Beidou Navigation System
Design and development of near field communication intelligent data acquisition terminal system in fresh agricultural product supply chain
Transactions of the Chinese Society of Agricultural Engineering,2015,Vol 31,No. 08
【Abstract】 In order to solve the issue that the information transfer of fresh product supply chain is discontinuous, incomplete and untrue, and to prevent agricultural health threat to people's lives, this study has developed a data collection terminal based on near-field communication technology. At present, China fresh product market for primary agricultural products, food processing and consumer demand increases year by year, but the infrastructure and information technology applications of fresh product supply chain are behind, resulting in high loss of fresh product throughout the supply chain in the circulation process, as well as low efficiency and poor reliability of the information, and therefore it is difficult to meet the needs of the modern market for fresh product. In recent years, the consumption of fresh agriculture products has been continuing to rise with the development of society and the growth in people’s living standard. However, an increasing number of safety problems like poisoning and polluting have been triggered because of the quality problem of fresh agricultural products, which directly influences consumers' health and environmental security. Eventually, it has aroused widespread concern in the whole society. The discontinuity of fresh agricultural product supply chain information is one of the important reasons for the emergence of faulty products. The backwardness of data acquisition equipment and means in each link of fresh agricultural product supply chain, and the data in key link being not able to be collected due to environmental factors, are the main reasons for discontinuous information of fresh agricultural product supply chain. The paper first analyzes data collecting equipment of fresh agricultural product supply chain and its corresponding working conditions. Then, based on near field communication (NFC), bei dou system (BDS) and global system for mobile communications (GSM), it develops the integration technology data collection terminal of fresh agricultural product supply chain. The integration applications of NFC technology and Internet of things have become a focus research issue at home and abroad. In this paper, authors review the research progress of supply chain information systems of domestic agricultural products; summarize the key function of information technology in the agricultural supply chain and information system platform; and analyze the application feasibility of NFC technology in the agricultural supply chain information systems. The data collection terminal mainly includes four modules, namely NFC module, CPU (central processing unit) module, Bei Dou module, GSM module as well as its electrical system. When the data terminal writes data, it simultaneously writes BDS encrypted data to NFC label through NFC chip PN532, and then through GSM module, it transmits the encrypted data to the backend database in text message; finally, it transmits the data information to node enterprises platform by RS232, thus achieving three copies of the backup on fresh agricultural product data information. By means of the advantages of Internet of things and sensor networks, the data terminal implements automatic and intelligent data acquisition and encryption in every link of fresh agricultural product supply chain. And on this basis, it meets the changing needs of data acquisition and storage during the production process, reduces the degree of information asymmetry among node enterprises and enhances the productivity of node enterprises. In short, the data terminal lays the foundation for the fresh agricultural product traceability and has practical value. Compared with other acquisition systems, the biggest difference the terminal system has is that the system not only has the function to read the data, but also has a tag write capability, and can read the offline data stored inside the NFC memory chip carried by the system itself. The terminal reads in extreme environments. Although the speed is reduced by 10%–25%, the saving rate is still at 100%, fully meeting the needs of data acquisition. The terminal can achieve the information continuousness between the nodes of the enterprise, and provide the reference for the realization of fresh product traceability.
Science of Surveying and Mapping,2016,Vol 41,No. 01
【Abstract】 In order to further analyze the correlative characteristic of BDS observations, the paper compared the different behaviors not only between the BDS and GPS satellites, but also among different types of BDS satellites, and proposed to investigate pseudorange multipath combination and GFIF combination with the method of between-station-differencing. Experiments with observations from the stations of Crustal Movement Observation Network of China (CMONOC) demonstrated that the SNR of B1 observables are the lowest among three BDS frequencies; when the elevation angles are relatively small, both the absolute values and dispersions of multipath combinations become large, with the absolute values reaching about 1.5 m; meanwhile, the multipath combinations of IGSO and MEO satellites decrease significantly with the increase of elevation; daily periodicity is found in the GFIF combinations of both GEO and IGSO satellites, with an variation of ±2 cm for carrier phase and ±2 m for pseudorange. Both the trend of multipath combination and the periodicity of carrier phase GFIF combination could be significantly mitigated through between-station-differencing, showing that some satellite dependent errors are likely contained in the two combinations. The above results would provide a reference for properly handling the errors in BDS observations.
Science of Surveying and Mapping,2016,Vol 41,No. 03
【Abstract】 Aiming at the problem that the difference of BDS orbital altitudes affects the precision of short-baseline solution, the paper used two measured BDS/GPS data sets to investigated the performance and reliability of short-baseline solution and discussed the stochastic models of BDS and BDS/GPS combined systems. Result showed that the solution precision of BDS system and BDS/GPS combined system could both reach to centimetre-level and the reliabilities would be higher than that of GPS; the performances of four stochastic models were similar, and the performance of MINQUE would degrade as baseline length increases; the elevation model should not be applied in BDS or BDS/GPS combined system directly due to the large differences of orbital altitudes of various types of satellites.
Science of Surveying and Mapping,2016,Vol 41,No. 03
【Abstract】 In order to improve the solution accuracy of BDS RTK, the paper studied a RTK algorithm of BDS single reference station and the calculation method of the undifferenced correction based on undifferenced observation model, and proposed a uniformed mathematical model of precise positioning, by which the error was corrected using undifferenced correction of the reference station with a single satellite as the object: the undifferenced wide lane integer ambiguities were fixed, and the undifferenced integer ambiguities were fixed. Experimental result showed that BDS single reference station RTK could be realized using the undifferenced observation model with the cm level of positioning accuracy.
Science of Surveying and Mapping,2016,Vol 41,No. 03
【Abstract】 Aiming at the current status that the study on BDS pseudo-range positioning is insufficiency, the paper analyzed the pseudo-range quality on frequencies B1, B2 and B3 of BDS, considered the biases of different frequencies in the positioning, and then presented the solution of multi-frequency SPP by using the broadcast navigation message. Experimental result showed that the multipath effect and the observation noise of frequency B3 would be better than those of B2 and B1; on single-frequency positioning, the horizontal accuracy of each frequency would be better than 5 m, while the vertical better than 10 m, with the best performance of B1 frequency; on double-frequency positioning, the performance of B1/B2 would be a little better than B1/B3, the horizontal accuracy of each combination would be better than 3 m, the vertical better than 5 m; besides, due to the big noise, B2/B3 could be not suitable for positioning and navigation.
Science of Surveying and Mapping,2016,Vol 41,No. 05
【Abstract】 Different from the other satellite navigation systems, BeiDou navigation system (BDS) adopts heterogeneous constellation design. The flying area of geostationary and inclined geostationary satellites only covers a small part of the constellation sphere. Traditional method can't be directly used for the ground monitoring network coverage ability analysis. In addition, the navigation satellites will not exactly fly through the designed routes since they are susceptible to various disturbing forces. In the paper, a novel method was put forward to definite the BDS satellites flying area according to the real measurement data. Then the monitoring ability was analyzed for two ground tracking networks.
Science of Surveying and Mapping,2016,Vol 41,No. 06
【Abstract】 Aiming at the problem of the ranging error caused by GEO satellite ephemeris was approximately 2 times that of MEO satellite under the same conditions, the paper analyzed the effects on positioning results caused by the particularity of the BDS GEO satellites. Based on the visible IGSO, MEO satellites during the observing session of the observed data, sequential tests were conducted to positioning that one satellite with bigger elevation angle was added each time, then both calculate the values of PDOP and the RMS, STD of the component error in the North, East, UP directions and the total error. The results of simulation experiment indicate that the positioning accuracy when 1 to 4 GEO satellites added equal to that the only one GEO satellite with the biggest elevation angle included; the positioning results were optimized when reducing the weights of the lowest elevation angle GEO satellite.
