Low ML-Decoding Complexity, Large Coding Gain, Full-Rate, Full-Diversity STBCs for 2 X 2 and 4 X 2 MIMO Systems

This paper1 deals with low maximum likelihood (ML) decoding complexity, full-rate and full-diversity space-time block codes (STBCs), which also offer large coding gain, for the 2 transmit antenna, 2 receive antenna (2× 2) and the 4 transmit antenna, 2 receive antenna (4× 2) MIMO systems. Presently, the best known STBC for the 2 × 2 system is the Golden code and that for the 4 × 2 system is the DjABBA code. Following the approach by Biglieri, Hong and Viterbo, a new STBC is presented in this paper for the 2× 2 system. This code matches the Golden code in performance and ML-decoding complexity for square QAM constellations while it has lower ML-decoding complexity with the same performance for non-rectangular QAM constellations. This code is also shown to be information-lossless and diversitymultiplexing gain (DMG) tradeoff optimal. This design procedure is then extended to the 4× 2 system and a code, which outperforms the DjABBA code for QAM constellations with lower ML-decoding complexity, is presented. So far, the Golden code has been reported to have an ML-decoding complexity of the order of M for square QAM of size M . In this paper, a scheme that reduces its ML-decoding complexity to M √ M is presented.