July/August 2021
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Global Navigation Satellite Systems Engineering, Policy, and Design
Global Navigation Satellite Systems Engineering, Policy, and Design
In-flight refueling requires sustained minimal separation between paired aircraft with little room for error. In or near combat zones, wide-area GPS-denial or spoofing means that an GPS-independent system must be available. Regardless of the selected sensor package, a common set of properties must be satisfied to facilitate mid-air docking: a high degree of accuracy, precision, and integrity.
The addition of alternative sensors such as cameras, magnetometers, and small ranging radios increases the likelihood of a mismodeled and/or faulty sensor, affecting the accuracy and performance of the overall navigation solution. Unlike two-sensor systems such as GPS-inertial integration, systems of three or more sensors present the problem of ambiguity as to which sensor is adversely affecting the solution. This presents the need for a robust framework that can maintain navigation integrity despite the additional sensor modalities.
Interference mitigation techniques should protect GNSS receivers from interference and jamming without biasing their final position, velocity and timing solution. This column analyses five popular interference mitigation techniques, including the Adaptive Notch Filter (ANF) and Pulse Blanking (PB), evaluating their impact on pseudoranges and on the final position and timing solution. Several GNSS modulations are considered, showing the advantage of using GNSS signals with similar spectral characteristics.
A Department of Homeland (DHS)-chartered May 2021 report concludes that PNT threat and resilience concerns are not as dire as some have made them out to be, and that funds for backup could be spent elsewhere. Why this runs counter to other recent government reports is not clear, nor is the fallout from this divergence of Congressionally mandated views. The Department of Transportation has distanced itself a bit from this report by the RAND Corporation—and even its issuer, the DHS, seems to have done so.
In the beginning, GPS was envisioned as a military program. A sign on the wall in the Joint Program Office where the system came into being during the early 1970s read: “The mission of this Program Office is to:
There has been much discussion of the need for resilient PNT over the past few years as dependencies have grown and an evolving threat matrix has become more active. As a nation, we need a measured and cost-effective response commensurate with the level of threats and the possible consequences.
