Analysis on BDS Satellite Internal Multipath and Its Impact on Wide-lane FCB Estimation

To the issue of the satellite internal multipath (SIMP) of BeiDou satellites, it proposed and emphasized that the SIMP model should be established as a function of the nadir angle with respect to the observed satellite rather than the elevation of the measurement, so that it can be used for receivers at various altitude. BDS data from global distributed stations operated by the International Monitoring and Assessment System (iGMAS) and the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) are collected and a new SIMP model as a piece-wise linear function of the nadir angle is released for the IGSO-and MEO-satellite groups and for B1, B2 and B3 frequency band individually. The SIMP of GEO,IGSO and MEO satellites is further analyzed with B1/B2 dual-frequency data onboard the FengYun-3 C(FY3C) satellite at an altitude of~830 km, and it showed that, for nadir angles smaller than 7°, the SIMP values for GEO is quite close to the IGSO's, especially for B2, which may suggest that the SIMP model for IGSO satellites possibly also works for GEO satellites. It also demonstrated that, when the nadir angle is smaller than 12°for the MEO and 7°for the IGSO, the estimated SIMP model with data from FY3C is considerable consistent with that estimated with data collected at ground stations. Experiments are carried out to investigate the impacts of the SIMP on wide-lane fractional cycle bias (FCB) estimation for BDS satellites. The result indicates that, with the correction of the estimated SIMP, the repeatability of the FCB series is significantly improved by more than 60% for all satellites. Specifically, for the MEO and IGSO satellites, the repeatability is smaller than 0.05 cycle; the repeatability of 0.023 and 0.068 cycles achieved for GEO satellites C01 and C02 respectively with the estimated SIMP model for IGSO satellites

Satellite Clock Estimation with Between-satellite Single Difference Phase Ambiguity Fixing

A large number of researches suggest that integer ambiguity resolution(IAR) significantly improve the precision and reliability of precise point positioning (PPP) and providing “integer” satellite clock corrections is one of the available approaches proposed in the past ten years. In this paper, we propose a novel approach to estimate integer satellite clock corrections to support IAR for PPP application, Our approach is based on between-satellite single difference (BSSD) ambiguity fixing which contains two key steps, namely to estimate wide-lane fractional cycle bias (FCB) for satellites and to select and fix the BSSD ambiguity datum, which would recover the integer property of the wide- and narrow-lane BSSD ambiguities, respectively. This approach has been implemented in the SPODS software developed at Xi'an Research Institute of Surveying and Mapping. Experiments for clock estimation with data collected at about 66 IGS stations have been carried out to validate the proposed approach. It is demonstrated that, in the clock estimation, 73%, on average, of the independent BSSD ambiguities were successfully fixed to integers and the mean RMS and STD of differences between our clocks and the IGS final clocks are 0.170 ns and 0.012 ns respectively. The fractional parts of the wide-lane and narrow-lane BSSD ambiguities from about 448 IGS stations were analyzed, which proves that the obtained satellite clocks together with the wide-lane FCB products have the ability to support IAR in PPP. Using our products, experiments for simulated kinematic PPP with data collected at 20 IGS stations were carried out. It is shown that, with IAR, the positioning accuracy (RMS) in N, E, U and 3D are 0.009, 0.010, 0.023 and 0.027 m, corresponding to improvements of 30.8%, 61.5%, 23.3% and 37.2%, respectively, compared with that without IAR or with IGS final clocks

Analysis of the Accuracy of Beidou Combined Orbit Determination Enhanced by LEO and ISL

In order to improve the precision of BeiDou orbit determination under the conditions of regional ground monitoring station and make good use of increasingly rich on-board data and upcoming ISL technology, a method of BeiDou precision orbit determination is proposed which combines the use of ground monitoring stations data, low earth orbit satellite(LEOs) data and Inter-Satellite Link(ISL) data. The effects of assisting data of LEOs and ISL on the precision orbit determination of navigation satellite are discussed. Simulation analysis is carried out mainly from the number of LEOs, orbit slot configuration and ISL. The results show that the orbit precision of BeiDou will greatly improve about 73% with a small number of LEOs, while improvement of clock bias is not remarkable; the uniform orbit slot configuration of the same number of LEOs has a modest effect on the accuracy of combined orbit determination; compared with LEOs, the increase of ISL will significantly improve the accuracy of orbit determination with a higher efficiency

Satellite precise orbit determination with ionospheric-free strategy using triple-frequency observations

