This paper (Part of the content of this manuscript has been accepted for presentation in IEEE Globecom 2008, to be held in New Orleans) 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 ($2\times 2$) and the 4 transmit antenna, 2 receive antenna ($4\times 2$) MIMO systems. Presently, the best known STBC for the $2\times2$ system is the Golden code and that for the $4\times2$ system is the DjABBA code. Following the approach by Biglieri, Hong and Viterbo, a new STBC is presented in this paper for the $2\times 2$ 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 \emph{information-lossless} and \emph{diversity-multiplexing gain} (DMG) tradeoff optimal. This design procedure is then extended to the $4\times 2$ 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 $M^4$ for square QAM of size $M$. In this paper, a scheme that reduces its ML-decoding complexity to $M^2\sqrt{M}$ is presented.

翻译：本手稿的内容部分已被接受, 以 IEEEE Globalcom (2008年, 新奥尔良) 格式化为 IMIMO 系统。 目前, 以 $2 的复杂度为 最著名的STBC 系统是 Golden 代码, 4\ time2 的系统是 DjABBA 代码。 按照 Bigelili、 Hong 和 Viterbo 的处理方法, 新的 STBC 也为 2\ time 2 的系统提供了很大的编码收益。 该代码符合 Gold 性能代码和 ML- deco 4 的传输天线, 而它比 ML- deco 复杂度低, 与 非矩式 QAM 系统相同的性能表现为 Goldy 。 这个代码也显示为 IMF$ QQQ 的 QQQQ 代码, 和 mB AS 格式化的系统 值值值 4- drouplex droupal 。 和MMMD AS AS 的系统 ASyal deal droup droup 。 这个系统是M- drodeal 。M- dism 。 AS 。 。 。 AS 和M- dismlated AS AS AS AS AS 。 AS 。 。 AS AS 。 。 AS 。 。 AS AS AS AS 。