METHOD AND APPARATUS FOR AUTOMATIC FREQUENCY CONTROL AND DEMODULATOR

摘要

A demodulator comprises a DSP. The DSP determines the amount of distortion of a transmission line based on a known signal included in a received radio signal, and estimates the frequency of the direct wave based on the amount of the distortion. The DSP also rotates the phase of the amount of distortion based on the amount of phase corresponding to the frequency of the estimated direct wave. Next, the DSP estimates the center frequency of the Doppler broadening based on the amount of phase-rotated distortion. The DSP combines the amount of the phase corresponding to the estimated center frequency of the Doppler broadening and the amount of the phase corresponding to the direct wave frequency to estimate a final frequency offset. The DSP then removes the frequency offset of the received radio signal based on the estimated frequency offset. According to this method, a preferable BER characteristic can be realized while maintaining a sufficient frequency offset compensation range.