Improved high-rate space-time codes via orthogonality and set partitioning

In this paper, we propose a new technique for constructing improved high-rate space-time codes. The proposed code construction is based on a concatenation of an orthogonal spacetime block code and an outer M-TCM encoder. However, unlike the existing STB-MTCM schemes which are rate-lossy, the proposed construction yields higher-rate space-time codes by expanding the cardinality of the orthogonal space-time block code before concatenating with an outer M-TCM encoder. An advantage of the proposed construction is that the standard techniques for designing a good TCM code, such as the classic set partitioning concept, can be adopted to realize the STB-MTCM designs with large coding gains. We present several design examples of improved full-rate space-time codes for a system with 2 transmit antennas. Simulation results show that the new space-time codes considerably outperform the existing ST-TCM designs. For example, the new 4-state 2-bits/symbol QPSK space-time code performs even better than the original 32-state design, while performance of the new 32-state QPSK code is only 1.5 dB away from the outage probability limit. Moreover, decoding complexity of the proposed M-TCM construction is made reasonably low by exploiting signal orthogonality.