Revisiting the doppler filter of LEO satellite GNSS receivers for precise velocity estimation

The theoretical aspects of the precise velocity determination of Low Earth Orbit (LEO) satellites’on board Global Navigation Satellite Systems (GNSS) receivers are derived. It shows that the receiver’s Phase Lock Loop (PLL) is required to feature extremely small group delay within its low frequency band, which is in contrast to existing work that proposed wide band linear phase filters. Following this theory, a Finite Impulse Response (FIR) filter is proposed. To corroborate, the proposed FIR filter and an Infinite Impulse Response (IIR) filter lately proposed in literals are implemented in a LEO satellite onboard GNSS receiver. Tests are conducted using a third party commercial GPS signal generator. The results show that the GNSS receiver with the proposed FIR achieves 11 mm/s R.M.S precision, while the GNSS receiver with the IIR filter has a filter-caused velocity error that can not be ignored for space borne GNSS receivers.     

光平方事件及其对“北斗”系统发展应用的若干启示

光平方事件是首次出现合法的地面移动通信系统大规模大范围干扰全球卫星导航系统(GPS)的事例。美国光平方公司的地面移动通信网在得到联邦通信管理委员会(FCC)批准后,经评估认为对GPS系统会产生有害干扰,得到了美国PNT委员会、联邦航空管理局(FAA)以及国会的高度重视,进行了大量的测试评估,量化分析了光平方系统对GPS的有害干扰。分析探讨了光平方事件深层次的原因是频率资源的争夺,结合我国对"北斗"系统发展,提出需要深入分析研究第四代移动通信系统对"北斗"系统S频段下行信号潜在有害干扰。     

基于超声波/INS信息融合的室内定位方法

室内定位方法中,低成本惯性导航系统(INS)的定位误差随着时间和距离的增加而积累,需要采用其他手段抑制误差发散。室内环境下GPS无法正常工作,从而失去对INS误差的抑制作用;因此,该文提出了基于超声波/INS信息融合的室内定位方法。以自主导引小车(AGV)为定位终端,根据超声波定位技术和非完整约束条件得到自主导引小车的位置和速度信息,并利用该信息辅助INS,通过卡尔曼滤波进行信息融合,从而抑制纯惯导情况下定位误差发散的问题。采用Matlab对所提出的室内定位方法进行仿真验证,结果表明,采用超声波/INS信息融合方法能将INS的误差抑制在一定范围内,该方法适用于室内移动物体的实时定位。     

基于JMS的RFID中间件的研究与实现

文中简单介绍了RFID技术以及RFID系统向企业级应用集成的关键技术--RFID中间件,并且在详细分析RFID中间件系统功能的基础上,重点阐述了基于JMS技术的RFID中间件消息系统的构建方法,并提出了一种消息系统的设计思想和实现方法,解决了RFID系统向企业级应用集成中数据共享的问题。     

基于多天线的GNSS压制式干扰与欺骗式干扰联合抑制方法

压制式干扰和欺骗式干扰是全球导航卫星系统(Global Navigation Satellite System, GNSS)面临的最常见且最有威胁的蓄意干扰。该文提出了一种基于多天线的GNSS压制式干扰与欺骗式干扰联合抑制方法。首先利用子空间技术抑制压制式干扰,然后利用解扩重扩算法获得的加权矢量进行欺骗式干扰识别和抑制,最后对无干扰信号再次使用解扩重扩技术形成指向真实卫星的高增益多波束。仿真结果证明所提方法可以同时抑制压制式干扰和欺骗式干扰。该方法不需要卫星来向信息,对阵列流形误差稳健。     

