Real-time FEXT crosstalk identification in ADSL systems

IEEE Journal on Selected Areas in Communications, 2001

Crosstalk among telephone lines in the same or neighboring bundles is a major impairment in current xDSL systems. This paper proposes a novel idea of an impartial third party that identifies the crosstalk coupling functions among the twisted pairs in these xDSL systems. The crosstalk identification technique includes the following four major procedures: 1) the transmitted and received signals from each DSL modem for a predefined time period are collected and sent to the third party; 2) the signals are resampled according to the clock rate of the receiver of interest; 3) the signals' timing differences are estimated by cross correlation; and 4) the crosstalk coupling functions are estimated using the least-squares method. The performance of the cross correlation and least-squares methods is analyzed to determine the amount of data needed for identification. Simulation results show that the proposed methods can identify the crosstalk functions accurately and are consistent with theoretical analysis. These identified crosstalk functions can be used to significantly improve the data rate (e.g., multiuser detection) and to facilitate provisioning, maintenance, and diagnosis of the xDSL systems.

IEEE Transactions on Instrumentation and Measurement, 2005

The performance of xDSL-systems is determined by the existing crosstalk interference. xDSL- systems are optimised to the existing crosstalk interferences in a cable bundle. The crosstalk interference leads to unwanted restrictions in the number of xDSL-systems, which are able to operate parallel in a cable bundle. Realistic crosstalk models are necessary for xDSL-system tests and for the design of future telephone networks. With the modified crosstalk model introduced in this paper, the crosstalk coupling functions between the twisted pairs of a cable bundle can be estimated with low effort in the frequency domain. The crosstalk coupling functions are calculated from the measured spectra of the transmitted signals along the interfering wire pairs and from the spectra of the crosstalk interference on the interfered twisted pair. The modified crosstalk model can be implemented in a flexible impairment generator, which reproduces realistic crosstalk interferences for xDSL-system tests ...

2010

As demands for higher data rates increase, DSL systems become incapable of keeping up due to the electromagnetic coupling present in the binders of the telephone lines. This electromagnetic coupling, known as crosstalk, is several orders greater in magnitude than the background noise. The reported techniques focusing on completely removing the crosstalk usually lead to computationally intensive solutions which may be infeasible to implement with existing hardware. For this reason, partial crosstalk removal has been proposed. In this work, we investigate the capability of the partial crosstalk cancellation for the fair or equal rate balancing among the users, subject to a constrained computational resource. Approaches which expend the computational resources in order to achieve fair or equal rates among the users were developed. Specifically, the proposed efficient Max-Min algorithm which is based on a dual optimization framework has a high convergence speed and low complexity for deployment in the xDSL systems.

IEEE Transactions on Signal Processing, 2000

Downstream (DS) crosstalk channels of digital subscriber line systems can be estimated based on the reported signal-to-noise ratio (SNR). In the case of an already active victim line (VL) impacted by the joining of a new disturber line (DL), sending perturbing signals on the VL and reporting the SNRs allow the estimation of the crosstalk channel from the DL to the VL. This paper generalizes that concept to include full startup, tracking and joining scenarios as well as the impact of different perturbation signal choices. Additionally, the sensitivity of the algorithm to different sources of imperfection is analyzed. Simulation results reveal that starting without precoding, and updating the precoder matrix based on the DS crosstalk channel estimates, the far-end crosstalk-free SNR can be reached in a limited number of iterations (e.g., 36 SNR measurements are needed for the four lines case). The SNR-assisted method is documented in an informative appendix of the draft G.vector recommendation as a backward compatible method for very high speed digital subscriber lines (VDSL2) and, hence, can be used for channel acquisition today.

Crosstalk is one of the problems that affect the performance operation of global system mobile (GSM) network. Among the effect of crosstalk are call mute, call drop, wire propagation delay, dynamic power dissipation etc. Crosstalk is an undesirable signal arising due to the coupling capacitances between adjacent interconnecting wires and measured in decibel. In this paper some literature were reviewed and different ways of measuring crosstalk such as Near end croosstalk (NEXT), far end crosstalk (FEXT), Power sum crosstalk (PSNEXT) and alien crosstalk (AXT) were analyzed.

2008

Rapid acquisition of accurate crosstalk estimates is a core requirement for effective precoding in digital subscriber line (DSL) systems. It is shown that signal-to-noise ratio (SNR) reports provided by customer premises equipment (CPE) can be used to perform this task by "tuning" the precoder, i.e., iterating alternate steps of estimation and precoder adaptation. Such an approach has the advantage that it can be applied to legacy CPEs. Estimation algorithms are designed using techniques from stochastic control.

So far ETSI TM6 considered in its simulation scenarios only scenarios where the victim system and the disturbing system are collocated. However, this assumption is longer valid in scenarios where victim and disturbing systems have different deployment reaches. This document describes a methodology how to calculate crosstalk in a distributed environment, i.e. when victim and disturbing terminals are no longer collocated.

Mobile Networks, 2012

Mobile Networks 138 traffic. It was assumed that the users may complain to the cellular operator (instead of broadband IP provider) when they experience delay or poor Mean Opinion Score (MOS) during a voice call. As in 3G cases, users may wait for FTP data transfer or surfing the internet web site. In the latter case, higher latency or packet loss will not create a question from users than if the same situation experienced by users use VoIP or video services. According to [2] and [3], most femtocell technologies provide good quality voice calls and sufficient support to data services when the broadband IP link provides a minimum performance of:  Less than 150 ms round-trip delay (more than 200 ms will not be practical for two ways conversation);  Less than 40 ms jitter;  A general packet loss of 3% or less is acceptable; however, packet loss is typically "bursty" by nature, and, as such, average rates below 0.25% should be maintained;  At least 1 Mbps in downlink, i.e. from the broadband IP provider network to the FAP GW;  At least 256 kbps in uplink, i.e. from the FAP GW to the broadband IP provider network. This chapter describes the femtocell performance over xDSL access network as the backhaul. This work has been conducted as part of TELKOM contribution to FREEDOM Project (www.ict-freedom.eu) which consists of two phases of measurements and analysis. The first phase addressed the performance of ADSL2, ADSL2+ as a function of distance. It also observes the population of user's density enjoying certain attainable rate or less. Furthermore it also addresses transmission delay of xDSL over different bandwidth profiles. DSL backhaul quality model is derived in order to address different qualities of backhaul. The model can be used in elaboration of RRM, scheduling and system level simulation which need to take into account the backhaul quality.

In xDSL technology, high-speed data are transferred between the central office and the customers, or between two or more central offices using unshielded telephone lines. A major impairment that hinders the increase in data-rate through the twisted-pair line is nearend crosstalk (NEXT) between the adjacent twisted pairs. DSL systems with overlapping transmit and receive spectra are susceptible to NEXT which significantly increases the interference noise in the received signal and also reduces the reliability and availablity of