The basic principle of OFDM is to transmit high-speed data streams through serial-parallel conversion and distribute them to multiple subchannels with relatively low transfer rates for transmission. Since the symbol period in each subchannel will increase relatively, the effect of the time dispersion caused by the multiple-way delay of the wireless channel on the system can be reduced. In addition, a protection interval between OFDM symbols can be inserted so that the protection interval is greater than the maximum delay spread of the wireless channel, so that inter-symbol interference due to multiple paths can be largely eliminated. Generally, the cyclic prefix is used as a protection interval, so that inter-subcarrier interference caused by multipath can be avoided.