The Journal of Quantitative & Technical Economics,2015,Vol 32,No. 08
【Abstract】 The study explores the characteristics of fiscal adjustments in China, especially the nonlinear characteristics, via the Granger causality test, BDS test and Markov regime switching vector error correction model. The results show that China’s fiscal policy is sustainable and fiscal adjustments are consistent with the “synchronization” hypothesis. Fiscal adjustments have significant nonlinear characteristics, and there are obvious differences in the speed of fiscal adjustment under different regimes. The adjustments are relatively weaker after the reform and opening up. To be specific, the speed and intensity of public finance’s return from disequilibrium to equilibrium obviously slows down and fiscal disequilibrium lasts longer. Although in recent years China’s volatility of fiscal expenditure and revenue seems to be reduced, but the fluctuation of disequilibrium error is expanding. Compared with fiscal revenue, adjustments of fiscal expenditure are stronger, which is more beneficial to economic growth. The nonlinear characteristics of fiscal adjustments in China can be explained from the aspects of the and the government’s response.
Science of Surveying and Mapping,2016,Vol 41,No. 05
【Abstract】 The regional navigation constellation of BeiDou Navigation Satellite System has been constructed currently, and has supplied services of navigation and positioning independently in Asia-Pacific area. The accuracy of BDS pseudo-range positioning can be enhanced by the method of network difference. The double difference model is used mostly in the method of network difference with GPS, but the method of network difference has some faults by using the double difference model. A method of un-differential network difference between long range at single epoch with single-frequency data of BDS was proposed in this paper. Firstly the long range BDS base station networks supplied un-differential error corrections to users of BDS which were covered by the regional networks. Then the un-differential error corrections which were requisite for users were calculated by themselves and the errors of BDS pseudo-range observations of singlefrequency were removed by these corrections. Finally the network difference positioning at single epoch with single-frequency was fulfilled. The result of test indicated that the positioning of BDS network difference between long range stations could be fulfilled at single epoch of single-frequency pseudo-range observations by this method.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 06
【Abstract】 In real-time deformation monitoring applications, ambiguity cannot be quickly and reliably resolved under poor conditions using dual-frequency observations. In this paper, we analyze the single-epoch ambiguity resolution success rate of GPS and BDS system under different calculating models. A new method based on triple-frequency BDS observations is proposed to fix the original ambiguity based on the TCAR (three-carrier ambiguity resolution). Sidereal day filtering based on observing domain reduces multipath errors in wide-lane observations under conditions where the original ambiguity cannot be fixed reliably. Real data is used to test the method, results show that the success rate and accuracy are improved in comparision to the dual-frequency models. A success rate of 100% was achieved using the wide-lane ambiguity resolution, and the RMS values for the wide-lane fixed solution reached 7 mm after filtering.
Science of Surveying and Mapping,2016,Vol 41,No. 12
【Abstract】 In order to make full use of the global navigation satellite system resources, to maximize the advantages of the BeiDou satellite navigation system and provide high precision, high reliability and stability and better service to the users, the performance of grid pseudo-range differential positioning of BDS/GPS/GLONASS triple system was analyzed. This paper introduced the principle of this method and analyzed the vehicle test. The results showed that the positioning accuracy and solution rate of grid pseudorange differential positioning of three systems was higher than other scheme, the number of visible satellites was greatly improved, and the reliability and stability were better.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 05
【Abstract】 We studied and implemented an algorithm for real-time precise satellite clock estimation based on the undifferenced code and phase observations. The BDS and GPS observations of 53 MGEX global sites were collected to generate the real-time clock that was compared with the final WHU 30 s precise clock product. The accuracy of our real-time GPS clock was better than 0.07 ns, comparable to that of the IGS final clock products, which verifies the processing accuracy of our software. The accuracy of the real-time BDS clock was 0.1–0.15 ns, a little worse than that of GPS satellites. A kinematic PPP test showed that, the horizontal accuracy of BDS solution was about 0.041 m, comparable to 0.058 m of GPS solution, while the vertical accuracy is 0.069 m, a slightly worse than 0.037 m of GPS. The kinematic PPP solution based on the real-time clock correction was consistent with the solution based on the final clock products, which verifies the real-time clock products.
Analysis of fixed performance of mixed double-difference ambiguity between GPS/BDS under the hostile environments
Science of Surveying and Mapping,2016,Vol 41,No. 12
【Abstract】 Aiming at the problem that each GNSS system observed only a small number of satellites, it is hard to implement the integer ambiguity fixed with the standard model of double difference under the hostile environments; the GPS/BDS system between mixed double-difference model was studied in this paper. The GPS/BDS system deviation was calculated using this model, based on which real hostile observation environments ambiguity fixed performance was analyzed using both experiment and simulation. The experimental results showed that mixed double-difference model performance of between GPS/BDS system under the hostile environment was good, the required time could be cut down by 43% and 33% on average and the fixed rate increased by 107% and 31% respectively comparing with the classical model of double difference.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 11
【Abstract】 Single-epoch ambiguity resolution is always a challenging issue in the satellite navigation and positioning. With the development of BeiDou navigation and positioning system, the combination observations of triple-frequency carrier phase can combine more excellent combination data, which could effectively improve the accuracy and reliability of the single-epoch ambiguity resolution. This paper adds a priori information of ionospheric delays, regards it and the location parameters and ambiguity as unknown parameters to be solved based on the traditional TCAR method and least squares collocation. Meanwhile, the ambiguity search space is constricted by the ambiguity related method of considering ionospheric delays. The results showed that adding a prior information of ionospheric delays in unknown parameters can greatly improve the single-epoch ambiguity success rate; the ambiguity related method of considering ionospheric delays correction can reduce the ambiguity search space, and effectively improve the success rate and the reliability of single-epoch ambiguity resolution.
Simultaneous Determination of Multiple Constituents in Scrophulariae Radix from Different Habitats and Commercial Herbs by UPLC-QTRAP-MS/MS
Chinese Pharmaceutical Journal,2016,Vol 51,No. 16
【Abstract】 OBJECTIVE To develop a method for the determination of iridoid, phenylpropanoid glycosides and organic acids in Scrophulariae Radix from different habitats and commercial herbs by UPLC-QTRAP-MS/MS. METHODS The analysis was carried out on a BDS HYPERSIL C18 column (4.6 mm × 250 mm, 5 μm) with elution by mobile phase of acetonitrile-water at a flow rate of 1.0 mL·min−1. The column temperature was maintained at 35 ℃. The target compounds were analyzed by the negative ion multiple reaction monitoring (MRM) mode. RESULTS Twelve multiple constituents showed good linearity (r > 0.999 4) in the range of the tested concentration. The average recoveries of the 12 constituents were 99.59%–101.24% with relative standard deviations of 0.93%–1.60%. CONCLUSION The established method is accurate and precise, which provides a reliable and effective technique for the quality evaluation of Scrophulariae Radix.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 12
【Abstract】 Differential Code Biases (DCBs) are the main systematic errors in ionosphere TEC monitoring and modeling. Meanwhile, satellite DCBs are important parameters for satellite navigation messaging. This article presents a satellite DCBs estimation algorithm and DCBs transformation formula derived under different zero-mean conditions as applied to the constellation average of the satellite DCBs. Using BeiDou Experimental Tracking Station (BETS) observations from 2013, the DCBs for BDS satellite were determined, and the BDS satellite DCBs monthly stability was analyzed and compared with the DCBs products published by MGEX under the same zero-mean conditions. Results show that the BDS satellite B1-B2 DCBs values were between −9–17 ns, and the stability was better than 0.4 ns. The stability for BDS IGSO satellites was better than GEO and MEO satellites. The BDS satellite DCBs determined using BETS and MGEX had system biases, where the largest discrepancy was about 1.7 ns. The probable reason lies in a discrepancy in the pseudo range code measurement. The difference of receiver material results in a discrepancy in receiver DCBs.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 02
【Abstract】 In order to analyze the stochastic characteristics of BDS (BeiDou satellite) observations, GEO (geostationary earth orbit), IGSO (inclined geosynchronous satellite orbit), MEO (medium earth orbit) satellites observations variance components are estimated. The observation variance components of different receivers and different types of BDS are proved to be significantly different in size and time-varying characteristics. To deal with the heterogeneous variances, a real-time estimating BDS observations stochastic model procedure is developed with the methods of iterative least-squares and MINQUE (minimum norm quadratic unbiased estimation). To demonstrate its performance, precise relative positioning experiments are carried out using 243 m, 645 m and 10 137 m baselines, respectively. In contrast to the empirical stochastic model, the real-time estimating stochastic model can improve the performance of BDS precise relative positioning, and improve more significantly for the longest baseline. The 10 137 m baseline test results indicate that the real-time estimating stochastic model can improve the mean positioning precision 41.3%, 54.5%, 51.6% and the RMS values of multi-epoch position offsets 38.4%, 17.7%, 39.7% in N (north), E (east), U (up) directions respectively.
