Downstream bit rate calculation for ADSL2+ loops limited with far-end crosstalk

In this paper an efficient method for downstream bit rate calculation on ADSL2+ local loops limited by crosstalk is presented. Crosstalk is one of the most limiting factors in broadband cable communications. In order to calculate bit rate of ADSL2+ loops we have done 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 a frequency range up to 2.2 MHz, we have derived theoretical models of far-end crosstalk (FEXT) and insertion gain. The measurements were performed on cables that are part of an operating infrastructure, not on cables on a reel, thus providing a true insight into the situation telecoms worldwide are facing today. The results indicate that number and assignment of ADSL2+ to loops in a cable binder have a great impact on a bit rate. Strategy of allocating ADSL2+ to loops inside the cable binder reduces level of interference between users, allowing, in this case, traffic prediction and dynamic access to spectrum available in a cable. Presented bit rate calculation method and crosstalk models are crucial foundation for spectrum management used in a process of local loop unbundling, which is lawful obligation of numerous incumbent telecom operators.