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The time-domain equalization for quasi-orthogonal space-timeblock codes (QO-STBC) is investigated by using the inherent quasi-orthogonality to design low-complexity receivers. The diversity gains are presented for the proposed scheme through pairwise error probability (PEP) derivation and analysis, which are confirmed by Monte Carlo simulations.

We investigate maximum-likelihood (ML) sequence estimation for space-time block coded systems without assuming channel knowledge. The quadratic form of the ML receiver in this case does not readily lend itself to efficient implementation. However, under quasi-static channel conditions, the likelihood function reduces to a simple form similar to the classical correlation receiver in matrix notation. It also allows the development of a recursive expression that can be easily implemented by a Viterbi-type algorithm with a reasonable complexity. Although the receiver is suboptimum for the nonstatic case, its performance is close to the optimum for a range of signal-to-noise ratios. Index Terms--Fading channels, maximum-likelihood (ML) sequence estimation, space-time block coding (STBC).