Performance of GPS Precise Time and Frequency Transfer with Integer Ambiguity Resolution

2021 ◽  
Author(s):  
Pengfei Zhang ◽  
Rui Tu ◽  
Xiaochun Lu ◽  
Yuping Gao ◽  
Lihong Fan
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Integer Ambiguity Resolution ◽  
Integer Ambiguity ◽  
Convergence Time ◽  
Processing Modes ◽  
Wide Lane ◽  
Frequency Transfer ◽  
Fixed Solution ◽  
Precise Time

Abstract The global positioning system (GPS) carrier-phase (CP) technique is a widely used spatial tool for remote precise time and frequency transfer. However, the performance of traditional GPS time and frequency transfer has been limeted because the ambiguity paramter is still the float solution. This study focuses on the performance of GPS precise time and frequency transfer with integer ambiguity resolution and discusses the corresponding mathematical model. Fractional-cycle bias (FCB) products were estimated by using an ionosphere-free combination. The results show that the satellite wide-lane (WL) FCB products are stable, with a standard deviation (STD) of 0.006 cycles. The narrow-lane (NL) FCB products were estimated over 15 min with the STD of 0.020 cycles. More than 98% of the WL and NL residuals are smaller than 0.25 cycles, which helps to fix the ambiguity into integers during the time and frequency transfer. Subsequently, the performances of the time transfers with integer ambiguity resolution at two time links between international laboratories were assessed in real-time and post-processing modes and compared. The results show that fixing the ambiguity into an integer in the real-time mode significantly decreases the convergence time compared with the traditional float approach. The improvement is ~49.5%. The frequency stability of the fixed solution is notably better than that of the float solution. Improvements of 48.15% and 27.9% were determined for the IENG–USN8 and WAB2–USN8 time links, respectively.

scholarly journals PPP with integer ambiguity resolution for GPS and Galileo using satellite products from different analysis centers

GPS Solutions ◽  
2021 ◽  
Vol 25 (3) ◽  
Author(s):  
Marcus Glaner ◽  
Robert Weber
Keyword(s):  
Ambiguity Resolution ◽  
Observation Interval ◽  
Theoretical Background ◽  
Integer Ambiguity Resolution ◽  
High Rate ◽  
Integer Ambiguity ◽  
Convergence Time ◽  
Integer Number ◽  
International Gnss Service ◽  
Satellite Product

AbstractInteger ambiguity resolution is the key for achieving the highest accuracy with Precise Point Positioning (PPP) and for significantly reducing the convergence time. Unfortunately, due to hardware phase biases originating from the satellites and receiver, fixing the phase ambiguities to their correct integer number is difficult in PPP. Nowadays, various institutions and analysis centers of the International GNSS Service (IGS) provide satellite products (orbits, clocks, biases) based on different strategies, which allow PPP with integer ambiguity resolution (PPP-AR) for GPS and Galileo. We present the theoretical background and practical application of the satellite products from CNES, CODE, SGG, and TUG. They are tested in combined GPS and Galileo PPP-AR solutions calculated using our in-house software raPPPid. The numerical results show that the choice of satellite product has an influence on the convergence time of the fixed solution. The satellite product of CODE performs better than the following, in the given order: SGGCODE, SGGGFZ, TUG, CNES, and SGGCNES. After the convergence period, a similar level of accuracy is achieved with all these products. With these satellite products and observations with an interval of 30 s, a mean convergence time of about 6 min to centimeter-level 2D positioning is achieved. Using high-rate observations and an observation interval of 1 s, this period can be reduced to a few minutes and, in the best case, just one minute.

scholarly journals Real-Time PPP-RTK Performance Analysis Using Ionospheric Corrections from Multi-Scale Network Configurations

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3012 ◽  
Author(s):  
Dimitrios Psychas ◽  
Sandra Verhagen
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Ionospheric Disturbance ◽  
The United States ◽  
Integer Ambiguity ◽  
Convergence Time ◽  
Dual Frequency ◽  
Multi Scale ◽  
Time Required ◽  
The Impact

