A new modem for two way satellite time and frequency transfer

A new time transfer modem for two-way satellite time and frequency transfer (TWSTFT) has been developed recently at Beijing Institute of Radio Metrology and Measurement (BIRMM). The DSSS and BPSK modulation techniques are used to generate a PRN signal. A FFT fast parallel algorithm is applied to achieve fast acquisition of the PRN modulated receiving signal. A 2^nd order FLL assisted 3^rd order PLL is designed to keep both of the performance of loop dynamic stress and carrier phase tracking accuracy, and a 2^nd order DLL is used to track and measure the code phase. A short baseline TWSTFT experiment was done with two 1.2 m VSAT earth stations and a commercial geosynchronous orbit communication satellite to evaluate the modem´s performance. The result shows very low noise with the standard deviation (1 σ) equal to 0.13 ns at a 2.5 MChip/s code rate.