Multi-strata codes: space-time block codes with low detection complexity

The multistrata space-time codes proposed by Wachsmann et al. were intended then to fix the drawback of orthogonal space-time block codes which is the relatively low spectral efficiency. However, these codes lack two things: 1) their performance is worse than codes designed using number theory like the Golden code. 2) The advantages of their structure were never exploited in reducing the detection complexity. In this paper, it is shown how the multistrata structure can potentially reduce the detection complexity of the sphere decoder in the uncoded case. The reduction in complexity is achieved in both the preprocessing and the search steps of the sphere decoder. Spacetime block codes having such a multistrata structure were found via optimization. Simulation results show that the obtained code has sufficiently high minimum determinant with a very small performance penalty compared to the best known 2 x 2 spacetime block code in literature, the Golden code. Also a simple means of generating bit log-likelihood ratios in a bit-interleaved coded modulation scenario is presented.