Precise-timing applications for GPS

自从商业全球定位系统（GPS）产品在1990年代中期进入市场以来，这项技术的采用及其与广泛的消费品（例如照相机、电话）的整合一直是惊人的，每年售出数百万台GPS设备。GPS接收机的测量精度有了显著的提高，虽然对大多数应用来说是足够的，但在需要更高精度的地方，可以进一步改进。本提案所涵盖的项目的目标是研究增强型GPS授时/导航接收器的商业潜力，该接收器使用的方法是从巴斯大学开展的电离层物理研究中发展而来的。GPS信号受到电离层传播的影响，这种失真是GPS总体误差预算中最大的组成部分。由GPS系统广播的现有电离层模型（创建于1980年代末）已被证明在可变电离层条件下是不可靠的。在某些时期，太阳释放出大量的辐射，这对地球的电离层有直接的影响，并可能引起电离层风暴，这可能严重干扰无线电波。GPS信号。巴斯大学开发了多仪器数据分析系统（MIDAS），该系统从欧洲和北美的许多免费实时资源中获取输入，能够在感兴趣的地理区域生成实时3D电离层地图。结果表明，利用这种实时映射可以计算出更精确、稳定和可靠的单频GPS授时/导航方案。这种实时地图可以通过无线电广播，或通过互联网提供，使其定时精度达到10毫秒以内成为可能。

Since the introduction of commercial Global Positioning System (GPS) products onto the market in the mid-1990's, the take-up of the technology and its integration into a wide range of consumer goods (e.g. cameras, telephones) has been phenomenal with millions of GPS units being sold annually. The measurement accuracy of GPS receivers has improved significantly and whilst adequate for most applications, further refinements are possible where greater accuracy is required. The objective of the project covered by this proposal is to investigate the commercial potential of an enhanced GPS timing/navigation receiver using an approach that has developed from ionospheric physics research undertaken by the University of Bath. GPS signals are affected by propagation through the ionosphere and this distortion represents the largest component in the overall GPS error budget. The existing ionospheric model (created in the late 1980's) broadcast by the GPS system has been shown to be unreliable under variable ionospheric conditions. There are periods during which the Sun emits larger quantities of radiation, which has a direct impact on the Earth's Ionosphere and can give rise to ionospheric storms, which can seriously disrupt radio waves, eg. GPS signals. The University of Bath has developed the Multi-Instrument Data Analysis System (MIDAS) which, taking input from a number of freely available real-time sources across Europe and N. America, is capable of producing real-time 3D ionospheric maps over geographic areas of interest. It has been demonstrated that by using this real-time mapping a more accurate, stable and reliable single-frequency GPS timing/navigation solution can be computed. This real-time map could be radio broadcasted, or made available via the internet and make it possible to achieve timing accuracies to within 10 ns.