Correction model of BDS satellite-induced code bias and its impact on precise point positioning

There are code biases on the pseudo-range observations of the Beidou Navigation Satellite System (BDS) that range in size from several decimeters to larger than one meter. These biases can be divided into two categories, which are the code biases in the pseudo-range observations of Inclined Geo-Synchronous Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites and the code biases in the pseudo-range observations of Geosynchronous Earth Orbit (GEO) satellites. In view of the code bias of the IGSO/MEO satellites, the code bias correction model is established using the weighted least square curve fitting method. After the correction, the code biases of the IGSO and MEO satellites are clearly mitigated. A methodology of correcting GEO code bias is proposed based on the empirical mode decomposition (EMD)-wavelet transform (WT) coupled model. The accuracies of the GEO multipath combination of the B1, B2 and B3 frequencies are improved by 39.9%, 17.9%, and 29.4%, respectively. Based on the corrections above, the ten days observations of three Multi-GNSS Experiment (MGEX) stations are processed. The results indicate that the convergence time of the precise point positioning (PPP) can be improved remarkably by applying a code bias. The mean convergence time can be improved by 14.67% after the IGSO/MEO code bias correction. By applying the GEO code bias, the mean convergence time can be further improved by 17.42%.     

Performance assessment of real-time multi-GNSS integrated PPP with uncombined and ionospheric-free combined observables

For precise position services, the real-time precise point positioning (PPP) is a promising technology. The real-time PPP performance is expected to be improved by multi-system combination. The performance of real-time multi-system PPP needs to be periodically investigated, with the increasing number of available satellites and the continuously improved quality of real-time precise products of satellite clocks and orbits. In this study, a comprehensive performance assessment is conducted for the four-system integrated real-time PPP (FSIRT-PPP) with GPS, BDS, Galileo and GLONASS in both static and kinematic modes. The datasets from 118 stations spanning approximately a month are used for analysis, and the real-time stream CLK93 is employed. The superior performance of FSIRT-PPP is validated by comparing with the results of GPS/BDS, GPS/Galileo, GPS/GLONASS, GPS-only, BDS-only, Galileo-only and GLONASS-only cases. The FSIRT-PPP using ionospheric-free (IF) combined observables can achieve a convergence time of 10.9, 4.8 and 11.8 min and a positioning accuracy of 0.4, 0.5 and 0.7 cm in the static mode in the east, north and up directions, respectively, while the derived statistic is 15.4, 7.0 and 16.4 min, and 1.6, 1.2 and 3.4 cm in the kinematic mode in the three directions, respectively. Moreover, we also compare the position solutions of real-time PPP adopting IF combined and uncombined (UC) observables, and prove the mathematical equivalence between the two PPP models in the converged stage, provided that there are no external ionospheric corrections or constraints given to the estimated ionospheric delays in the UC model. The difference between the fully converged positioning accuracy of IF-based and UC-based real-time PPP is marginal, but the UC-based real-time PPP has longer convergence time due to the influence of the significant unmodeled time-varying errors in the real-time precise products as well as the different parameterization between them. For completeness, the real-time kinematic PPP results in harsh environments and the post-processed PPP results are also presented.     

Ambiguity resolution in precise point positioning with hourly data for global single receiver

Integer ambiguity resolution (IAR) can improve precise point positioning (PPP) performance significantly. IAR for PPP became a highlight topic in global positioning system (GPS) community in recent years. More and more researchers focus on this issue. Progress has been made in the latest years. In this paper, we aim at investigating and demonstrating the performance of a global zero-differenced (ZD) PPP IAR service for GPS users by providing routine ZD uncalibrated fractional offsets (UFOs) for wide-lane and narrow-lane. Data sets from all IGS stations collected on DOY 1, 100, 200 and 300 of 2010 are used to validate and demonstrate this global service. Static experiment results show that an accuracy better than 1 cm in horizontal and 1–2 cm in vertical could be achieved in ambiguity-fixed PPP solution with only hourly data. Compared with PPP float solution, an average improvement reaches 58.2% in east, 28.3% in north and 23.8% in vertical for all tested stations. Results of kinematic experiments show that the RMS of kinematic PPP solutions can be improved from 21.6, 16.6 and 37.7 mm to 12.2, 13.3 and 34.3 mm for the fixed solutions in the east, north and vertical components, respectively. Both static and kinematic experiments show that wide-lane and narrow-lane UFO products of all satellites can be generated and provided in a routine way accompanying satellite orbit and clock products for the PPP user anywhere around the world, to obtain accurate and reliable ambiguity-fixed PPP solutions.     

