Two-step Kalman-filter-based AFC for direct conversion-type receiver in LEO satellite communications

We present a new two-step automatic frequency control (AFC) suited for direct conversion-type receivers to counteract large frequency offset with time variation in low Earth orbit (LEO) satellite communication systems. The proposed AFC scheme based on the Kalman-filter provides two steps of frequency estimations, i.e., coarse and fine estimations. Its performance is evaluated by computer simulation with the application to a differentially encoded QPSK/differential-detection system. The proposed scheme shows its excellent characteristic, extending the frequency acquisition range to even that comparable to or larger than the symbol rate. Furthermore, it can track well a time variation of frequency offset.