Turbo coded OFDM/TDM with Frequency-domain Equalization

Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM) bridges the conventional OFDM and single carrier (SC) transmission. For a coded OFDM/TDM system with frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion in a frequency-selective fading channel, there is a trade-off between coding gain and frequency diversity effect. In this paper, we evaluate by computer simulation the bit error rate (BER) performance of turbo coded OFDM/TDM. The number K of slots in an OFDM/TDM frame is an important design parameter. It was shown that K impacts the BER performance differently in the coded case from uncoded case. As K increases from 1, the better frequency diversity effect is obtained but coding gain tends to be lost due to less frequency interleaving effect; extreme cases are K=1 (conventional OFDM) and K=256 (SC). We have found that the BER performance is almost the same for K=1 and 256 while for other value of K, the BER performance degrades. We also consider the required peak transmit power because it is an important design parameter of transmit power amplifiers. It was found that OFDM/TDM reduces peak transmit power and improves the BER performance in comparison to conventional OFDM; for both uncoded and coded cases, the worst BER performance is achieved with K=1 (conventional OFDM) while the best performance is achieved with K=256 (SC). Keyword: OFDM/TDM, frequency-domain equalization, channel coding, frequency-selective fading