Quasi-Orthogonal STBC with Adaptive Power Allocation under Imperfect Channel Estimation

Multiple-input multiple-output (MIMO) wireless communication systems can offer significantly improved performance with an adaptive power allocation. Also, orthogonal space-time block codes (OSTBCs) are widely used to increase diversity. However, OSTBCs currently only yield a full transmit rate for two transmit antennas. When more than two transmit antennas are considered, quasi-orthogonal STBCs (QO-STBCs) are used to maintain the full transmit rate. In this paper, we present a new system model for four transmit antennas that supports quasi-orthogonal STBCs with an adaptive power allocation under imperfect channel estimation. In the proposed approach, the power allocation criterion depends on the side information based on relative channel phase differences. The power scaling factors are obtained from the quantized channel phase feedback. The feedback delay has the potential to cause degradation of the side information accuracy. Hence, dynamic links with QOSTBCs were found to attain better bit error rate (BER) performances regardless of imperfect channel estimation. As our transmit model is not perfectly orthogonal, some linear operations were needed to reduce interference influences. Thus, interference cancel criterion were applied to the minimization of error rates. Simulation results show that our system was particulary beneficial when the accuracy of estimated side information level is low.