GNSS空间信号连续性监测与评估

针对全球卫星导航系统GNSS（Global Navigation Satellite System）连续性指标性能评估对民航领域的用户的重要影响,本文以GPS（Global Position System）为代表,从可靠性原理出发提出了一种空间信号SIS（Signal-In-Space）连续性的基本评估模型;然后,对联邦航空局FAA（Federal Aviation Administration）发布的从1999年到2015年的GPS故障报告进行统计分析,得到每颗卫星的连续性概率;最后,与GPS 2008年版的标准定位服务性能标准（GPS SPS PS）发布的连续性指标进行对比,验证了GPS SIS的连续性的符合性。另外,文中针对我国北斗卫星导航系统的现状,提出了北斗卫星导航系统连续性性能监测与评估的建议。本文对北斗导航系统关于连续性的研究具有重要的参考价值。     

卡尔曼滤波直接法在INS/GPS组合导航系统中的应用

结合INS／GPS组合导航系统，讨论了卡尔曼滤波直接法的应用，仿真结果证明，采用卡尔曼滤波直接法可以有效地提高组合导航系统的导航精度。     

Functional Characterization of the Solute Carrier LAT-1 (SLC7A5/SLC2A3) in Human Brain Capillary Endothelial Cells with Rapid UPLC-MS/MS Quantification of Intracellular Isotopically Labelled L-Leucine

The solute carrier L-type amino acid transporter 1 (LAT-1/SLC7A5) is a viable target for drug delivery to the central nervous system (CNS) and tumors due to its high abundance at the blood–brain barrier and in tumor tissue. LAT-1 is only localized on the cell surface as a heterodimer with CD98, which is not required for transporter function. To support future CNS drug-delivery development based on LAT-1 targeting, we established an ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) assay for stable isotopically labeled leucine ([¹³C₆, ¹⁵N]-L-leucine), with a dynamic range of 0.1–1000 ng/mL that can be applied for the functional testing of LAT-1 activity when combined with specific inhibitors and, consequently, the LAT-1 inhibition capacity of new compounds. The assay was established in a 96-well format, facilitating high-throughput experiments, and, hence, can support the screening for novel inhibitors. Applicable recommendations of the US Food and Drug Administration and European Medicines Agency for bioanalytical method validation were followed to validate the assay. The assay was applied to investigate the IC₅₀ of two well-known LAT-1 inhibitors on hCMEC/D3 cells: the highly specific LAT-1 inhibitor JPH203, which was also used to demonstrate LAT-1 specific uptake, and the general system L inhibitor BCH. In addition, the [¹³C₆, ¹⁵N]-L-leucine uptake was determined on two human brain capillary endothelial cell lines (NKIM-6 and hCMEC/D3), which were characterized for their expressional differences of LAT-1 at the protein and mRNA level and the surface amount of CD98. The IC₅₀ values of the inhibitors were in concordance with previously reported values. Furthermore, the [¹³C₆, ¹⁵N]-L-leucine uptake was significantly higher in hCMEC/D3 cells compared to NKIM-6 cells, which correlated with higher expression of LAT-1 and a higher surface amount of CD98. Therefore, the UPLC-MS/MS quantification of ([¹³C₆, ¹⁵N]-L-leucine is a feasible strategy for the functional characterization of LAT-1 activity in cells or tissue.     

Neurotropic RNA Virus Modulation of Immune Responses within the Central Nervous System

The central nervous system (CNS) necessitates intricately coordinated immune responses to prevent neurological disease. However, the emergence of viruses capable of entering the CNS and infecting neurons threatens this delicate balance. Our CNS is protected from foreign invaders and excess solutes by a semipermeable barrier of endothelial cells called the blood–brain barrier. Thereby, viruses have implemented several strategies to bypass this protective layer and modulate immune responses within the CNS. In this review, we outline these immune regulatory mechanisms and provide perspectives on future questions in this rapidly expanding field.     

基于SAR辅助的INS/Doppler组合导航系统研究

INS/Doppler组合导航系统具有输出水平速度误差和平台角误差较小的优点,但经纬度误差仍随时间增大,故不能作为独立的精确导航定位系统;由于合成孔径雷达(SAR)能够提供高精度的经纬度和航向信息,文中对基于SAR辅助的INS/Doppler组合导航系统进行了研究。仿真结果表明,该系统导航定位精度高、自主性强,比较适用于对导航精度要求较高的大型飞机。