Seamless transition of power allocation in multi-user XDSL systems

In non-static scenarios where Dynamic Spectrum Management (DSM) Level 2 is employed, an optimal power allocation can become invalid e.g. due to a joining user and thus has to be recomputed. To not unnecessarily interrupt service, the spectra should be updated successively as individual users start a new session. If not done carefully, this results in sub-optimal intermediate joint power allocations where the actual signal-to-noise ratio (SNR) margin of users decreases drastically. This paper investigates a novel approach to gradually update transmit spectra of modems to a new optimal power allocation while assuring that the actual SNR margin of all users does not fall below a specified value during the transition phase. Also, a low-complexity solution for the involved hard optimization problem is described. Simulations carried out demonstrate the interdependency between the minimum margin value and convergence time of the proposed scheme.