A Low-Complexity Optimum Detection Based On High-Rate Full- Diversity Mimo Space Time Block Codes

The 2 × 2 MIMO profiles included in Mobile Wi-MAX specifications are Alamouti’s space-time block code (STBC) for transmit diversity and spatial multiplexing (SM). The former has full diversity and the latter has full rate, but neither of them has both of these desired features. An alternative 2×2 STBC, which is both full rate and full diversity, is the Golden code. It is the best known 2×2 STBC, but it has a high decoding complexity. Recently, the attention was turned to the decoder complexity, this issue was included in the STBC design criteria, and different STBCs were proposed. In this paper, we first present a high-rate full-diversity 2×2 STBC design leading to substantially lower complexity of the optimum detector compared to the Golden code with only a slight performance loss. We provide the general optimized form of this STBC and show that this scheme achieves the diversity multiplexing frontier for square QAM signal constellations. Then, we present a variant of the proposed STBC, which provides a further decrease in the detection complexity with a rate reduction of 25% and show that this provides an interesting trade-off between the Alamouti scheme and SM.