Synchronization in satellite communications is the process of aligning the time and phase scales of satellite ground hubs, satellite transponders, and user terminals so that the equipment operations occur at correct times and correct phases in correct orders. First, time synchronization requires the clocks at receiver ends to acquire and track periodic timing information in transmitted signals. Second, phase synchronization requires receiver carrier tracking loops to acquire and track carrier phase information in transmitted signals. There are several methods to obtain time and phase information through commercial communications infrastructures, including both coherent and non-coherent frequency hopping demodulations. However, levels of trust, accuracy, and robustness of these mechanisms limit potential usefulness for military communications missions. Prospective onboard satellite synchronization paradigms ought to consider the following technical challenges: (1) analysis of time and phase errors associated with ground satellite system controllers, (2) technical requirements of modeling and characterization for time and phase errors at user terminals, (3) uncertainty quantification and management of onboard satellite transponder’s timing and phase errors, and (4) performance assessment of both open- and closed-loop synchronization techniques for phase and timing jitters per hop and/or potential onboard computation solutions for fast phase and time synchronizations in the presence of radio interferences.

 

References

Schmidt TM, Cox DC: “Robust Frequency and Timing Synchronization for OFDM”. IEEE Transactions on Communications 45(12): 1613-1621, 1997

Minn H, Bhargava VK, Letaief KB: “A Robust Timing and Frequency Synchronization for OFDM Systems”. IEEE Transactions on Wireless Communications 2(4): 822-839, 2003

Tsang C-S, Nguyen TM: “Long Loop Time Tracking Performance for Satellite Communication System”. IEEE MILCOM Proceedings: 855-959, 1999

Duffett-Smith PJ, Hansen P: “Precise Time Transfer in a Mobile Radio Terminal”. Proceedings of the 2005 National Technical Meeting of the Institute of Navigation: 1101-1106, 2005

Nguyen TM, Hant J, Taggart D, Tsang C-S, Johnson DM, Chuang J-C: “Design Concept and Methodology for the Future Advanced Wideband Satellite System”. IEEE MILCOM Proceedings: 189-194, 2002

 

key words

Satellite communications; Radio interference; Frequency hopping spread spectrum; Timing synchronization; Phase synchronization; Timing jitter; Timing and phase errors; Transponder timing errors; Closed-loop synchronization; Open-loop synchronization;

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