Optimizing Bit-Interleaved Coded Modulation for Half-Duplex Relay Based on Protograph Codes

In this paper, we discuss the bit-interleaved coded modulation (BICM) for the half-duplex decode-and-forward (DF) relay network based on the protograph LDPC codes. The half- duplex relay BICM design problem can be transformed into a problem of rate-compatible BICM design, where the different segments of modulated symbols experience different SNRs. To optimize the BICM based on the rate-compatible protograph structure, we use the protograph extrinsic information transfer (EXIT) to evaluate the thresholds of different mapping patterns between the variable nodes in protographs and the modulated bits. With this tool, we search the efficient mapping pattern of BICM for the half-duplex DF network. Our work can achieve significant gains over the existing work.