Fine-granularity loading schemes using adaptive Reed-Solomon coding for discrete multitone modulation systems

In this paper, we present a fine granularity loading scheme using joint optimization of modulation and coding for discrete multitone (DMT) modulation towards achieving maximum information rate conveyed. While most existing algorithms strived for the optimal energy distribution to maximize rate, the bits loaded were always constrained to integers. It was initially believed that most (not all) of the granularity losses could be recovered through ´bit-rounding´ and ´energy re-scaling´ after an optimal ´water-filling´ approach. But this was observed only for the total power constrained case. With the advent of peak power constraint, we show that the room for optimization in the energy domain severely constrained and granularity losses constitute a significant percentage of the achievable data rate. To recover these losses, we propose a loading scheme that integrates the coding scheme with the bit-loading algorithm. For achieving near-continuous rate adaptation, the family of Reed-Solomon (RS) codes has been used for their low redundancy, high flexibility in correction capability and highly programmable architecture. Simulation results with very high bit rate digital subscriber line (VDSL)-DMT system show more than 20% improvement in most cases.