Linear-Time Encodable Rate-Compatible Punctured LDPC Codes with Low Error Floors

We consider efficiently encodable rate-compatible (E²RC) punctured low-density parity-check (LDPC) codes and show that punctured LDPC codes of the E²RC structure have high error floors at their base code rates. Efficient type-II hybrid Automatic Repeat reQuest (ARQ) protocols are possible with punctured LDPC codes since punctured LDPC codes can support a wide range of code rates with incremental redundancy transmissions. However, such high error floors may result in excessive number of retransmission requests and end up with poor efficiency of hybrid ARQ protocols. We find that the problem of the E²RC structure stems from dispersive right degree distribution and high maximum right degree which is an indispensable element in the E²RC structure. In this paper, we propose a modification to E²RC structure which eliminates the error-floor problem without compromising any of important advantages of the E²RC structure such as linear-time encodability and good bit-error rate (BER) performance over a wide range of code rates. Our claims will be verified with BER and frame error rate (FER) simulation results.