A new turbo coded QAM scheme with very low decoding complexity for ADSL system

For ADSL applications, very large constellation sizes are used, which can be as large as 32768QAM. It is a big challenge to design turbo TCM for such a large constellation size while still maintaining low decoding complexity. We propose a new turbo coded QAM scheme with a unique "concatenated Gray mapping" for an ADSL system. This new mapping can not only provide good performance for turbo coded bits but can also efficiently maximize the minimum Euclidean distance of uncoded bits. This new turbo coded QAM scheme not only has as good error correcting performance as the conventional bit-interleaved turbo coded QAM and symbol-interleaved turbo TCM schemes, but also has very low decoding complexity which is only about 17% of the conventional bit-interleaved turbo coded QAM