Efficient Branch and Bound Approach to Joint Multii-User Power Control and Partial Crosstalk Cancellation in xDSL Systems

Partial crosstalk cancellation has been proposed to reduce the online complexity of crosstalk canceller in xDSL systems. Because the crosstalk profile changes over time, there is additional requirement that partial crosstalk cancellation provide a very low pre-processing complexity. Also, a much lower online complexity can be obtained if the multi-user power control and partial crosstalk cancellation problems are solved jointly. Currently, this joint problem is formulated as a constrained optimization problem. However, it suffers from per-tone exhaustive search. This paper presents a solution for this joint problem. The problem is considered as a mixed binary-non-convex problem. Then it is reformulated as a mixed binary-convex problem via a successive linear convex relaxation. Finally it is solved by an efficient branch and bound method. The complexity analysis of our algorithm shows that it provide much lower pre-processing complexity than currently proposed algorithms, allowing it to work efficiently in time-varying crosstalk environment.