Types of Spoofing
Spoofers overpower relatively weak GNSS signals with radio signals carrying false positioning information. There are two ways of spoofing:
- Rebroadcasting GNSS signals recorded at another place or time (so-called meaconing)
- Generating and transmitting modified satellite signals
Spoof-proof: how to protect your receiver against spoofing?
In order to combat spoofing, GNSS receivers need to detect spoofed signals out of a mix of authentic and spoofed signals. Once a satellite signal is flagged as spoofed, it can be excluded from positioning calculation. There are various levels of spoofing protection that a receiver can offer. Let’s compare it to a house intrusion detection system. You can have a simple entry alarm system or a more complex movement detection system. For added security you might install video image recognition, breaking-glass sound detection or a combination of the above.
Like a house with an open door, an unprotected GNSS receiver is vulnerable to even the simplest forms of spoofing. Secured receivers, on the other hand, can detect spoofing by looking for signal anomalies, or by using signals designed to prevent spoofing such as Galileo OS-NMA and E6 or the GPS military code.
Advanced interference mitigation technologies, such as the Septentrio AIM+, use signal-processing algorithms to flag spoofing by detecting various anomalies in the signal. For example, a spoofed signal is usually more powerful than an authentic GNSS signal.
AIM+ won’t even be fooled by an advanced GNSS signal generator: Spirent GSS9000. With realistic power levels and with actual navigation data within the signal, AIM+ can identify it as a “non-authentic” signal. Other advanced anti-spoofing techniques such as using a dual-polarized antenna are being researched today.