Channel estimation technique for OFDM systems spread by chirp sequences

A frequency domain equalization for multipath fading is widely used for OFDM systems and accurate channel estimation is required. In conventional OFDM systems, pilot symbols are inserted periodically in time and frequency domain by a transmitter for channel estimation. Channel estimation error is quite large, especially in frequency-selective fading channel, because the estimates are interpolated with the restricted pilot subcarriers. The channel estimation error can be decreased by assigning pilot symbols to all subcarriers in specified OFDM blocks. In that case, however, no data symbols can be transmitted in OFDM blocks where pilot symbols are transmitted. In this paper we propose a new channel estimation scheme in which OFDM signal is transmitted after spread by chirp sequences, and channel estimation of all subcarriers is achieved with only one pilot symbol without interpolation. Simulation results show that the MSE performance of channel estimation and the BER performance can be significantly improved by the proposed scheme.