Diversity-multiplexing tradeoff of stacked cyclic delay diversity schemes

In addition to orthogonal and quasi-orthogonal space-time block codes (OSTBC, QSTBC), cyclic delay diversity (CDD) is a transmit diversity scheme that achieves full diversity gain of NnR, with N transmit antennas and nR receive antennas. The performance in terms of spatial multiplexing gain is quite limited, since all degrees of freedom are used to obtain diversity. Thus the gap between the diversity-multiplexing tradeoff (DMT) of these codes and the optimal DMT increases significantly for higher spatial multiplexing gain. In order to overcome this problem, we propose the so called stacked CDD (SCDD), where K blocks of standard CDD codes of size nT , with N = KnT , are stacked on top of each other. The DMT achievable with the proposed scheme for asymptotically high SNR is analyzed. Depending on the system parameters K, nT , and nR, the gains obtained over the standard CDD are significant and close to the optimal DMT curve.