  It is well known, that the Alamouti scheme is the only space-time code from
orthogonal design achieving the capacity of a multiple-input multiple-output
(MIMO) wireless communication system with n_T=2 transmit antennas and n_R=1
receive antenna. In this work, we propose the n-times stacked Alamouti scheme
for n_T=2n transmit antennas and show that this scheme achieves the capacity in
the case of n_R=1 receive antenna. This result may regarded as an extension of
the Alamouti case. For the more general case of more than one receive antenna,
we show that if the number of transmit antennas is higher than the number of
receive antennas we achieve a high portion of the capacity with this scheme.
Further, we show that the MIMO capacity is at most twice the rate achieved with
the proposed scheme for all SNR. We derive lower and upper bounds for the rate
achieved with this scheme and compare it with upper and lower bounds for the
capacity. In addition to the capacity analysis based on the assumption of a
coherent channel, we analyze the error rate performance of the stacked OSTBC
with the optimal ML detector and with the suboptimal lattice-reduction (LR)
aided zero-forcing detector. We compare the error rate performance of the
stacked OSTBC with spatial multiplexing (SM) and full-diversity achieving
schemes. Finally, we illustrate the theoretical results by numerical
simulations.
