Consideration of GLONASS Inter-Frequency Code Biases in Precise Point Positioning (PPP) International Time Transfer

Abstract

Abstract:International time transfer based on Global Navigation Satellite System (GLONASS) precise point positioning (PPP) is influenced by inter-frequency code biases (IFCBs) because of the application of frequency division multiple access technique. This work seeks to gain insight into the influence of GLONASS IFCBs on international time transfer based on GLONASS-only PPP. With a re-parameterization process, three IFCB handling schemes are proposed: neglecting IFCBs, estimating IFCB for each GLONASS frequency number, and estimating IFCB for each GLONASS satellite. Observation data collected from 39 globally distributed stations in a 71-day period (DOY 227-297, 2017) was exclusively processed. For the comparison reason, Global Positioning System (GPS)-only PPP solutions were regarded as reference values. The clock differences derived from GPS-and GLONASS-only PPP solutions were then analyzed. The experimental results demonstrated that considering GLONASS IFCBs could reduce standard deviation (STD) of the clock differences for both identical receiver types and mixed receiver types, of which reduction was from 3.3% to 62.6%. Furthermore, compared with neglecting IFCBs, STD of the clock differences with estimating IFCB for each GLONASS satellite in coordinate-fixed mode was reduced by more than 30% from 0.30 to 0.20 ns, and by 10% from 0.40 to 0.35 ns, for 1-day arc solutions and 10-day arc solutions, respectively. Moreover, different precise products from three International GNSS Service (IGS) analysis centers were also evaluated. Even though different IFCB handling schemes were adopted in GLONASS satellite clock estimation, our numerical results showed that international time transfer on the basis of estimating IFCB for each GLONASS satellite better than the other two processing schemes. To achieve high-precision GLONASS-only PPP-based international time transfer, it is highly recommended to estimate IFCB for each GLONASS satellite.

An Approach to a Clock Offsets Model for Real-Time PPP Time and Frequency Transfer During Data Discontinuity

“…where r indicates the receiver, S indicates the satellite; P S r,IF and L S r,IF denote the pseudo-range and the phase observables in metres, respectively; λ S IF is the carrier wavelength when ionosphere-free; Φ S r,IF is the original carrier phase measurement in cycles; ρ is the geometric distance in metres; c denotes the speed of light; dt S and dt r are the clock offsets of the satellite and receiver in seconds; e is the elevation angle of the satellite S; m f w (e) refers to wet mapping functions [19]; Z w represents the zenith wet delay; d S r,IF and d S IF are the uncalibrated code delays (UCDs) of the IF model at the receiver and satellite end, respectively; N S r,IF is an integer itself but is estimated as a floating point number from unmodeled effects; b S r,IF and b S IF are the uncalibrated phase delays (UPDs) of the IF model at the receiver and the satellite ends in cycles; and ε S r,IF and ξ S r,IF denote the sum of the measurement noise and the multipath error for the pseudo range and carrier phase observations, respectively. Since d S IF is absorbed by the satellite clock [20], the clock offset of the receiver dt r can be written as follows [8]:…”

“…Second, our approach does not produce jumps that may accelerate clock offset convergence. The Allan deviation (ADEV) is employed to obtain the frequency stability [8,28], which is also utilized to further assess the performance of RT-PPP solutions, using five kinds of precise products. In this contribution, Stable32 software (http://www.wriley.com/) is applied to calculate ADEV.…”

Enhancing multi-GNSS time and frequency transfer using a refined stochastic model of a receiver clock

“…The results showed that the accuracy and stability of the uncombined model can be identical to the conventional ionosphere-free (IF) model [13]. Ge et al investigated the contribution of inter-frequency bias (IFB) on time transfer based on GLONASS-only PPP and demonstrated that estimating IFB for each GLONASS satellite was better than estimating IFB for each frequency number [14]. Dach et al analyzed the influence of inter-frequency and intersystem bias on time transfer with GPS and GLONASS [15].…”

BDS-3/Galileo Time and Frequency Transfer with Quad-Frequency Precise Point Positioning

“…By the development of multi-GNSS, PPP with multi-GNSS observation has achieved a hot topic for time comparison. Ge, et al [25] presented GLONASS PPP time transfer with inter-frequency code biases (IFCBs) model. BDS PPP using triple-frequency observation was investigated by Tu, Zhang, Zhang, Liu and Lu [21].…”