Outage analysis and optimization of a stacked orthogonal space-time architecture and near-outage codes

We propose a stacked orthogonal space-time architecture for the quasi-static, MIMO Rayleigh fading channel where the K transmit antennas are divided into K/2 groups. Each group employs the Alamouti design as the inner code with the indeterminates being uncoded symbols or symbols from some outer code. Successive group interference suppression strategies based on decorrelating and MMSE filters are used to decode the component codes in some fixed or channel dependent order. These strategies exploit the specific structure of the inner codes to yield high diversity orders while preserving the decoupling property, thereby enabling the use of single-input, single-output (SISO) outer codes. The problems of finding the exact frame error probability (FEP) or outage probability of the interference suppression schemes are challenging. Nevertheless, these analysis problems are solved for the decorrelating case. Alternatively, the outage probability is minimized over channel dependent ordering rules via a greedy algorithm for any given rate and power tuples. We also demonstrate the intimate connection between outage probability and the achievable FEP for long frame-lengths. In the case of the optimized stacked space-time systems with (SISO) outer coding, we show that much better diversity orders and frame error probabilities (of about 4 dB in one example) are obtained relative to the codes of V. Tarokh et al. (1999) and these improvements are also obtained with a lower decoding complexity.