In many applications, including time synchronization, GNSS is now commonplace. The best known constellation is GPS. However, all these GNSS systems share a common vulnerability: the signals transmitted by these satellites are very weak. GNSS satellites operate from the Earth’s orbit. The transmitted signal is extremely weak when it reaches the earth’s surface. This low signal strength at the receivers makes GNSS use susceptible to intentional (malicious) or unintentional interference.