A method is presented for upgrading existing Global Navigation Satellite System (GNSS) user equipment, without requiring hardware or software modifications to the equipment, to improve the equipment’s position, velocity, and time (PVT) accuracy, to increase its PVT robustness in weak- signal or jammed environments, and to protect the equipment from counterfeit GNSS signals (GNSS spoofing). The method is embodied in a device, herein termed the GNSS Assimilator or simply the Assimilator, that couples to the radio frequency (RF) input of existing GNSS equipment, such as a GPS receiver. The Assimilator extracts navigation and timing information from RF signals in its environment—including non-GNSS signals—and from direct baseband aiding provided, for example, by an inertial navigation system, a frequency reference, or the GNSS user. The Assimilator optimally fuses the collective navigation and timing information to produce a PVT solution which, by virtue of the diverse navigation and timing sources on which it is based, is highly accurate and inherently robust to GNSS signal obstruction and jamming. The Assimilator embeds the PVT solution in a synthesized set of GNSS signals and injects these into the RF input of a target GNSS receiver for which an accurate and robust PVT solution is desired. The code and carrier phases of the synthesized GNSS signals can be aligned with those of the actual GNSS signals at the input to the target receiver. Such phase alignment implies that the synthesized signals appear exactly as the authentic signals to the target receiver, which enables a user to “hot plug” the Assimilator into a target receiver with no interruption in PVT. Besides improving the PVT accuracy and robustness of the target receiver, the Assimilator also protects the target receiver from GNSS spoofing by continuously scanning incoming GNSS signals for signs of spoofing, and, to the extent possible, eliminating spoofing effects from the GNSS signals it synthesizes.


Cite and download the paper:
Humphreys, T.E., B.M. Ledvina, "GNSS Assimilator:  A method for upgrading existing GNSS user equipment to improve accuracy, robustness, and resistance to spoofing,"  2009.