Crosstalk Channel Estimation via Standardized Two-Port Measurements
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Research Article Crosstalk Channel Estimation via Standardized Two-Port Measurements 1 Per Ola Borjesson, 1 ¨ ¨ Fredrik Lindqvist,1 Neiva Lindqvist,2 Boris Dortschy,3 Per Odling, 3 2 Klas Ericson, and Evaldo Pelaes 1 Department
of Electrical and Information Technology, Lund University, 221 00 Lund, Sweden Processing Laboratory (LaPS), Federal University of Para, 66075-110 Belem, PA, Brazil 3 Ericsson Research, Broadband Technologies, Ericsson AB, 16480 Stockholm, Sweden 2 Signal
Correspondence should be addressed to Fredrik Lindqvist, [email protected] Received 21 September 2008; Accepted 19 December 2008 Recommended by Jonathon Chambers 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 today’s 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. Copyright © 2008 Fredrik Lindqvist et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
One of the main impairments for high-speed digital subscriber line (DSL) systems is the destructive crosstalk from neighboring DSL systems. The interfering crosstalk occurs when neighboring systems transmit in the same spectrum due to the inherent electromagnetic coupling between the twisted-pair cables colocated in the same copper access binder (bundle). Both near-end crosstalk (NEXT) and farend crosstalk (FEXT) occur, where NEXT(FEXT) refers to the crosstalk caused by the transmitter(s) on the same (opposite) side of the line. The NEXT and FEXT interferences in a copper access binder are illustrated in Figure 1. In order to achieve higher data-rates in the access network, many new proposed multiuser transmission techniques utilize accurate knowledge of the transmission paths in the cable binder. An important multiuser transmission approach that has received a lot of attention recently is dynamic spectrum management (DSM) [1–4]. For DSM aiming at crosstalk
mitigation [5–11], the
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