Linearly precoded ST-OFDM systems in the presence of ISI

Recently it was shown that a linear precoder can greatly improve the performance of OFDM systems. In this paper, we study linear precoder for space-time coded OFDM (ST-OFDM) system for multiple antenna transmission. The effect of a linear precoder is analyzed when the ST-OFDM system suffers from intersymbol interference caused by undetected channel variations. For QPSK modulation, the optimal precoder that minimizes the bit error rate (BER) is derived. It is found that the optimal precoder is channel independent. Simulation results show that the optimal precoder can significantly lower the BER of ST-OFDM system