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Crosstalk channel estimation via standardized two-port measurements

The emerging multiuser transmission techniques for enabling higher data rates in the copper-access network relies upon accurate knowledge of the twisted-pair cables. In particular, the square-magnitude of the crosstalk channels between the transmission lines are of interest for crosstalk-mitigation techniques. Acquiring such information normally requires dedicated apparatus since crosstalk-channel measurement is not included in the current digital subscriber line (DSL) standards. We address this problem by presenting a standard-compliant estimator for the square-magnitude of the frequency-dependent crosstalk channels that uses only functionality existing in todays standards. The proposed estimator is evaluated by laboratory experiments with standard-compliant DSL modems and real copper access network cables. The estimation results are compared with both reference measurements and with a widely used crosstalk model. The results indicate that the proposed estimator obtains an estimate of the square-magnitude of the crosstalk channels with a mean deviation from the reference measurement less than 3 dB for most frequencies.

Use of Wavelet Transform and Generalized Regression Neural Network (GRNN) to the Characterization of Short-Duration Voltage Variation in Electric Power System.

This work presents the use of the wavelet transform and computational intelligence techniques to quantify voltage short-duration variation in electric power systems, with respect to time duration and magnitude. The wavelet transform is used to determine the event duration, as well as for obtaining a characteristic curve relating the signal norm as function of the number of cycles for a waveform without disturbance that is used as reference for the calculation of the magnitude of the event. A generalized regression neural network (GRNN) is used to interpolate not stored points of the characteristic curve. The method is part of a process to automate the post operation signal analysis in electric power systems, and it is used to quantify the voltage short-duration variation magnitude of previously selected signals. The method has been shown efficient, and some results obtained from the application of this method to power system real signals are presented.

Statistical adjustment of Walfisch-Ikegami model based in urban propagation measurements

Some theoretical and experimental models have been considered for the prediction of the path loss in systems of mobile communications. The Bertoni-Walfisch model for the effect of building with almost uniform height and are aligned. In this paper, a statistical model that consists of an adjustment of Walfisch-Ikegami model accomplished trough linear regression is presented, considering the height and the distance of the buildings as random variables. The verification of the validity of the considered model was made from the comparison between simulated measures and gotten through a measurement campaign that was carried in an urban environment.

Impact of crosstalk channel estimation on the DSM performance for DSL networks

The development and assessment of spectrum management methods for the copper access network are usually conducted under the assumption of accurate channel information. Acquiring such information implies, in practice, estimation of the crosstalk coupling functions between the twisted-pair lines in the access network. This type of estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of the inaccuracies in crosstalk estimation on the performance of dynamic spectrum management (DSM) algorithms. A recently proposed crosstalk channel estimator is considered and a statistical sensitivity analysis is conducted to investigate the effects of the crosstalk estimation error on the bitloading and on the achievable data rate for a transmission line. The DSM performance is then evaluated based on the achievable data rates obtained through experiments with DSL setups and computer simulations. Since these experiments assume network scenarios consisting of real twisted-pair cables, both crosstalk channel estimates and measurements (for a reference comparison) are considered. The results indicate that the error introduced by the adopted estimation procedure does not compromise the performance of the DSM techniques, that is, the considered crosstalk channel estimator provides enough means for a practical implementation of DSM.

Impact of Crosstalk Estimation on the Dynamic Spectrum Management Performance

The development and assessment of spectrum management methods for the copper access network are usually conducted under the assumption of accurate channel information. Acquiring such information implies, in practice, estimation of the crosstalk coupling functions between the twisted-pair lines in the access network. However, this estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of non-ideal crosstalk estimation on the dynamic spectrum management (DSM) performance. Two different crosstalk estimators are considered: a conventional model-based estimator and a novel estimation procedure. The DSM performance is evaluated based on the obtained crosstalk estimates for two different network scenarios consisting of real twisted-pair cables. For a reference comparison, the crosstalk channels are measured with a network analyzer. The simulation results indicate that the novel estimation procedure achieves DSM performance results close to the ones obtained with the network analyzer and that the model-based estimator can lead to an inaccurate rate estimation.

