Partial Crosstalk Cancellation for Upstream VDSL
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Partial Crosstalk Cancellation for Upstream VDSL Raphael Cendrillon Department of Electrical Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, Leuven-Heverlee 3001, Belgium Email: [email protected]
Marc Moonen Department of Electrical Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, Leuven-Heverlee 3001, Belgium Email: [email protected]
George Ginis Texas Instruments, 2043 Samaritan Drive, San Jose, CA 95124, USA Email: [email protected]
Katleen Van Acker Alcatel Bell, Francis Wellesplein 1, Antwerp 2018, Belgium Email: katleen.van [email protected]
Tom Bostoen Alcatel Bell, Francis Wellesplein 1, Antwerp 2018, Belgium Email: [email protected]
Piet Vandaele Alcatel Bell, Francis Wellesplein 1, Antwerp 2018, Belgium Email: [email protected] Received 5 March 2003 Crosstalk is a major problem in modern DSL systems such as VDSL. Many crosstalk cancellation techniques have been proposed to help mitigate crosstalk, but whilst they lead to impressive performance gains, their complexity grows with the square of the number of lines within a binder. In binder groups which can carry up to hundreds of lines, this complexity is outside the scope of current implementation. In this paper, we investigate partial crosstalk cancellation for upstream VDSL. The majority of the detrimental effects of crosstalk are typically limited to a small subset of lines and tones. Furthermore, significant crosstalk is often only seen from neighbouring pairs within the binder configuration. We present a number of algorithms which exploit these properties to reduce the complexity of crosstalk cancellation. These algorithms are shown to achieve the majority of the performance gains of full crosstalk cancellation with significantly reduced run-time complexity. Keywords and phrases: DSL, interference cancellation, reduced complexity, partial crosstalk cancellation, crosstalk selectivity, hybrid selection/combining.
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INTRODUCTION
VDSL is the next step in the on-going evolution of DSL systems. Supporting data rates up to 52 Mbps in the downstream, VDSL offers the potential of bringing truly broadband access to the consumer market. VDSL supports such high data rates by operating over short line lengths and transmitting in frequencies up to 12 MHz.
The twisted pairs in the access network are distributed within large binder groups which typically contain anything from 20 to 100 individual pairs. As a result of the close distance between twisted pairs within binders and the high frequencies used in VDSL transmission, there is significant electromagnetic coupling between nearby pairs. This electromagnetic coupling leads to interference or crosstalk between the different systems operating within a binder.
Partial Crosstalk Cancellation for Upstream VDSL There are two types of crosstalk, near-end crosstalk (NEXT) and far-end crosstalk (FEXT). NEXT occurs when the upstream (US) signal of one modem couples into the downstream signal of another or vice versa. FEXT
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