Space-time code design in OFDM systems

We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system in frequency-selective fading channels. By analyzing the pairwise error probability (PEP), we show that STC-OFDM systems can potentially provide a diversity order as the product of the number of transmitter antennas, the number of receiver antennas and the frequency selectivity order, and that the large effective length and the ideal interleaving are two most important principles in designing STCs for OFDM systems. Following these principles, we propose a new class of trellis-structured STCs. Compared with the conventional space-time trellis codes, our proposed STC's significantly improve the performance by efficiently exploiting both the spatial diversity and the frequency-selective-fading diversity.