Piester Dirk, Bauch Andreas, Becker Jürgen, Staliuniene Egle, Schlunegger Christian
Physikalisch-Technische Bundesanstalt Braunschweig, Germany.
IEEE Trans Ultrason Ferroelectr Freq Control. 2008 Sep;55(9):1906-12. doi: 10.1109/TUFFC.882.
Two-way satellite time and frequency transfer (TWSTFT) using geostationary telecommunication satellites is widely used in the timing community today and has also been chosen as the primary means to effect synchronization of elements of the ground segment of the European satellite navigation system Galileo. We investigated the link performance in a multistation network based on operational parameters such as the number of simultaneously transmitting stations, transmit and receive power, and chip rates of the pseudorandom noise modulation of the transmitted signals. Our work revealed that TWSTFT through a "quiet" transponder channel (2 stations transmitting only) leads to a measurement noise, expressed by the 1 pps jitter, reduced by a factor of 1.4 compared with a busy transponder carrying signals of 12 stations. The frequency transfer capability expressed by the Allan deviation is reduced at short averaging times by the same amount. At averaging times of >1 d, no such reduction could be observed, which points to the fact that other noise sources dominate at such averaging times. We also found that higher transmit power increases the carrier-to-noise density ratio at the receive station and thus entails lower jitter but causes interference with other station's signals. In addition, the use of lower chip rates, which could be accommodated by a reduced assigned bandwidth on the satellite transponder, is not recommended. The 1 pps jitter would go up by a factor of 2.5 when going from 2.5 MCh/s to 1 MCh/s. The 2 Galileo precise timing facilities (PTFs) can be included in the currently operated network of 12 stations in Europe and all requirements on the TWSTFT performance can be met, provided that suitable ground equipment will be installed in the Galileo ground segment.
利用地球静止通信卫星进行的双向卫星时间和频率传递（TWSTFT）如今在计时领域得到了广泛应用，并且已被选为实现欧洲卫星导航系统伽利略地面段各元件同步的主要手段。我们基于诸如同时发射站数量、发射和接收功率以及发射信号伪随机噪声调制的码片速率等运行参数，对多站网络中的链路性能进行了研究。我们的工作表明，通过“安静”转发器信道（仅2个站发射）进行的TWSTFT导致的测量噪声（以1pps抖动表示），与承载12个站信号的繁忙转发器相比降低了1.4倍。由阿仑偏差表示的频率传递能力在短平均时间内也降低了相同幅度。在平均时间大于1天的情况下，未观察到这种降低，这表明在这种平均时间下其他噪声源占主导。我们还发现，较高的发射功率会提高接收站的载噪比，从而导致较低的抖动，但会对其他站的信号造成干扰。此外，不建议使用较低的码片速率，虽然卫星转发器上减小的分配带宽可以容纳较低的码片速率。当码片速率从2.5MCh/s降至1MCh/s时，1pps抖动会增大2.5倍。如果在伽利略地面段安装合适的地面设备，2个伽利略精密授时设施（PTF）可以纳入欧洲目前运行的12个站的网络中，并且可以满足对TWSTFT性能的所有要求。