Science of Surveying and Mapping,2017,Vol 42,No. 04
【Abstract】 Aiming at the problem that the single-layer ionospheric model cannot meet the positioning accuracy for single-frequency user, the regional slant ionospheric model and single satellite polynominal function model were proposed in this paper. Experimental results of the observation of CORS in Hebei Province showed that comparing with the GIM model of CODE, the fitting precision of regional ionospheric model increased by 80%. The accuracy of SPP applying the regional slant ionosphere model could reach within 3 min vertical direction and 2 min horizontal direction for BDS and less than 1.5 min vertical direction and 1 min horizontal direction for GPS; comparing with CODE, the improvements in vertical direction and horizontal direction exceeded by 50% for GPS and BDS. The models can improve the phenomenon of accuracy losing by using traditional single-layer ionospheric model and reveal regional ionospheric fine structure.
Science of Surveying and Mapping,2017,Vol 42,No. 05
【Abstract】 Aiming at data acquisition and application of geographic information, based on the BDS navigation system and MapWinGIS technology, this paper develops the Geographic Information Acquisition Platform Based on BDS for integration. The key problems such as synchronous acquisition of multi-source data, adaptive transformation of coordinate system and fast matching are solved. Different scheme tests indicate that the platform has the high precision for positioning and mapping, and can meet the general geographic information data acquisition and map annotation needs. And it also can be widely used in geographic conditions monitoring, field digital mapping and outside data acquisition services and other industries.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 10
【Abstract】 Ambiguity fixing is the key to GNSS high-precision dynamic positioning. In order to analyze the performance of a GPS/BDS combined system on ambiguity search efficiency and the success rate of ambiguity fixing on a short baseline, this paper proposes an ambiguity search region correlation method based on the square roots of the eigenvalues of the variance-covariance matrix of ambiguity. This method compares and analyzes the ambiguity search region in a single system GPS, a single system BDS and combined GPS/BDS system, respectively. Experimental results show that the GPS and BDS combination influences the variance-covariance matrix of each single system, and reduces the search region of each single system. Furthermore, the statistical results show that the combined GPS/BDS system can improve the success rate of ambiguity fixing and the ambiguity search efficiency significantly within single- and dual-frequency observations.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 06
【Abstract】 Satellite Laser Ranging (SLR), is completely independent of microwave measurement, and offers an indispensable tool for external validation of GNSS broadcast ephemeris. Currently, all satellites in the BeiDou Satellite Navigation System (BDS) are equipped with laser ranging reflector arrays enabling high-precision two way ranging measurements. Based on SLR data from BeiDou satellites collected in the period April 2013 to July 2014, the broadcast ephemeris of BDS were validated using SLR data. The approximate equation of SLR residual for the BDS GEO satellites were derived, and the SLR residual characteristic for BDS IGSO and MEO satellites under different attitude modes were analyzed. The validation results show that, the orbit error of C01, C08, C10 and C11 are 0.97 m, 0.43 m, 0.41 m and 0.41 m respectively.
Geomatics and Information Science of Wuhan University,2016,Vol 41,No. 11
【Abstract】 Currently, analysis centers (ACs) of international GNSS continuous monitoring and assessment system (iGMAS) could provide precise GNSS orbit products. To improve the stability and reliability of orbit products for high-precision users, we usually combine the orbit products from ACs. In this paper, we present a robust least square method of combining satellite orbits from different solutions. We first verify this method by combining GPS and GLONASS final orbit products provided by IGS Analysis Centers. Results show that the RMS differences between our combined GPS orbits and those from IGS are about 4 mm, and the RMS differences between our combined GLONASS orbits and those from IGS are about 5 mm. As the orbits of different IGS ACs are calculated in different reference frames, we first transform the orbits of different IGS ACs to the reference frame of IGS combined solution independent exchange format (SINEX) solutions before orbit combination. Results show that this transformation can improve the quality of combined orbits up to 2 mm. We then apply this method to analyze and combine GNSS satellite orbit products provided by ten of iGMAS ACs. For most iGMAS ACs, results show that the precision of GPS final and rapid orbits are better than 2.5 cm, and the precision of GPS ultra-rapid orbits are better than 6 cm and 15 cm for observed part and predicted part, respectively. The precision of iGMAS combined final orbits are 2 cm, 2–3 cm and 6 cm for GPS, GLONASS and Galileo satellites, respectively. The precision of iGMAS combined final orbits are 1.5 m and 20 cm for IGSO and MEO/IGSO of BDS, respectively. The relatively lower precision for combined GEO orbits is due to the different satellite antenna phase center offset (PCO) models adopted by different iGMAS ACs.
Precision analysis of orbit determination with space-borne BDS and GPS measurements for LEO satellite
Science of Surveying and Mapping,2017,Vol 42,No. 06
【Abstract】 Based on real-time orbit determination and precision orbit determination with space-borne BDS and GPS measurements, the mathematical models of real-time orbit determination and precision orbit determination with space-borne BDS and GPS measurements were put forward in this paper in order to deal with the issues in real-time orbit determination and precision orbit determination of LEO satellite with BDS and GPS receiver. And then the difference of real-time orbit determination and precision orbit determination was presented in details. Based on the self-developed program, feasibility and precision of real-time orbit determination and precision orbit determination were analyzed using the stimulated BDS and GPS measurements generated by high dynamic signal simulator. The results showed that the orbit accuracy of real-time orbit determination with space-borne BDS and GPS measurements can achieve 1.19 meter and the velocity accuracy can achieve 2.35 millimeter per second. The orbit accuracy of real-time orbit determination with space-borne BDS measurements only can achieve 3.73 meter when the GPS signals were unavailable. And that the orbit accuracy of precision orbit determination can achieve 2.30 centimeter. The orbit accuracy of precision orbit determination with space-borne BDS measurements only can achieve 8.26 centimeter.
Systematic Bias Compensation Model of Inter-system Bias and Its Performance Analysis for BDS/GPS Fusion Positioning
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 10
【Abstract】 Navigation users will significantly benefit from BDS and GPS positioning fusion in terms of availability, accuracy and reliability. However, for single point positioning, systematic biases between multi-GNSS systems cannot be eliminated completely, and thus the accuracy of positioning and navigation is not always improved with the un-difference measurements of multi-GNSS systems. In this paper, an integrated BDS/GPS positioning model with unknown systematic parameters that compensates for systematic bias is proposed. Furthermore, a Bayesian estimation of fusion positioning model is specifically investigated in which the priori information of the additional parameters is taken into account. The real data collected from different areas with different types of receivers are used to verify those new algorithms. The results show that (a) the receiver-dependent inter-system biases are quite evident, while the size of the system bias varies with the receiver type; (b) the precision of fusion positioning is improved significantly by introducing additional parameters into the functional model; and (c) Bayesian estimation of fusion positioning model can still obtain ideal position solution when the number of visible satellites is not enough.
