The problem of summing crosstalk from mixed sources

Digital subscriber lines (DSL) are fundamentally limited by crosstalk. The case where all crosstalk is from the same type of DSL has been studied over the years and accurate models have been standardized. However, crosstalk from multiple different types of DSLs is a relatively new area of study and models of summing mixed crosstalk have only recently been postulated. The goal of this paper is twofold: firstly, to point out the lack of this subject in the current literature; secondly, to propose a new method of summing crosstalk due to mixed sources. This new method consists of deriving a lower bound to the worst-case method, which is intrinsically too pessimistic. Moreover, it is shown here for the first time that the full service access network (FSAN) method is a particular case of the proposed method.