Research on PPP Time Transfer Method Based on Observable-Specific Signal Bias

Precision time transfer is an integral part of precision time systems, ensuring that multiple clocks maintain high-precision time synchronization. Currently, the GNSS carrier phase time transfer technology mainly uses PPP (Precise Point Positioning) technology, which has the advantages of global, all-weather, high precision and low cost. However, the traditional PPP time transfer technology has the problems of long initial time, low accuracy and reliability. If the ambiguity can be fixed correctly, the accuracy and reliability of PPP time transfer can be greatly improved. The key to realizing the fixed ambiguity is to effectively separate the initial phase and hardware delay deviation of the satellite end, and then restore the integer characteristics of the ambiguity. In the multi-frequency and multi-system environment, with the increase of navigation system, signal and receiver type, increasing types of signal delay deviation are generated, the rich signal resources cause various and complex problems in the combination form of deviation, and difficult to achieve a unified and convenient ambiguity fixed PPP time transfer method for phase deviation correction. This paper using a simple and uniform code/phase absolute deviation product of the observations, correcting the absolute deviation to the observations, and implementing ambiguity fixed PPP time transfer method considering the deviation correction of the observations. Experimental results show that: the time transfer accuracy of static mode is 0.02ns, and that of multi-system time is 0.017ns, the single system time transfer of dynamic mode is 0.06ns, which is superior than the traditional PPP time transfer.