Predictive Analysis of GNSS Signal Reception on Aircraft Amid In-Flight Jamming
Veenu Tripathi and Stefano Caizzone, Institute of Communications and Navigation, German Aerospace Center (DLR)
Date/Time: Friday, Sep. 20, 11:03 a.m.
GNSS-based positioning is widely used in the modern era for various applications across land, air and water. The possibility of a navigation receiver being jammed by a stronger electromagnetic signal is a potential challenge for navigation systems. [1-3]. The GNSS signals that reach the Earth's surface have extremely low power levels, ranging from -160 to -130 dBm, due to the distance of about 20,000 km between GNSS satellites and the Earth's surface, which increases the susceptibility of GNSS signals to jamming risks [4]. Jammers transmit radio frequency signals in the same frequency bands as GNSS satellites. As the power of the jamming signal increases, the carrier-to-noise density (C/N_0) of the GNSS satellites being tracked by the receiver decreases, overwhelming the legitimate, much weaker GNSS signals. As a result, receivers lose the ability to process satellite signals or provide inaccurate positioning information within a radius of several kilometers [5]. Quite little is known publicly on the RF environment characteristics that a GNSS system experiences while flying, making more difficult to take proactive measures to mitigate the risk of interference and ensure the system’s dependability [6].
Multi-antenna systems are known to be an effective countermeasure and have been the subject of extensive research in the last few years [7-11]. In order to better study the flight behavior of these antennas, our institute at the German Aerospace Centre (DLR) is conducting a series of flight measurement campaigns at its Cochstedt site: the first one took place in 2022, then in 2023, with more to follow in 2024.
In the paper, we will be discussing a prediction tool that can give researchers a good approximation in advance of the performance that will be achieved later in the flight. The tool uses a hybrid approach, mixing measured and simulated data, to predict the performance at antenna level as obtained during flight. First, the antenna design is carried out using commercial software Ansys HFSS (3D High Frequency Simulation Software). Subsequently, the antenna is manufactured and measured in a semi-anechoic near-field chamber (MVG’s Starlab) at the DLR facility. The measured electromagnetic fields in the anechoic chamber are then converted to equivalent currents on an enclosing box. These equivalent currents are used as the antenna source in electromagnetic simulations performed on a digital twin of the DO 228-101 (D-CODE) airplane. More detailed explanation of the approach is presented in [12]. Simplified CAD (Computer Aided Design) model of the desired aircraft can be used for simulating the installed performance once the antenna is on the airplane. The reflections originating from the aircraft contribute to the installed radiation pattern of the antenna, resulting in a change in the overall pattern of the installed antenna.
By leveraging specialized softwares, i.e. Ansys HFSS for installed performance and Ansys STK (Systems Tool Kit) for system performance along with developed technique, we can moreover replicate real-world interference conditions and access how GNSS receivers respond to different antenna-aircraft configurations in a specific interference scenario. STK provides a physics-based modeling environment for analyzing platforms and payloads in a realistic mission context and provides canonical antenna patterns for the analysis. We can predict the number of satellites available during the period and also the power level of the signals received. Then we validate the simulation data with the data collected during flight trials that involve GNSS reception in the presence of jammer.
REFERENCES
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[11] K. A. Yinusa, E. P. Marcos and S. Caizzone, “Robust Satellite Navigation by Means of a Spherical Cap Conformal Antenna Array", 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM), pp. 1-2, Waterloo, ON, Canada, 2018.
[12] S. Caizzone, V. Tripathi and S. Hehenberger, “Investigating GNSS Multipath in Aeronautic Applications Through Antenna Installed Performance," 2021 15th European Conference on Antennas and Propagation (EuCAP), pp. 1-5, Dusseldorf, Germany, 2021.
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