An efficient low-complexity joint multi-user power control and partial crosstalk cancellation in xDSL systems

• Authors: M. Measoumi;M. A. Masnadi-Shirazi
• Venue: IMACS'08 Proceedings of the 7th WSEAS International Conference on Instrumentation, Measurement, Circuits and Systems
• Year: 2008

Perfect crosstalk cancellation techniques have been proposed to mitigate the effect of crosstalk. However, the online complexity of these crosstalk cancellation techniques grows with the square of the number of lines in the binder. Fortunately, most of the crosstalk originates from a limited number of lines on a limited number of tones. As a result, a fraction of the complexity of perfect crosstalk cancellation suffices to cancel most of the crosstalk. This is known as partial crosstalk cancellation. 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 and solved by employing Lagrange dual decomposition method. However, it suffers from per-tone exhaustive search because of non-convexity of its per-tone problem. This paper presents a solution for the joint multi-user power control and partial crosstalk cancellation problem with significantly lower pre-processing complexity than the currently proposed algorithms. The problem is considered as a mixed binary-non-convex problem. Then it is reformulated as a mixed binary-convex problem via a successive 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. Moreover, the analytical and simulation results demonstrate that our algorithm is close to the optimal solution from the crosstalk cancellation point of view.