1. A method for processing data for transmission over multiple transmission channels in a multi-channel communication system, comprising: determining characteristics of a plurality of transmission channels available for data transmission; segregating the plurality of transmission channels into one or more groups of transmission channels; and for each group of transmission channels, selecting one or more available transmission channels in the group based on the determined characteristics and a threshold, and coding and modulating data for all selected transmission channels in the group based on a particular coding and modulation scheme to provide modulation symbols.