Two Adaptive Space - Time Block Coded MIMO Systems Exploiting Partial Channel Knowledge at the Transmitter

In this contribution two new closed loop transmission schemes over wireless MIMO channels with only partial channel knowledge at the transmitter are presented. Utilizing Space Time Block Codes (STBCs) with additional preand post signal processing provides nT independent virtual channels, where nT is the number of transmit antennas. In most cases we consider nT = 4. The first scheme is based on the Extended Alamouti (EA) code, transmitting R=1 information symbol per channel use. This scheme requires only a very low feedback rate. The second scheme achieves a higher rate of R=2 information symbols per channel use, but it needs more feedback information. This high rate data transmission is achieved by utilizing the Double Space Time Transmit Diversity (D-STTD) code. The modulation format (from 2PSK to 256QAM) used on the resulting nT independent virtual channels is adapted to the individual quality of the virtual channels. For a given target Bit Error Ratio (BER) and a fixed mean transmit power an adaptive algorithm maximizes the data throughput. With these two closed loop schemes very high data rates at reasonably low values of SNR are achieved. Simulation results show that the first scheme is very robust against spatial correlation with respect to the mean information bit rate.