# Evaluating GNSS Receiver Resilience: A Study on Simulation Environment Repeatability
## 3 Impacts of GNSS Variability  
In practice, each GNSS receiver operates under unique conditions, dictated by its received signals, unless all receivers share a common antenna. Each receiver might detect different satellites from at least one of the four constellations globally available, each transmitting at varying power levels, following distinct orbital planes, and being at different stages of their operational lifespan. The signals then traverse the ionosphere (which fluctuates with solar activity) and may be reflected by natural or man-made structures before reaching the antenna. The receiver's software must process and compensate for these variations to provide users with accurate time, position, heading, and speed informa  
Figure 2: Block diagram of a modern multi-frequency multi-channel GNSS receiver, highlighting points susceptible to interference. Interference at these points can propagate and severely degrade or disable signal processing in downstream stages. tion [41]. Remarkably, even when connected to a shared antenna and receiving identical signals, different GNSS receivers still yield varying results. Figure 3 illustrates this phenomenon, with measurements taken at a fixed location on June 10, 2024. Three distinct receivers, connected to a common signal source and thus operating under identical external conditions, were used. This figure shows the dispersion of position deviations around the reference location (46\({}^{\circ}\)02\({}^{\prime}\)55.6\({}^{\prime\prime}\) N 14\({}^{\circ}\)30\({}^{\prime}\)30.7\({}^{\prime\prime}\) E) over a four-hour observation period. The receivers operated in a completely offline mode, without connection to a backend network for RTK corrections or internet access for almanac downloads, and were subjected to an interference-free environment. The results demonstrate the inherent variability of GNSS positioning. Even with a stationary receiver location, measurements fluctuate over time, and calculated positions differ significantly between receivers. As expected, newer receivers, such as the U-blox 10-Series, show considerably higher positioning accuracy compared to older models like the U-blox 6-Series. This improvement is primarily due to their ability to simultaneously receive signals from multiple systems and satellites. While deviation of the measurements from the true position cannot be entirely eliminated without auxiliary systems, the time-varying receiver position can be estimated by averaging time-based measurements and calculating the median, assuming the receiver is known to be stationary (black dots in Figure 3). The complexity of this issue increases significantly when interference is introduced within the GNSS frequency range. Each receiver's software will react to this interference, potentially by re-synchronizing satellites, switching to a different primary constellation, or attempting to digitally filter out the interfering signal. The exact response remains unpredictable due to the inaccessibility of the receiver's source code. Consequently, the  
Figure 3: Comparison of calculated latitude and longitude deviations for three low-cost GNSS receivers: Ai-Thinker GP-01, U-blox NEO-6M (6-Series), and U-blox MAX-M10 (10-Series). The red dot represents the true receiver position, while the black dot indicates the median value of measurements. receiver's unknown reaction to interference becomes an additional variable in the challenge of localization in jamming environments. An unpredictable response of a GNSS receiver to a disturbance is shown in Figure 4. To analyze this response, the problem's complexity must first be reduced. While satellite movement and ionospheric variations are uncontrollable, the receiver can be transferred to a simulation environment. Here, a specific GNSS signal, including interference, can be precisely recreated and replayed. This eliminates the uncertainty of unpredictable environmental variables.