Skip to content

News

Drifted by GPS jamming

by LIU YIFA 19 Apr 2022

GPS/GNSS interference at sea

From building offshore wind farms and harbor dredging to marine surveying and laying submarine cables, GPS receivers have established themselves as a critical component in many offshore and nearshore applications. Any interruption of GPS positioning at sea can have dangerous and costly repercussions. Increasingly, GPS downtime is attributed to interference.

The location of an in-car noise jammer on Shelter Island used to simulate the effects of GPS interference in San Diego Bay
Transmitted with power equivalent to that of a standard light bulb, GPS signals are expected to travel over 20,000 km (12,400 miles) and still arrive capable of high-precision position calculations. In most cases the signals arrive relatively unscathed, however, being barely discernible above the thermal background noise, they can be sitting ducks for any passing interference.

RTK and PPP are particularly vulnerable

Maritime applications are increasingly using high precision positioning such as RTK and PPP which not only use the modulated code information on the signals, but also the phase of the signal itself. In the presence of interference, these phase-based modes are the first to suffer.

How bad can it be

The use of GPS jammer is strictly prohibited but their effect can be estimated using a GPS simulator. Using the Port of San Diego as an example, a simulator was programmed to generate the GPS signals that a receiver would see on a boat at that location. Interference from GPS signals was mimicked by mixing the signal from the simulator with that from a jammer. With the jammer at the location shown in Figure 1 and the GPS receiver on a nearby boat in the bay, the effect of interference throughout the bay could then be extrapolated using radio wave propagation models standard.

38W 16 Bands  Adjustable Desktop Cell Phone Jammer GPS WIFI Blocker

Effect of a chirp jammer

The results in Figure 2 show that without AIM+ interference mitigation, a small 10 mW chirp jammer can neutralize RTK positioning over several hundred meters. When AIM+ is enabled, the non-RTK zone is reduced to a few meters in direct proximity to the jammer.

The effect of a 10 mW chirp jammer on GPS positioning in San Diego Bay with and without AIM+ interference mitigation

Effect of a continuous wave jammer

Repeating the tests with a continuous wave (CW) jammer of the same power, the results using AIM+ are even more dramatic as shown in Figure 3. Without AIM+, a CW interferer in the parking lot near the shore prevents RTK positioning or any GPS positioning over a large part of the bay and extends for several kilometers out to sea within line of sight of the jammer.

The effect of a 10 mW continuous wave jammer on GPS positioning in San Diego Bay with and without AIM+ interference mitigation

Troubleshoot Interference

A comprehensive approach puts interference considerations at the forefront of receiver design and incorporates them into every step of signal processing. In the case of the AsteRx4 OEM and AsteRx-U, the antenna signal is immediately digitized after filtering and automatically cleaned of interference using several adaptive notch filters.

Depending on the nature of the interference, the stopband bandwidth is automatically adjusted between a few kHz notch to 1 MHz rejection. Notch filters are complemented by an adaptive filter capable of rejecting more complex types of interference such as those from chirp jammers, frequency hopping signals from DME/TACAN devices as well as high power Inmarsat transmitters.

Sample Image Gallery

Prev post
Next post

Thanks for subscribing!

This email has been registered!

Shop the look

Choose options

topsignaljammer
Sign Up for exclusive updates, new arrivals & insider only discounts

Recently viewed

Social

Edit option
Have Questions?
Back In Stock Notification
Terms & conditions
What is Lorem Ipsum? Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. Why do we use it? It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).

Choose options

this is just a warning
Login
Shopping cart
0 items