Receiver position errors in harsh environment.

Global navigation satellite systems (GNSSs) are commonly used to measure the position and time globally. A GNSS is convenient owing to its ability to measure accurate position relatively without using assistive tools for navigation by comparing with other sensors. Based on these benefits, the applicable area is expanding to commercial and social uses (e.g., vehicle navigation, smart grids, and smartphone apps). In the future, various services and technologies (e.g., the use of autonomous vehicles, unmanned delivery, and industrial field robots), which make Internet of Things (IOT) more active, will be used in our society. Conversely, the performance of GNSS can degrade in harsh environments, such as urban areas, owing to the property of GNSS, which calculates position and time via satellite signal reception. However, buildings in a city can block navigation satellite signals and generate multi-path errors. The blocked signals exacerbate the dilution of precision (DOP), which indicates the accuracy of the navigation solution and increases the navigation solution error. This study proposes methods to improve navigation performance by leveraging various techniques (e.g., range differences, receiver clock error hold, and virtual satellites). The methods were validated in harsh environments where visible satellites were reduced. In the simulation, each proposed method improved the navigation performance by creating an environment similar to a normal situation, despite the receiver entering a harsh environment. The results confirmed that the navigation performance deteriorated compared to the normal situation where the number of visible satellites decreased. However, the navigation performance was recovered gradually by applying the proposed techniques. Using the proposed methods, navigation performance can be maintained continuously even in situations where satellite signals are blocked.全球导航卫星系统（Global Navigation Satellite Systems，GNSS）是当前全球范围内用于定位与授时的主流技术方案。GNSS凭借无需搭配辅助导航传感器、仅通过自身信号比对即可实现相对高精度定位的特性，具备极高的便捷性。依托这类核心优势，其应用场景正持续拓展至商业与社会各领域，例如车载导航、智能电网以及智能手机应用等。未来，各类推动物联网（Internet of Things，IOT）生态愈发活跃的服务与技术，如自动驾驶车辆、无人配送以及工业现场机器人等应用，将在社会中得到大规模落地。但GNSS依靠接收卫星信号完成位置解算与授时的固有特性，使其在城市等复杂恶劣环境下的性能会出现显著衰减：城市中的建筑物不仅会直接遮挡导航卫星信号，还会引发多径误差。被遮挡的信号会加剧精度衰减因子（Dilution of Precision，DOP）的恶化——该指标用于表征导航解算的精度水平，进而增大导航解算的误差值。本研究提出了多种可有效提升导航性能的技术手段，例如测距差分、接收机时钟误差保持以及虚拟卫星技术。这些方法在可见卫星数量缩减的复杂恶劣环境中完成了有效性验证。在仿真实验中，尽管接收机处于复杂恶劣环境，但各所提方法通过构建与正常环境相似的信号条件，实现了导航性能的优化提升。实验结果证实，当可见卫星数量减少时，导航性能相较正常环境出现了明显劣化；但通过应用所提技术，导航性能可逐步得到恢复。采用本研究提出的方法后，即便在卫星信号被遮挡的场景下，导航性能也能够得到持续保障。