Orthogonal Impulse Postfix OFDM Transmission for Efficient MIMO Channel Estimation

The estimation of channel state information in MIMO-OFDM systems is considered as a significant issue. In the conventional MIMO-OFDM systems, time divided or orthogonal pilot patterns are adopted to estimate the MIMO channel coefficients. However, the performance of the estimation sometimes becomes insufficient to make the full use of the MIMO benefits, especially under a fast varying channel environment. In the previous literature, we proposed a novel type of SISO-OFDM system, denoted as Impulse Postfix OFDM (IP-OFDM), which inherently posses a superior channel estimation performance. Our objective of this paper is to extend our IP-OFDM to MIMO case to resolve aforementioned channel estimation problem. The IP-OFDM scheme is characterized by the impulse postfix inserted in the guard interval with zero-padding. For the extension to MIMO, we propose to use orthogonal wave shapes as the impulse-postfix for each transmit antenna. These orthogonal shapes, stored at the receiver, are correlated to produce the time-domain channel response for each transmit-receive path. As the number of transmit antennas increases, the proposed scheme just needs to adopt additional orthogonal waves without the loss of data slots, which is unavoidable for the conventional pilot based scheme. Furthermore, the proposed MIMO-IP-OFDM scheme yields significantly improved bit-error-rate (BER) performance compared with the conventional pilot-aided MIMO-OFDM systems, providing the robustness against the time-frequency selectivity of the MIMO channel.