Science of Surveying and Mapping,2017,Vol 42,No. 12
【Abstract】 Aiming at the problem of rapid solution of ambiguity and the precision of rover position in BeiDou navigation satellite system real-time kinematic (RTK), an algorithm of BeiDou navigation satellite system double difference network RTK was introduced in this paper. The ambiguities of B1 and B2 carrier phase between reference stations were fixed, and the bias of reference stations was calculated by the fixed ambiguities of carrier phase between reference stations. Then, the combined bias interpolation method was used to calculate the combined bias, and the ambiguities of carrier phase of rover station were fixed with removing the bias of rover station by the combined bias. The test of algorithm was realized by CORS data, and the results indicated that the BeiDou navigation satellite system network RTK could be realized and the centimeter level positioning accuracy was achieved by this algorithm.
Science of Surveying and Mapping,2017,Vol 42,No. 11
【Abstract】 Aiming at the problem of determining measurement’s weight ratio in GPS/GLONASS/BDS combined positioning, this paper calculated the positions of satellites via broadcast ephemeris, with reference to the precise ephemeris provided by IGS, the root-mean-square of coordinate of satellite and user equivalent range error with weight factor as accuracy indication. Then the law of orbit error was explored through comparison and analysis of the indications. The analysis of orbit errors in each August of 2013, 2014 and 2015 showed that the BeiDou satellite navigation and positioning system was being improved gradually, and the orbit errors’ weight ratio of GPS/GLONASS/BDS was changing at 5:2:1, 5:2:2, 5:2:3 during the three years. Future measurement’s weight ratio can refer to the weight of 2015.
Science of Surveying and Mapping,2017,Vol 42,No. 12
【Abstract】 For the precise ephemeris can only provide discrete but not arbitrary satellite position, this essay put forward to make use of interpolation method to calculate satellite position at any time. It takes advantage of GFZ precise ephemeris data to calculate medium earth orbit (MEO), inclined geo-synchronous orbits (IGSO), geostationary earth orbit (GEO) satellite position at some time by using Lagrange interpolation, Newton interpolation, Chebyshev fitting, Legendre fitting respectively, which has a deeply analysis in the precision of four interpolation methods. The results showed that the Newton interpolation method was optimal for C01 satellite, and Lagrange interpolation method was optimal for C09 and C12 satellites in the calculation of BeiDou three types of different satellites.
Accuracy analysis of pseudorange point positioning of BDS based on inter-satellite single difference method
Science of Surveying and Mapping,2017,Vol 42,No. 06
【Abstract】 In view of the influence of the accuracy of single point positioning based on inter-satellite single difference method and the receiver clock error, the difference of satellite numbers, PDOP value and precision of the pseudorange point positioning of three calculating formulas including BDS single point positioning, BDS inter-satellite single difference method, and GPS inter-satellite single difference method were analyzed; the positioning results of different positioning formulas in the same time period were compared with true value. The results showed as follows. The results of inter-satellite single difference of BDS were stable and its accuracy was close to BDS single point positioning, and had slightly higher stability than GPS inter-satellite single difference; in terms of accuracy, the accuracy in directions of E and N were improved to a certain extent compared to the other two formulas, and the accuracy in the direction of U was between the other two kinds of positioning methods.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 11
【Abstract】 We present the principals for BDS and BDS/GPS real-time kinematic (RTK) positioning. An experiment was conducted on Songshan calibration field using a UAV-based low altitude photograph platform which carried a double frequency GNSS system simultaneously receiving BDS and GPS signals. By comparing the positioning result of GPS, BDS, and the BDS/GPS-combined RTK models, and using these three groups of camera exposure station coordinates to carry out GNSS-supported aerotriangulation, these experiments demonstrated that the performances of GPS, BDS and BDS/GPS-combined RTK positioning model were very close in bundle block adjustment. For all three groups, the overall root mean square errors were all lower than ±0.17 m for the planimetry and ±0.25 m for height, which satisfied the Chinese National specifications of aerial photogrammetric 1:500 mapping in hilly regions.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 01
【Abstract】 By improving the satellites clock offsets estimation method with epoch-differenced phase and un-differenced pseudo-range observations, we realize the estimation of GPS, GLONASS, BDS, and Galileo satellites clock offsets. Moreover, 50 GNSS stations distributed worldwide were used to acquire multi-GNSS satellites clock offsets. Their precisions were analyzed. PPP was used to validate the estimated satellite clock offsets. The experimental results illustrate that the biases between satellites clock offsets as estimated and the final multi-GNSS precise satellites clock offsets generated using PANDA software package of Wuhan University were less than 0.2 ns. The PPP results using the estimated satellites clock offsets were close to the results estimated using the final multi-GNSS satellites clock offsets generated with the Wuhan University PANDA software.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 09
【Abstract】 As the number of visible satellites is increasing in the age of multiple global navigation systems of the global navigation satellite system (GNSS), Chinese BeiDou satellite navigation system (BDS) offer three frequencies signals to users, so the accuracy and reliability of GNSS-RTK positioning are improved. In general, ionosphere-free combinations are used in single-epoch real-time kinematic (Real-Time Kinematic) for medium-baseline. But this algorithm amplifies the measurement noise, and the ambiguity resolution performance deteriorates as the length of baseline increases. In this paper, a single-epoch and multi-frequency RTK positioning algorithm for medium-baseline was presented, based on the BDS/GPS dual system combination. Two BDS extra-wide-lane ambiguities were fixed at a high success rate, and the BDS wide-lane ambiguity was solved through a simple transformation. Ambiguity-fixed WL was used to improve the success rate of GPS WL ambiguity fixing, and parameterization strategy of ionospheric delay error was used to improve the success rate of BDS/GPS NL ambiguity fixing. This algorithm was validated with real-time data. The results show that the proposed algorithm is feasible for ambiguity resolution and positioning accuracy.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 04
【Abstract】 Aiming at the acquisition problem brought by NH code in the signal of BD2 which leads to sensitivity reduction problem by traditional acquisition methods, this paper presents a weak BD2 signal acquisition method based on adaptive stochastic resonance algorithm. By combining the DBZP method with adaptive stochastic resonance algorithm, the method can eliminate the data hopping and NH hopping, and significantly improve the signal-to-noise ratio. The method can be adopted to achieve the fast signal acquisition with high sensitivity characteristic. The simulation and test results verify that, this method provides stronger capacity of acquainting BD2 signal, has more advantages in real-time, high sensitivity and has a higher application value.
Science of Surveying and Mapping,2018,Vol 43,No. 02
【Abstract】 In high-accuracy GNSS surveying, the existence of cycle slip directly affects the ambiguity resolution and the ultimately positioning accuracy. The continuously operating reference stations of each province got multi-system observations, which led to increased workload of cycle slip detection. This paper gave a new method for multi-system cycle slip detection based on Gansu continuously operating reference stations (GSCORS) dual frequency observations, which could meet the general conditions. Using the method of phase reduce pseudorange combining with ionospheric residuals for GPS and BDS cycle slip detection and repair respectively, the corresponding carrier’s simulated cycle slips detection found that, BDS larger satellite clock error and pseudo noise affected the quality of the data, and the cycle slip detection time series of BDS fluctuated more than the amount of GPS, with 1 cycle of deviation for more than seven cycles slip detection accuracy of BDS than the GPS, but the method of ionospheric residuals was capable of detecting and repairing the BDS cycle slip such as one cycle which remained by using the method of phase reduce pseudorange. Final tests confirmed that this method could effectively detect and correctly separate GPS and BDS each frequency’s more than one cycle slip.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 05
【Abstract】 BeiDou Navigation Satellite System (BDS) has yet to meet the needs of global navigation and positioning as the satellite tracking and the geometry of reference station are not precise. These situations influence the precision of satellite orbit determination. In view of these problems, based on dynamic orbit determination theory and methods, the analytical contribution value of multi-GNSS combined orbit determination was applied to improve the precision of parameter solutions. Using measured data, the statistical contribution values of BDS/GPS combined orbit determination to the solution precision of orbit and clock error was analyzed. The results show that the contribution of combined orbit determination to the solution precision of common parameters shared by different systems is significant. The solution precision for orbit and clock error is significantly improved except in the case of GEO satellites. The statistical contribution values of BDS/GPS combined orbit determination to the precision of BDS satellite orbit, the RMS of BDS satellite clock error and the RMS of receiver clock error are 36.21%, 26.88% and 20.88% respectively. The contribution of receivers in areas with few visible satellites to the clock error is particularly significant, and the contribution value is 45.95%.
