As an alternative to the traditional cyclic prefixed OFDM (CP-OFDM) technology, time-domain synchronous OFDM (TDS-OFDM) provides higher spectrum efficiency due to no pilot in the transmitted signal. However, the pilot-Aided channel estimation techniques in CP-OFDM cannot be applied to TDS-OFDM. In this paper, channel impulse responses are estimated in time domain based on the linear correlation between the received samples and the locally generated PN sequence. The iterative threshold detection (ITD), as well as the combination with decision feedback equalization (DFE), is proposed to improve the precision of channel estimation. It is shown by simulation that the proposed algorithm, ITD combined with DFE (ITD-DFE), performs very well even in multipath environments with long- delay and large-amplitude echoes.