As the development of global navigation satellite system (GNSS), GNSS satellites transmitting multi-frequency signals has become a prevailing trend. However, recently the international GNSS service (IGS) analysis centers still use dual-frequency (DF) observations to derive the orbits, clocks and other products. The additional observations from the third frequency are not considered. We use two DF ionospheric-free (IF) combinations as the observation model, the improvements from the third frequency on orbits, clocks and station positions are assessed. In the carrier phase observation model, the satellite-dependent time-invariant and time-variant components are introduced. The two DF IF observation equations are re-parameterized to make the clock parameter aligned to the IGS clock products, and then the full-rank TF observation model is derived. Based on the strategy of building up extra wide lane, wide lane and narrow lane double-differenced ambiguities, the TF ambiguity resolution (AR) method is deduced. First taking 12 GPS Block IIF satellites as example, three precise orbit determination (POD) schemes, the L1/L2 DF IF POD (denoting as S1), the L1/L5 DF IF POD (denoting as S2), the L1/L2 and L1/L5 TF IF POD (denoting as S3), are processed in two station layouts. Results show that the S3 scheme in two station layouts can obtain the optimal precision. The orbit improvements of S3 with respect to S1 in cases of even and uneven distribution are within 10% and about 10%, respectively. The improvement of clocks RMS is slight, while STD is improved by 6.4% and 10.0%. The improved percentages of S3 vs. S2 are about less one times than that of S3 vs. S1, with the improved percentage of about 5%. Then the BDS-only POD test is processed and the orbits are validated by satellite laser ranging residuals. Results show that comparing with B1/B3 POD, the orbit and clock accuracy of TF POD can be improved. However, the improvement of TF POD comparing to B1/B2 POD is slight or even worse. The possible reason is the inaccuracy antenna phase values

The Preliminary Result and Analysis for BD Orbit Determination with Inter-satellite Link Data

The experimental satellite of BD navigation system has assembled inter-satellite link (ISL) payloads and has obtained the real ISL observation data. The paper presents the preprocessing method of ISL and the POD method and result for Ka only observation and the combination Ka observation with L-band. It's showed that:the radial orbit error is less than 0.5 m with Ka only observation; the radial orbit error is less than 0.3 m with the observation by combining the Ka ISL with L-band data which has improved the orbit accuracy remarkably in contrast to L-band only data; the accuracy of calibrating device delay is better than 0.1 m

The PPP Precision Analysis Based on BDS Regional Navigation System

BeiDou navigation satellite system(BDS) has opened service in most of the Asia-Pacific region, it offers the possibility to break the technological monopoly of GPS in the field of high-precision applications, so its performance of precise point positioning (PPP) has been a great concern. Firstly, the constellation of BeiDou regional navigation system and BDS/GPS tracking network is introduced. Secondly, the precise ephemeris and clock offset accuracy of BeiDou satellite based on domestic tracking network is analyzed. Finally, the static and kinematic PPP accuracy is studied, and compared with the GPS. The actual measured numerical example shows that the static and kinematic PPP based on BDS can achieve centimeter-level and decimeter-level respectively, reaching the current level of GPS precise point positioning

A Facile Approach towards Fluorescent Nanogels with AIE-Active Spacers

A facile and efficient approach for design and synthesis of organic fluorescent nanogels has been developed by using a pre-synthesized polymeric precursor. This strategy is achieved by two key steps: (i) precise synthesis of core–shell star-shaped block copolymers with crosslinkable AIEgen-precursor (AIEgen: aggregation induced emission luminogen) as pending groups on the inner blocks; (ii) gelation of the inner blocks by coupling the AIEgen-precursor moieties to generate AIE-active spacers, and thus, fluorescent nanogel. By using this strategy, a series of star-shaped block copolymers with benzophenone groups pending on the inner blocks were synthesized by grafting from a hexafunctional initiator through atom transfer radical copolymerization (ATRP) of 4-benzoylphenyl methacrylate (BPMA) or 2-(4-benzoylphenoxy)ethyl methacrylate (BPOEMA) with methyl methacrylate (MMA) and tert-butyldimethylsilyl-protected 2-hydroxyethyl methacrylate (ProHEMA) followed by a sequential ATRP to grow PMMA or PProHEMA. The pendent benzophenone groups were coupled by McMurry reaction to generate tetraphenylethylene (TPE) groups which served as AIE-active spacers, affording a fluorescent nanogel. The nanogel showed strong emission not only at aggregated state but also in dilute solution due to the strongly restricted inter- and intramolecular movement of TPE moiety in the crosslinked polymeric network. The nanogel has been used as a fluorescent macromolecular additive to fabricate fluorescent film

Satellite Positioning and Orbit Determination System SPODS:Theory and Test

The Satellite Positioning and Orbit Determination System(SPODS)is a software package for GNSS positioning/orbit determination,developed by the Xi'an Research Institute of Surveying and Mapping.So far it has been able to treat GPS data and has the capability of high precision GPS positioning and orbit determination.The underlying theory and the performance test are briefly addressed.The test utilizes the GPS data collected from some 127IGS stations during days 4~10of 2009.The results show that the rms 1D difference is 1.1cm between SPODS orbits and final IGS combined orbits,and that the repeatability of daily solutions of station coordinates is 1.5mm for horizontal components,and 4.5mm for height component,and that the consistency of ERP solutions with final IGS values is 0.025mas,0.093mas and 0.013ms/d respectively for pole coordinates and changes in length of day