The concatenation of coset (trellis) codes with multichannelmodulation is studied. It is found that at a conceptual level, thisconcatenation is straightforward. Multichannel modulation partitions thedigital communication channel into a set of memoryless subchannels, eachof which can be separately encoded and decoded. However, the approach isalso found to be unacceptable in practice because of latency andcomplexity. Encoding/decoding methodologies that can be used to reducelatency significantly and that also use the same encoder on allsubchannels are studied. It is shown that using multidimensional cosetcodes (four or eight dimensions) to achieve a granularity in bitdistribution that will closely approximately the continuous distributionthat is optimum is best. A loading algorithm is introduced for assigningbits and energies to the subchannels. It easily and quickly produces anoverall modulated signal that is near optimum. The technique isillustrated using example channels based on a high-bit-rate digitalsubscriber line at 1.6 Mb/s
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