TWSTFT activities at NTSC

NTSC (National Time Service Center) is responsible for Chinese national time scale generation and has being applied TWSTFT (two-way satellite time and frequency transfer, TW for short) for time transfer since 1998. NTSC was one of the first UTC laboratories practicing TWSTFT in China. From 2002 to 2004, TWSTFT was the major technique for NTSC contributing to UTC. Since 2007, direct NTSC-European TWSTFT time links have been established between NTSC, VSL (Delft, Netherlands) and OP (Paris, France). In 2008, TWSTFT time link between NTSC and PTB (Braunschweig, Germany) becomes operational and will be used as the primary technique for UTC time transfer. In this paper, we present the major activities in TWSTFT at NTSC, especially the accurate time transfer between NTSC and other Asian national time laboratories, NMIJ (Japan) (NMIJ is not mentioned is this paper), NICT (Japan), SG (Singapore), KRIS (Korea) and TL (Chinese Taipei) as well as the NTSC-European time links. We compare the TWSTFT and GPS time transfer results, analyze the error sources in the measurements and discuss the uncertainties in the time transfers and in the calibrations.