Combination of TWSTFT and GNSS for accurate UTC time transfer

Abstract

The international UTC/TAI time and frequency transfer network is based on two independent space techniques: Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Navigation Satellite System (GNSS). The network is highly redundant. In fact, 28% of the national time laboratories, which contribute 88% of the total atomic clock weight and all the primary frequency standards to UTC/TAI, operate both techniques. This redundancy is not fully used in UTC/TAI generation. We propose a combination that keeps the advantages of TWSTFT and GNSS and offers a new and effective strategy to improve UTC/TAI in terms of accuracy, stability and robustness. We focus on the combination of two BIPM routine products, TWSTFT and GPS PPP (time transfer using the precise point positioning technique), but the proposed method can be used for any carrier phase-based GNSS product.