Driton Statovci

Dynamic spectrum management for energy-efficient transmission in DSL

Dynamic spectrum management (DSM) is an important technique for mitigating crosstalk noise in multi-user digital subscriber line (DSL) environments. Until now, most of the proposed algorithms for DSM have been designed solely for the purpose of bitrate maximization. These algorithms assume a fixed maximum total power and neglect the energy consumption in DSL modems. However, since recently there is a strong interest in the DSL field to reduce energy consumption as shown, e.g., by the European Commissions¿ code of conduct on energy consumption of broadband equipment. In contrast to traditional DSM, this paper will show how DSM can be used for minimizing the energy consumption. We will formulate a global optimization problem for energy minimization and discuss several of its peculiarities compared to the current DSM problems. Furthermore, we derive an iterative, dual-based and semi-distributed algorithm for its local solution, which we call energy-efficient spectrum balancing (EESB). The performance of the algorithm is evaluated through simulations, which show similar results to optimal schemes. In addition, EESB achieves substantial energy savings that can be exploited by adapting the transmit powers to users¿ bitrate demand.

A PLC broadband channel simulator for indoor communications

In this paper we propose a frequency-domain broadband channel simulator for indoor power line communications (PLC). We follow a bottom-up approach by defining the topology in a fixed mode or in a random mode. The channel matrix coefficients are derived by using the well-known two-port ABCD line modeling. The channel simulator takes into account cable characteristics, effective lengths of branches, and also loads by selecting the load impedances from a predefined set. We will show how to use our bottom-up channel simulator to generate random PLC channels and to match measurement results with a predefined approximation.

Measurement and simulation framework for throughput evaluation of narrowband power line communication links in low-voltage grids

High-data-rate narrowband Power Line Communication (PLC) is a prominent candidate for smart grid communications in the low-voltage grid at low operational costs. However, the power-line channel is fairly harsh in terms of time-variance, frequency selectivity, and observable impulsive and narrowband noise sources. These unpredictable phenomena motivate selective measurement campaigns in addition to common channel modeling. While previously published measurement studies were fairly limited in duration, we report on a measurement setup for capturing power-line channels over weeks and show measurement results highlighting day-dependent channel effects on selected communication links. Furthermore, previous performance simulations are typically based on simplified channel models and limited in terms of the detail level at the physical layer or lack a consideration of higher-layer protocol overhead. We present a novel simulation methodology which is based on detailed physical-layer simulations exploiting measured, time-varying channel data, and incorporates protocol overhead models for transport-layer throughput estimation. Exemplary simulation results include the newest, commercially available narrowband PLC standards in their latest version, that is ITU-T G.9903 (G3) and G.9904 (PRIME), as well as IEEE 1901.2.

Dynamic Spectrum Management for Standardized VDSL

Dynamic spectrum management (DSM) improves the capacity utilization of twisted-pair cables by adapting the transmit power spectral density (PSD) of modems to the actual noise environment and channel conditions. Earlier proposed DSM algorithms do not take into account the standardized very high speed digital subscriber line (VDSL) constraints on the allowable transmit PSDs. However, VDSL modems support only restricted transmit PSD shapes resulting from the standardized power back-off (PBO) method, which is controlled by a small set of parameters. Furthermore, since all modems are currently using the same PBO parameters their bit rate performance is severely limited. In this paper, we show how to effectively exploit the standardized PBO concept for DSM to significantly boost bit rates. We also present a low complex DSM algorithm, the user unique PBO (UUPBO) algorithm, for calculating PBO parameters that are uniquely optimized for each modem.

Robust Spectrum Management for DMT-Based Systems

In recent years an increasing effort was made to reduce the energy consumption in digital subscriber line equipment. Dynamic spectrum management (DSM) has been identified as one promising method to achieve energy-efficiency in discrete multitone based systems. An open research question is how to ensure system robustness when applying highly optimized energy-efficient spectrum management. In this paper, we study the problem of uncertainty in crosstalk noise and parameters, the knowledge of which is indispensable for many DSM algorithms. We introduce robust optimization for spectrum balancing as a technique to achieve feasibility of the optimal power-allocation under a deterministic parameter uncertainty model. This can be seen as an extension of current schemes for spectrum balancing. As a special case we consider the simple strategy of scaling the crosstalk parameters to their worst-case values, which corresponds to a specific uncertainty model and entails no changes to current DSM algorithms. Finally, we quantify the benefit in worst-case performance and the price in terms of energy by simulations.

