Timing and synchronization are always important parts in communication system. OFDM system has more stringent requirements on timing due to its wide bandwidth transmission. Carrier frequency offset introduces a stationary error to all the symbols or samples, while sampling clock error accumulates, leading to an undetected sample. Synchronization is necessary for OFDM receiver to find an ISI free section and get the original data back. In order to get the original data, we have to use equalizer to get rid of the channel distortion. Channel estimation is required in channel-aided equalization. The estimated channel will be taken out of the received signal, so that the original data are retrieved. This work can be done in the frequency domain.