Precise-timing applications for GPS

自从20世纪90年代中期商业全球定位系统(GPS)产品进入市场以来，该技术的采用及其与各种消费品(如相机、电话)的集成一直是惊人的，每年售出数以百万计的GPS设备。GPS接收器的测量精度已经显著提高，虽然对大多数应用来说已经足够，但在需要更高精度的地方可能会进一步改进。该提案所涉项目的目标是利用巴斯大学开展的电离层物理研究开发的一种方法，调查增强型GPS定时/导航接收器的商业潜力。GPS信号受电离层传播的影响，这种失真是整个GPS误差预算中最大的组成部分。现有的由全球定位系统广播的电离层模型(创建于20世纪80年代末的S)已被证明在变化的电离层条件下是不可靠的。在某些时期，太阳会发出大量的辐射，这会直接影响地球的电离层，并会引起电离层风暴，从而严重扰乱无线电波，例如。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提供的实时来源获取信息，能够在感兴趣的地理区域制作实时三维电离层地图。实践证明，利用这种实时映射可以计算出更准确、更稳定、更可靠的单频GPS定时/导航解算方案。这一实时地图可以通过无线电广播，或者通过互联网提供，从而有可能实现10 ns以内的定时精度。

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.