BICM-ID with mixed symbol-mapping and irregular LDPC

Abstract

When LDPC code designed by step function EXIT chart in memoryless channel is used, we know that the gray mapping provides the best performance rather than any other mappping rules at Bit-Interleaved Coded Modulation (BICM) system. However, there is little gain in using iterative demapping with gray mapping at Bit Interleaved Coded Modulation-Iterative Demapping/ Decoding (BICM-ID) system. The demapper EXIT curve with Gray mapping is relatively flat. The left-most( LM ) point of the demapper EXIT curve has the highest value with the Gray mapping. The right-most( RM ) point of the demapper EXIT curve has the highest value with the D23 mapping. The EXIT curve with mixed mapping is located between the Gray and D23 mapping. A mapping rule with mixed mapping based on gray and d23 provides iterative demapping performance gain at high SNR when applied to existing LDPC code.