Performance comparison of space-time codes and channel estimation in OFDM systems with transmit diversity for wireless LANs

Channel estimation in OFDM systems with space- time coding is essential. While the conventional channel estimation schemes using both IFFT and FFT are effective for OFDM system with all sub-carriers occupied by data, it will result in the performance deterioration in OFDM system with null data as in IEEE802.11a. In this paper, we propose a channel estimation technique operating in frequency domain without using both IFFT and FFT. The proposed scheme basically uses curve fitting technique. The performance of the channel estimation using curve fitting depends on channel delay spread. Thus, we present a method to change the group size for curve fitting in unknown channels. In addition, we compare the performance of STBC-OFDM with STTC-OFDM. We expect that. the proposed channel estimation technique can be effectively used for OFDM system not only with transmit diversity but also without transmit diversity.