Quasi-Orthogonal Space-Time Block Coding with Closed-Loop Control in MIMO Communication Systems

In the paper, we proposed a method of space-time diversity on the transmitting side, combining a closed feedback and quasi-orthogonal space-time coding technique called closed-loop control with quasi-orthogonal space-time block coding (QO-STBC). For a configuration 4x1-4x4 with four transmit and one receive antennas and four symbols per four resource elements, our method allows the QO-STBC to be completely orthogonalized what maximizes the diversity gain. It is shown that the developed approach can also be used for the $4\times 2-4\times 2$ configuration. In this case, it is not possible to orthogonalize QO-STBC completely, but the level of inter-channel correlation is considerably reduced. A statistical modeling was carried out to study the characteristics of noise immunity of the proposed transmission scheme. We show that it is sufficient to use a one-bit command to control the phase of two transmitting antennas. A gain of 1.4 dB is achieved for the $4\times 1-4\times 4$ scenario and 2.5 dB - for the $4\times 2-4\times 2$ case. Phase control of transmitting antennas used in this method of signal transmission does not change the interference conditions.