Study On Ldpc Coded Modulation

With the fast development and widely use of the telecommunication technologies, frequency spectrum gradually becomes a rare resource. We can take advantage of the frequency spectrum more effectively by designing the error-correct coding and the modulation as a whole. Low-Density Parity-Check Code is a kind of linear block codes with outstanding performance. Using LDPC Codes as component codes to design Block Coded Modulation enables us to get very close to coded modulation capacity. The analyzing methods, constructing methods and decoding algorithms of LDPC Coded Modulation have been discussed in this paper.Firstly, we introduce the LDPC Code and its decoding algorithms. Then we compare the main constructing methods and decoding algorithms of LDPC Coded Modulation. By using a new kind of method, trichotomy graph, to analyze the LDPC Coded Modulation, we draw two conclusions: no length-4 cycle should exist between symbols and decoding methods should take the statistical dependencies among the bits in the same symbol into consideration. After that, we derive a method from PEG to construct the BICM-LDPC component codes which have no length-4 cycle between symbols. Finally, an improved Coded Modulation Belief Propagation decoding algorithm is provided. Based on the analysis of the simulation results, the improved CMBP algorithm outperforms the BP algorithm in all kinds of mappings.