Maximum-likelihood detection for distributed space-time block coding

We investigate maximum likelihood (ML) sequence estimation for distributed space-time block coded cooperative diversity schemes over time-varying fading channels 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 sub-optimum for the non-static case, its performance is close to the optimum for a range of SNRs. It also outperforms pilot symbol assisted techniques, which are widely used in practical applications.