A novel carrier frequency estimator suitable for the FFT-based multicarrier demodulator

In practical FDMA satellite systems, there may be substantial uncertainties in the carrier frequencies due to Doppler effect or oscillator instability. Since individual carriers within the block of spectrum originate from different earth stations, they will all have different frequency offset. It is therefore not appropriate to feed back an error signal to any local oscillator in the common stages. Alternatively, a feed forward carrier frequency correction, seems to be an attractive solution. A novel carrier frequency estimator suitable for the FFT-based multicarrier demodulator that operates in a feed forward configuration is introduced. A theoretical derivation is obtained and the s-curve is shown. Carrier frequency correction is performed in two stages: the first stage, which precedes the matched filter, reduces the frequency offset to a fraction of the symbol rate, while the second stage performs a fine frequency correction to put the frequency error at an acceptable value for the operation of the Viterbi and Viterbi phase estimator