Multidimensional Optimal Signal Constellation Sets and Symbol Mappings for Block-Interleaved Coded-Modulation Enabling Ultrahigh-Speed Optical Transport

In this paper, we introduce the optimal signal constellation design (OSCD) in both 2-D and multidimensional cases, which is obtained by minimization of mean square error of optimal source distribution. In addition, by analyzing block-interleaved coded modulation with iterative decoding, in which the bit error rate is reduced by iteration of extrinsic information between a multilevel/multidimensional demapper and an LDPC decoder, with the help of EXIT chart, we propose new mapping methods for OSCDs outperforming previously known ones. The simulation results show that optimized mappings for LDPC-coded OSCDs outperform natural mappings by 0.5 dB in 8-ary 2-D case and 0.6 dB in 16-ary 2-D case. Meanwhile, our proposed optimized mappings for 3-D-8-ary OSCD outperform natural mapping by 0.2 dB and sphere packing constellation by 0.5 dB in coherent optical OFDM few-mode fiber system.