Science of Surveying and Mapping,2017,Vol 42,No. 12
【Abstract】 Aiming at the problem that BeiDou navigation satellite system has not formed a unified satellite attitude model and antenna phase center corrections model and the strategy of orbit determination, this paper analyzed the precision of BeiDou navigation satellite system (BDS) precise orbit products and precise clock products between Wuhan University and Geo Forschungs Zentrum. Based on the real data, the positioning accuracy of precision point positioning was analyzed between two different providers. The results showed that the precision of BeiDou orbit was assessed by different characteristics among geostationary earth orbit (GEO) and inclined geosynchronous satellite orbit (IGSO) and medium earth orbit (MEO) constellations. The precision of GEO orbits was at meter level, and the precision of IGSO was at decimeter level. The precision of MEO orbits was 10.81 cm in along direction, 5.41 cm in cross direction, and 3.37 cm in radical direction. The precision of GEO clock, IGSO clock, MEO clock was 0.38 ns, 0.25 ns, and 0.15 ns respectively. The positioning accuracy of precision point positioning was quiet between two different analysis centers providers in horizontal direction. The positioning accuracy of static BeiDou precise point positioning was about 3 cm in horizontal direction and 7 cm in vertical direction.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 06
【Abstract】 Presently, most of the errors caused by the B3 frequency, antenna phase center offset are corrected by the satellite clock a0 parameter. The errors caused by the variance of different frequencies are corrected by timing group delay (Tgd) parameter for BeiDou navigation satellite system (BDS) through navigation messaging. In order to improve the broadcast ephemeris, we put forward a satellite antenna phase center offset correction and fitting broadcast ephemeris methods. The two approaches are compared in two ways, including the influence on user ranging error and precise point positioning. The results show that the two methods can correct most errors caused by antenna phase center offset. The correction accuracy of the new method is improved by 76% compared with the method using satellite clock a0 parameter, and the positioning accuracy is improved by 12.5%. Accuracy is not affected by time-space factor. The positioning accuracy when correcting the satellite position before ephemeris fitting is about 38.1% higher than that when the satellite antenna phase center offset is not corrected. The correction of the variance of different frequencies of the antenna phase center by Tgd residuals is analyzed. The results show that the influence is at the mm order, so we can correct the variance by Tgd parameter.
Study on range signal evaluation and precise point positioning application of Beidou navigation satellite system (BDS)
Chinese Journal of Scientific Instrument,2017,Vol 38,No. 11
【Abstract】 With the construction and development of global navigation system, the high quality of positioning navigation and time service are gradually provided by Beidou navigation satellite system (BDS) in China. In this paper, the data of BDS receiver operated in time keeping laboratory of national time service center (NTSC) are used, and the BDS range signal evaluation and precise point positioning (PPP) are studied. Based on the measurement data, the signal-to-noise ratio and multipath effect of B1 and B2 frequencies are analyzed. And the algorithm of BDS PPP is discussed in detail. The precision positioning and timing information is calculated by using the data and the products of precise orbit and precise satellite clock from MGEX of IGS. The results show that reception performance of B2 frequency point is better than that of B1 frequency point, and the BDS PPP error of X, Y, Z directions is kept at cm level. The short-term frequency stability of time difference between local time and IGST is in 10 −14, and the performance is approximately the same as global positioning system (GPS). It is proved that the BDS can be used in ns level time transfer.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 07
【Abstract】 Multi-GNSS combination is helpful to improve the accuracy and reliability of satellite navigation and positioning. However, in case of BDS/GPS combined carrier phase positioning systems, it is difficult to fix all the ambiguities due to the increasing number of ambiguities, high measurement noises or residual atmosphere delays with the traditional Lambda method. But it is of greater probability to fix a subset of ambiguities. In this paper, we divided the current partial ambiguity fixing methods into three categories and analyzed the characteristics of every method. Finally, the effects of the three partial resolution methods were tested with the measured BDS/GPS data. The results show that the success rate and ratio value are obviously improved when using partial ambiguity fixing. At the same time, the initialization time of RTK is shortened, and the precision of kinematic positioning is also improved.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 08
【Abstract】 Different from other navigation system, there is a divergence between code and phase observables of BeiDou Navigation Satellite System (BDS). In this paper, we analyze the characteristic of code bias variations and propose a polynomial correction model of GEO, IGSO and MEO satellites. Firstly, different stations and observables of different receiver types of BeiDou Experiment Tracking Stations (BETS) of Wuhan University, Crustal Movement Observation Network of China (CMONOC) and Multi-GNSS Experiment campaign (MGEX) of IGS are used for analysis and verification. The results show that the code bias variations, which are dependent with satellite types and frequency and independent with receiver type, station position and observation time, vary with satellite elevations. Besides, the code bias variations of satellites may reach up to 1.5 m and can be divided into two groups (GEO/IGSO and MEO). Secondly, based on the analysis of code bias variations of BDS, we establish a polynomial correction model of IGSO/MEO code bias variations. Besides, since the elevation of a GEO satellite remains unchanged, we propose to model the single-difference fractional cycle bias with wide-spread ground stations. Then, a correction model for code bias variations of GEO satellites is established by using the consistency of the fractional cycle of wide-lane ambiguity of single difference between satellites. Finally, the improvement brought by applying our correction model is validated by various strategies, e.g., the residual distribution of pseudo-range is more close to normal distribution, and the positioning accuracy of dual-frequency single point positioning as well as the single-frequency precise point positioning is improved.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 09
【Abstract】 The Beidou Regional Satellite Navigation System (BDS) has an uneven distributed constellation, containing five satellites in geostationary earth orbit, five in inclined geosynchronous orbits and four in medium earth orbits. With this hybrid constellation, the quantity and the geometrical structure of observed BDS satellites are different at different latitudes. The latitude effect in BDS application performance of positioning and navigation. In this paper, theoretical models and actual observations were described to analyze the difference in quantity and geometrical structure of the observed BDS satellites and the performance of positioning as well as navigation at different latitudes. An experiment was conducted at different latitudes with receivers from separate companies. The results show the latitude effect and impact in BDS applications, which means the BDS positioning accuracy decreases with the increase of latitude. In contrast, there is no obvious latitude effect in Global Positioning System (GPS) applications. The implementation of BDS/GPS data fusion weakens the latitudinal impacts on the results and improves the accuracy and reliability of navigation and positioning services.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 08
【Abstract】 Currently, there are five test satellites of BeiDou Global Satellite Navigation System broadcasting new signals. Quality analysis of test satellite observations is a significant content for the verification of the new signal system. Based on single station measurement of BeiDou test satellites, the code minus phase combination (CC) and multipath combination (MP) are employed to analyze the pseudorange noises and multipath errors of civil signals and Bs signal of the test satellites. The result shows that the pseudorange measurement accuracy of inclined geosynchronous satellite orbit (IGSO) satellite is better than that of the medium earth orbit (MEO) satellite; B2a + b signal has the highest pseudorange measurement accuracy as well as the best anti-multipath performance, while the B1C signal performs the worst in both aspects; the pseudorange measurement accuracy of Bs signal is relatively poor, yet better than that of the B1C signal and a systematic error related to elevation exists in the pseudorange multipath series of Bs signal with its maximum value up to 0.5 m.
