Rate-compatible Low Density Parity Check Codes for Capacity-approaching ARQ Schemes in Packet Data Communications

Strong rate-compatible codes is important to achieve high throughput in hybrid automatic repeat request with forward error correction (ARQ/FEC) systems in packet data transmission. This paper focuses on the construction of efficient rate-compatible low density parity check (RC-LDPC) codes over a wide rate range. The conventional approach of puncturing is first studied. Analysis on the code ensemble and the asymptotic performance shows that it works well only at high rates and only when the amount of puncturing is small. To extend the dynamic rate range, a special approach of extending is proposed and is shown to produce good RC-LDPC codes at low rates. Combining both approaches, efficient RC-LDPC codes are constructed and a hybrid ARQ/FEC system using RC-LDPC codes is evaluated. The proposed LDPC-ARQ system can achieve information rate about 1 dB away from the theoretical limit, which is comparable to turbo ARQ systems [1][2], yet with lower decoding complexity.