Protograph LDPC codes for STBC Rayleigh fading channels

In wireless communications, spatial diversity techniques, such as space-time block code (STBC) and multiple-input multiple-output (MIMO), have attracted much attention in recent years because they possess powerful robustness against signal fading. In this paper, we investigate the performance of the protograph low-density parity-check (LDPC) codes over space-time block code (STBC) Rayleigh fading channels. Taking into consideration the Alamouti STBC structure, we propose a modified protograph extrinsic information transfer (PEXIT) algorithm in order to analyze the convergence performance of protograph codes in such scenarios. We further compare the decoding thresholds and bit error rates (BERs) of two typical protograph codes, i.e., accumulate-repeat-by-3-accumulate (AR3A) code and accumulated-repeat-by-4-jagged-accumulate (AR4JA) code, with the regular LDPC code and optimized irregular LDPC codes. The results illustrate that the AR3A code outperforms other three codes in the high signal-to-noise-ratio (SNR) region. As a consequence, the AR3A code appears to be a better candidate for use in the wireless communication systems with multiple antennas.