Multilevel Reed-Solomon coding in asymmetric digital subscriber lines

The ADSL standard is based on using hard decision decoding of Reed-Solomon (RS) codes. The standard states that as an option a four dimensional 16-state trellis code can be concatenated with an RS code. The resulting structure is rather complex mainly because of the associated complexity of the Viterbi decoder of the trellis code. An alternative to this complex structure is to improve the performance when only RS codes are used. We propose to use a multilevel RS coding structure in ADSL systems based on discrete multitone (DMT) technique. The multilevel RS coding is shown to provide 1 to 2 dB additional coding gain improvements over conventional RS coding.