Active ingredients screening by cell membrane chromatography and simultaneous quantitation of ginsenosides in bulk drug of secondary ginsenoside H dripping pills
Chinese Traditional and Herbal Drugs,2018,Vol 49,No. 11
【Abstract】 Objective To establish a HPLC-MS/MS method for simultaneous determination and active ingredients screening of pseudoginsenoside RT5, 20( S)-ginsenoside Rh 1 and 20( S)-ginsenoside Rh 2 by cell membrane chromatography (CMC) in secondary ginsenoside H dripping pills (SGHDP). Methods The samples were separated on Century SIL BDS C 18 column (250 mm × 4.6 mm, 5 μm) eluted with 0.2% formic acid aqueous solution–acetonitrile in a gradient mode, and the target compounds were analyzed by positive ion multiple reaction monitoring (MRM) mode, and active ingredients of SGHDP obtained in solid-phase of biomembrane by CMC technology were determined at the same time. Results The linear ranges of pseudoginsenoside RT5, 20( S)-ginsenoside Rh 1, and 20( S)-ginsenoside Rh 2 were 0.095–0.235, 0.042–0.168, and 0.105–0.419 mg/mL; the extraction recoveries were 99.95%, 100.12%, and 100.06%; and RSD were 1.06%, 0.96%, and 0.91%, respectively. The contents of pseudoginsenoside RT5, 20( S)-ginsenoside Rh 1, and 20( S)-ginsenoside Rh 2 in SGHDP were 21.24%, 21.42%, and 29.70%, respectively. 20( S)-Ginsenoside Rh 2 was the active ingredient obtained by biomembrane using as a new quality control maker for SGHDP. Conclusion The developed method is accurate and reliable for the determination of three ginsenosides in SGHDP, and provides a new reference for quality control of SGHDP. 20( S)-Ginsenoside Rh 2 is a immobilization component of red cell membrane, speculated to be the active ingredient of SGHDP, which is in consistent with previous studies on antitumor and antidepression.
Preliminary Assessment of Positioning Performance of BeiDou Navigation Satellite System at Zhongshan Station, Antarctica
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 08
【Abstract】 This paper assesses the navigation and positioning performance of BeiDou Navigation Satellite System (BDS) at Zhongshan Station, Antarctic, after it is officially announced in operation. The availability of satellites, position dilution of precision (PDOP), pseudorange data quality, precision of ionosphere model and positioning precision are analyzed by the measured data. The results show that: 1) BeiDou is currently capable of providing basic navigation positioning services through all day at Zhongshan Station, Antarctic. The overall availability and quality of pseudorange measurements of BeiDou are as good as those of GPS. However, there are some problems, such as uneven distributed satellites over the sky, low elevation angle of GEO satellites, and the low precision of ionosphere model, which will reduce the positioning performance. 2) The precision of BeiDou-only positioning is much worse than that of GPS-only system; for the single-frequency point positioning, we can only expect precisions higher than 22 m, 9 m and 25 m in the north, east and elevation components, respectively; for the single-frequency pseudorange differential positioning, the precision is 3.6 m, 2.3 m and 3.3 m in the north, east and up components, respectively. 3) The combined system of GPS/BeiDou provides increased reliability and improves the 3D precision of GPS by approximately 10%, 22% for the single-frequency point positioning and the single-frequency pseudorange differential positioning, respectively.
Science of Surveying and Mapping,2017,Vol 42,No. 07
【Abstract】 GNSS data quality provides basic reference information for high-precision data processing. At present, GPS data quality inspection methods are mature and rich in data resources, while BDS data quality is lack of systematic and comprehensive analysis. This paper introduces the contents and methods of BDS observation data quality inspection, and calculates the quality results of BDS data multi-path effect, cycle jump, signal to noise ratio based on national reference stations, analyzes the quality characteristics and influencing factors of BDS, and the data quality of BDS and GPS is compared. The results show that the value of MP and SN of BDS data are related to the elevation angle and signal frequency. Under the same environment, the MP of the BDS data is superior to the GPS data quality, and the BDS’s SN2 is superior to the GPS, SN1 and SN3 are slightly worse than GPS.
Chinese Journal of Scientific Instrument,2018,Vol 39,No. 06
【Abstract】 Global navigation satellite system (GNSS) time comparison is one of the major technologies in the generation of international standard time. Global positioning system (GPS) and global navigation satellite system (GLONASS) have been authorized as the official method by BIPM. To promote the application of Beidou in the realization of international standard time, Beidou common view time comparison is firstly implemented through the pseudo-code measured data among the National Time Service Center, Chinese Academy of Sciences, Technical Research Institutes of Sweden and Royal Observatory of Belgium in the frame of GNSS time comparison standard. Experimental results are summarized as follows. The STDEV of Beidou zero-baseline with common view time transfer is less than 1 ns. The RMS of Asia-Euro long baseline Beidou common view time comparison is better than 2.5 ns. The stability can reach 10 −14 (1 day). This is almost the same level with GPS common view time comparison. It is proved that Beidou can be adopted as the nanosecond level of time transfer or time comparison. The experiment can support that Beidou will be involved as the official method in the calculation of the international standard time in future.
Science of Surveying and Mapping,2019,Vol 44,No. 01
【Abstract】 In view of the uneven distribution of the BeiDou ground reference station, which affects the precision of BeiDou orbit determination, the grid based stochastic optimization method was adopted in this paper. The method took account of factors such as quality, distribution and station stability of the monitoring stations to evenly select the global distribution of MGEX stations. The weighted GDOP index was used to evaluate the effectiveness of the selected stations. And the influence of the number, distribution and quality of the monitoring stations on the orbit determination precision was comprehensively analyzed. The results showed that the precise orbit determination of GEO, IGSO and MEO satellites of BeiDou satellite was 221.56, 12.59 and 6.81 cm, respectively when 30 monitoring stations are selected by this method, there was a greater improvement than the grid method. Within a certain range, the more number of stations indicated the higher precision of orbit determination.
Science of Surveying and Mapping,2018,Vol 43,No. 11
【Abstract】 In order to improve the success rate of ambiguity fixing, the paper researched a partial ambiguity resolution strategy based on sub-step combination control. First, the SNR, satellite elevation, and satellite tracking number were used to screen the ambiguity; second, the ambiguity is resolved by LAMBDA algorithm. If the ambiguity resolution failed, the best subset of ambiguity which selected based on satellite tracking number, variances of ambiguity floating solution and residuals of ambiguity floating solution are re-searched and fixed; finally, on the basis of the Ratio test, the ambiguity history information test was added. A low-latitude static and kinematic GPS/BDS/BDS medium-short baseline observation data were processed by our own software. The results of the static case and kinematic case showed that the influence of un-convergence ambiguity can be controlled efficiently and the success rate of ambiguity fixing was improved. At the same time, the strategy ensured ambiguity’s reliability.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 11
【Abstract】 The precise point positioning (PPP) mode has been widely used in many fields, such as vehicle navigation, surveying and mapping, and earthquake monitoring etc. In recent years, multi-GNSS is an obvious trend with the increasing number of satellites. In this paper, BDS/GPS PPP is researched by comparing the calculation of the data from global Multi-GNSS Experiment (MGEX) with BDS and GPS PPP. The results show that the average RMS of BDS static PPP is 4.35 cm, 3.01 cm, 6.40 cm while the average RMS of GPS static PPP is 1.21 cm, 0.48 cm, 1.79 cm in east, north and up directions, respectively. The average RMS of BDS/GPS static PPP is 1.21 cm, 0.50 cm, 1.87 cm in east, north and up directions, respectively. In kinematic PPP, the accuracy of positioning in BDS is better than 10 cm and 15 cm in horizontal and vertical directions respectively. While the accuracy of GPS and BDS/GPS is all better than 5 cm and 8 cm in horizontal and vertical directions, respectively. The number of satellites in BDS/GPS is the double of that in single system. And the spatial structure of combined system is greatly enhanced which can improve the stability of positioning. In addition, whether in static PPP or kinematic PPP, the combined system can greatly shorten the convergence time and reduce jitter compared with single system especially with BDS PPP.