Adaptive subcarrier allocation, power control, and power allocation for multiuser FDD-DMT systems

This paper considers the problem of adaptive subcarrier allocation, power control, and power allocation for multiuser frequency division duplex-discrete multitone (FDD-DMT) systems in a Gaussian interference channel. Assuming perfect knowledge of all channel and crosstalk transfer functions, we formulate the problem as an optimization problem to maximize jointly the sets of downstream and upstream bit rates for given user priorities. We show that the optimization problem belongs to the class of nonlinear mixed-integer optimization problems. We explain that for the multiuser FDD-DMT systems such problems can not be solved with existing algorithms. Instead, this paper introduces a new suboptimal normalized-rate iterative algorithm of low complexity.

Energy-saving by low-power modes in ADSL2

The large number of broadband users and its forecast growth has recently triggered research on energy-efficiency in digital subscriber lines (DSLs). A promising technique are low-power modes (LPMs) as standardized in asymmetric DSL 2 (ADSL2) which let the DSL connection operate in downstream direction with reduced transmit rate and power. We study the problem of optimizing the LPM rate-level for energy-efficiency. A traffic-independent rate setting is proposed based on an analytical competitive framework. Also, a Markov chain based LPM model is derived which facilitates the fast numerical optimization of the LPM rate-level under realistic traffic models and system constraints. Simulation results under various traffic settings and DSL scenarios demonstrate energy savings by LPMs of around 30-40% of the ADSL2 transceivers power consumption. Furthermore, they provide insights on how to set the LPM rate-levels in practice for energy-efficient DSL operation.

Energy-Efficient DSL Using Vectoring

A multi-user signal coordination scheme known as Vectoring will play a crucial role in next generation digital subscriber lines (DSL). Previous studies have demonstrated that vectoring increases the bitrate of DSL systems due to its ability to mitigate the interference. In this work we show how Vectoring improves the energy-efficiency of DSL over state-of-the-art spectrum balancing methods. In addition we investigate the impact of channel-state information errors and low-complexity implementations on the performance of Vectoring. We find that Vectoring yields large energy savings in terms of line-driver power consumption even under high channel estimation errors.

Enabling greener DSL access networks by their stabilization with artificial noise and SNR margin

Low-power modes (LPM) are a standardized means in asymmetric digital subscriber lines (ADSL) 2 for reducing the power consumption at the central office. However, the activation of LPMs is hampered by the operators’ concern for instability introduced by frequent transmit power changes. The injection of artificial noise (AN) has been proposed as a standard-compliant stabilization technique. We develop an analytical solution for setting the AN power spectrum. Based on this solution we jointly optimize the AN power spectrum and the signal-to-noise ratio (SNR) margin. Simulation results show the performance gain in terms of rate and energy compared to heuristic rules for setting the AN power spectrum. We propose and demonstrate three approaches for evaluating the performance of AN-enabled DSL systems, including (a) joint spectrum balancing, AN, and margin optimization, (b) single-user worst-case-stable optimization, and (c) worst-case-stable optimization based on sequential initialization. Simulation results confirm a strong dependency of the performance under AN on the selected SNR margins, and highlight the total AN power consumption as well as the residual energy savings under low-power modes stabilized by AN.

Coexistence analysis of asynchronous digital subscriber lines with different sampling rate and carrier frequency spacing

G.fast is the next-generation digital subscriber line (DSL) technology targeting bit-rates of up to 1 Gbps. Very high speed digital subscriber line 2 (VDSL2) is the the latest DSL technology delivering bit-rates of up to 100 Mbps. Replacement of VDSL2 by G.fast modems will be gradual, which implies coexistence of these two systems. G.fast and VDSL2 use different symbol durations, carrier frequency spacings, and sampling rates, which results in inter-carrier and inter-symbol interference (ICSI). We derive an analytical model of ICSI capturing these differences in modulation. Furthermore, through simulations we show that for particular network topologies coexistence of the two systems results in significant bit-rate losses compared to an interference-free scenario.