Rate-Compatible Protograph LDPC Codes for Spin-Torque Transfer Magnetic Random Access Memory (STT-MRAM)

This paper proposes novel rate-compatible protograph LDPC (RCP-LDPC) codes to correct memory cell errors and mitigate the raw bit error rate (BER) diversity for spin-torque transfer magnetic random access memory (STT-MRAM). Since the STT-MRAM channel is asymmetric, we first apply an independent and identically distributed (i.i.d.) channel adapter to force the channel to be symmetric. We then propose to use the protograph extrinsic information transfer (PEXIT) algorithm, the asymptotic weight distribution (AWE) analysis, as well as the actual error rate performance as the combined guideline for designing protograph LDPC codes with short codeword lengths for STT-MRAM. By further applying a code extension approach, we construct novel RCP-LDPC codes that can work with a single encoder/decoder. Simulation results show that our proposed RCP-LDPC codes outperform the well-known rate-compatible AR4JA protograph codes.