The long convergence time required to achieve high-precision position solutions with integer ambiguity resolution-enabled precise point positioning (PPP-RTK) is driven by the presence of ionospheric delays. When precise real-time ionospheric information is available and properly applied, it can strengthen the underlying model and substantially reduce the time required to achieve centimeter-level accuracy. In this study, we present and analyze the real-time PPP-RTK user performance using ionospheric corrections from multi-scale regional networks during a day with medium ionospheric disturbance. It is the goal of this contribution to measure the impact the network dimension has on the ambiguity-resolved user position through the predicted ionospheric corrections. The user-specific undifferenced ionospheric corrections are computed at the network side, along with the satellite phase biases needed for single-receiver ambiguity resolution, using the best linear unbiased predictor. Such corrections necessitate the parameterization of an estimable user receiver code bias, on which emphasis is given in this study. To this end, we process GPS dual-frequency data from four four-station evenly distributed CORS networks in the United States with varying station spacings in order to evaluate if and to what extent the ionospheric corrections from multi-scale networks can improve the user convergence times. Based on a large number of samples, our experimental results showed that sub-10 cm horizontal accuracy can be achieved almost instantaneously in the ionosphere-weighted partially-ambiguity-fixed kinematic PPP-RTK solutions based on corrections from a network with 68 km spacing. Most of the solutions (90%) were shown to require less than 6.0 min, compared to the ionosphere-float PPP solutions that needed 68.5 min. In case of sparser networks with 115, 174 and 237 km spacing, 50% of the horizontal positioning errors are shown to become less than one decimeter after 1.5, 4.0 and 7.0 min, respectively, while 90% of them require 10.5, 16.5 and 20.0 min. We also numerically demonstrated that the user’s convergence times bear a linear relationship with the network density and get shorter as the density increases, for both full and partial ambiguity resolution.

scholarly journals A Multi-Frequency Galileo PPP-RTK Convergence Analysis with an Emphasis on the Role of Frequency Spacing

2021 ◽  
Vol 13 (16) ◽  
pp. 3077
Author(s):  
Dimitrios Psychas ◽  
Peter J. G. Teunissen ◽  
Sandra Verhagen
Keyword(s):  
Ambiguity Resolution ◽  
Formal Analysis ◽  
Integer Ambiguity Resolution ◽  
Global Navigation Satellite Systems ◽  
Integer Ambiguity ◽  
Convergence Time ◽  
Frequency Separation ◽  
Dual Frequency ◽  
Single Receiver

The single-receiver integer ambiguity resolution-enabled variant of precise point positioning (PPP), namely PPP-RTK, has proven to be crucial in reducing the long convergence time of PPP solutions through the recovery of the integerness of the user-ambiguities. The proliferation of global navigation satellite systems (GNSS) supports various improvements in this regard through the availability of more satellites and frequencies. The increased availability of the Galileo E6 signal from GNSS receivers paves the way for speeding up integer ambiguity resolution, as more frequencies provide for a stronger model. In this contribution, the Galileo-based PPP-RTK ambiguity resolution and positioning convergence capabilities are studied and numerically demonstrated as a function of the number and spacing of frequencies, aiming to shed light on which frequencies should be used to obtain optimal performance. Through a formal analysis, we provide insight into the pivotal role of frequency separation in ambiguity resolution. Using real Galileo data on up to five frequencies and our estimated PPP-RTK corrections, representative kinematic user convergence results with partial ambiguity resolution are presented and discussed. Compared to the achieved performance of dual-frequency fixed solutions, it is found that the contribution of multi-frequency observations is significant and largely driven by frequency separation. When using all five available frequencies, it is shown that the kinematic user can achieve a sub-decimeter level convergence in 15.0 min (90% percentile). In our analysis, we also show to what extent the provision of the estimable satellite code biases as standard PPP-RTK corrections accelerates convergence. Finally, we numerically demonstrate that, when integrated with GPS, the kinematic user solution achieves convergence in 3.0 and 5.0 min on average and at 90%, respectively, in the presence of ionospheric delays, thereby indicating the single-receiver user’s fast-convergence capabilities.

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