| With the development of Super Large Scale Integration, communication systems develop towards all-digital demodulation. But the demodulators of Fengyun-2 meteorological satellite are partially implemented in digital way in current ground application system. This demodulator is of high complexity, poor reliability and extendibility, and easily impacted by human and environmental factors. To avoid these disadvantages, an all-digital demodulator scheme is given in this paper. And carrier recovery, which is the key technology of digital demodulation, is fully discussed. Based on the simulation and analysis of classical algorithms, a carrier recovery algorithm which is combination of swept and DD algorithm is adopted in all-digital demodulator. In swept algorithm, the traditional lock detection easily causes lost lock or fake lock, which makes the system unstable. The method for detecting the height difference of the MSE is given to improve the reliability of the lock. Because swept modes have a great influence on capture time of frequency offset, several swept modes are given to reduce the overall capture time. Finally, the performances of this digital demodulator are tested through the simulation of BER and the system joint lock-time, and a carrier recovery module is implemented in FPGA. |
