In this paper, we investigate novel strategies for generating rate-compatible(RC) irregular low-density parity-check (LDPC) codes with short/moderate blocklengths. We propose three puncturing and two extension schemes, which aredesigned to determine the puncturing positions that minimize the performancedegradation and the extension that maximize the performance. The firstpuncturing scheme employs a counting cycle algorithm and a grouping strategyfor variable nodes having short cycles of equal length in the Tanner Graph(TG). The second scheme relies on a metric called Extrinsic Message Degree(EMD) and the third scheme is a simulation-based exhaustive search to find thebest puncturing pattern among several random ones. In addition, we devise twolayer-structured extension schemes based on a counting cycle algorithm and anEMD metric which are applied to design RC-LDPC codes. Simulation results showthat the proposed extension and puncturing techniques achieve greater rateflexibility and good performance over the additive white Gaussian noise (AWGN)channel, outperforming existing techniques.
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