Enhanced TCM based on a multilevel hierarchical trellis coded modulation (HTCM)

This paper introduces a new multilevel coding scheme, identified as hierarchical trellis coded modulation (HTCM), that significantly improves a given TCM, while maintaining a 100% compatible fallback mode into the original trellis structure. HTCM exhibits a reasonable complexity increase when compared to higher order trellises or full turbo schemes that could reach similar gains. HTCM combines a given TCM code and a very high protection code (HPC), such as turbo code or low-density parity-check (LDPC) code. The HPC encodes the least significant bits of a large constellation, thus increasing the minimum Euclidean distance between TCM coded signals. The paper derives the theoretical HTCM asymptotic gain. HTCM is then applied to enhance the 16-state 4D Wei scheme by 1.76 dB of net coding gain., making use of a rate 1/2 parallel concatenated turbo code for the HPC and a new DSQ (diagonally shifted QAMs) constellation mapping. HTCM modularity, efficiency and relative simplicity open new ways to TCM enhancement that would help many broadband communication fields including wireless, satellite and wired systems.