Enhanced HARQ Schemes Based on LDPC Coded Irregular Modulation

The bit-interleaved coded irregular modulation (BICIM) was initially proposed for convolutional code and turbo code cases, which applies different signal constellations and mappings within one codeword. We firstly extend this idea to irregular LDPC codes and present an optimized mapping rule for LDPC coded irregular modulation according to the code degree distribution. Furthermore, we apply this optimized LDPC coded irregular modulation to chase combing (CC) HARQ and propose two enhanced HARQ schemes. The improved schemes can efficiently reduce the reliability variances of bits after soft combining. Simulation results show that they can not only achieve better BER performance but also provide a throughput performance enhancement.