Nonbinary LDPC-Coded Sphere-Packed Transmit Diversity

A recently proposed space-time block-coding (STBC) signal construction method that combines orthogonal design with sphere packing (SP) (referred to here as STBC-SP) has shown useful performance improvements over Alamouti´s conventional orthogonal design. In this paper, we propose a purely symbol-based, low-density parity-check (LDPC)-coded scheme, demonstrating that the performance of STBC-SP systems can further be improved by concatenating SP-aided modulation with nonbinary LDPC and by performing symbol-based turbo detection between the nonbinary LDPC decoder and a rate-1 nonbinary inner precoder. We also investigate the convergence behavior of this symbol-based concatenated scheme with the aid of novel nonbinary extrinsic information transfer (EXIT) charts. Finally, we demonstrate that in the investigated scenarios, it requires 1-2 dB lower power in comparison with the equivalent effective-throughput 0.5-, 0.75-, and 1-bit/symbol systems employing bit-based turbo detection.