Split complex/quaternary space-time block coded multicarrier-CDMA in downlink Rayleigh fading channel

The paper suggests a new scheme for space-time block coded MC-CDMA to enable transmission of complex and quaternary symbols while maintaining bandwidth requirements. An adaptive power scheme is proposed to keep the transmitted power at an optimal level. An important aspect of diversity techniques is maximizing the spectral efficiency. Most systems are bandwidth limited, whereby the only option to increase the data rate is through the use of complex information symbols of different orders. However, not all systems support transmitting complex symbols. MC-CDMA is one of them (Hajian, M. et al., EUMWC, 2003). A possible workaround is to double the number of subcarriers and split the complex symbol into a real part and an imaginary part, each having its own subcarrier. A disadvantage is that the required bandwidth is doubled if the same data rate is maintained. Transmit diversity using multiple antennas at the transmit side is another method of solving the complex symbol problem. Using two transmit antennas, the real part can be sent through the first antenna and the imaginary part through the second antenna. The paper builds further on the STBC (space-time block coded) MC-CDMA analyzed earlier (Hajian et al., 2003). The results show the ability of the system to modify the data rate and the corresponding robustness of the system against fading and noise.