Sampling frequency offset estimation and correction in OFDM systems

In Orthogonal Frequency Division Multiplexing (OFDM) systems, symbols are transmitted in parallel on several narrow-band subchannels, which are overlapping and orthogonal. Modulation and demodulation is achieved by using Fast Fourier Transform (FFT) algorithms. Mismatch in sampling frequencies between transmitter and receiver can lead to serious degradation due to the loss of orthogonality between the subcarriers. Therefore, the sampling frequency offset has to be estimated, and the error has to be compensated at the receiver side. In this paper, a novel sampling frequency offset estimation algorithm is proposed, which is based on the repetition of a symbol at the communication start-up. The estimate is calculated from the phase difference between successive symbols. Furthermore, sampling frequency correction algorithm that does not require interpolation of signal samples is presented. Simulations were performed for both algorithms separately. High improvement in system performance was achieved.