Science of Surveying and Mapping,2018,Vol 43,No. 09
【Abstract】 Ambiguity solution is a key to obtain high precision positioning results in GNSS precise positioning, where LAMBDA algorithm is regard as the classic algorithm. In view of the BDS tri-frequency precise positioning problem, LAMBDA algorithm is applied to the BDS tri-frequency ambiguity resolution. Based on the ambiguity resolution of BDS ultra-short baseline data by using LAMBDA algorithm, the single epoch success rate of ambiguity resolution for BDS tri-frequency and baseline increment of E, Nand U direction are analyzed to verify the validity of LAMBDA algorithm in this paper respectively. Results show that the ambiguity solution and baseline resolution of BDS tri-frequency could be realized by the LAMBDA algorithm, through them, in comparison with B2 and B3 frequency points, the single epoch success rate of ambiguity resolution for B1frequency is relative low, while more than 93.7% epoch for the single epoch success rate of ambiguity resolution in B1frequency is higher than 95%, and the average single epoch success rate of ambiguity resolution for the whole time is better than 98.7%; the increment results of baseline E, N and U directions in B2 and B3 frequency points are basically identical, but they have a certain differences compared with B1 frequency point, which may be due to the fact that wavelength difference of B1 frequency point with that of B2 or B3 frequency point is larger.
Science of Surveying and Mapping,2018,Vol 43,No. 12
【Abstract】 Aiming at the problem of verifying and analyzing the precision of the earth rotation parameters (ERP) which needs to be determined independently by using BeiDou navigation satellite system (BDS) data in China, this paper used the global positioning system (GPS) reference station data in and around China and the BDS data of MEGX network to calculate the ERP, and the accuracy of the calculation results were compared and analyzed. The calculation results showed that RMS of the difference calculated by BDS data and the International Earth Rotation Service (IERS) was 0.657 6 mas in X direction polar motion, 1.032 4 mas in the Y direction polar motion, and 0.085 3 ms in UT1-UTC; RMS of the difference calculated by GPS data and IERS was 0.451 6 mas in X direction polar motion, 0.547 5 mas in the Y direction polar motion, which was obviously better than that of BDS data, and RMS was 0.215 3 ms in UT1-UTC, which was worse than that of BDS data. Using two techniques to solve the ERP, it was found that there were obvious systematic errors in the pole motion parameters, and there was no obvious systematic error in the UT1-UTC values. The research results showed that using BDS technology to determine the accuracy of the ERP was worse than GPS, but the data accuracy was greatly improved compared with the previous ones.
Science of Surveying and Mapping,2019,Vol 44,No. 02
【Abstract】 In view of the advantage that BeiDou navigation system is the only positioning system that can broadcast the practical triple-frequency signal at present, the merits and demerits of the least-square ambiguity decorrelation adjustment (LAMBDA) method and three carrier ambiguity resolution (TCAR) method were analyzed in this paper. Extra wide lane and wide lane ambiguity that were fixed were functioned as constraint condition for triple-frequency positioning model and narrow lane (NL) ambiguity was fixed by LAMBDA in this paper. It was shown that triple-frequency positioning model with constraint condition promoted the ambiguity resolution (AR) success rate under the case of short length baseline and accelerated ambiguities and coordinate parameter speed compared with traditional triple-frequency positioning model by experiments.
Design and experiment of motion controller for information collection platform in field with Beidou positioning
Transactions of the Chinese Society of Agricultural Engineering,2017,Vol 33,No. 12
【Abstract】 With the development of precision agriculture technology, agricultural robots which improve efficiency and save labors for agriculture are used for information collection in field, instead of the traditional manual recording and observation. At home and abroad, most of navigation researches of walking platform meet the requirement of tracking precision. However, they mainly use RTK-DGPS (real-time kinematics-differential GPS) positioning system, and it is so expensive that it restricts the large-scale promotion of automatic navigation of walking platform to some extent. Consequently, aiming at uniform speed and line tracking problem in complex field environment for information collection platform, a motion controller with lateral correction and longitudinal constant-speed control was designed. This paper constructed the motion control hardware system using the information collection platform as the carrier, STM32F4 32-bit microcontroller was as the control center and multiple sensors were used for obtaining the vehicle status information, including three-dimensional (3D) electronic compass, low-precision Beidou module, rotary encoder and angle sensor. The working principle of the controller could be described as follows. Firstly, two points were chosen to determine the tracking path. Then, the current position information and the heading angle of the platform in the field were obtained by Beidou module and electronic compass. They were used to calculate the lateral offset and course deviation, which were two inputs of fuzzy controller, and the output of fuzzy controller was got through designing control algorithm to control the steering angle of front wheel. It ensured the information collection platform to always track the goal line. Meanwhile, the speed information of the platform was measured by the rotary encoder, which was the input of PID (proportion, integral, derivative) controller. It realized constant-speed walking through speed feedback regulation. On the other hand, in order to improve the positioning precision of Beidou module, a method was presented, which was that three Beidou modules of low precision were placed in the way of an equilateral triangle, and the average positioning data of three Beidou modules were obtained at the same time. Then, they were used as the final location data of the center point of the equilateral triangle, which took advantage of compensatory principle of random error to reduce the random error and improve the positioning precision of the Beidou module. By this way, the average positioning precision of the Beidou receiving module was increased from 2.06 to 1.50 m, and the dynamic positioning precision was improved to within 0.78 m. The speed tracking experiment was carried out in the field of Modern Agricultural Science and Technology Experiment Site of Huazhong Agricultural University. The result showed that the control system could work steadily when the vehicle ran at the speed of 0.4 m/s; the proportion coefficient was 100, the differential coefficient was 40, and the integral coefficient was 50. The adjustment time was less than 3 s and the maximum error of speed was less than 7%. When running at the same speed, the initial lateral offset was set to 1.4, 2.0 and 2.5 m, the time required for stable tracking was 11, 15 and 25 s, respectively, and the maximum linear deviation after stabilization was all less than 0.31 m. The research of motion controller on the information collection platform not only promotes the acquisition ability of field information but also provides technical support for the efficient and intelligent operation of the information collection platform in field. At the same time, it offers the possibility of greatly reducing the cost in linear tracking, which is of benefit to the promotion of precision agriculture.
Science of Surveying and Mapping,2018,Vol 43,No. 12
【Abstract】 Aiming at the problems that single satellite navigation system real-time kinematic (RTK) positioning accuracy and stability are not insufficient, an undifferenced RTK Kalman filter positioning method based on BDS/GPS was proposed in this paper. Firstly, the pseudorange and carrier-phase correction of undifferenced error on reference station were calculated; then single satellite observation error was corrected by undifferenced correction on rover station, based on uncombined RTK model; short baseline static and dynamic data were solved with Kalman filter method which based on the additional ambiguity parameter. The results indicated that dual-system combined positioning confirmed the satellite geometry, realized real-time kinematic combined calculating with BDS/GPS dual-system multi-frequency and achieved the centimeter level of positioning accuracy. Rover station began to positioning by received correction number; the volume of data transmission in real time became smaller than double-difference mode; user side positioning algorithm was simple.
