperature factory trim, the frequency of the LCO is determined and the result is digitally stored. An on-chip calibration engine tunes the CCO to the target frequency based on the LCO frequency, temperature sensor information, and digitally stored trimming information, thus effectively improving the frequency stability of the ring oscillator. The relatively high-power LCO is heavily duty-cycled to minimize the overall power consumption. A prototype fabricated in a 0.13- μ m high-voltage (HV) CMOS SOI process and assembled in a plastic package demonstrates an inaccuracy lower than ±93 ppm over a temperature range from -63 °C to 165 °C across 18 samples. The presented frequency reference system, including on-chip voltage regulators and a temperature sensor, occupies a chip area of 0.69 mm2 and consumes about 64 μA from a single 3.3-V supply. The frequency error due to supply variation is roughly 92 ppm/V. The mean frequency shift due to aging, measured before and after a six-day storage bake at 175 °C, is only 52 ppm.</p

DSM in Practice: Iterative Waterfilling Implemented on ADSL Modems

New techniques emerge in the DSL world to increase the bit rate and deployment range of particular services. These techniques are better known as Dynamic Spectrum Management (DSM) applied at different levels. The increasing DSM levels can be seen as an evolution towards increasing coordination between multiple DSL lines: from level 1 and 2 (multi-user power allocation resulting in crosstalk avoidance) to level 3 (multi-user detection resulting in crosstalk mitigation). In this paper we focus on DSM at level 1 and in particular on a specific algorithm called iterative water-filling which has been implemented on ADSL modems. Measured performance results are given showing a big performance increase

ANSI Standard Contribution 2004-460: Proof of the Optimality of Optimal Spectrum Management

This contribution has been prepared to assist Accredited Standards Committee T1–Telecommunications