On The Performance of Pre-Transformed Space-Time Block Coded OFDM Systems

In a previous work by Wu et al., it is shown that the performance of the pre-transformed space-time block coded orthogonal frequency division multiplexing (PT-STBC-OFDM) system has much superior performance compared to the normal STBC-OFDM system. In this paper, we present an analytical study on the bit error rate (BER) of the PT-STBC-OFDM system. We derive the noise distribution of PT-STBC-OFDM system and hence, obtain the BER numerically. We also derived two closed-form BER approximations for the PT-STBC-OFDM system at two different SNR regions. We show that by adding the PT operation, the system has better diversity compared to STBG OFDM system at the medium SNR region. Using linear detection, the diversity of both systems at the high SNR regions are the same. Moreover, we demonstrate that at high SNR, a PT-STBC-OFDM system of transform size N requires 5log(10)(N) dB less SNR to achieve the same BER as without PT.