Research On Time-frequency Synchronization For 800 Megabits Per Second Throughput With Satellite Communications

Satellite communications have become the necessity of the space activities, which satisfies the high broadband, the wide area covered and the real-time communication.Broadband satellite communications, one of them, have become the tendency of the future satellite communications. Synchronization is the key to solve the transmission delay and doppler frequency shift between the information transmission of the spacecrafts and the earth. Time synchronization marks the starting point of the timing location, and the frequency synchronization estimates the offsets of the carrier frequency.The communications between the satellite and the earth, especially the low-orbit satellite communications, have the low antenna gain and a lot of multipath components on the receiving end. The down link uses the OFDM(Orthogonal Fequency Division Multiplexing) technology to recede the affect of multipath fading. OFDM, named orthogonal frequency division multiplexing, is kind of multicarrier modulations, which performs high broadband utilization and excellent resisting multipath fading. However,the delays and doppler frequency shift limit the application of OFDM.This paper focuses on the synchronization of the timing and frequency in communication between satellite and the earth of the transmission speed in 800 billion bits per second. It analyzes some classic algorithms of synchronization, and researches the performance of the ML, Schmidl&Cox, Minn, Park, and CAZAC(Const Amplitude Zero Auto-Corelation) sequence algorithms. It also analyzes the affects on the offset of the timing and carrier frequency in OFDM systems. It designed the reasonable training sequences to meet the data throughput and the synchronization, and put forward the parallel time-frequency synchronization to reduce the delay and the error of the frequency estimation. At last, it realized the algorithm on the FPGA.