transmit, the well known Alamouti scheme [@Alamouti], and $n_R=1$ receive antennas due to the rate loss inherent in OSTBC with higher number of transmit antennas. Recently, it was shown in [@SezgJorICASSP05] that due to this rate loss, OSTBC with odd number of antennas are always outperformed by OSTBC with even number of antennas, restricting even more the deployment of OSTBC. On the one hand, we have the OSTBC with low complexity and low rates. On the other hand, we have the space-time trellis codes, which achieve higher spectral efficiency in addition to high performance with respect to frame error rates. However, the decoding complexity of space-time trellis codes is increasing exponentially with the number of transmit antennas and the transmission rate. In order to achieve higher spectral efficiency combined with low complexity maximum likelihood detectors, [@Jafarkhani01; @PapadiasFoschi01; @TirkkonenHottinenNON; @A.Sezgin2004; @SezginInfoTheory] designed quasi-orthogonal space-time block codes (QSTBC) with transmission rate one for more than two transmit antennas.

Other approaches aimed at reducing the decoding complexity of space-time trellis codes. For instance, a layered space-time architecture was proposed in [@TarokhNagSesCa99], where the transmit antennas were partitioned into two-antenna groups and on each group space-time trellis codes were used as component codes. In 