Using flexible turbo-like codes for simplified water-filling

A method for approaching the water-filling (WF) capacity of parallel Gaussian channels is presented. This method relies on the existence of modern turbo-like codes (TLCs) with a high degree of rate flexibility. The algorithm is a constant power WF algorithm with the active sub-channels and associated modulations selected based on the performance limits of the available TLC and modulation formats. A single TLC block is used over all sub-channels with rate imposed by the modulation assignments and the total capacity limits of the channel. Simulation results demonstrate that this approach can yield performance within approximately 3-5 dB of the ideal WF capacity for Rayleigh channel gains.