Abstract: Aimed at the channel estimation of OFDM-based (orthogonal frequency division multiplex based) transform domain communication (TDCS) systems under low SNR scenarios, channel estimation techniques fou suppressing noise in time domain and/or transform domain are proposed. In time domain, the noise is mitigated through three schemes:time-sliding average, time-forgetting average, and their combination as the channel is slowly time-varying. To further reduce the influence of noise, the time-domain-based channel estimation methods are also combined with IDFT transform domain technique. Simulation results show the proposed channel estimation methods can achieve nearly the same performance as that of perfect channel estimation.