Evaluating Inpainting Methods to the Satellite Images Clouds and Shadows Removing

This paper presents the evaluation of two approaches widely used in the inpainting literature, applied in the context of atmospheric noise removal, such as fog, dense and sparse clouds and shadows, which often occurs in remote sensing images. One approach uses the technique of nearest neighbor interpolation for the information dissemination by a DCT-based smoothing method, and the other is based on second-order partial differential equations methods that uses the heat diffusion and thin-plate spline methods, achieving their solutions by using the finite-difference method. Finally, the evaluation uses the Kappa coefficient and the PSNR index. The metrics indicate the effectiveness of the nearest neighbor interpolation strategy, which produces higher quality images, specially when comparing the results obtained by the use of differential equations modeled by thin-plate spline.

The use of high-pass filters and the inpainting method to clouds removal and their impact on satellite images classification

This paper proposes a new technique to smooth undesirable elements of the atmosphere, such as fogs, clouds and shadows, which damage and lead to loss of image data. In our approach, an efficient way to detect clouds and shadows is presented. The method applies constants related to such undesirable elements, as well as a High boost Filter in the homomorphic filtering for scattered clouds removal. We highlight the use of the Inpainting method, which replaces contaminated pixels using a nearest neighbor interpolation. Beside this, the proposed algorithm adopts a morphologic opening of the image that aims to suppress some isolated occurrences in the scene. The results are evaluated by Kappa coefficient and PSNR index, proving the good performance of the method.

An evolutionary algorithm for improved diversity in DSL spectrum balancing solutions

There are many spectrum balancing algorithms to combat the deleterious impact of crosstalk interference in digital subscriber lines (DSL) networks. These algorithms aim to find a unique operating point by optimizing the power spectral densities (PSDs) of the modems. Typically, the figure of merit of this optimization is the bit rate, power consumption or margin. This work poses and solves a different problem: instead of providing the solution for one specific operation point, it finds a set of operating points, each one corresponding to a distinct matrix with PSDs. This solution is useful for planning DSL deployment, for example, helping operators to conveniently evaluate their network capabilities and better plan their usage. The proposed method is based on a multiobjective formulation and implemented as an evolutionary genetic algorithm. Simulation results show that this algorithm achieves a better diversity among the operating points with lower computational cost when compared to an alternative approach.

Feasibility of alien crosstalk mitigation with receiver-side MIMO processing on G.fast systems

G.fast is the most recent ITU-T standard for copper-based transmission, which targets at short distances and adopts a bandwidth of 106 MHz extensible to 212 MHz. In several scenarios G.fast systems will be composed by or coexist with uncoordinated lines, which are sources of strong crosstalk. This work focuses on evaluating an alien (out-of-domain) crosstalk mitigation method based on noise prediction that was proposed for predecessors of G.fast. Simulation results show that alien crosstalk mitigation methods can indeed improve the performance of G.fast systems, but under specific conditions. We have contrasted these situations and we provide guidelines about the feasibility of the crosstalk mitigation technique. As support for the simulations, we also present a set of alien crosstalk measurements.

A simple root-like bit mapping to improve the performance of LDPC-Coded QAM systems

This paper presents a new bit mapping strategy which aims to improve the performance of a LDPC-Coded QAM system such as the one specified in the G.hn standard. The proposed bit mapping is based on the assumption that bits transmitted in “good” sub-channels, with higher gains, help bits transmitted in “bad” sub-channels. This is possible by enforcing and prohibiting some connections between variable and check nodes in the Tanner graph, akin to Root-LDPC codes. The bit mapping is applied to G.hn, with QC-LDPC codes and QAM modulation. Simulation results show that the new bit mapping strategy improves performance for both single-carrier and OFDM-based systems.