Adaptive switching between space-time and space-frequency block coded OFDM systems

In this paper, we propose an adaptive transmission technique for MIMO-OFDM systems which selects one of space-time block coded OFDM (STBC-OFDM) and space-frequency block coded OFDM (SFBC-OFDM). STBC-OFDM and SFBC-OFDM undergo severe performance degradation in time-varying and frequency-selective channel, respectively. In the adaptive scheme, either STBC-OFDM or SFBC-OFDM is selected by using the proposed switching criteria. Two selection criteria, correlation of the channel and magnitude of the interference, are proposed for transmission mode selection. In criterion I, based on the observation of the theoretical performance in [9], correlation between successive OFDM symbols for STBC-OFDM and correlation between neighboring subcarriers for SFBC-OFDM are compared and the mode which has higher correlation value is selected to maximize the SNR. Next, in criterion II, we choose the mode which has smaller interference to reduce the performance degradation due to the interference. Simulation results show that the proposed adaptive switching system outperforms the nonadaptive system.