Turbo detection of channel-coded space-time signals using sphere packing modulation

A recently proposed space-time signal construction method that combines orthogonal design with sphere packing, referred to as (STBC-SP), has shown useful performance improvements over Alamouti´s conventional orthogonal design. In recent years, iterative decoding algorithms have attained substantial performance improvements in the context of wireless communication systems. We demonstrate that the performance of STBC-SP systems can be further improved by concatenating sphere packing aided modulation with channel coding and performing demapping as well as channel decoding iteratively. The sphere packing demapper is modified for the sake of accepting a priori information that is obtained from the channel decoder. Bit-wise mutual information measures are also employed for the sake of searching for the optimum bits-to-symbol mapping. We present simulation results for the proposed scheme communicating over a correlated Rayleigh fading channel. At a BER of 10^-5, the proposed turbo-detected STBC-SP scheme employing optimum mapping, is capable of achieving a coding gain of approximately 19 dB over the identical-throughput 1 bit/symbol uncoded STBC-SP benchmarker scheme. The proposed scheme also achieved a coding gain of approximately 2 dB over the 1 bit/symbol channel-coded STBC-SP benchmarker scheme that employed Gray mapping.