Trellis Coded Modulation with partially overlapped signal subsets

We present a simple yet effective scheme of Trellis Coded Modulation (TCM) codes using partially overlapped signal subsets as a shaping technique. The optimum enlargement of the QAM signal constellation is reported. We show that 2-state TCM with 4 partially overlapped signal subsets has a coding gain of 2.5 dB in comparison with uncoded transmission, which is about 0.5 dB higher than the Ungerboeck TCM code with the same number of states. The construction is then extended to any number of trellis states using 4-, 8-, 16-way partitions of the QAM constellation.