Work boat drifts due to GPS interference
GPS/GNSS maritime interference
From building offshore wind farms and dredging ports to marine surveys and laying underwater cables, GPS receivers have become a critical element in many offshore and nearshore applications. GPS downtime is increasingly attributed to gps jammers. Any downtime for GPS positioning at sea can have dangerous and costly consequences.
Maritime applications are increasingly using high-precision positioning such as RTK and PPP, which use not only the code information modulated onto the signal, but also the phase of the signal itself. In most cases, the signals arrive relatively unscathed, but are nearly indistinguishable above the thermal background noise, which can be a haven for any passing interferers.
The GPS signal transmits the power of a standard light bulb, is expected to transmit over 20,000 kilometers (12,400 miles), and is still suitable for high-precision position calculations. In the presence of gps jammer interference, these phase-based modes are first affected.
GPS receivers are located on boats near the bay, and standard radio wave propagation models can then be used to infer interference effects across the bay. Use a GPS simulator to estimate its effect. In the case of the Port of San Diego, the simulator was programmed to generate a GPS signal that would be visible to a ship with receivers at that location.
Simulates jamming of GPS signals by mixing the emulator signal with the signal from the jammer.
Without AIM+ jammer suppression, a small 10 mW chirp jammer can disrupt RTK positioning at hundreds of meters. When AIM+ is activated, the non-RTK area shrinks to a few meters near the jammer.
Repeating the test with a continuous wave (CW) interferer of the same power, the results with the AIM+ are even more pronounced. Without AIM+, a CW jammer in a parking lot near the coast would prevent RTK positioning or actually any GPS positioning over much of the bay, and within the jammer's line of sight extending kilometers into the sea.
Depending on the nature of the interference, the stopband bandwidth is automatically adjusted from a notch of a few kHz to a rejection of 1 MHz wide. An integrated approach puts interference considerations at the forefront of receiver design and incorporates them into every stage of signal processing.