Spoofing occurs when bad actors try to interfere with a GNSS receiver so that the position it reports is not its current location but meters or thousands of meters away. But how does this happen?
GNSS receivers, like Trimble’s Alloy, track low-power signals transmitted from satellites. With the availability of low-cost programmable radios, it is now possible to develop a transmitter that will broadcast a spoofing signal that a GNSS reference receiver will use instead of the true signal. Depending on the sophistication of the spoofer, this can cause various positioning and timing errors. These false or spoofed signals could potentially result in a receiver calculating positions in error by many miles.
Although spoofing is uncommon in today’s high-precision applications, Trimble has integrated protection into its Alloy GNSS reference receivers to mitigate the increasing threat of false GNSS signals.
Taking Action with Maxwell 7
Trimble receivers that incorporate our latest Maxwell™ 7 technology include a number of features to protect from spoofing. This technology provides robust precision positioning by fusing all GNSS constellation signals with additional sensor data.
Trimble receivers defend against spoofing to provide users with reliable position data via several forms:
1. Rejection of spoofed signals in digital signal processing (DSP)
Advanced tracking algorithms detect when multiple signals are received for each satellite and ensure only the true signal is tracked. The spoofed signal generally shows as a stronger secondary correlation peak, which the tracking channel isolates and rejects from reaching the positioning algorithm.
2. Satellite data checking
By keeping a historical record of the orbital parameters transmitted by each satellite, Trimble Maxwell 7 technology can detect if these change unexpectedly or fall outside reasonable bounds, and can also cross-check orbital data from multiple sources.
3. Receiver autonomous integrity monitoring (RAIM)
With more measurements than unknowns, the receiver has the ability to detect measurements that do not fit into the positioning solution. Newly tracked satellites that fail this test are put through additional tests before inclusion while existing satellites are immediately removed from the solution. RAIM is also calculated between GNSS constellations with complete systems being rejected, if necessary. This assumes a simplistic spoofing event where a subset of constellations are affected.
For example, if only GPS is spoofed then by calculating multiple position solutions from subsets of measurements from GLONASS, BeiDou, Galileo, QZSS, NavIC and SBAS, the GNSS receiver can confidently determine the GPS measurements need to be removed.
4. Position sanity checks
If the receiver detects positions have jumped by an unrealistic amount since the last computed position, this is also a valuable indicator of spoofing.
5. Limiting satellite search window
Utilizing recent tracking information, the GNSS receiver will limit the search window for reacquiring satellites that are temporarily lost and prevent a spoofing attack.
Trimble GNSS technology is used for critical applications across numerous industries, so taking proactive preventative measures to ward off potential spoofing attacks is key. The inclusion of Trimble’s Maxwell 7 technology assures the receivers will identify and remove unwanted signals. As spoofing becomes more sophisticated, Trimble technology continues to evolve and mitigate these challenges so users can feel confident with advanced protection and the accuracy expected from their high-precision positioning solution.