Margin maximization in multiuser interference digital subscriber line channels

Multiuser margin maximization algorithms are developed for multi-carrier digital subscriber loops (DSL) employing dynamic spectrum management (DSM). Margin maximization is desirable for constant bit rate applications and provides protection against various non-stationary and bursty noise sources. Most single-user margin maximization algorithms rely on a fixed crosstalk assumption, which does not hold in DSM. Thus with direct extension of single-user algorithms in DSM scenarios, one user´s margin maximization can lead to the failure of other users in meeting their target rates. In this paper, we explore the favorable monotonicity and fairness properties in multiuser margin and use them to formulate a box-constrained non-linear least squares (NLSQ) problem that can be solved by using a scaled gradient trust region approach with Broyden Jacobian update. This algorithm efficiently converges to a solution providing the best common equal margin to all users while explicitly guaranteeing that each user´s target rate requirement is satisfied. The algorithm can be implemented in practical DSL-DSM scenarios with only Level-1 coordination.