engleski

CROSSTALK MODELING FOR CALCULATION OF ADSL2+ DOWNSTREAM BIT RATES

Crosstalk is the main limiting factor in DSL (Digital Subscriber Line) transmission services ; especially in cases when number of DSL transmission systems in a cable binder increases. Successful methods for decreasing crosstalk will improve reach, and bit rate of DSL systems. As well, from the spectrum management point of view, it is very important to have convenient positions of transmission systems in a cable binder, because of the way they generate crosstalk on a given DSL transmission system. In this paper we provide calculation of downstream bit rate on ADSL2+ local loops limited by crosstalk noise. Two parameters are crucial for our calculation method: number of active ADSL2+ systems in a cable binder, and their positions inside the binder. In order to calculate bit rate on ADSL2+ loops we have provided an in-depth analysis of a local telecom operator's cable infrastructure in terms of crosstalk. On the basis of measurements carried out on twisted quad cables in the frequency range from 20 kHz up to 2.2 MHz, and on twisted pair lengths between 300 m and 1700 m, we have derived theoretical models of far-end crosstalk (FEXT) and insertion gain. The measurements were performed on cables that are part of operating infrastructure, not on cables on a reel, thus providing a true insight into the situation telecoms worldwide are facing today. Simulation results indicate that number and selection of active loops in a cable binder have a great impact on a bit rate. Presented bit rate calculation method and crosstalk models are a useful tool for planning of access network and ADSL-based services.

ADSL2+; star quads; FEXT; insertion gain; spectrum management

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