Geomatics and Information Science of Wuhan University,2018,Vol 43,No. 12
【Abstract】 Three kinds of triple-frequency precise point positioning (PPP) models containing two ionosphere-free combined models, the model of triple-frequency ionosphere-free linear combination and uncombined model are achieved based on Trip software. Triple-frequency PPP models and traditional dual-frequency ionosphere-free combined PPP model are tested by BDS data from 12 stations of Crustal Movement Observation Network of China. The results show that for most stations, daily static positioning accuracy is better than 1 cm in horizontal, 2 cm in vertical, and is better than 4 cm in horizontal and 6 cm in vertical for kinematic positioning accuracy. The average convergence time for each triple-frequency is about 120 min for static case and about 180 min for kinematic case. Comparing with traditional dual-frequency PPP models, triple-frequency PPP models can obtain higher accuracy. To be specific, root mean square (RMS) in daily static solutions of triple-frequency uncombined PPP models can be improved by 36.1% and 6.3% horizontally and vertically, and RMS in daily kinematic solutions can be improved by 9.1% and 6.3% horizontally and vertically.
Geomatics and Information Science of Wuhan University,2019,Vol 44,No. 04
【Abstract】 A multi-GNSS precise point positioning (PPP) algorithm considering the inter-system bias (ISB) is adopted to process the multi-GNSS data obtained from seven stations of the multi-GNSS experiment (MGEX). Using the proposed algorithm, the ISBs values can be achieved between Galileo, GLONASS, BDS (BeiDou Navigation Satellite System) and GPS (Global Positioning System). The results of static multi-GNSS PPP solutions show that RMS (root mean squares) values are 8.9 mm, 5.3 mm and 10.9 mm for the east, north and up directions respectively. One-day stabilities of ISBs described by STD (standard deviation) values are better than 0.12 ns for different systems, and especially Galileo is the best one. From the sequence of multi-day ISBs, significantly irregular ISB jumps can be found where the change range can reach nearly 20 ns. There are some differences on ISB values for different types of receivers, and the ISB values are similar for same types of receivers. On the whole, the ISB for Galileo is the most stable and optimal, and the results of BDS and GLONASS are almost equivalent.
Science of Surveying and Mapping,2019,Vol 44,No. 04
【Abstract】 In order to study the effects of the solar radiation pressure model on orbit prediction, the final precise orbit products from August 1, 2017 to November 30, 2017 were adopted, and the effects of different solar radiation pressure on orbit prediction of BeiDou IGSO, MEO satellite and Galileo satellite were studied in this paper. The solar radiation pressure model includes ECOM 5 parameters model, ECOM 9 parameters model and the adjustable Box-wing (A-BOXW) model. The predicted orbits were compared with final precise orbits and satellite laser ranging (SLR) observations, and the residuals were used to evaluate the accuracy of predicted orbits. For BeiDou satellite, the results of ECOM 5 parameter model and ECOM9 parameter model were similar. The A-BOXW model was the worst, but in the radial direction of satellite, the ECOM 9 parameter model was superior to the ECOM 5 parameter model. For the Galileo satellite, the ECOM 9 parameter model was better than the ECOM 5 parameter model as a whole.
Geomatics and Information Science of Wuhan University,2019,Vol 44,No. 02
【Abstract】 Comprehensive zone correction is a new type of differential corrections for BeiDou wide-area augmentation system. As broadcasted together with the equivalent satellite clock (ESC) and orbit corrections by BDS satellites, they enable user decimeter-level real-time positioning capability using the carrier-phase observations. In this paper, we give a brief introduction of comprehensive zone corrections, and the function model of precise point positioning (PPP) for dual-and single-frequency users using the comprehensive zone corrections. Tracking data of 30 stations in mainland China are used to evaluate the PPP performance, including convergence time, positioning accuracy and its relation with the user’s distance from the zone center. Results show that the dual-frequency PPP convergences to 0.5 m in 25 minutes and the positioning accuracy are 0.15 m in horizontal and 0.2 m in vertical, respectively. As for single-frequency PPP, the positioning accuracy convergences to 0.8 m in 20 minutes, while the positioning accuracy is 0.3 m in horizontal and 0.5 m in vertical. We conclude that the BDS PPP accuracy using the broadcasted wide-area differential corrections reaches decimeter-level within the distance of 1 000 km around zone center, and the accuracy becomes slightly worse with the user’s distance from the zone center increasing.
Linear combination optimization model of BeiDou triple-frequency integral coefficient carrier phase observation
Science of Surveying and Mapping,2019,Vol 44,No. 08
【Abstract】 According to the application requirements of BeiDou triple-frequency observation, the linear combination observation model was established. Based on the error analysis of the model, a spatial analysis of the real coefficient ionosphere-free combination, troposphere-free combination, and minimum noise combination weakening or eliminating errors was conducted from a geometric perspective. Then, the relationship between the ionosphere-free plane, the troposphere-free plane, and the minimum noise line was more intuitively described. Upon this basis, the linear combination of the BeiDou integral coefficient was derived, and the combination of long wavelengths, weak ionospheric delay and weak observation noise was analyzed. Moreover, the number of lanes, the ionospheric delay coefficient and the noise amplification factor were used as the judgment indicators for the linear combination of the optimal triple-frequency integral coefficient. Finally, several sets of the linear combination of the optimal triple-frequency integral coefficient with different characteristics represented by (−1, −5, 6), (0, −1, 1), and (1, 4, −5) were obtained, and the sum of the coefficients of the optimized liner combination model of triple-frequency integral coefficient was generally S = 0 or S = ±1.
Geomatics and Information Science of Wuhan University,2017,Vol 42,No. 11
【Abstract】 The realization and maintenance of the China geodetic coordinate system 2000 (CGCS2000) depends on GPS technologies, which is a national security risk. BDS began offering services to customers in the Asia-Pacific region in December 2012. It provides a good opportunity to realize and maintain the national terrestrial reference frame (TRF) with BDS system. We focus on how to use BDS observations of BDS/GPS stations with dual-mode receivers to realize the National TRF, aligned to the international terrestrial reference frame (ITRF). Results show that the precision of the horizontal velocity derived from BDS data is comparable to that derived from GPS data at about 2–3 mm/a, with more than two years of observation data. The RMS of the station coordinate residuals, with the linear velocity removed, are better than 0.8 cm and 1.7 cm for the horizontals and verticals, respectively. The current precision of BDS data can allow observation of seasonal displacements in the verticals. System errors related to the longitude and latitude are found in the coordinate differences between BDS and GPS data based on PPP mode. Thus the current BDS system can be used to realize and maintain the national terrestrial reference frame at cm level.
Science of Surveying and Mapping,2019,Vol 44,No. 11
【Abstract】 In view of the problem that the differential inter-system deviation DISB cannot be calibrated in advance between the BDS second-generation system and the GPS, a strategy for fixed BDS GEO satellites as reference satellites was proposed in this paper. Detailed derivation of a tightly-combined relative positioning model of BDS and GPS short baselines was performed, and the stability of the DISB value between the same receiver and different receivers of frequency points including BDS-B1, BDS-B2, GPS-L1, and GPS-L2 was analyzed. The results showed that the deviation between BDS and GPS differential systems was not zero even for the same type of receiver. When the reference satellite of the BDS system was fixed to the GEO satellite, the carrier and pseudo-range DISB values changed with time, which could be calibrated in advance. Finally, the shielding environment was simulated with different elevation cut-off angles. The results of the short baseline experiment showed that when the number of satellites was small, the tightly combined model had a positioning accuracy of more than 20% compared with the traditional loose combination. Moreover, using the tightly combined model after correcting the DISB could significantly shorten the initialization time of the ambiguity, thereby improving the performance and usability of positioning in an environment of severe shielding.