# Detecting and Mitigating Attacks on GPS Devices
## 4 Factors Contributing to GPS-Denied or GPS-Disrupted Environments
### GPS jamming and Unintentional Interference
The studies presented in [54; 55] provided insight into the performance variability of different GPS receivers in the presence of jamming. The authors of [54] presented an analysis of GPS performance against chirp jamming, commonly found in commercially available GPS jammers. The authors primarily considered linear chirp jamming against two GPS receivers and measured the corresponding GPS carrier-to-noise (C/No), DOP, and position solution accuracy. One of the test receivers was a multi-GNSS receiver; therefore, it was tested in GPS-only and multi-GNSS configurations. This study reported significant differences in performance between these GPS receivers, with some scenarios resulting in minimal error in one device and errors of up to 10 m in the other device. The authors also noted that the multi-GNSS configuration resulted in the best performance, with little-to-no performance degradation in the presence of GPS jamming. This result is expected since other GNSS systems, such as GLONASS, operate in different frequency bands, and the receiver always receives unaffected signals from at least one GNSS system. The authors of [55] conducted an empirical study of five different GPS receivers in the presence of jamming, attempting to gain insight into the variability of GPS receiver performance. This study presented the minimum jammer power levels required to make the different receivers lose GPS signal lock; however, the authors failed to describe the propagation path between \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Authors** & **Reference** & \begin{tabular}{c} **Diffulty of** \\ **Implementation** \\ \end{tabular} & \begin{tabular}{c} **Type of** \\ **System** \\ \end{tabular} & \
\begin{tabular}{c} **RF Hardware** \\ **Platform** \\ \end{tabular} &
\begin{tabular}{c} **Signal Generation** \\ **Environment** \\ \end{tabular} \\ \hline [PERSON] et al. & [48] & Low & Commercial & Commercial & Commercial GPS \\ [PERSON] et al. & [50] & Low & SDR-based & BladeRF x40 & GNU Radio \\ [PERSON] et al. & [49] & Low & SDR-based & BladeRF x40 & GNU Radio \\ [PERSON] and & [51] & Low & SDR-based & Unknown & GNU Radio \\ [PERSON] & [52] & Low & SDR-based & BladeRF x40 & GNU Radio \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of low-cost GPS jammer implementations. \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Jamming** & **Resulting BER (\%)** \\ \hline Pulse Jamming & 4–8\% \\ \hline CW Jamming & 18\% \\ \hline Barrage Noise Jamming & 14\% \\ \hline Swept PBN Jamming & 2–4\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Summary of effectiveness of different GPS jamming presented in [53]. the jammer and target receivers, and it is not possible to determine meaningful receiver metrics such as Signal Power to Jammer Power (S/J). The data from [55] provided insight into the variability of GPS receivers in jamming conditions. The five GPS receivers that were tested required jammer power ranging from \(-45\) dBm to \(-60\) dBm to disrupt their GPS signal reception. These results suggest a 15 dB variability in S/J performance across the five tested GPS receivers, assuming receivers were collocated such that GPS signal power was comparable across all receivers. This variability is significant and suggests that different GPS receivers will respond significantly differently to a jamming signal or unintentional interference.