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Abstract：
This paper implements and analyzes a tightly coupled single-frequency global navigation satellite system precise point positioning/inertial navigation system (GNSS PPP/INS) with insufficient satellites for land vehicle navigation using a low-cost GNSS receiver and a microelectromechanical system (MEMS)-based inertial measurement unit (IMU). For land vehicle navigation, it is inevitable to encounter the situation where insufficient satellites can be observed. Therefore, it is necessary to analyze the performance of tightly coupled integration in a GNSS-challenging environment. In addition, it is also of importance to investigate the least number of satellites adopted to improve the performance, compared with no satellites used. In this paper, tightly coupled integration using low-cost sensors with insufficient satellites was conducted, which provided a clear view of the improvement of the solution with insufficient satellites compared to no GNSS measurements at all. Specifically, in this paper single-frequency PPP was implemented to achieve the best performance, with one single-frequency receiver. The INS mechanization was conducted in a local-level frame (LLF). An extended Kalman filter was applied to fuse the two different types of measurements. To be more specific, in PPP processing, the atmosphere errors are corrected using a Saastamoinen model and the Center for Orbit Determination in Europe (CODE) global ionosphere map (GIM) product. The residuals of atmosphere errors are not estimated to accelerate the ambiguity convergence. For INS error mitigation, velocity constraints for land vehicle navigation are adopted to limit the quick drift of a MEMS-based IMU. Field tests with simulated partial and full GNSS outages were conducted to show the performance of tightly coupled GNSS PPP/INS with insufficient satellites: The results were classified as long-term (several minutes) and short-term (less than 1 min). The results showed that generally, with GNSS measurements applied, although the number of satellites was not enough, the solution still could be improved, especially with more than three satellites observed. With three GPS satellites used, the horizontal drift could be reduced to a few meters after several minutes. The 3D position error could be limited within 10 m in one minute when three GPS satellites were applied. In addition, a field test in an urban area where insufficient satellites were observed from time to time was also conducted to show the limited solution drift.
摘要：
本文利用低成本GNSS接收机和基于微机电系统(MEMS)的惯性测量单元(IMU),实现并分析了一种紧耦合的单频全球导航卫星系统精密单点定位/惯性导航系统(GNSSPPP/INS),卫星不足用于陆地车辆导航。对于陆地车辆导航，不可避免地会遇到无法观测到卫星不足的情况。因此,在具有挑战性的GNSS环境中，有必要分析紧耦合集成的性能。此外,研究为提高性能而采用的最少数量的卫星也很重要，与没有使用卫星相比。在本文中,使用卫星不足的低成本传感器进行了紧密耦合集成，与根本没有GNSS测量相比，这清楚地表明了卫星不足的解决方案的改进。具体来说,在本文中，单频PPP被实施以达到最佳性能，一个单频接收机。INS机械化是在本地框架（LLF）中进行的。应用扩展卡尔曼滤波器来融合两种不同类型的测量。更具体地说,在PPP处理中，使用Saastamoinen模型和欧洲轨道测定中心（CODE）全球电离层图（GIM）产品纠正了大气误差。不估计大气误差的残差以加速模糊收敛。对于INS错误缓解，采用陆地车辆导航的速度限制来限制基于MEMS的IMU的快速漂移。进行了模拟的部分和全部GNSS中断的现场测试，以显示在卫星不足的情况下紧密耦合的GNSSPPP/INS的性能：结果分为长期（几分钟）和短期（少于1分钟）。结果表明,在应用GNSS测量的情况下，虽然卫星数量不够,解决方案仍然可以改进，特别是观察到的三颗以上的卫星。使用了三颗GPS卫星，几分钟后，水平漂移可以减少到几米。当应用三颗GPS卫星时，3D位置误差可以在一分钟内限制在10m以内。此外,还在不时观察到卫星不足的城市地区进行了现场测试，以显示有限的溶液漂移。
