Abstract
Positioning, navigation, and timing (PNT) is a strategic key technology widely used in military and civilian applications. Global navigation satellite systems (GNSS) are the most important PNT techniques. However, the vulnerability of GNSS threatens PNT service quality, and integrations with other information are necessary. A chip scale atomic clock (CSAC) provides high-precision frequency and high-accuracy time information in a short time. A micro inertial measurement unit (MIMU) provides a strap-down inertial navigation system (SINS) with rich navigation information, better real-time feed, anti-jamming, and error accumulation. This study explores the coupled integration of CSAC, MIMU, and GNSS to enhance PNT performance. The architecture of coupled integration is designed and degraded when any subsystem fails. A mathematical model for a precise time aiding navigation filter is derived rigorously. The CSAC aids positioning by weighted linear optimization when the visible satellite number is four or larger. By contrast, CSAC converts the GNSS observations to range measurements by “clock coasting” when the visible satellite number is less than four, thereby constraining the error divergence of micro inertial navigation and improving the availability of GNSS signals and the positioning accuracy of the integration. Field vehicle experiments, both in open-sky area and in a harsh environment, show that the integration can improve the positioning probability and accuracy.
Highlights
Positioning, navigation, and timing (PNT) is important for vehicles, aircrafts, robots, and pedestrians, especially for military use
The integration of chip scale atomic clock (CSAC), micro inertial measurement unit (MIMU), and Global navigation satellite systems (GNSS) cannot be degraded to inertial navigation even when only one satellite is visible
The architecture of CSAC, MIMU, and GNSS coupled integration is described in Figure 1; it includes four blocks, namely, timing, GNSS, inertial navigation systems (INS), and precise time-aiding navigation filters
Summary
Positioning, navigation, and timing (PNT) is important for vehicles, aircrafts, robots, and pedestrians, especially for military use. An integrated navigation system combining GNSS and MIMU can provide information regarding position, velocity, altitude, angular velocity, acceleration, and time. For PNT applications, CSAC improves timing accuracy but can be treated as a satellite for GNSS. Sturz [22], Van Graas [23], Misra [24], Kline [25], Zhang [26], and Bednarz [27] found that traditional rubidium clocks improve dilution of precision of GNSS and positioning accuracy. The integration of CSAC, MIMU, and GNSS cannot be degraded to inertial navigation even when only one satellite is visible. This study explores the coupled integration of CSAC, MIMU, and GNSS for PNT performance.
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