Multiuser Spectrum Balancing under Inter-Carrier Interference

Inter-carrier interference (ICI) in multicarrier systems results in a coupling among all subcarriers. This greatly complicates the problem of multiuser bit and power allocation, also referred to as spectrum balancing. We propose a Lagrange relaxation of the ICI coupling terms, and an optimal algorithm for solving the resulting relaxed spectrum balancing problem. While this gives us a rate-performance upper bound, based on it we also propose a novel heuristic for computing a lower bound. The relaxation is exemplarily applied to digital subscriber lines (DSL) with asynchronous far-end crosstalk in near-far scenarios. The results confirm the existence of scenarios where the performance upper and lower bounds obtained by the relaxation are significantly tighter than those previously proposed.