An efficient bit-loading algorithm for DMT applications

This paper describes an efficient bit allocation algorithm for digital subscriber line (DSL) applications that use the discrete modulation tone (DMT) technology. The proposed algorithm computes the optimum bit allocation profile with fewer computations than the conventional "water-filling" approach described in the literature. In certain cases of high attenuation loops with high level of interference the conventional algorithms are unable to assign data bits to the higher frequency bins, due to the power spectrum mask limitation recommended by the ANSI standard, even if the total power budget is not expended. The algorithm described in this paper proposes a novel scheme to distribute data over multiple bins at correspondingly reduced power in these, otherwise unpopulated bins. Finally, the algorithm also proposes the use of orthogonal coding in conjunction with the multi-bin data allocation that can reduce the near-end crosstalk (NEXT) between cooperating modems on wire pairs in common cable bindings.