Frequency domain vs time domain equalization
Frequency domain equalization requires a certain block structure to be efficient. In OFDM, adding a cyclic prefix to the transmitted block, and using IDFT at the transmitter and DFT at the receiver allows the use of one-tap frequency equalizer. In the time domain, the equalizer length is proportional to the number of channel taps. We can use frequency domain equalization in single carrier systems as well, again with proper block structure, and operations.