The Design of Rate-Compatible LDPC Codes for IR-HARQ Systems over Erasure Channels

Application-layer forward error correcting (AL-FEC) codes, providing error protection across blocks of packetized data, are becoming increasingly important in emerging networking applications. In this paper, we investigate AL-FEC solutions based on rate- compatible low-density parity-check (RC LDPC) codes, as they may offer excellent performance with low system complexity. Recent studies on RC LDPC codes are focused on physical layer incremental redundancy hybrid automatic-repeat-request (IR-HARQ) systems and typical wireless channel models. The focus of our study is RC LDPC code design as an AL-FEC solution in packet-level IR-HARQ systems assuming erasure channels between the source and the destination(s). We propose novel design methods for RC LDPC codes over erasure channels motivated by the dependance of finite-length LDPC code performance on the size of the smallest stopping set of its code graph. Simulation experiments demonstrate that the proposed RC LDPC design significantly outperforms the state-of-the-art RC LDPC codes in the error-floor region, and in particular, in the domain of poor channel conditions.