# Evaluating GNSS Receiver Resilience: A Study on Simulation Environment Repeatability
## 4 Automated Testbed  
When jamming occurs, a receiver initiates procedures to mitigate its effects. However, the receiver's response can vary slightly due to the multiple available jamming elimination methods and the receiver's current signal processing step for position and time calculations. To characterize this response reliably, repeated measurements under jamming conditions are essential. To isolate the receiver's behavior from dynamic real-world influences, we utilize a GNSS signal simulator. This simulator employs mathematical models to recreate the received signal spectrum at a specified location. It simulates all relevant factors, including satellite orbital motion, ionospheric errors, signal degradation during transmission and reception, and potential transmission errors. The simulator generates a time sequence of raw I/Q samples, which are then fed to a high-frequency source with an output modulator to produce the desired  
Figure 4: This figure illustrates 50 repeated measurements of the GP01 GNSS receiver’s positional deviation in response to a jamming signal (present at times denoted as shaded red area). Each colored line represents an individual measurement. The first and last 100 s show an undisturbed environment, highlighting repeatability and recovery after the disturbance. Deviation is calculated as the magnitude of the displacement vector from the simulated reference position. simulated signals. This approach allows for repeatable testing under identical conditions, provided the source's output power, frequency, and quadrature stability remain consistent. Laboratory tests have demonstrated that the setup depicted in Figure 5 provides the most reliable testing environment for receiver response assessment. The Keysight N7609C Signal Studio for Global Navigation Satellite Systems software generates the simulation waveforms, and the raw I/Q samples are then transferred to a Keysight N5182B high-frequency generator. This generator offers a wide power range (\(-137\) dBm to \(30\) dBm), enabling precise control of the signal strength, thus eliminating the influence of the LNA amplifier. The GNSS signal is then routed through an HP 776D directional coupler, where an interfering signal, generated by a separate Keysight N5182B, is injected into the coupling connection. The unused port is terminated with a \(50\)\(\Omega\) load. The combined signal is then fed to the GNSS receiver under test, and its output data are captured via USB on a personal computer. The directional coupler is crucial for preventing the interfering signal from distorting the GNSS simulator's output spectrum, which would compromise the test's integrity. The personal computer software manages several concurrent tasks. It can initiate a cold start on the GNSS receiver, clearing its RAM and ensuring no residual data influence the test. Alternatively, the receiver's power can be electronically cycled to guarantee a clean cold start. This is vital for observing the receiver's response to sudden interference without the influence of prior data that might aid in positioning and error correction. The software also controls the GNSS simulator and jammer, executing pre-programmed scenarios with synchronized playback. This allows for precise timing of the jamming signal within the simulated environment. Finally, the software logs all received GNSS data, including NMEA sentences, along with simulation and jamming signal status information. Figure 6 shows a photograph of the measurement setup, which also includes an Ethernet switch for communication between the PC and the GNSS simulator/jammer and an Agilent E4445A Spectrum Analyzer for monitoring the output spectrum and estimating the signal-to-interference ratio. Off-the-shelf GNSS receiver modules, specifically Ai-Thinker GP-01, U-blox NEO-6M (6-Series, GPS-only), and U-blox MAX-M10 (10-Series, multi-GNSS), were selected to validate the main research question.