Performance analysis of space-time codes with channel information errors

Many space-time codes (STC) have been proposed to enhance the performance of wireless communications in flat fading channels. All of them rely on knowledge of the channel, and hence are affected by channel estimation errors. Most previous research on STC performance evaluation assumed perfect channel information. We investigate STC robustness under imperfect channel knowledge. We first define the concept of "closeness" by comparing the BER under channel estimation errors with that of perfect channel knowledge, aiming to characterize STC performance degradation due to imperfect channel knowledge. Then the robustness of STC can he compared by their "closeness" to perfect results. In our computer simulations, we apply the same channel estimator to different STCs in OFDM communication systems. We find that for systems with two and three transmit antennas, space time block codes (STBC) are always more robust to channel estimation errors than space time trellis codes (STTC). With the increase of receive diversity, all STCs become more robust to channel estimation errors. For STTC, as the number of trellis states increases, the codes become less robust to channel estimation errors. We also compare the BER performance of STC in the presence of channel estimation errors. For a two-transmit-antenna system, the performance of STBC is always better than that of 4-state STTC, but is always worse than 16-state STTC. For systems with three transmit antennas, the BER performance of STTC is much better than that of STBC.