Iterative spectrum balancing for digital subscriber lines

Dynamic spectrum management (DSM) is an important technique for mitigating crosstalk in DSL. One of the first DSM algorithms proposed, iterative waterfilling (IW), has a low complexity and demonstrates the spectacular performance gains that are possible. Unfortunately IW tends to be highly sub-optimal in mixed CO/RT deployments and upstream VDSL. Another DSM algorithm, optimal spectrum balancing (OSB), uses a weighted rate-sum to find the theoretically optimal transmit spectra. Unfortunately its complexity scales exponentially with the number of lines in the binder N. Typical binders contain 25-100 lines, for which OSB is intractable. This paper presents a new iterative algorithm for spectrum management in DSL. The algorithm optimizes the weighted rate-sum in an iterative fashion, which leads to a quadratic, rather than exponential, complexity in N. The algorithm is tractable for large N and can be used to optimize entire binders. Simulations show that the algorithm performs very close to the theoretical optimum achieved by OSB.