  We present a phase-aligned space-time coding scheme that expands the original
Alamouti codeword to three or four transmit antennas ($N_t = 3$ or 4) with
phase alignment. With $1 \sim 2$ bits feedback for the phase information, the
fundamental performance penalty of $10log_{10}(N_t)$ dB of orthogonal
space-time coding compared to the optimum beamforming is reduced by 1 dB (for
$N_t=3$) or 2 dB (for $N_t = 4$) on average. With the proposed scheme, the full
diversity order of $N_t$ is achievable, whereas the receiver architecture
remains the same as the legacy Alamouti decoding with codeword size of two,
since the spatial expansion is transparent to the receiver. Our results show
the proposed scheme outperforms open-loop space-time coding for three or four
transmit antennas by more than 3 dB.
