A space-time trellis code design method for OFDM systems

We introduce a new design method for space-time trellis codes (STTC's) in orthogonal frequency-division multiplexing (OFDM) systems with frequency-selective fading. First, by analyzing the pairwise error probability (PEP), we conclude that large effective length and random interleaving are two critical principles in designing robust space-time codes (STC's) for OFDM systems. Then, based on the analogy between the proposed STC design principles for multiple-antenna OFDM systems and the trellis-coded modulation (TCM) code design criteria for single-antenna flat-fading channels, we develop a new STTC design method. At each trellis stage, this method converts the single output code symbol of a traditional TCM code into several STTC code symbols, which are to be simultaneously transmitted from multiple transmitter-antennas, and hence results in a new class of STTC's. In this way, the effective lengths that have been optimized for traditional TCM codes are preserved in the resulting STTC's; together with a random interleaver, the proposed new class of STTC's can robustly and efficiently exploit both the spatial and the frequency-selective fading diversity resources in multiple-antenna OFDM systems. Finally, the excellent performance of the proposed STTC's are demonstrated through computer simulations.