Performance Evaluation of the Cable Bundle Unique Power Back-Off Algorithm

The latest digital subscriber line (DSL) technology, VDSL2, used for broadband access over twisted-pairs, promises up to 100 Mbit/s for both transmission directions on short loops. Since these systems are designed to operate in a far-end crosstalk (FEXT) limited environment, there is a severe performance degradation when deployed in distributed network scenarios. With power back-off (PBO) the network operators attempt to protect modems deployed on long loops by reducing the transmit power of the short ones. However, currently very little guidance has been given to operators on how to set and optimize the parameters for PBO. In this paper we explore one promising method, the cable bundle unique PBO (CUPBO), which optimizes these parameters according to the actual situation in the cable with regard to noise and network topology. Using real VDSL systems and cables we show that CUPBO algorithm achieves a significant increase in performance compared to the case when one naively takes the PBO values given in the VDSL standard.