Improvement of the Asia-Pacific TWSTFT network solutions by using DPN results

Two major time and frequency transfer techniques, two-way satellite time and frequency transfer (TWSTFT) and global navigation satellite systems (GNSS: GPS, GALILEO, GLONASS, etc.), are used for the generation of Coordinated Universal Time (UTC)/International Atomic Time (TAI). These time and frequency transfer links comprise a worldwide network and the utilization of the highly redundant time and frequency data is an important topic. Two methods, either TW-only network (i.e., TWSTFT) or singlelink combination of TW and Global Positioning System (GPS), have been developed for combining the redundant data from different techniques. In our previous study, we have proposed a feasible method, utilizing full time-transfer network data, to improve the results of TWSTFT network. The National Institute of Information and Communications Technology (NICT) has recently developed a software-based two-way time-transfer modem using a dual pseudo-random noise (DPN) signal. The first international DPN TWSTFT experiment, using these modems, was performed between NICT (Japan) and Telecommunication Laboratories (TL; Taiwan) and its ability to improve the time transfer precision was demonstrated. In comparison with the conventional NICT-TL TWSTFT link, the DPN time transfer results have higher precision and lower diurnal effects. The estimation also shows that DPN is comparable to GPS precise point positioning (PPP). Because the DPN results show better performance than the conventional TWSTFT results, we would adopt the DPN data for the NICT-TL link and solve the TW+DPN network solutions by using our proposed method. The concept of this application is similar to the so-called multi-technique-network time/ frequency transfer. The encouraging results confirm that the TWSTFT network performance can benefit from DPN data by improving short-term stabilities and reducing diurnal effects. The results of TW+PPP network solutions are also illustrated.