可数非扩张映像族公共不动点迭代算法

提出一种计算可数个非扩张映像族公共不动点的新的迭代算法，并证明了算法的强收敛性。本算法由于避免使用形一映像，因而使得算法简洁，计算工作量较小。     

民用客机液压系统逻辑控制单元故障分析及排除

通过采用故障树的分析方法,运用故障机理分析、故障定位及故障复现的故障归零思路,分析了逻辑控制单元的设计规范及其变更,进行了新旧逻辑控制单元的对比试验,检查了逻辑控制单元与飞机的交联信号等,最终定位故障在逻辑控制单元内部元件失效,顺利排除了故障。     

数控机床回零的控制方法及常见故障分析

数控机床有挡块返回参考点方式是数控机床上广泛采用的一种回零方式,同时,有挡块返回参考点在数控机床故障中发生的概率也比较大,快速而有效的排除此类故障是保证企业顺利生产的必然要求。本文重点介绍有挡块回参考点的工作原理、动作方式、参数设置、PMC控制及常见故障分析与排除方法,以期为数控机床此类故障的排除提供可借鉴的方法。     

工业 S型热电偶1100℃以上温度点校准方法

越来越多的单位要求对工业S型热电偶1100℃以上温度点进行校准，但目前没有任何技术规范可供参考。本文就这一需求提供了三种解决方案，并对这三个方案的校准结果及不确定度进行对比分析，为计量机构根据客户的需求制定科学合理的校准方案提供参考。     

Modeling and Simulation of Pipeline Security Monitoring System Based on Line-Structure Sagnac Interferometer with 3×3Coupler

The third damage action,human disruption behavior,is one of the major threats to pipeline operation.It is necessary to monitor and locate the perturbation behavior that may threat pipeline safety in real-time.Therefore,a new pipeline security monitoring system is designed by using line-structure Sagnac optic fiber interferemeter with the characteristic of 3×3coupler that can modulate the phase of optic signal,with no need for phase modulation and demodulation.The optic structure of the new system is simplified,the signal processing accuracy is improved,and the polarization effect is reduced.The working principle of the monitoring in ideal condition is described,the phase demodulation is analyzed and the location of the possible damage action point is formulated.By using simulink,the optic signal propagation and interference is simulated and interference signals in different frequencies are obtained.The results validate the feasibility of the monitoring system and indicate that the low frequency signal less than 1kHz resulting from the human damage action can be detected.The disturbance set at 10 km can be located by calculating the demodulation signal accurately over a long monitoring distance.     

自动化立体仓库货位优先级生成算法设计

简单描述了自动化立体仓库系统构成,货物存取工作流程;结合堆垛机工作特性及货位综合属性,提出了一种在单作业工作方式下确定货位优先级方法;给出了基于货位优先级的立体仓库出入库算法;货位信息存储采用数据库技术;实验结果表明,系统按优先级实现货位分配与随机分配比较,可以提高系统工作效率。     

改进的ICCP地磁匹配算法

本文在分析等值线约束迭代最近点(ICCP)匹配算法基本原理的基础上,针对ICCP算法在非刚性变换情形下,就难以取得理想匹配效果的情况,提出了改进的ICCP算法。该算法首先用ICCP匹配算法修正初始位置误差和航向误差,然后采用逐点匹配,再迭代该过程的方法,逐点修正位置误差。仿真实验表明,改进的ICCP算法能够实现准确定位,定位精度在一个网格精度以内。