An improved HARQ scheme based on irregular LDPC coding

The hybrid auto repeat request (HARQ) is an efficient retransmission technique which can guarantee highly reliable communication over noisy channels, and nowadays it has been widely adopted in packet-based data communication systems. In this paper, we propose an improved Type-II Hybrid-ARQ scheme that can degrade the average number of the iteration and improve the performance. In this scheme, the source transmits the whole codeword to the destination, and only the parity bits are retransmitted, if the decoder fails. Irregular LDPC codes, which have different degrees, are utilized in the proposed HARQ scheme. Before the retransmission, the parity bits have been treated as a set of bits specified by the node´s degrees. The nodes with same degree are classified into one subset. When the retransmissions are needed, only the parity bits are retransmitted, and the subset which has the larger degree is transmitted firstly, then the smaller subset is transmitted. The simulation results demonstrate that the proposed HARQ scheme can outperform the Type-II HARQ scheme.