Summary
Most drones use GNSS/GPS, meaning Global Navigation Satellite System, to determine their precise location, navigate, and follow their automated flight paths.
Interference in satellite signals from other electronic devices is becoming a growing issue, not only for drones, and not only due to malicious intent!
A degraded GNSS/GPS signal, or the loss of signal during a flight, can start for many reasons, mainly interferences from the environment. It is a known vulnerability and it is therefore mitigated and managed. Mitigation and safety measures may include the redundancy of sources of positioning data with inertial sensors onboard, automatic fail-safe modes such as Return to Home, anti-jamming equipment. Some drones on the market are specifically conceived to navigate in a GNSS/GPS denied environment, such as indoor inspections, using onboard camera and sensor-based situational awareness for obstacle avoidance – some drones are combining both sensor-based situational awareness and GNSS-based navigation.
What is GNSS? difference between GPS and GNSS?
Global Navigation Satellite System (GNSS) refers to a constellation of satellites providing signals from space that transmit positioning and timing data to GNSS receivers. The receivers then use this data to determine location. By definition, GNSS provides global coverage.
Examples of Global Navigation Satellite Systems, or GNSS, include:
· USA’s GPS
· Europe’s GALILEO
· Russia’s GLONASS
· China’s BEIDOU
You will know GNSS from mobile devices like phones, where apps like google maps or “Find My” use your geo-position to help you reach your destination or orientate yourself.
Why do most drones need GNSS/GPS input?
Most drones rely on GNSS to determine their precise location and navigate.
Of course, smaller drones such as toys do not need satellite-based navigation: the remote flyer can simply pilot his/her drone, like a car toy with a remote control.
For professional applications however, precise navigation, and precise geo-tagging of the data collected is often required. For more advanced operations such as long range automated flights, satellite-based navigation system is the norm. It is overall cost-effective, accurate and reliable.
Can a drone lose its GNSS signal?
Unintentional interferences
Interferences, obstacles and loss of satellite signal is becoming an increasing issue, but not only for drones! Satellites’ signals coming from their orbit at around 20 000km are in a way competing with many signals on our busy and connected planet earth. There can be a lot of “noise” around the receiver, and there can be a lot of obstacles between the satellites and the receiver.
For example, a drone can lose its GNSS signal when operating:
· Indoor – unlike mobile phone signals, satellite signals do not go through walls
· in an area with lots of obstacles such as buildings, trees, bridges, structures… all forming potential obstacles to GNSS reception
· close to electric power lines or other electric or electronic devices, or metallic structures that may create signal interferences.
Intentional interferences, jamming, spoofing
Satellite signals may also be interrupted or jammed or spoofed intentionally, as illustrated in other GNSS/GPS applications.
For example, some truck drivers may use a GPS jammer, readily available online at a modest price, to jam their trucks’ GPS trackers, so that their company may not be aware of all their whereabouts. Some employees may consider the same when using their company cars outside of business hours.
Also, did you know that a number of options are openly described on the internet to fake your mobile phone’s GPS position and collect more points at Pokemon Go?
What happens if a drone loses its GNSS signal?
A degraded GNSS/GPS signal, or the loss of signal during a flight, for whatever reason and starting by interferences from the environment, is a known vulnerability. It is therefore mitigated and managed. Mitigation measures and safety responses include for example:
Redundancy of sources of positioning data, for example with inertial sensors onboard
Fail-safe modes automatically triggered by the loss of GNSS signal, without the need for human input. Typically, drones on the market would perform one of three things: return to home (RTH), hover on the spot, or land, or a combination of those.
“Return to Home” RTH is the most typical solution used in the industry and simply means that if the GNSS signal is lost and can’t be recovered, the drone will automatically reverse (whether this is straight away or after a set amount of time) and go back to the home point where the flight started, or to a pre-determined safe landing point. This will also activate when the battery charge is running low.
Paired with the RTH function are the landing protection mechanisms. The drone has sensors and gyros onboard so that it will first hover then find a safe area to land without risking contact with uneven terrain or other objects e.g., rocky terrain or forested areas – or people of course.
Anti-jamming equipment onboard. There are various solutions to the jamming threat available on the market, providing anti-jamming protection to drones in many scenarios, from low-cost jammers to high-power ground jammers.
What about drones operating in a GNSS/GPS-denied environment?
Although it is industry standard to use GNSS, many companies are now utilising drones to carry out tasks in GNSS denied environment such as power plants, underground tunnels, or warehouses. These drones are designed specifically for indoor environment and use on-board sensors, camera-based visual situation awareness, to detect their immediate surroundings and avoid collisions while providing reference points. Already we see on the market drones that combine GNSS-based navigation and enhanced situational awareness based on sensors onboard, for collision avoidance.
By Robert Burns and Anne-Lise Scaillierez
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