# Evaluating GNSS Receiver Resilience: A Study on Simulation Environment Repeatability
## 2 GNSS Jamming and Detection Mechanisms  
### Interference in GNSS Reception  
The challenge of receiving signals from the global network of orbiting satellites is fundamentally rooted in an extremely poor signal-to-noise ratio. This degradation is primarily caused by the scattering of radio signals as they interact with water molecules in the Earth's atmosphere. While directional antennas can significantly improve this ratio by focusing their main beam on a specific transmitter, as seen in satellite internet, or by maintaining a fixed orientation toward geostationary satellites, as in satellite television, these solutions are not universally applicable [4].  
A major hurdle emerges when a system requires hemispherical Earth coverage while simultaneously managing signals from numerous satellites positioned at diverse angles relative to multiple ground users [29]. In such scenarios, directional antennas, which would normally enhance the signal-to-noise ratio, become impractical. To overcome the resulting signal degradation, GNSS designers implemented spread spectrum code [30]. This technique broadens the signal's bandwidth far beyond the data's minimum requirement, effectively spreading it. By employing code multiplexing and de-spreading at the receiver, the system gains inherent resistance to narrowband interference. This interference is transformed into benign noise during demodulation, provided it lacks substantial correlation with the authentic satellite signals [31].  
Modern receiver architecture allows for the reliable reception of navigation data from all four major GNSS constellations--Galileo, BeiDou, GLONASS, and GPS--even in the presence of relatively strong unintentional interference [32]. Such interference often originates from the suboptimal operation of terrestrial systems, notably the saturated output stages of mobile telephony base stations attempting to maximize their range [33]. However, the situation is markedly different with intentional jamming, which has become increasingly prevalent since the introduction of electronic tachygraphs in trucks [34]. Drivers seeking to conceal violations of driving time limits employ jammers to disrupt GNSS signal reception. A simple jammer, such as one designed for a 12 V cigarette lighter socket, can completely obscure GNSS signals within a range of tens of meters [35]. This has consequences beyond just the jammer user, endangering critical infrastructure such as airport systems and aircraft receivers (Figure 1) [36]. Intentional jamming typically involves transmitting directly at the carrier frequency of a specific GNSS system or randomly varying across the entire allocated frequency band, attempting to circumvent jamming detection systems. While GNSS receivers employ adaptive filtering and gain adjustments to counter jamming, sufficiently strong jamming signals can completely overwhelm the satellite signal during code de-spreading [37].  
While a complete failure to de-spread a signal typically provides a clear indication of jamming conditions, more subtle disruptions can occur. A jammer might interfere with precise time synchronization without fully disabling signal reception, leading to inaccurate location calculations before the receiver software detects any deviations. To address these risks, researchers have developed countermeasures like ground station signal authentication and auxiliary RTK systems for precise positioning [6; 38; 39; 40]. However, these solutions are also susceptible to disruption, as transmitting correction and authentication data over separate networks introduces additional vulnerabilities. Even kinematic auxiliary systems, such as gyroscopes and accelerometers, offer limited protection, especially during continuous motion. In such instances, the GNSS receiver, along with all of the components of its processing chain, constitutes an isolated system, relying solely on its software to interpret the situation and provide accurate positioning.