Enhanced HARQ Employing LDPC Coded Constellation Rearrangement with 64QAM

In this paper, a novel algorithm for searching optimal HARQ methods with constellation rearrangement is proposed. This novel method tries to average the combined reliability of demodulated bits after retransmissions. According to this idea, two constellation rearrangement schemes for 64QAM with restricted retransmission times are presented through the proposed search algorithm, which can well equalize the reliabilities of various bit positions after chase combining (CC) HARQ so as to improve the LDPC decoder's performance. Simulation results show that the two presented schemes outperforms than the traditional HARQ methods with constellation rearrangement in term of BER and throughput performance. It not only can be used in LDPC coded HARQ but also apply to Turbo coded HARQ with arbitrary MQAM constellation rearrangement.