Precise point positioning time transfer with multi-GNSS single-frequency observations

The dual-frequency precise point positioning (DF-PPP) technique has been widely used for time transfer. Actually, DF GNSS receivers are much more expensive than single-frequency (SF) receivers. In addition to high precision, cost is also a key issue for market applications. Furthermore, dual-frequency receivers increase the difficulty of hardware delay calibrations with respect to single frequencies. In this contribution, the SF-PPP technique is first employed for time transfer. Three SF-PPP models, namely, the ionospheric-free, ionospheric-corrected, and ionospheric-constraint SF-PPP models, are compared and assessed. With respect to the GPS-only DF-PPP solutions, the type A uncertainty of SF-PPP time transfer is at the scale of subnanoseconds, which can meet the demands of most time transfer applications. Overall, the ionospheric-constraint SF-PPP model outperforms the other two SF-PPP models. With the ionospheric-constraint SF-PPP model, the contribution of multi-GNSS observations to SF-PPP time transfer is also investigated under simulated constrained conditions with different satellite elevation cut-off angles ranging from 10 degrees to 40 degrees. Compared with GPS only, the reductions in the multi-GNSS combinations range from 2.3 to 16.25% at a mask angle of 20 degrees and vary from 4.2% to 29.04% at a cut-off elevation angle of 30 degrees. (C) 2019 Elsevier Ltd. All rights reserved.