the MIMO capacity is at most twice the rate achieved with the proposed scheme for all SNR. However, achieving high portions of the capacity does not guarantee good performance in terms of error probability. Thus, we compare the error-rate performance of the proposed scheme with spatial multiplexing (SM), a rate oriented space-time transmission schemes which achieve a high portion of the capacity of MIMO systems, and with the aforementioned diversity-oriented QSTBC by deploying LR-aided linear ZF and ML detectors at the receiver, respectively.

The remainder of this paper is organized as follows. In Section \[seq:system\_model\], we introduce the system model and establish the notation. The structure of the stacked Alamouti scheme and the equivalent channel model are shown in section \[sec:Diversity\_analy\]. The analysis of the mutual information is presented in section \[sec:MutInfo\]. LR-aided linear ZF detection is shortly described in section  \[sec:Schemes\] including the analysis of the probability density function of the condition number of the equivalent channel generated by the different transmission schemes (SM,QSTBC, and stacked OSTBC). Section \[seq:simulations\] provides simulation results, followed by some concluding remarks in Section \[sec:Conclusion\].

System model {#seq:system_model}
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We consider a system with $n_T$ transmit and $n_R$ receive antennas. Our system model is 