A channel estimation algorithm for OFDM over LEO satellite channels in the presence of frequency offset

For the study of Orthogonal frequency division multiplexing (OFDM) system for Low earth orbits (LEO) satellite communication, a channel estimation algorithm by Kalman filtering based on comb-type pilot subcarriers is proposed in this paper. According to the statistical characteristics of LEO channel, an OFDM system model on frequency domain is deduced. Since comb-type aid channel estimation is sensitive to orthogonality, to suppress Inter carrier interference (ICI), an estimation of Fractional frequency offset (FFO) between the transmitter and the receiver is derived based on the correlation of two consecutive identical pilot signals. After the FFO is compensated, the channels at pilot frequency are estimated by the proposed algorithm and the channel of data are interpolated by piecewise linear interpolation method. In the recursions of channel estimation, the autocorrelation of the process noises is modeled as the first Markov chain. The variances of the noises are estimated using the previous variance estimation of channel and the previous received data. The proposed channel estimator has been compared with Least square (LS) channel estimator by measuring Bit error rate (BER) with QPSK (Quadrature phase shift keying), 16-QAM (Quadrature amplitude modulation) and 64-QAM as modulation schemes in both AGWN (Additive white Gaussian noise) and Rayleigh fading channels. Mean square error (MSE) illustrates the effectiveness of the FFO estimator.