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A New Modem for Two Way Satellite Time and Frequency Transfer

Published

Author(s)

Shengkang Zhang, Xueyun Wang, Haifeng Wang, Hongbo Wang, Yuan Yuan, Keming Feng

Abstract

Two Way Satellite Time Frequency Transfer (TWSTFT) is a highly precise time & frequency remote comparison technique, which is widely used in time metrology, satellite navigation, etc. Nowadays, most of the time metrology laboratories in Europe, America and Asia established TWSTFT links. Time transfer Modem is the most crucial instrument in the TWSTFT system. By means of the Modem, the one pulse per second (1PPS) is modulated into intermediate frequency (IF) at the local site. The signal is then up-converted to the radio frequency (RF), amplified, and transmitted to the satellite. At the remote site the RF signal is again amplified, down-converted to the IF, and demodulated by the modem. The time interval be-tween the local 1PPS and reconstructed 1PPS from the received TWSTFT signal is measured on each site. Based on the reciprocity of the TWSTFT signals' bidirectional paths, the time offset of the two clocks are gained by exchanging and differencing the time interval measurements at the two sites. A new time transfer Modem for TWSTFT is developed recently at Beijing Institute of Radio Metrology and Measurement. In this instrument, we use direct sequence spread spectrum and BPSK modulation to generate the IF signal. And the FFT fast parallel algorithm is applied to quickly acquire the pseudo noise modulated signal. A 2nd order FLL assisted a 3rd order PLL are designed in order to solve the paradox of the performance of loop dynamic stress and carrier phase tracking accuracy. A 2nd order DLL is used to track and measure the code phase. The receiver unit of Modem is accomplished by an all-digital structure. The FFT algorithm and correlation process are realized on a FPGA chip. The carrier & code phase discriminator, loop filter, etc. are realized on a DSP processor. Using this structure, we can maximize the processing ability of the chips. So the receiving channel can be extended easily to about 8 channels or even more without any changes on the hardware, which will
Proceedings Title
Proceedings of the 2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum
Conference Dates
April 12-16, 2015
Conference Location
Denver, CO
Conference Title
2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum

Keywords

Acquisition, delay lock loop, Modem, phase lock loop, Two Way Satellite Time and Frequency Transfer (TWSTFT)

Citation

Zhang, S. , Wang, X. , Wang, H. , Wang, H. , Yuan, Y. and Feng, K. (2015), A New Modem for Two Way Satellite Time and Frequency Transfer, Proceedings of the 2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum, Denver, CO, [online], https://doi.org/10.1109/FCS.2015.7138834 (Accessed April 21, 2024)
Created April 13, 2015, Updated November 10, 2018