Bandwidth-Efficient Modulation Codes Based on Nonbinary Irregular Repeat Accumulate Codes

Due to the random nature of LDPC codes, most of the good LDPC codes found in the literature do not possess a simple encoding structure. Thus, the encoding complexity of those LDPC codes can be as high as O(N ²), where N is the codeword length. To reduce the encoding complexity, in this paper, binary irregular repeat accumulate (IRA) codes are extended to the nonbinary cases for bandwidth-efficient modulation schemes. By proper selection of nonuniform signal constellations, the constructed codes are inherently capable to obtain shaping gains even without shaping codes. Under Gaussian approximation, extrinsic information transfer (EXIT) charts for nonbinary IRA codes are developed and several codes of different spectral efficiencies are designed based on EXIT charts. Simulation results indicate that the proposed codes not only have simple encoding schemes, but also have remarkable performances that are comparable to those of nonbinary LDPC codes.