Implementation of trellis shaping on LDPC coded modulation DSL systems

Shaping gain for trellis shaping is presented in LDPC-coded QAM DSL system. A labelling scheme is designed for current constellations to derive regional shaping effects. The performance of BER results are investigated for various QAM orders from 256QAM to 32768QAM. It is found that for even bits QAM the shaping gain is more evident than odd bits QAM, especially when the QAM order is high; and larger order QAMs are in general have better shaping gains than smaller order QAMs. Based on the BER results with regard to normalized SNR, it is concluded that overall shaping gains of 0.51dB (even bits QAM) and 0.45dB (odd bits QAM) can be derived at BER 10-7 from the presented scheme.