Abstract: This paper analyzes the calculation for frequency offset relative to given functions. It is found that it has a smaller range of frequency offset and can be easily attested by Doppler frequency offset. Considering this, the paper introduces a calculation method of carrier demodulation based on the orthogonal algorithm, which the frequency offset can be omitted. The results of computation simulation indicates that the orthogonal demodulation is applicable to the AM modulated OFDM signal, in that not only can frequency offset be ignored in it, but it can be available in the channel with a low SNR.

Key words: frequency offset, pseudo-random sequence, orthogonal demodulation